U.S. patent application number 10/714819 was filed with the patent office on 2004-10-07 for bone fixation system with radially extendable anchor.
Invention is credited to Cachia, Victor V., Culbert, Brad S..
Application Number | 20040199165 10/714819 |
Document ID | / |
Family ID | 46257681 |
Filed Date | 2004-10-07 |
United States Patent
Application |
20040199165 |
Kind Code |
A1 |
Culbert, Brad S. ; et
al. |
October 7, 2004 |
Bone fixation system with radially extendable anchor
Abstract
Disclosed is a bone fixation device of the type useful for
connecting soft tissue or tendon to bone or for connecting two or
more bones or bone fragments together. The device comprises an
elongate body having a distal anchor thereon. A proximal anchor is
axially movably disposed with respect to the distal anchor, to
accommodate different bone dimensions and permit appropriate
tensioning of the fixation device.
Inventors: |
Culbert, Brad S.; (Rancho
Santa Margarita, CA) ; Cachia, Victor V.; (San Juan
Capistrano, CA) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
46257681 |
Appl. No.: |
10/714819 |
Filed: |
November 17, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10714819 |
Nov 17, 2003 |
|
|
|
09832289 |
Apr 10, 2001 |
|
|
|
6648890 |
|
|
|
|
09832289 |
Apr 10, 2001 |
|
|
|
09558057 |
Apr 26, 2000 |
|
|
|
09558057 |
Apr 26, 2000 |
|
|
|
09266138 |
Mar 10, 1999 |
|
|
|
09266138 |
Mar 10, 1999 |
|
|
|
08745652 |
Nov 12, 1996 |
|
|
|
5893850 |
|
|
|
|
Current U.S.
Class: |
606/75 ; 606/326;
606/331; 606/907; 606/908; 623/13.11; 623/13.14; 623/16.11 |
Current CPC
Class: |
A61B 17/844 20130101;
A61B 17/683 20130101; A61F 2/0811 20130101; A61B 2017/00004
20130101 |
Class at
Publication: |
606/075 ;
623/013.11; 623/013.14; 623/016.11; 606/072 |
International
Class: |
A61B 017/56 |
Claims
What is claimed is:
1. A bone fixation device, for securing a first bone fragment to a
second bone fragment, comprising: an elongate pin, having a
proximal end and a distal end; at least one radially advanceable
anchor carried by the pin; an actuator, axially moveable with
respect to the pin; and at least one retention structure in between
the pin and the actuator, for permitting proximal movement of the
pin with respect to the actuator but resisting distal movement of
the pin with respect to the actuator; wherein axial proximal
movement of the pin with respect to the actuator causes at least a
portion of the anchor to advance along a path which is inclined
radially outwardly from the pin in the proximal direction.
2. A bone fixation device as in claim 1, wherein the actuator
comprises a tubular body axially slidably carried on the pin.
3. A bone fixation device as in claim 2, wherein the anchor
comprises at least one axially extending strip carried by the pin,
the strip moveable from an axial orientation to an inclined
orientation in response to axial proximal retraction of the
pin.
4. A bone fixation device as in claim 3, wherein the anchor
comprises at least two axially extending strips.
5. A bone fixation device as in claim 4, comprising four axially
extending strips.
6. A bone fixation device as in claim 3, wherein the strip has a
proximal end and a distal end and the proximal end is free.
7. A bone fixation device as in claim 6, further comprising a hub
carried by the pin, and the distal end of the strip is connected to
the hub.
8. A bone fixation device as in claim 6, wherein the hub comprises
an annular ring, axially movably carried by the pin.
9. A bone fixation device as in claim 6, wherein the hub is fixed
with respect to the pin.
10. A bone fixation device as in claim 1, further comprising a
first retention structure on the actuator for cooperating with a
second retention structure on the pin to retain the device under
compression.
11. A bone fixation device as in claim 1, wherein at least one of
the actuator and the pin comprise a bioabsorbable material.
12. A bone fixation device as in claim 11, wherein the material is
selected from the group consisting of poly (L,co-D,L-lactide).
13. A bone fixation device as in claim 1, further comprising a
tapered surface on the distal end of the actuator, so that proximal
retraction of the pin with respect to the actuator causes the
anchor to incline outwardly as it slides along the tapered
surface.
14. A bone fixation device as in claim 1, wherein the pin has a
proximal end, a distal end, and an outside diameter, and the pin
has a relatively larger diameter near the distal end and a
relatively smaller diameter proximally of the distal end.
15. A bone fixation device as in claim 11, wherein the anchor
comprises a nonabsorbable material.
16. A bone fixation device for fixing two or more bone fragments,
comprising: an elongate tubular body, having a proximal end, a
distal end and a longitudinal axis; a distal anchor on the fixation
device, moveable from an axial orientation for distal insertion
through a bore in the bone to an inclined orientation to resist
axial movement through the bore; an elongate pin axially moveable
within the tubular body and linked to the anchor such that proximal
retraction of the pin with respect to the tubular body advances the
distal anchor from the axial orientation to the inclined
orientation.
17. A bone fixation device as in claim 16, further comprising a
retention structure for retaining the distal anchor in the inclined
orientation.
18. A bone fixation device as in claim 16, further comprising a
proximal anchor.
19. A bone fixation device as in claim 16, wherein the distal
anchor comprises at least two axially extending strips spaced
circumferentially apart around the tubular body.
20. A bone fixation device as in claim 17, wherein the retention
structure comprises at least one ramped surface that inclines
radially inwardly in the proximal direction.
21. A bone fixation device as in claim 17, wherein the retention
structure comprises at least one annular ridge.
22. A bone fixation device as in claim 16, further comprising a
first retention structure on the tubular body, and a second,
complimentary retention structure on the pin.
23. A bone fixation device as in claim 16, wherein the tubular body
comprises a first tapered surface and the pin comprises a second
tapered surface such that proximal retraction of the pin with
respect to the tubular body causes a radial enlargement of the
tubular body.
24. A method of implanting a fixation device in a bone, comprising
the steps of: advancing a fixation device into bone; proximally
retracting a portion of the fixation device; and advancing at least
one tine on the fixation device into bone in response to the
proximally retracting step; the advancing step comprising advancing
the tine along a path which inclines radially outwardly from an
axis of the fixation device in the proximal direction.
25. A method of implanting a fixation device as in claim 24,
wherein the advancing a fixation device step comprises advancing
the fixation device through a predrilled bore.
26. A method of implanting a fixation device as in claim 24,
wherein the advancing a fixation device step comprises rotating the
fixation device to drill a bore into the bone.
27. A method of implanting a fixation device as in claim 24,
further comprising the step of seating a proximal anchor against
the bone prior to the proximally retracting step.
28. A method of implanting a fixation device as in claim 24,
comprising advancing at least four tines into bone.
29. A method of fixing a first bone fragment with respect to a
second bone fragment, comprising the steps of: advancing a fixation
device through a first bone fragment and into a second bone
fragment; proximally retracting a portion of the fixation device;
and advancing at least one tine on the fixation device into the
second bone fragment in response to the proximally retracting step;
the advancing step comprising advancing the tine along a path which
inclines radially outwardly at an angle from an axis of the
fixation device in the proximal direction.
30. A method of fixing a first bone fragment with respect to a
second bone fragment as in claim 29, wherein the angle is within
the range of from about 15 degrees to about 90 degrees.
31. A method of fixing a first bone fragment with respect to a
second bone fragment as in claim 30, wherein the angle is within
the range of from about 30 degrees to about 60 degrees.
32. A method of fixing a first bone fragment with respect to a
second bone fragment as in claim 29, comprising advancing at least
four tines into the second bone fragment.
33. A method of fixing a first bone fragment with respect to a
second bone fragment as in claim 29, wherein the first and second
bone fragments are separated by a fracture.
34. A method of fixing a first bone fragment with respect to a
second bone fragment as in claim 33, wherein the fracture comprises
a malleolar fracture.
35. A method of fixing a first bone fragment with respect to a
second bone fragment as in claim 33, wherein the fracture comprises
a condylar fracture.
36. A method of fixing a first bone fragment with respect to a
second bone fragment as in claim 33, wherein the fracture comprises
an epicondylar fracture.
37. A method of fixing a first bone fragment with respect to a
second bone fragment as in claim 33, wherein the fracture comprises
a colles fracture.
38. A method of embedding a tine in cancellous bone, comprising the
steps of: providing a bone anchor having at least one tine thereon,
the tine having an elongate body with a longitudinal axis, a
proximal end, and a distal end, wherein the distal end is connected
to the bone anchor and a leading edge is provided on the proximal
end; nonrotatably introducing the bone anchor into bone, with the
longitudinal axis of the tine substantially parallel to a
longitudinal axis of the bone anchor; manipulating the proximal end
of the bone anchor to drive the leading edge along a path which
inclines radially outwardly from the longitudinal axis of the bone
anchor, such that the tine lies along the path.
Description
[0001] This is a continuation-in-part of Ser. No. 09/558,057, filed
on Apr. 26, 2000, which is a continuation-in-part of Ser. No.
09/266,138 filed on Mar. 10, 1999 which is a divisional of Ser. No.
08/745,652 filed on Nov. 12, 1996, now U.S. Pat. No. 5,893,850.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to bone fixation systems and,
more particularly, absorbable or nonabsorbable bone fixation pins
of the type for fixing soft tissue or tendons to bone or for
securing two or more adjacent bone fragments or bones together.
[0003] Bones which have been fractured, either by accident or
severed by surgical procedure, must be kept together for lengthy
periods of time in order to permit the recalcification and bonding
of the severed parts. Accordingly, adjoining parts of a severed or
fractured bone are typically clamped together or attached to one
another by means of a pin or a screw driven through the rejoined
parts. Movement of the pertinent part of the body may then be kept
at a minimum, such as by application of a cast, brace, splint, or
other conventional technique, in order to promote healing and avoid
mechanical stresses that may cause the bone parts to separate
during bodily activity.
[0004] The surgical procedure of attaching two or more parts of a
bone with a pin-like device requires an incision into the tissue
surrounding the bone and the drilling of a hole through the bone
parts to be joined. Due to the significant variation in bone size,
configuration, and load requirements, a wide variety of bone
fixation devices have been developed in the prior art. In general,
the current standard of care relies upon a variety of metal wires,
screws, and clamps to stabilize the bone fragments during the
healing process. Following a sufficient bone healing period of
time, the percutaneous access site or other site may require
re-opening to permit removal of the bone fixation device.
[0005] Long bone fractures are among the most common encountered in
the human skeleton. Many of these fractures and those of small
bones and small bone fragments must be treated by internal and
external fixation methods in order to achieve good anatomical
position, early mobilization, and early and complete rehabilitation
of the injured patient.
[0006] The internal fixation techniques commonly followed today
frequently rely upon the use of Kirschner wires (K-wires),
intramedullary pins, wiring, plates, screws, and combinations of
the foregoing. The particular device or combination of devices is
selected to achieve the best anatomic and functional condition of
the traumatized bone with the simplest operative procedure and with
a minimal use of foreign-implanted stabilizing material. A variety
of alternate bone fixation devices are also known in the art, such
as, for example, those disclosed in U.S. Pat. No. 4,688,561 to
Reese, U.S. Pat. No. 4,790,304 to Rosenberg, and U.S. Pat. No.
5,370,646 to Reese, et al.
[0007] Notwithstanding the common use of the K-wire to achieve
shear-force stabilization of bone fractures, K-wire fixation is
attended by certain known risks. For example, a second surgical
procedure is required to remove the device after healing is
complete. Removal is recommended, because otherwise the bone
adjacent to an implant becomes vulnerable to stress shielding as a
result of the differences in the modulus of elasticity and density
between metal and the bone.
[0008] In addition, an implanted K-wire may provide a site for a
variety of complications ranging from pin-tract infections to
abscesses, resistant osteomyelitis, septic arthritis, and infected
nonunion.
[0009] Another potential complication involving the use of K-wires
is in vivo migration. Axial migration of K-wires has been reported
to range from 0 mm to 20 mm, which can both increase the difficulty
of pin removal as well as inflict trauma to adjacent tissue.
[0010] As conventionally utilized for bone injuries of the hand and
foot, K-wires project through the skin. In addition to the
undesirable appearance, percutaneously extending K-wires can be
disrupted or cause damage to adjacent structures such as tendons if
the K-wire comes into contact with external objects.
[0011] Notwithstanding the variety of bone fasteners that have been
developed in the prior art, there remains a need for a bone
fastener of the type that can accomplish shear-force stabilization
with minimal trauma to the surrounding tissue both during
installation and following bone healing.
[0012] In addition, there remains a need for a simple, adjustable
bone fixation device which may be utilized to secure soft tissue or
tendon to bone.
SUMMARY OF THE INVENTION
[0013] There is provided in accordance with one aspect of the
present invention, a fixation device for securing a first bone
fragment to a second bone fragment. The fixation device comprises
an elongate pin, having a proximal end and a distal end. At least
one radially advanceable anchor is carried by the pin. An actuator,
which is axially moveable with respect to the pin is also provided.
The device includes at least one retention structure in between the
pin and the actuator, for permitting proximal movement of the pin
with respect to the actuator but resisting distal movement of the
pin with respect to the actuator. Axial proximal movement of the
pin with respect to the actuator causes at least a portion of the
anchor to advance along a path which is inclined radially outwardly
from the pin in the proximal direction.
[0014] The actuator may comprise a tubular body axially slidably
carried on the pin. The anchor comprises at least one axially
extending strip, having a free proximal end and a distal end,
carried by the pin. The strip is moveable from an axial orientation
to an inclined orientation in response to axial proximal retraction
of the pin. In certain embodiments, at least two or four or more
axially extending strips are provided.
[0015] The device may also comprise a hub carried by the pin. The
distal end of the strip is connected to the hub. The hub preferably
comprises an annular ring, axially movably carried by the pin. The
hub may be fixed with respect to the pin.
[0016] The device may also include a first retention structure on
the actuator for cooperating with a second retention structure on
the pin to retain the device under compression. At least one of the
actuator and the pin may comprise a bioabsorbable material, such as
poly (L-lactide-co-D, L-lactide).
[0017] The distal end of the actuator may have a tapered surface,
so that proximal retraction of the pin with respect to the actuator
causes the anchor to incline outwardly as it slides along the
tapered surface. The proximal end of the anchor may have a
complementary tapered surface to slide along the tapered surface on
the actuator. The pin may also have a relatively larger diameter
near the distal end and a relatively smaller diameter proximally of
the distal end.
[0018] In accordance with another aspect of the present invention,
there is provided a bone fixation device for fixing two or more
bone fragments. The fixation device comprises an elongate tubular
body, having a proximal end, a distal end and a longitudinal axis.
A distal anchor is on the fixation device, moveable from a low
profile orientation for distal insertion through a bore in the bone
to an inclined orientation to resist axial proximal movement
through the bore. An elongate pin is axially moveable within the
tubular body and associated with the anchor, such that proximal
retraction of the pin with respect to the tubular body advances the
distal anchor from the axial orientation to the inclined
orientation.
[0019] The bone fixation device may also comprise at least one
retention structure for retaining the anchor in the inclined
orientation. The retention structure may comprise at least one
ramped surface that inclines radially inwardly in the proximal
direction. Alternatively, the retention structure includes at least
one annular ridge. A first retention structure may be on the
tubular body, and a second, complimentary retention structure may
be provided on the pin.
[0020] The device may also comprise a proximal anchor. The distal
anchor comprises at least two axially extending strips spaced
circumferentially apart around the tubular body.
[0021] The tubular body may comprise a first tapered surface and
the pin may comprise a second tapered surface such that proximal
retraction of the pin with respect to the tubular body causes a
radial enlargement of at least a portion of the tubular body.
[0022] Further features and advantages of the present invention
will become apparent to those of skill in the art in view of the
detailed description of preferred embodiments which follows, when
considered together with the attached claims and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a cross-sectional schematic view of a bone
fixation device of the present invention positioned within a
fractured bone.
[0024] FIG. 2 is a longitudinal cross-sectional view through the
pin body of the present invention.
[0025] FIG. 3 is a distal end elevational view of the pin body of
FIG. 2.
[0026] FIG. 4 is a longitudinal cross-sectional view of the
proximal anchor of the bone fixation device.
[0027] FIG. 5 is a proximal end elevational view of the proximal
anchor of the bone fixation device.
[0028] FIG. 6 is a side elevational view of an alternate embodiment
of the bone fixation device of the present invention.
[0029] FIG. 7 is a side elevational view of an alternate embodiment
of the pin body in accordance with the present invention.
[0030] FIG. 8 is a longitudinal cross-sectional view through the
pin body of FIG. 7.
[0031] FIG. 9 is a distal end elevational view of the pin body of
FIG. 7.
[0032] FIG. 10 is an enlarged detail view of the distal end of the
device shown in FIG. 8.
[0033] FIG. 11 is a cross-sectional view through a proximal anchor
for use with the pin body of FIG. 7.
[0034] FIG. 12 is a proximal end elevational view of the proximal
anchor end of FIG. 11.
[0035] FIG. 13 is a side elevational view of a guide wire that may
be used with the pin body of FIG. 7.
[0036] FIG. 14 is a longitudinal cross-sectional view of the guide
wire of FIG. 13 and the pin body of FIG. 7.
[0037] FIG. 15 is a side elevational view of an alternate fixation
device in accordance with the present invention, in the low profile
configuration.
[0038] FIG. 16 is a side elevational view as in FIG. 15, with the
fixation device in the implanted (radially enlarged)
configuration.
[0039] FIG. 16A is a side elevational cross section through an
alternate distal anchor, in the implanted configuration.
[0040] FIG. 16B is a side elevational fragmentary view of an anchor
positioned along the length of the fixation device, shown in the
implanted configuration.
[0041] FIG. 17 is a side elevational view of the pin illustrated in
FIG. 15.
[0042] FIG. 18 is a side elevational detail view of the distal end
of the pin illustrated in FIG. 17.
[0043] FIG. 19 is a side elevational detailed view of the retention
structures on the pin illustrated in FIG. 17.
[0044] FIG. 20 is a side elevational view of a distal anchor and
hub assembly of the fixation system illustrated in FIG. 15.
[0045] FIG. 21 is an end view of the anchor assembly illustrated in
FIG. 20.
[0046] FIG. 22 is a side elevational view of the actuator of the
device illustrated in FIG. 15.
[0047] FIG. 23 is a cross sectional view taken along the line 23-23
of the actuator illustrated in FIG. 22.
[0048] FIG. 24 is an end elevational view of the actuator
illustrated in FIG. 22.
[0049] FIG. 25 is a detail view of a portion of the actuator
illustrated in FIG. 23.
[0050] FIG. 26 is an anterior view of the distal tibia and fibula,
with fixation devices across medial and lateral malleolar
fractures.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0051] Although the application of the present invention will be
disclosed in connection with the simplified bone fracture of FIG.
1, the methods and structures disclosed herein are intended for
application in any of a wide variety of bones and fractures, as
will be apparent to those of skill in the art in view of the
disclosure herein. For example, the bone fixation device of the
present invention is applicable in a wide variety of fractures and
osteotomies in the hand, such as interphalangeal and
metacarpophalangeal arthrodesis, transverse phalangeal and
metacarpal fracture fixation, spiral phalangeal and metacarpal
fracture fixation, oblique phalangeal and metacarpal fracture
fixation, intercondylar phalangeal and metacarpal fracture
fixation, phalangeal and metacarpal osteotomy fixation as well as
others known in the art. A wide variety of phalangeal and
metatarsal osteotomies and fractures of the foot may also be
stabilized using the bone fixation device of the present invention.
These include, among others, distal metaphyseal osteotomies such as
those described by Austin and Reverdin-Laird, base wedge
osteotomies, oblique diaphyseal, digital arthrodesis as well as a
wide variety of others that will be known to those of skill in the
art. Fractures and osteotomies and arthrodesis of the tarsal bones
such as the calcaneus and talus may also be treated. Spiked washers
can be used, attached to the collar or freely movable beneath the
collar. The bone fixation device may be used with or without
plate(s) or washer(s), all of which can be either permanent,
absorbable or comprising both.
[0052] Fractures of the fibular and tibial malleoli, pilon
fractures and other fractures of the bones of the leg may be
fixated and stabilized with the present invention with or without
the use of plates, both absorbable or non-absorbing types, and with
alternate embodiments of the current invention. One example is the
fixation of the medial malleolar avulsion fragment fixation with
the radially and axially expanding compression device. Each of the
foregoing may be treated in accordance with the present invention,
by advancing one of the fixation devices disclosed herein through a
first bone component, across the fracture, and into the second bone
component to fix the fracture.
[0053] The fixation device of the present invention may also be
used to attach tissue or structure to the bone, such as in ligament
reattachment and other soft tissue attachment procedures. Plates
and other implants may also be attached to bone, using either
resorbable or nonreabsorbable fixation devices disclosed herein
depending upon the implant and procedure. The fixation device may
also be used to attach sutures to the bone, such as in any of a
variety of tissue suspension procedures.
[0054] For example, peripheral applications for the fixation
devices include utilization of the device for fastening soft tissue
such as capsule, tendon or ligament to bone. It may also be used to
attach a synthetic material such as marlex mesh, to bone or
allograft material such as tensor fascia lata, to bone. In the
process of doing so, retention of the material to bone may be
accomplished with the collar as shown, with an enlarged collar to
increase contact surface area, with a collar having a plurality of
spikes to enhance the grip on adjacent tissue, or the pin and or
collar may be modified to accept a suture or other material for
facilitation of this attachment.
[0055] Specific examples include attachment of the posterior tibial
tendon to the navicular bone in the Kidner operation.
Navicular-cuneiform arthrodesis may be performed utilizing the
device and concurrent attachment of the tendon may be accomplished.
Attachment of the tendon may be accomplished in the absence of
arthrodesis by altering the placement of the implant in the
adjacent bone.
[0056] Ligament or capsule reattachment after rupture, avulsion of
detachment, such as in the ankle, shoulder or knee can also be
accomplished using the devices disclosed herein.
[0057] The fixation devices may be used in combination with semi
tubular, one-third tubular and dynamic compression plates, both of
metallic and absorbable composition, preferably by modifying the
collar to match the opening on the plate. The cannulated design
disclosed below can be fashioned to accept an antibiotic
impregnated rod for the slow release of medication and/or bone
growth or healing agents locally. This may be beneficial for
prophylaxis, especially in open wounds, or when osteomyelitis is
present and stabilization of fracture fragments is indicated. The
central lumen can also be used to accept a titanium or other
conductive wire or probe to deliver an electric current or
electromagnetic energy to facilitate bone healing.
[0058] A kit may be assembled for field use by military or sport
medical or paramedical personnel. This kit contains an implanting
tool, and a variety of implant device size and types, a skin
stapler, bandages, gloves, and basic tools for emergent wound and
fracture treatment. Antibiotic rods would be included for wound
prophylaxis during transport.
[0059] Referring to FIG. 1, there is illustrated generally a bone
10, shown in cross-section to reveal an outer cortical bone
component 12 and an inner cancellous bone component 14. A fracture
16 is schematically illustrated as running through the bone 10 to
at least partially divide the bone into what will for present
purposes be considered a proximal component 19 and distal component
21. The fracture 16 is simplified for the purpose of illustrating
the application of the present invention. However, as will be
understood by those of skill in the art, the fracture 16 may extend
through the bone at any of a wide variety of angles and depths. The
bone fixation device of the present invention may be useful to
stabilize two or more adjacent components of bone as long as each
component may be at least partially traversed by the bone fixation
device and anchored at opposing sides of the fracture to provide a
sufficient degree of stabilization.
[0060] A proximal aperture 18 is provided in the proximal component
19 of the bone 10, such as by drilling, as will be discussed. A
distal aperture 20 is provided in an opposing portion of bone such
as in distal bone component 21 and is connected to the proximal
aperture 18 by way of a through hole 22, as is known in the art, in
a through hole application. The fixation device may also be useful
in certain applications where the distal end of the device resides
within the bone.
[0061] The bone fixation device 24 is illustrated in FIG. 1 in its
installed position within the through hole 22. The bone fixation
device 24 generally comprises an elongate pin 26 having a proximal
end 28, a distal end 30, and an elongate pin body 32 extending
therebetween.
[0062] The distal end 30 of pin 26 is provided with a distal anchor
34, as will be discussed. A proximal anchor 36 is also provided,
such as a radially outwardly extending collar 38 connected to a
tubular housing 40 adapted to coaxially receive the pin body 32
therethrough.
[0063] The radially interior surface of the tubular housing 40, in
the illustrated embodiment, is provided with a plurality of
retention structures 42. Retention structures 42 cooperate with
corresponding retention structures 44 on the surface of pin body 32
to permit advancement of the proximal anchor 36 in the direction of
the distal anchor 34 for properly sizing and tensioning the bone
fixation device 24. Retention structures 42 then cooperate with
retention structures 44 to provide a resistance to movement of the
proximal anchor 36 in the proximal direction relative to pin body
32.
[0064] In use, the proximal projection of pin 26 which extends
beyond the proximal anchor 36 after tensioning is preferably
removed, such as by cutting, to minimize the projection of the bone
fixation device 24 from the surface of the bone.
[0065] One embodiment of the pin 26, adapted for fixing oblique
fractures of the fibula or metatarsal bone(s) is illustrated in
FIG. 2. The bone fixation device 24 of this embodiment uses a
generally cylindrical pin body 32. Although the present invention
is disclosed as embodied in a pin body 32 having a generally
circular cross section, cross sections such as oval, rectangular,
square or tapered to cause radial along with axial bone compression
or other configurations may also be used as desired for a
particular application.
[0066] Pin body 32 generally has an axial length of within the
range of from about 5 mm or about 10 mm to about 70 mm in the
as-manufactured condition. In one embodiment intended for small
bones in the foot, the pin body 32 has an axial length of about 19
mm. The illustrated embodiment shows a solid pin body 32. However,
a cannulation may be provided along the longitudinal axis of the
body to allow introduction of the pin over a wire as is understood
in the art. Hollow tubular structures may also be used.
[0067] The retention structures 44 on the surface of pin body 32 in
the illustrated embodiment comprise a plurality of annular ramp or
ratchet-type structures which permit the proximal anchor 36 to be
advanced in a distal direction with respect to pin body 32, but
which resist proximal motion of proximal anchor 36 with respect to
pin body 32. Any of a variety of ratchet-type structures can be
utilized in the present invention. The annular ramped rings
illustrated in FIG. 2 provide, among other advantages, the ability
of the ratchet to function regardless of the rotational orientation
of the proximal anchor 36 with respect to the pin body 32. In an
embodiment having a noncircular cross section, or having a
rotational link such as an axially-extending spline on the pin body
32 for cooperating with a complementary keyway on proximal anchor
36, the retention structures 42 can be provided on less than the
entire circumference of the pin body as will be appreciated by
those of skill in the art. Thus, ratchet structures can be aligned
in an axial strip such as at the bottom of an axially extending
channel in the surface of the pin body.
[0068] A single embodiment of the bone fixation device can be used
for fixing fractures in bones having any of a variety of diameters.
This is accomplished by providing the retention structures 44 over
a predetermined axial working length of the pin body 32. For
example, in the illustrated embodiment, the retention structures 44
commence at a proximal limit 46 and extend axially until a distal
limit 48. Axially extending the retention zone between limits 46
and 48 will extend the effective range of bone thicknesses which
the pin 32 can accommodate. Although the retention structures 44
may alternatively be provided throughout the entire length of the
pin body 32, retention structures 44 may not be necessary in the
most distal portions of pin body 32 in view of the minimum diameter
of bones likely to be fixed.
[0069] In one embodiment of the invention, the distal limit 48 of
retention structures 44 is spaced apart from the distal end 30 of
pin body 32 by a distance within the range of from about 4 mm to
about 20 mm, and, in embodiments for small bones in the foot, from
about 4 mm to about 8 mm. The axial length of the portion of the
pin body 32 having retention structures 44 thereon, from proximal
limit 46 to distal limit 48, is generally within the range of from
about 4 mm to about 8 mm, and was approximately 6 mm in an
embodiment having a pin body length of about 19 mm. Depending upon
the anchor design, the zone between proximal limit 46 and distal
limit 48 may extend at least about 50%, and in some embodiments in
excess of about 75% or even in excess of 90% of the length of the
pin body.
[0070] In general, the minimum diameter of the pin body 32 is a
function of the construction material of the pin and the desired
tensile strength for a given application. The maximum diameter is
established generally by the desire to minimize the diameter of the
through hole 22 while still preserving a sufficient structural
integrity of the fixation device 24 for the intended
application.
[0071] The diameter of pin body 32 will generally be in the range
of from about 1.5 mm or 1.8 mm for small bones of the foot and hand
to as large as 7.0 mm or larger for bones such as the tibia. In one
absorbable embodiment of the invention intended for use in the
first metatarsal, the pin 24 comprises poly (L, co-D,L-lactide) and
has a diameter of about 1.8 mm. Any of a variety of other materials
may also be used, as discussed infra.
[0072] The distal anchor 34 in the illustrated embodiment comprises
a plurality of ramped extensions 50 which incline radially
outwardly in the proximal direction. Extensions 50 are positioned
or compressible radially inwardly for the purpose of advancing the
pin 32 into, and, in some applications, through the through hole
22. Extensions 50 preferably exert a radially outwardly directed
bias so that they tend to extend radially outwardly from the pin
body 32 once the distal anchor 34 has advanced out through the
distal aperture 20 in bone 10. Proximal traction on the proximal
end 28 of pin body 32 will thereafter tend to cause extensions 50
to seat firmly against the outside surface of distal bone component
21, as illustrated in FIG. 1. In accordance with an optional
feature which can be included in any of the embodiments herein, the
pin body 32 is provided with a central lumen extending axially
therethrough (cannulated) for introduction over a guide pin as will
be understood by those of skill in the art.
[0073] Although any of a variety of alternate designs for distal
anchor 34 may be utilized in the context of the present invention,
any such distal anchors 34 preferably permit axial distal motion of
pin body 32 through the through hole 22, and thereafter resist
proximal withdrawal of the pin body 32 from through hole 22. As
will be appreciated by those of skill in the art, this feature
allows the bone fixation device 24 to be set within a bone through
a single proximal percutaneous puncture or incision, without the
need to expose the distal component 21 or "backside" of the bone.
This can be accomplished by biased anchors which are formed
integrally with the pin, or which are attached during
manufacturing. Distal anchors may also be hinged to the pin body,
and may be deployed by a push or pull wire extending through the
pin body if the desired construction material does not permit
adequate spring bias.
[0074] For a through hole having a diameter of about 2.3 mm, pin
bodies 32 having an outside diameter of about 1.8 mm in the areas
other than retention structures 44, and a maximum outside diameter
of about 2.24 mm in the area of retention structures 44 have been
found to be useful. In this embodiment, the maximum outside
diameter of the distal anchor 34 was approximately 2.92 mm in the
relaxed state. The axial length from the distal tip of distal end
30 to the proximal extent of extensions 50 was about 1.21 mm.
[0075] The pin body 32, together with the distal anchor 34 and
other components of the present invention can be manufactured in
accordance with any of a variety of techniques which are well known
in the art, using any of a variety of medical-grade construction
materials. For example, the pin body 32 and other components of the
present invention can be injection-molded from a variety of
medical-grade polymers including high or other density
polyethylene, nylon and polypropylene. Distal anchor 34 can be
separately formed from the pin body 32 and secured thereto in a
post-molding operation, using any of a variety of securing
techniques such as solvent bonding, thermal bonding, adhesives,
interference fits, pivotable pin and aperture relationships, and
others known in the art. Preferably, however, the distal anchor 34
is integrally molded with the pin body 32, if the desired material
has appropriate physical properties.
[0076] Retention structures 44 can also be integrally molded with
the pin body 32. Alternatively, retention structures 44 can be
machined or pressed into the pin body 32 in a post-molding
operation, or secured using other techniques depending upon the
particular design.
[0077] A variety of polymers which may be useful for the anchor
components of the present invention are identified below. Many of
these polymers have been reported to be biodegradable into
water-soluble, non-toxic materials which can be eliminated by the
body:
[0078] Polycaprolactone
[0079] Poly (L-lactide)
[0080] Poly (DL-lactide)
[0081] Polyglycolide
[0082] Poly (L-Lactide-co-D, L-Lactide)
[0083] 70:30 Poly (l-Lactide-co-D, L-Lactide)
[0084] 95:5 Poly (DL-lactide-co-glycolide)
[0085] 90:10 Poly (DL-lactide-co-glycolide)
[0086] 85:15 Poly (DL-lactide-co-glycolide).
[0087] 75:25 Poly (DL-lactide-co-glycolide)
[0088] 50:50 Poly (DL-lactide-co-glycolide)
[0089] 90:10 Poly (DL-lactide-co-caprolactone)
[0090] 75:25 Poly (DL-lactide-co-caprolactone)
[0091] 50:50 Poly (DL-lactide-co-caprolactone)
[0092] Polydioxanone
[0093] Polyesteramides
[0094] Copolyoxalates
[0095] Polycarbonates
[0096] Poly (glutamic-co-leucine)
[0097] The desirability of any one or a blend of these or other
polymers can be determined through routine experimentation by one
of skill in the art, taking into account the mechanical
requirements, preferred manufacturing techniques, and desired
reabsorption time. Optimization can be accomplished through routine
experimentation in view of the disclosure herein.
[0098] Alternatively, the anchor components can be molded, formed
or machined from biocompatible metals such as Nitinol, stainless
steel, titanium, and others known in the art. In one embodiment,
the components of the bone fixation device 24 are injection-molded
from a bioabsorbable material, to eliminate the need for a
post-healing removal step. One suitable bioabsorbable material
which appears to exhibit sufficient structural integrity for the
purpose of the present invention is poly-p-dioxanone, such as that
available from the Ethicon Division of Johnson & Johnson. Poly
(L-lactide, or co-DL-lactide) or blends of the two may
alternatively be used. As used herein, terms such as bioabsorbable,
bioresorbable and biodegradable interchangeably refer to materials
which will dissipate in situ, following a sufficient bone healing
period of time, leaving acceptable byproducts. All or portions of
any of the devices herein, as may be appropriate for the particular
design, may be made from allograft material, or synthetic bone
material as discussed elsewhere herein.
[0099] The bioabsorbable implants of this invention can be
manufactured in accordance with any of a variety of techniques
known in the art, depending upon the particular polymers used, as
well as acceptable manufacturing cost and dimensional tolerances as
will be appreciated by those of skill in the art in view of the
disclosure herein. For example, any of a variety of bioabsorbable
polymers, copolymers or polymer mixtures can be molded in a single
compression molding cycle, or the surface structures can be
machined on the surface of the pin or sleeve after the molding
cycle. It is also possible to use the techniques of U.S. Pat. No.
4,743,257, the entire disclosure of which is incorporated herein by
reference, to mold absorbable fibers and binding polymers together,
to create a fiber-reinforced absorbable anchor.
[0100] An oriented or self-reinforced structure for the anchor can
also be created during extrusion or injection molding of absorbable
polymeric melts through a suitable die or into a suitable mold at
high speed and pressure. When cooling occurs, the flow orientation
of the melt remains in the solid material as an oriented or
self-reinforcing structure. The mold can have the form of the
finished anchor component, but it is also possible to manufacture
the anchor components of the invention by machining
injection-molded or extruded semifinished products. It may be
advantageous to make the anchors from melt-molded, solid state
drawn or compressed, bioabsorbable polymeric materials, which are
described, e.g., in U.S. Pat. Nos. 4,968,317 and 4,898,186, the
entire disclosures of which are incorporated herein by way of this
reference.
[0101] Reinforcing fibers suitable for use in the anchor components
of the present invention include ceramic fibers, like bioabsorbable
hydroxyapatite or bioactive glass fibers. Such bioabsorbable,
ceramic fiber reinforced materials are described, e.g., in
published European Patent Application No. 0146398 and in
WO/96/21628, the entire disclosures of which are incorporated
herein by way of this reference.
[0102] As a general feature of the orientation, fiber-reinforcement
or self-reinforcement of the anchor components, many of the
reinforcing elements are oriented in such a way that they can carry
effectively the different external loads (such as tensile, bending
and shear loads) that are directed to the anchor as used.
[0103] The oriented and/or reinforced anchor materials for many
applications have tensile strengths in the range of about 100-2000
MPa, bending strengths in the range of about 100-600 MPa and shear
strengths in the range of about 80-400 MPa, optimized for any
particular design and application. Additionally, they are
relatively stiff and tough. These mechanical properties may be
superior to those of non-reinforced or non-oriented absorbable
polymers, which often show strengths between about 40 and 100 MPa
and are additionally may be flexible or brittle. See, e.g., S.
Vainionpaa, P. Rokkanen and P. Tormnld, "Surgical Applications of
Biodegradable Polymers in Human Tissues", Progr. Polym. Sci., Vol.
14, (1989) at 679-716, the full disclosure of which is incorporated
herein by way of this reference.
[0104] The anchor components of the invention (or a bioabsorbable
polymeric coating layer on part or all of the anchor surface), may
contain one or more bioactive substances, such as antibiotics,
chemotherapeutic substances, angiogenic growth factors, substances
for accelerating the healing of the wound, growth hormones,
antithrombogenic agents, bone growth accelerators or agents, and
the like. Such bioactive implants may be desirable because they
contribute to the healing of the injury in addition to providing
mechanical support.
[0105] In addition, the anchor components may be provided with any
of a variety of structural modifications to accomplish various
objectives, such as osteoincorporation, or more rapid or uniform
absorption into the body. For example, osteoincorporation may be
enhanced by providing a micropitted or otherwise textured surface
on the anchor components. Alternatively, capillary pathways may be
provided throughout the pin and collar, such as by manufacturing
the anchor components from an open cell foam material, which
produces tortuous pathways through the device. This construction
increases the surface area of the device which is exposed to body
fluids, thereby generally increasing the absorption rate. Capillary
pathways may alternatively be provided by laser drilling or other
technique, which will be understood by those of skill in the art in
view of the disclosure herein. In general, the extent to which the
anchor can be permeated by capillary pathways or open cell foam
passageways may be determined by balancing the desired structural
integrity of the device with the desired reabsorption time, taking
into account the particular strength and absorption characteristics
of the desired polymer.
[0106] One open cell bioabsorbable material is described in U.S.
Pat. No. 6,005,161 as a poly(hydroxy) acid in the form of an
interconnecting, open-cell meshwork which duplicates the
architecture of human cancellous bone from the iliac crest and
possesses physical property (strength) values in excess of those
demonstrated by human (mammalian) iliac crest cancellous bone. The
gross structure is said to maintain physical property values at
least equal to those of human, iliac crest, cancellous bone for a
minimum of 90 days following implantation. The disclosure of U.S.
Pat. No. 6,005,161 is incorporated by reference in its entirety
herein.
[0107] The anchors of the present invention may be sterilized by
any of the well known sterilization techniques, depending on the
type of material. Suitable sterilization techniques include heat
sterilization, radiation sterilization, such as cobalt 60
irradiation or electron beams, ethylene oxide sterilization, and
the like.
[0108] In the embodiment illustrated in FIG. 4, the proximal anchor
36 comprises a collar 38 for contacting the proximal bone component
19. Collar 38 preferably comprises a radially-outwardly extending
annular flange to optimize contact with the proximal bone component
19. Alternatively, proximal collar 38 may comprise one or more
radially-outwardly extending stops, a frusto-conical plug, or other
structures which stop the distal progress of proximal anchor 36
with respect to the through hole 22 or blind hole, depending upon
the application.
[0109] The pin body 32 cooperates with a proximal anchor 36 to
accomplish the fixation function of the present invention. Proximal
anchor 36 is preferably axially movably carried by the pin body 32
throughout a sufficient axial range of motion to accommodate a
variety of bone diameters.
[0110] Collar 38 is axially movably disposed with respect to pin
body 32 such as by connection to a tubular housing 40. Tubular
housing 40 is concentrically positioned on pin body 32, and is
provided on its interior surface with at least one, and preferably
a plurality, of retention structures 42. Retention structures 42
are configured to cooperate with the complementary retention
structures 44 on the pin body 32 to permit axial distal advancement
of collar 38 with respect to pin body 32, but resist proximal
motion of collar 38 with respect to pin body 32, as has been
discussed.
[0111] In one embodiment of the present invention, the minimum
interior diameter of the tubular housing 40 is about 2.00 mm. The
maximum interior diameter of the tubular housing 40, at the radial
outwardmost bottom of the annular recesses adapted to cooperate
with annular ridges 44 on pin body 32, is about 2.17 mm. The
outside diameter of the collar 38 is about 2.70 mm, and the
thickness in the axial direction of annular collar 38 is about 0.20
mm.
[0112] The retention structures 42 may comprise any of a variety of
complementary surface structures for cooperating with the
corresponding structures 44 on the pin 32, as is discussed
elsewhere herein. In the illustrated embodiment, the retention
structures are in the form of a plurality of annular rings or
helical threads, which extend axially throughout the length of the
tubular housing 40. The retention structure 42 may alternatively
comprise a single thread, ridge or groove or a plurality of
structures which extend only part way (e.g., at least about 10% or
25% or more) along the length of the tubular housing 40. Retention
force may be optimized by providing threads or other structures
along a substantial portion, e.g., throughout at least 75% or 80%
of the axial length of the tubular housing 40.
[0113] The overall length of the tubular housing 40 may be
maximized with respect to the depth of the target borehole for a
particular application. For example, in a device intended to fix
bones having a diameter within the range of from about 15-20 mm,
the axial length of the tubular body 40 is preferably at least
about 8 mm or 10 mm, and, more preferably, at least about 12 mm or
14 mm. In this manner, the axial length of the zone of retention
structures 42 is maximized, thereby increasing the tensile strength
of the implanted device. The proximal anchor 36 can be readily
constructed using other dimensions and configurations while still
accomplishing the desired function, as will be apparent to those of
skill in the art in view of the disclosure herein.
[0114] In use, a bone is first identified having a fracture which
is fixable by a pin-type fixation device. The clinician assesses
the bone, selects a bone drill and drills a through hole 22 in
accordance with conventional techniques.
[0115] A bone fixation device 24 having an axial length and outside
diameter suitable for the through hole 22 is selected. The distal
end 30 of the bone fixation device 24 is percutaneously or
otherwise advanced towards the bone, and subsequently advanced
through the through hole 22 until distal anchor 34 exits the distal
aperture 20. The proximal anchor 36 may be positioned on the bone
fixation device 24 prior to positioning of the pin body 32 in the
through hole 22, or following placement of the pin body 32 within
through hole 22.
[0116] Proximal traction is applied to the proximal end 28 of pin
body 32, to seat the distal anchor 34. While proximal traction is
applied to the proximal end 28 of pin body 32, such as by
conventional hemostats or a calibrated loading device, the proximal
anchor 36 is advanced distally until the anchor 36 fits snugly
against the proximal component 19 of the bone. Appropriate
tensioning of the bone fixation device 24 is accomplished by
tactile feedback or through the use of a calibration device for
applying a predetermined load on implantation.
[0117] Following appropriate tensioning of the proximal anchor 36,
the proximal end 28 of the pin body 32 may be cut off and removed.
Pin body 32 may be cut using conventional bone forceps which are
routinely available in the clinical setting. Alternatively, a pin
may be selected such that it is sized to fit the treatment site
such that following tension no proximal extension remains.
[0118] Following trimming the proximal end 28 of pin 26, the access
site may be closed and dressed in accordance with conventional
wound closure techniques.
[0119] Preferably, the clinician will have access to an array of
bone fixation devices 24, having different diameters and axial
lengths. These may be packaged one or more per package in sterile
envelopes or peelable pouches, or in dispensing cartridges which
may each hold a plurality of devices 24. Upon encountering a bone
for which the use of a fixation device is deemed appropriate, the
clinician will assess the dimensions and load requirements of the
bone, and select a bone fixation device from the array which meets
the desired specifications.
[0120] Referring to FIG. 6, there is disclosed an alternate
embodiment of the fixation pin. The fixation pin 26 illustrated in
FIG. 6 may be identical to the embodiments previously discussed,
except with respect to the proximal anchor 52. Proximal anchor 52
comprises a radially outwardly extending annular collar 54 or other
structure for resisting motion of the proximal anchor 52 in a
distal direction through the aperture in the bone. Collar 54 is
connected to a proximal portion of the tubular housing 56,
analogous to housing 40 previously discussed. Tubular housing 56 is
adapted to receive the pin body 32 therethrough.
[0121] The radially inwardly facing surface of tubular housing 56
is provided with a plurality of retention structures 58. In this
embodiment, retention structures 58 comprise a plurality of
recesses or grooves which extend radially outwardly into the
tubular housing 56. Retention structures 58 are adapted to
cooperate with corresponding retention structure 60 secured to or
integral with the pin 32. Retention structure 60 in this embodiment
comprise a plurality of radially outwardly extending annular rings
or threads, which are adapted to be received within the
corresponding retention structures 58. In this embodiment, the
proximal anchor 52 is unable to move in an axial direction with
respect to pin 32 unless sufficient axial force is applied to
plastically-deform the retention structures 58 and/or retention
structures 60 so that the tubular housing 56 snaps, ridge by ridge,
in the direction of the axial force. The precise amount of axial
force necessary to overcome the resistance to motion of proximal
anchor 52 with respect to pin 32 can be optimized through
appropriate tolerancing of the corresponding retention structures,
together with the selection of materials for the proximal anchor 52
and/or pin 32. Preferably, the tolerances and construction details
of the corresponding retention structures 58 and 60 are optimized
so that the proximal anchor 52 may be advanced distally over the
pin 32 using manual force or an installation tool, and the proximal
anchor 52 will have a sufficient retention force to resist movement
of the bone fragments under anticipated use conditions.
[0122] Referring to FIGS. 7-14, there is illustrated an alternate
embodiment of the fixation device of the present invention. This
embodiment is optimized for construction from a metal, such as
titanium or titanium alloy, although other materials including
those disclosed elsewhere herein may be utilized for the present
embodiment. Referring to FIGS. 7 and 8, the fixation device
includes a body 32 which is in the form of a pin 26 extending
between a proximal end 28 and a distal end 30. The distal end 30
includes a plurality of friction enhancing or interference fit
structures such as ramped extensions or barbs 50, for engaging the
distal cortical bone or other surface or interior cancellous bone
as has been described.
[0123] Although the illustrated embodiment includes four barbs 50,
oriented at 90.degree. with respect to each other, anywhere from
one to about twelve or more barbs 50 may be utilized as will be
apparent to those of skill in the art in view of the disclosure
herein. The barbs 50 may be radially symmetrically distributed
about the longitudinal axis of the pin 26. Each barb 50 is provided
with a transverse engagement surface 21, for contacting the distal
surface of the cortical bone or other structure or surface against
which the barb 50 is to anchor. Transverse engagement surfaces 21
may lie on a plane which is transverse to the longitudinal axis of
the pin 26, or may be inclined with respect to the longitudinal
axis of the pin 26.
[0124] Each of the transverse engagement surfaces 21 in the
illustrated embodiment lies on a common plane which is transverse
to the longitudinal axis of the pin 26. Two or more planes
containing engagement surfaces 21 may alternatively be provided.
The transverse engagement surfaces 21 may also lie on one or more
planes which are non-normal to the longitudinal axis of pin 26. For
example, the plane of a plurality of transverse engagement surfaces
21 may be inclined at an angle within the range of from about
35.degree. or 45.degree. to about 90.degree. with respect to the
longitudinal axis of the pin 26. The plane of the transverse
engagement surface may thus be selected to take into account the
angle of the distal surface of the bone through which the pin may
be positioned, as may be desired in certain clinical
applications.
[0125] In order to facilitate the radially inward compression of
the barbs 50 during the implantation process, followed by radially
outward movement of the barbs 50 to engage the distal bone surface,
each barb 50 in the illustrated embodiment is carried by a flexible
or hinged lever arm 23. Lever arms 23 may be formed by creating a
plurality of axial slots 15 in the sidewall of the pin 26. The
axial slots 15 cooperate with a central lumen 11 to isolate each
barb 50 on a unique lever arm 23. The axial length of the axial
slots 15 may be varied, depending upon the desired length over
which flexing is desirably distributed, the desired range of
lateral motion, and may vary depending upon the desired
construction material. For a relatively rigid material such as
titanium, axial lengths of the axial slot 15 in excess of about 0.1
inches and preferably in excess of about 0.2 inches are utilized on
a pin 26 having an outside diameter of about 0.1 inches and a
length of about 1.25 inches. Axial slots 15 will generally extend
within a range of from about 5% to about 90%, and often within
about 10% to about 30% of the overall length of the pin 26.
[0126] The circumferential width of the slots 15 at the distal end
30 is selected to cooperate with the dimensions of the barbs 50 to
permit radial inward deflection of each of the barbs 50 so that the
pin 26 may be press fit through a predrilled hole having an inside
diameter approximately equal to the outside diameter of the pin 26
just proximal to the transverse engagement surfaces 21. For this
purpose, each of the slots 15 tapers in circumferential direction
width from a relatively larger dimension at the distal end 30 to a
relatively smaller dimension at the proximal limit of the
axial-slot 15. See FIG. 7. In the illustrated embodiment, each slot
15 has a width of about 0.20 inches at the proximal end and a width
of about 0.035 inches at the distal end in the unstressed
orientation. The width of the slot 15 may taper continuously
throughout its length, or, as in the illustrated embodiment, is
substantially constant for a proximal section and tapered over a
distal section of the slot 15. The wall thickness of the lever arm
23 may also be tapered to increase the diameter of the central
lumen 11 in the distal direction. This will allow a lower
compressed crossing profile before the inside surfaces of the lever
arms bottom out against each other.
[0127] The pin 26 is additionally provided with a plurality of
retention structures 44 as has been discussed. Retention structures
44 are spaced apart axially along the pin 26 between a proximal
limit 46 and a distal limit 48. The axial distance between proximal
limit 46 and distal limit 48 is related to the desired axial travel
of the proximal anchor 36, and thus the range of functional sizes
of the pin. In one embodiment of the pin 26, the retention
structures 44 comprise a plurality of threads, adapted to cooperate
with the complimentary retention structures 42 on the proximal
anchor 36, which may be a complimentary plurality of threads. In
this embodiment, the proximal anchor 36 may be distally advanced
along the pin 26 by rotation of the proximal anchor 36 with respect
to the pin 26. Proximal anchor 36 may advantageously be removed
from the pin 26 by reverse rotation, such as to permit removal of
the pin 26 from the patient. For this purpose, collar 38 is
preferably provided with a gripping configuration or structure to
permit a removal tool to rotate collar 38 with respect to the pin
26. Any of a variety of gripping surfaces may be provided, such as
one or more slots, flats, bores, or the like. In the illustrated
embodiment, the collar 38 is provided with a polygonal, and in
particular, a hexagonal circumference, as seen in FIG. 12.
[0128] The proximal end 28 of the pin 26 is similarly provided with
a structure 29 for permitting rotational engagement with an
installation or a removal tool. Rotational engagement may be
accomplished using any of a variety of shapes or configurations, as
will be apparent to those of skill in the art. One convenient
structure is to provide the proximal end 26 with one or more flat
side walls, for rotationally engaging a complimentary structure on
the corresponding tool. As illustrated in FIG. 9, the proximal end
26 may be provided with a structure 29 having a square
cross-section. Alternatively, the exterior cross-section through
proximal end 28 may be any of a variety of configurations to permit
rotational coupling, such as triangular, hexagonal, or other
polygons, or one or more axially extending flat sides or channels
on an otherwise round body.
[0129] The foregoing structures enable the use of an installation
and/or deployment tool having a concentric core within a sleeve
configuration in which a first component (e.g. a sleeve) engages
the proximal anchor 36 and a second component (e.g. a core) engages
the proximal rotational engagement structure 29 of pin 26. The
first component may be rotated with respect to the second
component, so that the proximal anchor 36 may be rotated onto or
off of the retention structures 44 on pin 26. In a modified
arrangement, a first tool (e.g., a pair of pliers or a wrench) may
be used to engage the proximal anchor 36 and a second tool (e.g., a
pair of pliers or a wrench) may be used to engage the proximal
rotational engagement structure 29 of pin 26. In such an
arrangement, the first tool may be rotated with respect to the
second tool (or vice versa), so that the proximal anchor 36 may be
rotated onto or off the retention structures 44 on the pin 26.
[0130] Alternatively, the retention structures 42 on the proximal
anchor 36 may be toleranced to permit distal axial advancement onto
the pin 26, such as by elastic deformation, but require rotation
with respect to the pin 26 in order to remove the proximal anchor
36 from the pin 26.
[0131] Any of a variety of alternative retention structures may be
configured, to permit removal of the proximal anchor 36 such as
following implantation and a bone healing period of time. For
example, the retention structures 44 such as threads on the pin 26
may be provided with a plurality of axially extending flats or
interruptions, which correspond with a plurality of axial flats on
the retention structures 42 of proximal anchor 36. This
configuration enables a partial rotation (e.g. 90.degree.) of the
proximal anchor 36 with respect to the pin 26, to disengage the
corresponding retention structures and permit axial withdrawal of
the proximal anchor 36 from the pin 26. One or both of the
retention structures 44 and 42 may comprise a helical thread or one
or more circumferentially extending ridges or grooves. In a
threaded embodiment, the thread may have either a fine pitch or a
course pitch. A fine pitch may be selected where a number of
rotations of proximal anchor 36 is desired to produce a relatively
small axial travel of the anchor 36 with respect to the pin 26. In
this configuration, relatively high compressive force may be
achieved between the proximal anchor 36 and the distal anchor 34.
This configuration will also enable a relatively high resistance to
inadvertent reverse rotation of the proximal anchor 36.
Alternatively, a relatively course pitch thread such as might be
found on a luer connector may be desired for a quick twist
connection. In this configuration, a relatively low number of
rotations or partial rotation of the proximal anchor 36 will
provide a significant axial travel with respect to the pin 26. This
configuration may enhance the tactile feedback with respect to the
degree of compression placed upon the bone. The thread pitch or
other characteristics of the corresponding retention structures can
be optimized through routine experimentation by those of skill in
art in view of the disclosure herein, taking into account the
desired clinical performance.
[0132] Referring to FIG. 7, at least a first break point 31 may be
provided to facilitate breaking the proximal portion of the pin 26
which projects proximally of the collar 38 following tensioning of
the fixation system. Break point 31 in the illustrated embodiment
comprises an annular recess or groove, which provides a designed
failure point if lateral force is applied to the proximal end 28
while the remainder of the attachment system is relatively securely
fixed. At least a second break point 33 may also be provided,
depending upon the axial range of travel of the proximal anchor 36
with respect to the pin 26.
[0133] In one embodiment having two or more break points 31, 33,
the distal break point 31 is provided with one or more perforations
or a deeper recess than the proximal break point 33. In this
manner, the distal break point 31 will preferentially fail before
the proximal break point 33 in response to lateral pressure on the
proximal end 28. This will ensure the minimum projection of the pin
26 beyond the collar 38 following deployment and severing of the
proximal end 28 as will be appreciated in view of the disclosure
herein.
[0134] Proximal projection of the proximal end 28 from the proximal
anchor 36 following implantation and breaking at a breakpoint 31
may additionally be minimized or eliminated by allowing the
breakpoint 31 or 33 to break off within the proximal anchor 36.
Referring to FIG. 11, the retention structure 42 may terminate at a
point 61 distal to a proximal surface 63 on the anchor 36. An
inclined or tapered annular surface 65 increases the inside
diameter of the central aperture through proximal anchor 36, in the
proximal direction. After the proximal anchor 36 has been distally
advanced over a pin 26, such that a breakpoint 31 is positioned
between the proximal limit 61 and the proximal surface 63, lateral
pressure on the proximal end 28 of pin 26 will allow the breakpoint
31 to break within the area of the inclined surface 65. In this
manner, the proximal end of the pin 26 following breaking resides
at or distally of the proximal surface 63, thus minimizing the
profile of the device and potential tissue irritation.
[0135] For any of the (axially deployable) embodiments disclosed
above, installation can be simplified through the use of an
installation tool. The installation tool may comprise a pistol grip
or plier-type grip so that the clinician can position the tool at
the proximal extension of pin 32 and through one or more
contractions with the hand, the proximal anchor 36, 52 and distal
anchor 34 can be drawn together to appropriately tension against
the bone fragments. The use of a precalibrated tool can permit the
application of a predetermined tension in a uniform manner from pin
to pin.
[0136] Calibration of the installation device to set a
predetermined load on the pin can be accomplished through any of a
variety of means which will be understood to those of skill in the
art. For example, the pin 32 may be provided with one or more score
lines or transverse bores or other modifications which limit the
tensile strength of the part at one or more predetermined
locations. In this manner, axial tension applied to the proximal
end 28 with respect to the collar 54 will apply a predetermined
load to the bone before the pin 32 will separate at the score line.
Alternatively, internal structures within the installation tool can
be provided to apply tension up to a predetermined limit and then
release tension from the distal end of the tool.
[0137] FIG. 13 illustrates a locking guide wire 150 that may be
used with the fixation device described above. The guide wire has a
distal end 152 and a proximal end 154. The illustrated guide wire
150 comprises a locking portion 156 that is located at the distal
end 152 of the guide wire 150 and an elongated portion 158 that
preferably extends from the distal portion 156 to the proximal end
154 of the guide wire 150. The diameter D1 of the elongated portion
158 is generally smaller than the diameter D2 of the distal portion
154. The guide wire 150 can be made from stainless steel, titanium,
or any other suitable material. Preferably, in all metal systems,
the guidewire 150 and locking portion 156 are made from the same
material as the remainder of the fixation device to prevent
cathodic reactions.
[0138] The locking portion 156 on guidewire 150 can take any of a
variety of forms, and accomplish the intended function as will be
apparent to those of skill in the art in view of the disclosure
herein. For example, a generally cylindrical locking structure, as
illustrated, may be used. Alternatively, any of a variety of other
configurations in which the cross section is greater than the cross
section of the proximal portion 158 may be used. Conical,
spherical, or other shapes may be utilized, depending upon the
degree of compression desired and the manner in which the locking
portion 156 is designed to interfit with the distal end 30 of the
pin.
[0139] The guide wire 150 is configured such that its proximal end
can be threaded through the lumen 11 of the pin 26. With reference
to FIG. 8, the lumen 11 preferably comprises a first portion 160
and a second portion 162. The first portion 160 is generally
located at the distal end 30 within the region of the lever arms of
the pin 26. The second portion 162 preferably extends from the
first portion 160 to the proximal end 28 of the pin 26. The inside
diameter of the first portion 160 is generally larger than the
diameter of the second portion 162. As such, the junction between
the first portion 160 and the second portion 162 forms a transverse
annular engagement surface 164, which lies transverse to the
longitudinal axis of the pin 26.
[0140] As mentioned above, the guide wire 150 is configured such
that its proximal end can be threaded through the lumen 11 of the
pin 26. As such, the diameter D1 of the elongated portion 158 is
less than the diameter of the second portion 162 of the lumen 11.
In contrast, the diameter D2 of distal portion 156 preferably is
slightly smaller than equal to or larger than the diameter of the
first portion 160 and larger than the diameter of the second
portion 162. This arrangement allows the distal portion 156 to be
retracted proximally into the first portion 160 but prevents the
distal portion 156 from passing proximally through the pin 26.
[0141] In addition, any of a variety of friction enhancing surfaces
or surface structures may be provided, to resist distal migration
of the locking guidewire 150, post deployment. For example, any of
a variety of radially inwardly or radially outwardly directed
surface structures may be provided along the length of the locking
guidewire 150, to cooperate with a corresponding surface structure
on the inside surface of the lumen 11, to removably retain the
locking guidewire 150 therein. In one embodiment, a cylindrical
groove is provided on the inside surface of the lumen 11 to
cooperate with a radially outwardly extending annular flange or
ridge on the outside diameter of the locking guidewire 150. The
complementary surface structures may be toleranced such that the
locking guidewire or guide pin may be proximally retracted into the
lumen 11 to engage the locking structure, but the locking structure
provides a sufficient resistance to distal migration of the locking
guidewire 150 such that it is unlikely or impossible to become
disengaged under normal use.
[0142] In use, after the clinician assesses the bone, selects a
bone drill and drills a through hole 22, the distal end 152 of the
guide wire 150 and the distal end 30 of the pin 26 are advanced
through the through hole until the distal portion 156 and the barbs
50 exit the distal aperture 20. The proximal anchor 36 may be
positioned on the bone fixation device 24 prior to positioning of
the pin body 32 in the through hole 22, or following placement of
the pin body 32 within through hole 22.
[0143] The guide wire 150 is preferably thereafter retracted until
the distal portion 156 enters, at least partially, the first
portion 160 of the pin 26 (see FIG. 14). The proximal anchor 36 can
then be rotated or otherwise distally advanced with respect to the
pin body 26 so as to seat the distal anchor 34 snugly against the
distal component 21 of the bone. As such, at least a part of the
distal portion 156 of the guide wire 150 becomes locked within the
first portion 150 of the pin 26. This prevents the barbs 50 and
lever arms 24 from being compressed radially inward and ensures
that the barbs 50 remain seated snugly against the distal component
21' of the bone.
[0144] Following appropriate tensioning of the proximal anchor 36,
the proximal end 28 of the pin body 32 and the proximal end 154 of
the guide wire 150 are preferably cut off or otherwise removed.
These components may be cut using conventional bone forceps which
are routinely available in the clinical setting, or snapped off
using designed break points as has been discussed.
[0145] FIG. 15 shows a bone fixation device 200, which may be used
either in a through hole application such as that illustrated in
FIG. 1, or in a blind hole as in FIG. 26 in which the distal anchor
is deployed within cancellous bone. The fixation device 200 has a
distal portion 215 and a proximal portion 220. In general, as a
component of the proximal portion 220 of the device is axially
moved, an anchor component on the distal portion 215 of the device
advances away from the longitudinal axis of the device to engage
cancellous bone.
[0146] As with other embodiment disclosed herein, the bone fixation
device 200 may be used alone, in multiples such as two or three or
four or more per fixation, and/or together with plates,
intramedullary nails, or other support structures. The bone
fixation device 200 may also be used in any of a variety of
locations on the body, as has been discussed previously. These
include, for example, femur neck fractures, medial and lateral
malleolar fractures, condylar fractures, epicondylar fractures, and
colles fractures (distal radius and ulnar).
[0147] The bone fixation device generally comprises an elongate pin
205 having a proximal end 222, a distal end 224 and an actuator
210. As the actuator 210 is advanced distally with respect to the
pin 205, the distal portion of the pin 205 expands, engaging the
bone. FIG. 16 shows the device 200 in a deployed mode, such that
the distal portion of the pin 205 is in an expanded state.
[0148] The pin 205 can have any of a variety of dimensions,
depending upon the intended use environment. In one embodiment,
useful, for example, in a malleolar fracture, the pin has an
overall length of about 2.5 inches and a diameter of about 0.136
inches between the retention structures 240 and the distal end 224.
See FIG. 17. The outside diameter of the pin 205 proximally of the
retention structures 240 may be somewhat smaller, and, in the
illustrated embodiment, the outside diameter is about 0.130 inches.
The axial length of the retention zone which includes retention
structures 240 can also be varied widely, depending upon the range
of travel desired for the proximal anchor as has been discussed in
connection with previous embodiments. In the illustrated
embodiment, the axial length of the retention structure 240 zone is
about 0.240 inches.
[0149] The distal end 224 of pin 205 comprises a transverse surface
225 such as an annular flange formed by a radially enlarged head
227. See FIG. 18. The head 227 is provided with a frusto conical
tapered surface 229, to facilitate introduction of the device into
and advancement through a bore in a bone. The transverse surface
225 is provided to retain a hub 235, as will be discussed below. In
one embodiment, the distal end of the pin 224 immediately proximal
to the transverse surface 225 has an outside diameter of about
0.144 inches, and the adjacent portion of the head 227 has an
outside diameter of about 0.172 inches to provide a transverse
surface 225 having a radial dimension of about 0.014 inches. The
pin 205 may be cannulated as has been previously discussed.
[0150] In the illustrated embodiment, the distal tapered surface
229 is substantially smooth, to permit insertion into a predrilled
borehole. Alternatively, the distal surface 229 may include a drill
tip, such as one or more sharpened edges to enable introduction of
the fixation device 200 into a bone without the requirement of
predrilling a borehole. In a self drilling embodiment of the bone
fixation device 200, the proximal end 222 of the pin 205 may be
attached directly to a drill using a conventional chuck connection,
or may be provided with a slot, or a hexagonal cross section or
other rotational interlock structure for coupling to a rotational
driving device.
[0151] FIG. 19 shows a detailed view of the retention structure 240
on the pin for restricting movement between the actuator 210 and
the pin 205. The retention structure may comprise a plurality of
recesses, grooves, or serrations, including helical threads, which
extend radially inwardly or outwardly often in an annular
configuration. The retention structure 240 may include one or more
ramped surfaces that incline radially inwardly in the proximal
direction. These structures, and the complementary structures which
may be used on the actuator 210 have been disclosed elsewhere
herein. In the illustrated embodiment, the retention structure 240
comprises a plurality of annular ramped rings, each ramp having a
length in the axial direction of about 0.016 inches. The ramped
surfaces incline radially outwardly in the distal direction, to
facilitate distal advancement of the proximal anchor with respect
to the pin 205, and resist proximal motion of the proximal anchor
with respect to the pin 205, as is discussed elsewhere herein.
[0152] A radially advanceable anchor 230 (FIGS. 20 and 21) is
provided at the distal end of the pin. The anchor 230 is shown as
having four axially extending strips or tines 231, 232, 233, 234
carried by the pin; however, the anchor 230 may have one or two or
a plurality of axially extending strips. The strips 231-234 are
moveable from an axial orientation (for insertion) to an inclined
orientation in response to an axial proximal retraction of the pin
relative to the actuator 210. The proximal end of the strips
231-234 are free, to permit radial enlargement. The distal end of
the strips 231-234 are attached to the distal end of the pin 205
either directly (e.g. FIG. 16A), or indirectly such as in FIGS.
15-16. The collapsed anchor 230 may be provided with an outside
diameter that is less than the outside diameter of the actuator
tube 210 and the head 227 of the pin 205, to facilitate insertion
into the hole without placing stress on the anchor 230.
[0153] In the illustrated embodiment, the anchor 230 is formed as a
separate component of the fixation system. This enables the pin 205
and the actuator 210 to be conveniently manufactured from a
bioabsorbable material, while the anchor assembly 230 may be made
from any of a variety of biocompatible metals such as stainless
steel, titanium or nickel titanium alloys such as nitinol. This
variety of a hybrid absorbable-nonabsorbable fixation device takes
advantage of the strength and flexibility of nitinol or other metal
in the area of the strips 231-234, yet leaves only a minimal amount
of metal within the bone following dissolution of the bioabsorbable
component. In addition, the long term indwelling component (the
metal anchor) does not span the fracture.
[0154] Although sometimes referred to herein as "strips" the
moveable anchor components 231-234 may take any of a variety of
shapes, depending upon the desired construction materials,
manufacturing technique and performance. In the illustrated
embodiment, the anchor 230 may formed from a piece of tubing stock,
such as nitinol tubing, by laser etching or other cutting
technique. The anchor 230 has an outside diameter of about 0.172
inches, and an axial length of about 0.394 inches. Each of the
strips 231-234 has a width in the circumferential direction of
approximately 0.08 inches and a radial direction wall thickness of
no more than about 0.014 inches. However, any of a variety of
dimensions may be utilized, as will be apparent to those of skill
in the art in view of the disclosure herein. In addition, more or
fewer than four axially extending tines 231-234 may be readily
provided.
[0155] The strips 231-234 may alternatively be formed from a round
cross section material such as wire, or other separate component
which is assembled or fabricated into a finished multi strip anchor
230.
[0156] In the illustrated anchor 230, the proximal end 237 of each
strip is provided with a ramped surface 239. The ramped surface
causes the radial thickness of the strip to decrease in the
proximal direction. This ramped surface 239 cooperates with a
complementary ramped surface on the actuator, discussed elsewhere
herein, to facilitate radial outward advancement of the anchor in
response to proximal retraction of the pin 205 with respect to the
actuator 210.
[0157] The ramped surface 239 on each tine or strip also acts as a
leading cutting edge to permit each tine to cut into cancellous
bone as it advances along a path which will normally be inclined
radially outwardly in the proximal direction, in response to
proximal retraction of the pin with respect to the actuator.
Placing the ramped surface on the radially inwardly facing surface
of the tine may allow the tine to seek a maximum angle with respect
to the longitudinal axis of the pin, following deployment. This
anchor construction thus enables each of the tines to create its
own path through the bone such that the cross section of the tine
substantially fills the cross section of the path which it creates.
The length of the path along the axis of the tine is generally at
least about two times, and in certain embodiments is at least as
much as three times or five or more times the average cross section
of the tine. The path may be substantially linear or curved, such
as slightly concave outwardly from the axis of the pin.
[0158] The pin 205 may comprise two or more anchors 230 along its
length, each anchor comprising one or two or more (e.g., 4) axial
strips. The anchors are each moveable from an axial orientation for
distal insertion through a bore in the bone to an inclined
orientation to resist proximal axial movement through the bone. In
certain embodiments, the anchor 230 and pin 205 are provided with a
mechanical interlock such as a projection and slot or other
complementary surface structures to prevent rotation of the anchor
230 with respect to the pin 205.
[0159] Referring to FIG. 16B, there is illustrated an in-line or
intermediate anchor 230, which may be used in combination with a
distal anchor such as that illustrated in FIG. 220, to provide two
cancellous bone anchors spaced axially apart along the fixation
device. In one embodiment, each of the two cancellous bone anchors
is provided with four axially extending anchor strips 231-234. In
the embodiment of FIG. 16B, each of the anchor strips 232 and 234
may be provided with an inclined surface 239 as has been discussed,
to cooperate with a complementary inclined surface on the actuator
210. Actuator 210 may be provided with an opening 242 corresponding
to each strip 232, to permit functioning of the anchor as will be
understood by reference to FIG. 16B. In a hybrid
absorbable-nonabsorbable fixation device, the intermediate anchor
230 may be formed from a structure similar to that illustrated in
FIG. 20, which is molded into the pin or fit into a recess or
against a transverse stop surface on the pin 205. Alternatively,
the pin 205 may be formed from a tubular metal stock, and each of
the axial strips 232 is formed by cutting a channel 244 such as a U
shaped channel using conventional laser cutting or other techniques
to isolate the anchor strip. The anchor strips may then be biased
radially outwardly by prebending them slightly in excess of the
elastic limit, to facilitate each strip 232 entering the
corresponding aperture 242. Variations on the foregoing anchor
structures may be readily envisioned by those of skill in the art
in view of the disclosure herein.
[0160] The illustrated anchor assembly 230 (FIG. 20) includes a hub
235 carried by the pin, such that the distal end of each axially
extending strip is attached to the hub. The hub may comprise an
annular ring, which is rigidly affixed to or slidably carried by
the pin 205. The axial strips may also be fixed directly to the pin
205, such as illustrated in FIG. 16A in which the strips are
integrally formed with the pin 205. The shaft of pin 205 can be
solid or cannulated to allow for insertion of guides such as
k-wires.
[0161] The hub 235 or other structure which carries the anchor
tines may be rotationally locked to the pin 205 and/or the actuator
210. Any of a variety of key or spline type relationships between
the hub 235 and the pin 205 may be used. For example, an axially
extending recess or groove in the pin 205 can receive a radially
inwardly directed projection or extension of the hub 235.
Alternatively, nonround complementary cross sectional
configurations can be utilized for the pin 205 in the area of the
hub 235. As a further alternative, the hub 235 or anchor tines can
be insert molded within a bioreasorbable or other polymeric pin
205. Similar antirotation locks can be utilized for the proximal
anchor or collar, as discussed elsewhere herein. Antirotation
structures may be desirable in certain applications where rotation
of the first and second bone fragments about the axis of the
fixation pin may be clinically disadvantageous.
[0162] The actuator 210, as shown in FIG. 22, comprises a tubular
body 212 axially slidable on the pin. FIGS. 23-25 show additional
views of the actuator. The distal end of the actuator may be
provided with a tapered surface 246, such that proximal retraction
of the pin with respect to the actuator causes the anchor to
incline outwardly as it slides along the tapered surface. In one
embodiment, the tapered surface 246 is provided on a metal leading
ring 247, on an otherwise polymeric (e.g., absorbable) tubular
body.
[0163] The actuator 210 can take any of a variety of forms, in
addition to the tubular structure illustrated in FIGS. 22-25. For
example, the actuator 210 may extend axially moveably within an
internal lumen inside of the pin 205. Alternatively, the actuator
210 may comprise an axially extending pull wire or strip which
extends along side of the pin 205. In an embodiment of the type
illustrated in FIG. 22, and dimensioned, for example, for use in a
malleolar fracture, the tubular body 210 has an axial length of
about 1.55 inches, and an outside diameter of about 0.172 inches.
The inside diameter is approximately 0.138 inches, and the distal
ramped surface 246 inclines at an angle of about 30.degree. with
respect to the longitudinal axis of the device. At least one
axially extending stress release slot 242 extends through the
retention structure 244, discussed below. The stress release slot
has an axial length of about 0.200 inches, and a width of about
0.018 inches. The proximal collar 238, discussed below, has an
outside diameter of about 0.275 inches.
[0164] The actuator 210 further comprises a collar 238. Collar 238
is axially movably disposed with respect to pin 205 by connection
to actuator 210. The collar 238 seats against the proximal bone
fragment to retain compression across the fracture. Collar 238 can
be any of a variety of shapes or sizes, as has been discussed. The
outer periphery of collar 238 can also have a radius in the axial
direction or other adaptations to allow for countersinking or for
cooperation with or to function as a fixation plate. The collar can
act as a washer, with or without spikes for engaging tissue.
[0165] A retention structure 242 is preferably located on the
actuator 210, permitting proximal movement of the pin with respect
to the actuator, but resisting distal movement of the pin with
respect to the actuator as has been discussed. The retention
structure 242 may comprise a plurality of inwardly or outwardly
extending annular rings or threads. The retention structure 242 on
the actuator cooperates with the retention structure 240 on the pin
to retain the device under compression. The retention structure may
also include a rotational link or axially extending spline for
cooperating with a complementary keyway or structure on the pin 205
to prevent rotation of the pin with respect to the actuator
210.
[0166] The actuator can be made from any of a variety of suitable
materials or combination of materials. Preferably, the anchor is
made from a metallic material, such as titanium or titanium alloy,
although other materials including those disclosed elsewhere herein
may be utilized for the present invention. The pin and actuator are
preferably made of a bioabsorbable material, as previously
discussed herein, such as Poly (L-lactide-co-D, L-lactide).
[0167] The proximal portion of the pin 205 can be sized to length
or longer than required. The proximal portion of pin 205 which
extends beyond the proximal end of actuator 210 after tensioning is
preferably removed to minimize the projection of bone fixation
device 200 from the surface of the bone. As previously discussed,
at least a first break point may be provided on the pin 205 to
facilitate breaking the proximal portion of the pin 205. A break
point, which may be an annular recess, groove, or notch, provides a
designed failure point if lateral force is applied to the proximal
end 220 while the remainder of the fixation device 200 is securely
fixed. At least a second break point may also be provided.
Alternative methods of sizing to length may also be utilized, as
known to those of skill in the art.
[0168] Although the present invention is disclosed as embodied in a
bone fixation device 200 having a generally circular cross section,
cross sections such as oval, rectangular, or square may be used.
Independently, the pin 205 may be tapered along its length to cause
radial along with axial bone compression. Furthermore, the device
may be used in combination with support features, such as plates or
intramedullary nails.
[0169] FIG. 26 demonstrates the device 200 deployed for fracture
fixation of the medial and lateral malleolar fractures. As the pin
is proximally retracted with respect to the actuator, the anchor
deploys radially outwardly from the pin in the proximal direction.
The anchor 230 is typically embedded into the cancellous portion of
the bone. The collar supports the proximal fragment of bone,
provides compression as locking tension increases on the shaft, and
initiates expansion of the umbrella.
[0170] The specific dimensions of any of the bone fixation devices
of the present invention can be readily varied depending upon the
intended application, as will be apparent to those of skill in the
art in view of the disclosure herein. Features from the various
embodiments described above may also be incorporated into the
other.
[0171] Although the present invention has been described in terms
of certain preferred embodiments, other embodiments of the
invention including variations in dimensions, configuration and
materials will be apparent to those of skill in the art in view of
the disclosure herein. In addition, all features discussed in
connection with any one embodiment herein can be readily adapted
for use in other embodiments herein. The use of different terms or
reference numerals for similar features in different embodiments
does not imply differences other than those which may be expressly
set forth. Accordingly, the present invention is intended to be
described solely by reference to the appended claims, and not
limited to the preferred embodiments disclosed herein.
* * * * *