U.S. patent application number 16/572087 was filed with the patent office on 2020-04-09 for devices and methods for repairing bone fractures.
The applicant listed for this patent is Syntorr, Inc.. Invention is credited to Jeremi M. LEASURE, Daniel L. MARTIN.
Application Number | 20200107869 16/572087 |
Document ID | / |
Family ID | 63582030 |
Filed Date | 2020-04-09 |
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United States Patent
Application |
20200107869 |
Kind Code |
A1 |
MARTIN; Daniel L. ; et
al. |
April 9, 2020 |
DEVICES AND METHODS FOR REPAIRING BONE FRACTURES
Abstract
Devices and methods for repairing bone fractures are described
herein. A pin directing device for steering a flexible bone screw
is disclosed. A fluted entry tool for penetrating into cancellous
bone without penetrating the far cortex of the bone is disclosed. A
flexible bone screw having a rotational position marker positioned
thereon at a terminal twenty-five percent of the shaft is
disclosed. A flexible bone screw comprising at least eighty percent
cold work hardened alloy is disclosed. A pin bending clamp having a
transverse hole in the jaws is disclosed. A flexible bone screw
with a cortex climbing thread portion at the tip, which is
helicoid, is also disclosed.
Inventors: |
MARTIN; Daniel L.; (Palo
Alto, CA) ; LEASURE; Jeremi M.; (San Francisco,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Syntorr, Inc. |
Palo Alto |
CA |
US |
|
|
Family ID: |
63582030 |
Appl. No.: |
16/572087 |
Filed: |
September 16, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15891346 |
Feb 7, 2018 |
10413344 |
|
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16572087 |
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62455953 |
Feb 7, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 17/8635 20130101;
A61B 17/8863 20130101; A61B 17/866 20130101; A61B 17/7233 20130101;
A61B 17/7208 20130101; A61B 17/863 20130101; A61B 17/8861
20130101 |
International
Class: |
A61B 17/86 20060101
A61B017/86; A61B 17/72 20060101 A61B017/72; A61B 17/88 20060101
A61B017/88 |
Claims
1. A threaded orthopedic device, comprising: a flexible shaft; and
a threaded portion that is disposed on one end of the shaft,
wherein the threaded portion includes a tip region with a tip
thread, a body portion with a body thread that has a major diameter
that is equal to or greater than the largest major diameter of the
tip thread, and a transition point disposed where an edge surface
of the tip thread meets an edge surface of the body thread, and
wherein the tip region is disposed within a cone that is 1)
centered on a longitudinal axis of the shaft and 2) passes through
the transition point.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/891,346, filed Feb. 7, 2018, which
application claims the benefit of U.S. Provisional Patent
Application Ser. No. 62/455,953, filed Feb. 7, 2017, which are
incorporated by reference herein.
BACKGROUND
Field
[0002] The present disclosure generally relates to devices and
methods for repairing bone fractures, and more specifically to
improved flexible bone screw devices and methods.
Description of the Related Art
[0003] Surgical techniques for the treatment of bone fractures
commonly known and used in the art include external fixation,
pinning, and joint replacement. In some situations, each of these
techniques can be inadequate for facilitating satisfactory recover
of the bone fracture. A proximal humerus fracture, i.e., a fracture
of the humerus near the humeral head, is one such case. Replacement
of the shoulder joint with a prosthesis is a complex and invasive
procedure that can lead to the death of elderly patients, for whom
proximal humerus fractures are common. Similarly, internal fixation
of a proximal humerus fracture with one or more humeral plates and
bone screws may successfully maintain the correct position of the
humerus fragments, but the extensive dissection of soft tissue that
is an integral part of this approach leads to high morbidity.
[0004] In light of the above, flexible bone screws have been
developed for treatment of certain fractures, such as the
percutaneous fixation of softer bone tissue to stronger bone
tissue. For example, in a proximal humerus fracture, one or more
flexible bone screws can be employed to fix the cancellous bone of
the humeral head to the cortical bone of the humerus bone shaft.
Specifically, a flexible bone screw is introduced into the
intramedullary cavity of a humerus through an opening in the
antero-lateral cortex on a first side of the humerus. The flexible
bone screw is then advanced, via rotation, into the intramedullary
cavity along an interior surface of the cortex on a second side of
the humerus, and threaded into the subchondral bone of the humeral
head.
[0005] When initially advanced into the intramedullary cavity,
threads at the tip of the flexible bone screw typically contact an
interior surface of the cortex at some angle of incidence. Rotation
of the flexible bone screw and contact between the threads and the
interior surface of the cortex then cause the bone screw to move
along the interior surface of the cortex toward the humeral head.
Thus, during installation, the flexible bone screw undergoes
significant bending while being rotated, similar to that
experienced by a material sample undergoing a rotating beam test.
As a result, the bone screw can subject to significant fatigue
during a normal installation procedure, and plastically deform,
heat, or even fail during the installation, each of which is highly
undesirable.
[0006] Accordingly, there is a need in the art for a flexible bone
screw capable of bending during rotation.
SUMMARY
[0007] Devices and methods for repairing bone fractures are
described herein. A pin directing device for steering a flexible
bone screw is disclosed. A fluted entry tool for penetrating into
cancellous bone without penetrating the far cortex of the bone is
disclosed. A flexible bone screw having a rotational position
marker positioned thereon at a terminal twenty-five percent of the
shaft is disclosed. A flexible bone screw comprising at least
eighty percent cold work hardened alloy is disclosed. A pin bending
clamp having a transverse hole in the jaws is disclosed. A flexible
bone screw with a cortex climbing thread portion at the tip, which
is helicoid, is also disclosed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] So that the manner in which the above recited features of
the present disclosure can be understood in detail, a more
particular description of the disclosure, briefly summarized above,
may be had by reference to examples, some of which are illustrated
in the appended drawings. It is to be noted, however, that the
appended drawings illustrate only exemplary examples and are
therefore not to be considered limiting of its scope, may admit to
other equally effective implementations.
[0009] FIG. 1 illustrates the installation of a flexible bone screw
for percutaneous fixation of a proximal humerus fracture, according
to various embodiments of the disclosure.
[0010] FIG. 2 illustrates the elastic bending arc of a flexible
bone screw 202, where flexible bone screw 202 represents flexible
bone screw 100 described in FIG. 1.
[0011] FIG. 3A is cross-sectional view of an orthopedic screw
device, according to the present disclosure.
[0012] FIG. 3B is an end-view projection of the orthopedic screw
device of FIG. 3A, according to an embodiment of the present
disclosure.
[0013] FIG. 4 is cross-sectional view of the orthopedic screw
device of FIGS. 3A and 3B, a surface of rotation, and a projected
surface area of helicoid surfaces that are coincident with the
surface of rotation, according to an embodiment of the present
disclosure.
[0014] FIG. 5 is a side view of a screw tip that includes a
significant surface area that is coincident with a surface of
rotation, according to an embodiment of the present disclosure.
[0015] FIG. 6 depicts multiple views of a tip of a fluted entry
tool according to embodiments of the present disclosure.
[0016] FIG. 7 is an illustration of a fluted entry tool tilted to
initiate oblique entry into the bone in an approximately orthogonal
direction to the surface of a bone, according to an embodiment of
the present disclosure.
[0017] FIG. 8 is an illustration of the fluted entry tool of FIG. 7
tilted to initiate oblique entry into a bone, according to an
embodiment of the present disclosure.
[0018] FIG. 9 includes multiple views of a pin directing device,
according to embodiments of the present disclosure.
[0019] FIG. 10 is an illustration of a pin directing device slipped
onto the shaft end of a flexible bone screw, according to an
embodiment of the present disclosure.
[0020] FIG. 11 is an illustration of a flexible bone screw and pin
directing device passing through a hole in the cortex of the bone
into the intramedullary space of the bone, according to an
embodiment of the present disclosure.
[0021] FIG. 12 is a flexible bone screw with a rotary position
marker, according to an embodiment of the present disclosure.
[0022] FIG. 13A is a view of one bending tool of a pair of bending
tools that make up a pin bending clamp, according to embodiments of
the present disclosure.
[0023] FIG. 13B is a close-up view of the tips of one bending tool,
according to embodiments of the present disclosure.
[0024] FIG. 13C is a view of one bending tool of a pin bending
clamp holding a shaft of a flexible bone screw, according to
embodiments of the present disclosure.
[0025] FIG. 13D is a view of a pin bending clamp being used to bend
a shaft of a flexible bone screw, according to embodiments of the
present disclosure.
[0026] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures. It is contemplated that elements
and features of one implementation may be beneficially incorporated
in other implementations without further recitation.
DETAILED DESCRIPTION
[0027] Flexible Bone Screw with Cold Worked Alloy
[0028] Cortical bone screws, which are designed for fixation of
cortical bone, typically have a rounded tip, often a surface of
revolution, that will not penetrate into cortical bone without a
pilot hole, and will start to penetrate into cancellous bone only
with considerable forward force. Cancellous bone screws, which are
designed for fixation of cancellous bone, may have a reduced core
diameter of the thread near a tapered tip, to facilitate
penetration of both cortical bone and cancellous bone, without
drilling a pilot hole. Some have cutting flutes, to facilitate
cutting of threads into the bone, especially when there has been a
pilot hole drilled. Some have trocar points, which are highly
inclined to penetrate directly into cortical bone or cancellous
bone, and not walk along the surface of the bone. Generally, the
prior art screws have a geometry that is designed either to
penetrate without a pilot hole, or to penetrate only with a pilot
hole.
[0029] In the use of the flexible bone screw, penetration of the
far cortex is not wanted. Rather, it is preferable to have the
screw walk its way up the inside of the far cortex, without
penetrating the far cortex, as illustrated in FIG. 1. FIG. 1
illustrates the installation of a flexible bone screw 100 for
percutaneous fixation of a proximal humerus fracture 130, according
to various embodiments of the disclosure. Specifically, flexible
bone screw 100 fixes humeral head 152 of a humerus 100 to a bone
shaft 153. First, humeral head 152 is returned to its proper
position on bone shaft 153, using methods standard to the art of
orthopedic surgery. Then, one or more flexible bone screws 100 are
introduced into the intramedullary cavity 110 of humerus 150
through an entry hole 154 in the side cortex 155 of humerus 100.
For clarity, only one flexible bone screw 100 is depicted in FIG.
1. Each flexible bone screw 100 is then advanced into the
intramedullary cavity 110, along an inner surface 159 of a far
cortex 157, and threaded into cancellous bone 156 of humerus 150.
Thus, the flexible bone screw converts to an axial intramedullary
device, with a tip 109 advanced across proximal humerus fracture
130, and further advanced into cancellous bone 156 in humeral head
152 without a pilot hole being formed.
[0030] As shown, during and after the installation process, there
is significant bending of flexible bone screw 100. Thus, flexible
bone screw 100 should be configured to allow elastic bending to a
relatively small radius of curvature before plastic bending occurs.
In addition, there is a need for a thread on tip 109 of flexible
bone screw 100 that will climb along the inner surface of far
cortex 107 during installation, rather than penetrate into cortical
bone. Further, tip 109 should be configured to penetrate directly
into a cancellous bone volume in response to being rotated during
installation. Direct penetration into cancellous bone is especially
desired when flexible bone screw 100 is engaging the cancellous
bone while tip 109 is moving substantially along the axis of
flexible bone screw 100 and tip 109.
[0031] According to various embodiments, an orthopedic screw device
with cortex climbing thread, such as flexible bone screw 100,
enables a tip to perform both functions. Flexible bone screw 100 is
fabricated from stainless steel and includes a shaft 101 with a
shaft diameter 102 and a threaded portion 103 located at tip 109.
The surface of shaft 101 is substantially smooth, having a surface
roughness, Ra, of less than about 3 micrometers, where the surface
roughness is measured parallel to the axis of shaft 101. The smooth
shaft surface allows easy gliding of shaft 101 into entry hole 154,
so that if humeral head 152 should collapse, shaft 101 slides out
of entry hole 154 rather than being engaged therewith, which would
force threaded portion 103 through cancellous bone 156. Threaded
portion 103 is positioned at one end of shaft 101 for engagement
with bone material, has a length 105 and has an outer diameter 104
that is larger than shaft diameter 102. A tool engagement portion
is positioned at the opposite end of shaft 101 to facilitate
attachment of flexible bone screw 100 to a manual or powered
screw-rotating device, and does not engage against bone. One
example of such a tool engagement portion is tool engagement
portion 1228, shown in FIG. 12. Flexible bone screw 100 is
configured so that tool engagement portion 107 and any extra length
of shaft 101 can be cut off at the completion of surgery. In this
embodiment, shaft diameter 102 is between 1.7 mm and 3 mm; the
overall length of flexible bone screw 100 is at least about 200 mm,
preferably 300 mm; length 105 is between 6 mm and 25 mm, and outer
diameter 104 is between 3 mm and 5 mm. Having a shaft diameter less
than about 3 mm allows a shaft stiffness which is not excessive for
manipulation by the surgeon during surgery. In order for flexible
bone screw 100 to have sufficient flexibility for many
applications, i.e., an elastic bending arc of at least 15.degree.,
in some embodiments, the ratio of the length of shaft 101 to shaft
diameter 102 is at least about 50:1. In some embodiments, flexible
bone screw 100 has an elastic bending arc that is at least about
30.degree. and the ratio of the length of shaft 101 to shaft
diameter 102 is at least about 100:1. Such an elastic bending arc
avoids use of flexible bone screw being employed in the plastic
deformation range, thereby preventing possible mechanical failure
of flexible bone screw 100 during installation. The elastic bending
arc of flexible bone screw 100 is described below in conjunction
with FIG. 3.
[0032] In other embodiments, one or more features of flexible bone
screw 100, as described above, may have different dimensions based
on what bone is being treated, the location of the fracture, and
other factors. For example, the ratio of length 105 to the overall
length of shaft 101 may be as high as 0.20, the ratio of outer
diameter 104 to shaft diameter 102 may vary between about 1.2 and
about 4.0, and the possible elastic bending arc may be greater than
20.degree. to 30.degree.. Other features that may have different
values include shaft diameter 102, outer diameter 104, length 105,
and the overall length of shaft 101. Flexible bone screw 100
permits a large amount of strain prior to plastic deformation.
Stated differently, shaft 101 allows elastic bending to a
relatively small radius of curvature before plastic bending occurs.
According to various embodiments described herein, while flexible
bone screw 100 is spinning in a bent configuration, there is
minimal or no plastic deformation of shaft 101. Plastic deformation
in this situation is analogous to a rotating beam fatigue test, and
may contribute to failure of flexible bone screw 100 through
breakage. It is noted that flexible bone screw prototypes that were
manufactured with standard stainless steel showed plastic
deformation during the course of normal insertion as well as
associated heating of the shaft during insertion. In some
embodiments, such plastic deformation is prevented in flexible bone
screw 100 by forming shaft 101 with a cold-worked alloy, i.e., with
a material that has been strain hardened, as described below, or by
choosing alloys that have a higher yield strain than standard
stainless steel.
[0033] The motivation for choosing a cold worked alloy for flexible
bone screw 100 is different than in conventional bone pins and
screws. Specifically, flexible bone screw 100 is bent into an arc
during spinning insertion, whereas other pins and screws generally
have bending elastic strain requirement only after insertion.
Conventional bone screws and pins are inserted strictly along a
straight line, and do not require a high yield strain to prevent
plastic deformation during insertion. Flexible bone screw 100
benefits from the high yield strain offered by cold working during
the insertion process, which is different from other surgical
screws and pins. That is, the high yield strain of the cold-worked
material of shaft 101 protects shaft 101 from fatigue damage and
failure during insertion. Manufacturing with cold-worked stainless
steel alloy is more expensive than with a non cold worked (i.e.,
annealed) alloy, but the value offered by cold working is an
unexpected added feature that justifies the added expense of
manufacture.
[0034] The elastic bending tolerance of shaft 101 of flexible bone
screw 100 may be approximated by the analytic consideration of
Youngs modulus E, yield strength and dimensions of shaft 101, where
yield strength (or yield stress) is the stress at which a material
begins to deform plastically. During the spinning insertion of
shaft 101 along an arcuate path, as shown in FIG. 1, there is a
risk of continuous plastic deformation of shaft 101, such that
there is reduced strength, and possible breakage. Such plastic
deformation and associated breakage can be avoided by having the
material of shaft 101 remain within the yield strain (elastic
deformation regime) of the material while shaft 101 is bent during
insertion. According to various embodiments, shaft 101 is formed
from a material with higher yield strength than the conventional
annealed stainless steel that is commonly employed in orthopedic
devices. Increasing the yield strength of the material of shaft 101
directly increases the strain to yield of shaft 101, i.e., the
amount of deflection that shaft 101 can undergo before beginning to
plastically deform. When shaft 101 is formed of a material with
higher strain to yield, the elastic bending arc of shaft 101 is
increased, for example from 5.degree. or less up to 30.degree. or
more. This increased elastic bending arc enables the radius of
curvature of the bend during insertion to be shorter while shaft
101 remains within an elastic bending range. The elastic bending
arc of a flexible bone screw is described below in conjunction with
FIG. 2.
[0035] FIG. 2 illustrates the elastic bending arc 201 of a flexible
bone screw 202, where flexible bone screw 202 represents flexible
bone screw 100 described in FIG. 1. Elastic bending arc 201 is
defined as the maximum arc of curvature, in degrees, that can be
produced by flexible bone screw 202 without flexible bone screw 202
undergoing substantial plastic deformation. Hence, a more flexible
bone screw has an elastic bending arc of greater degree than a less
flexible bone screw. Elastic bending arc 201 defines how easily
flexible bone screw 202 can be manipulated by the surgeon.
Generally, the surgeon bends a flexible bone screw to a minimum arc
of 15.degree., and preferably to an arc of 30.degree., without the
use of excessive force or localized glove pressure, in order to
insert the bone screw with hand held tools. For larger shaft
diameters, the surgeon obtains greater bending leverage by having a
correspondingly longer bone screw length, but elastic bending arc
201, in such a case, typically remains the same, and is preferably
as large an angle as practicable.
[0036] The elastic bending arc of a flexible bone screw, according
to various embodiments of the invention, is by design much greater
than any other prior art bone screws formed from a metal or metal
alloy that is not cold-worked. Such improved flexibility addresses
specific previously unsolved needs in fracture treatment. This
characteristic has been achieved by selecting a cold-worked alloy,
i.e., a strain-hardened material, for forming a shaft of a flexible
bone screw. It is noted that machining and other manufacturing
processes are more difficult when performed on strain-hardened
metal allow compared to an annealed metal alloy of the same
composition. However, as set forth above, the increased flexibility
of a flexible bone screw formed from a cold-worked metal alloy
provides unique, novel advantages, as has been demonstrated by the
inventor.
[0037] To achieve high yield strain for stainless steel, yield
strain can be increased by nearly a factor of between five and ten,
between the annealed state and fully cold worked state.
[0038] The Young's modulus of 316L is 193-200 GPa. In the
non-cold-worked state, the yield strength is approximately 170 MPa.
Fully cold worked yield strength is in the range of 1070-1600 MPa.
The radius of curvature R achieved without plastic deformation
is
R=dE/2(yield strength)
[0039] Where d is the shaft diameter. In an example, for a shaft
diameter of 2 mm, the non-plastic deformation radius of curvature
for non cold worked 316L: E=200 GPa, and yield strength=170 MPa,
which gives a radius R of 1.18 m. By contrast, in an example of
same shaft diameter of 2 mm, fully cold worked 316L, E=200 GPa, and
yield strength=1600 MPa. This gives a radius R of 0.125 m. The
forgoing comparison shows the dramatically increased safety
achieved by using the cold worked material for shaft 101 of
flexible bone screw 100.
[0040] 316L stainless steel may be chosen in different grades of
cold work tempers, as in ASTM A 666. Progressive increases in yield
strength, and therefore reduction in elastic bending radius, are
achieved with cold work, progressing from annealed, 1/4 hard, 1/2
hard, 3/4 hard, to full hard. The above examples represent the
extremes from annealed to full hard. Similarly, Grade 5 Ti alloy
and other mechanically similar Ti alloys, with a yield strength of
1100 MPa, also offer a high degree of safety with fatigue bending
during spinning insertion, over non-cold worked 316L. Similarly,
Grade 5 Ti alloy is more expensive in manufacture, compared to
grades of commercially pure titanium. Therefore the choice of grade
5 Ti alloy may also be made to achieve the bending requirements
found at insertion of the flexible bone screw.
[0041] There are no prior art bone screws that are designed to be
threadedly advanced while bent into a 10.degree. arc or greater.
Thus, the flexible bone screw prevents a unique design challenge,
requiring a combination of both dimensions and materials to render
the device effective. More specifically, the special demands on the
flexible bone screw shafts make the material requirements unique in
combination with the dimensions and methodology of use. Smooth pins
and bone screws made with non-cold-worked material are usable in
other orthopedic applications, although they have lower yield
strength. There are no other threaded orthopedic devices that are
advanced while spinning and bent into a curve of 10.degree. to
15.degree. or more, as are flexible bone screws. The purpose for
use of cold worked materials in other orthopedic implants is to
achieve high yield strength, and they are generally designed to
avoid having the intraosseous portion being bent into an arc while
being advanced. Threaded orthopedic devices are generally designed
to be stiff, rather than with dimensions and material properties to
allow flexibility.
[0042] This disclosure specifies flexible bone screws having a
length to shaft diameter ratio of greater than 50, and greater than
100, as well as a thread diameter to shaft diameter ratio of
greater than 1.2, being fabricated from cold worked titanium or
stainless steel alloys. In one example, the flexible bone screw 420
is made of a cold worked 300 series stainless steel, such as 316
stainless steel. In another example, the flexible bone screw 202 is
made of a titanium alloy, especially grade 5 Titanium, or other
mechanically equivalent Titanium alloy. In yet another example, the
flexible bone screw 202 is made of an alloy that is hardened by an
at least 49 percent cold work process. In one example, the cold
work of the flexible bone screw 202 is greater than 80%. In another
example, the cold work of the flexible bone screw 202 is greater
than 90%. In some embodiments, the fabrication material of the
disclosed flexible bone screw 202 with cold worked alloy may be
"spring hard," the flexible bone screw 202 is flexible and may
spring, but is not too hard for use in repairing bone fractures,
when resiliency is desired to maintain the integrity of the
flexible bone screw 202 that has been inserted into the
patient.
[0043] The cold working is one of the only means to achieve the
required hardness, or yield strength, in the stainless steel alloys
and metals that are typically used for orthopedic implant
applications. The combination of the design dimensions of the
flexible bone screw 202 with the cold working of the metal provides
advantages that cannot be accrued with adding cold working to the
metal of other orthopedic implants having different dimensional
features. The cold working allows the flexible bone screw 202 to be
more effective in its role as a flexible device, whereas use of
cold worked alloys does not allow other orthopedic devices to be
used effectively as flexible bone screws. Cold worked materials can
add to the unique attributes of the flexible bone screw 202, i.e.,
as a device that is elastically bent during insertion, compared to
other orthopedic devices that are not designed to be substantially
elastically bent during the normal course of insertion. Use of
grade 5 titanium is another example of selection of an implant
material with a high yield strain, making it in combination with
the dimensions of the flexible bone screw, suitable for elastic
bending during insertion.
[0044] In some embodiments, a flexible bone screw comprises an
elongated shaft that is configured for elastic bending and a
threaded portion at one end of the shaft for engagement with a
bone. In such embodiments, the threaded portion has an outer
diameter that is larger than a diameter of the shaft. In some
embodiments, the flexible bone screw comprises at least eighty
percent cold worked hardening alloy. In some embodiments, the
flexible bone screw comprises an alloy that is hardened by an at
least 49 percent cold work process. In some embodiments, the
flexible bone screw comprises grade 5 titanium.
Orthopedic Screw Device with Cortex Climbing Thread
[0045] FIG. 3A is cross-sectional view of an orthopedic screw
device 300, such as a flexible bone screw with a cortex climbing
thread 250, according to the present disclosure. FIG. 3B is an
end-view projection of the orthopedic screw device 300 of FIG.
3A.
[0046] The tip of the orthopedic screw device 300 is designed with
a cortex climbing thread 350, which is configured to penetrate
cancellous bone without a pilot hole and to avoid penetration into
cortical bone. Cortex climbing thread 350 is part of a threaded
portion 320 of orthopedic screw device 300. The special application
for cortex climbing thread 350 is in a flexible bone screw, where
the screw is inserted obliquely through a hole in the side of the
bony cortex, and the screw encounters the far cortex at an acute
angle. Usually this angle is less than about 45.degree.. For
example, threaded portion 320 can be employed as threaded portion
103 of flexible bone screw 100 in FIG. 1.
[0047] The cortex climbing thread 350 is an orthopedic bone screw
thread that is at a tip of the orthopedic screw device 300, and
includes a body region 321 and a tip region 322. Body region 321
includes a body thread 323 and tip region 322 includes a tip thread
324 and a tip 325. Tip thread 324 includes helicoid surfaces 326.
In some embodiments, tip 325 is rounded. Generally body thread 323
has a cylindrical profile, but sometimes body thread 323 has a
gentle taper or other diametric variation, such as less than
5.degree. angulation of opposing sidewalls of the body thread. By
contrast, tip thread 324 is configured as a helicoid with a
decreasing (or tapering) radius. This disclosure describes a cortex
climbing thread 350 that is between tip 325 of orthopedic screw
device 300 and is within a distance of approximately two diameters
proximal to tip 325 of orthopedic screw device 300.
[0048] The spatial domain of the cortex climbing thread 350 is
between tip 325 and a transition point 340 where body thread 323
joins or becomes tip thread 324, i.e., where the outer diameter
(thread major diameter of tip thread 324 equals a thread major
diameter 327 of body thread 323. It is noted that the thread major
diameter of tip thread 324 decreases to tip 325 and is less than
thread major diameter 327 except at transition point 340. The
spatial domain of cortex climbing thread 350 may be described
according to a cone 345 (shown as dashed lines in FIG. 3A) in space
proximate the tip of threaded orthopedic screw device 300. Cone 345
is oriented such that an apex 346 of cone 345 is generally near tip
325, is centered about an axis 347 of threaded orthopedic screw
device 300, and intersects transition point 340. Often there is
also a small rounding of the very tip of the screw, to prevent
undesired occurrences, such as ripping of the surgeons gloves. In
some embodiments, a typical aperture angle 348 of cone 345 is
90.degree.. In addition, the base of cone 345 is coincident with
the circle where the cylinder of the thread body is intersected,
i.e., a circle perpendicular to axis 347 and including transition
point 340. Tip thread 324 is included entirely within cone 345. The
cortex climbing thread 350 may contact the surface of cone 345, but
does not extend beyond the surface of cone 345. The cone containing
the physical domain of cortex climbing thread 350 can be with an
aperture angle 348 of as low as 45.degree. at the tip or as high as
120.degree. at the tip. By restricting the physical domain of
cortex climbing thread 350 to remaining within cone 345 as
described herein, cortex climbing thread 350 is prevented from
penetrating far cortex 157 (shown in FIG. 1) when contacting far
cortex 157 at an oblique angle, and is much more likely to advance
along far cortex 157 during installation, as desired. The cone
containing the thread may also be defined by contact with thread
crests near the axis 347, and a distance away from the axis, for
example the thread crest that is halfway between the axis 347 and
the diameter 327. Such a thread will also contact a cortical wall
before the tip, when impinging at an angle less than 1/2 the angle
of the cone. As such it will also serve as a climbing thread.
[0049] As shown in FIG. 3B, when viewing the end of orthopedic
screw device 300 from the tip end, the surface of the tip that is
seen may be a surface having a form that is a helicoid. The
helicoid surface seen does not form part of a cone or other surface
of revolution about the screw axis (i.e., about axis 347). A vector
line from axis 347 of the screw and partially lying in the surface
of the helicoid may make an angle with the axis that is different
from 90.degree.. The converging spiral of the crest of the cortex
climbing thread 350 may contact a surface of a cone, but there is
not a substantial surface area of the thread (when viewed on an
end-view along axis 347) that is coincident with a conical surface
or other surface of revolution. Stated another way, less than 20%
of the surface seen in an end view (a projected surface) coincides
with a conical or other surface of revolution. Stated another way,
the end view does not reveal a thread surface that is cut onto the
surface of a cone or other surface of revolution, with residual
surface of revolution. Stated another way, the end view does not
reveal a thread that is part of the surface of a cone or other
surface of revolution, leaving residual cone or surface of
revolution in more than 20%, or 10%, of the area of the end-on
view. Stated another way, the surface area in FIG. 4 (described
below) that represents a surface of revolution, is less than 20%,
or 10%, of the surface area shown in the end-on view in FIG.
3B.
[0050] To enable cortex climbing thread 350 to positively engage
with and advance into the intended bone material, such as
cancellous bone 156 in FIG. 1, no more than a small portion of
helicoid surfaces 326 are coincident with a surface of rotation
that is centered on axis 347. One such embodiment is described
below in conjunction with FIG. 4.
[0051] FIG. 4 is cross-sectional view of orthopedic screw device
300, a surface of rotation 401, and a projected surface area 402 of
helicoid surfaces 326 that are coincident with surface of rotation
401, according to an embodiment of the present disclosure. As
shown, surface of rotation 401, shown in profile in FIG. 4, is
centered about axis 347. Surface of rotation 401 can be defined by
the rotation about axis 347 of any curve segment that includes
transition point 340 and intersects axis 347, and can have any
continuous cross-sectional profile. For purposes of illustration,
in the embodiment illustrated in FIG. 4, surface of rotation 401 is
configured to coincide with, as closely as possible, helicoid
surfaces 326. Thus, in FIG. 4, surface of rotation 401 includes a
curved portion 411 that is proximate tip 325 and a straight-walled,
cone-like portion 412 that includes transition point 340. In other
embodiments, surface of rotation 401 can include any arbitrary
shape that is rotated about axis 347. It is noted that, because
helicoid surfaces 326 have a decreasing radius that tapers towards
tip 325, cone-like portion 412 does not coincide with a significant
portion of helicoid surface 326.
[0052] Projected surface area 402 indicates a projected area of
helicoid surfaces 326 that are coincident with surface of rotation
401. Projected surface area 402 is the projected area (when viewed
along axis 347) that is coincident with any portion of any possible
surface of rotation for example surface of rotation 401 or tip 325.
In the embodiment illustrated in FIG. 4, the somewhat spherical
surface 403 of tip 325 is itself a surface of revolution, and
therefore is coincident with curved portion 411 of surface of
rotation 401. However, helicoid surfaces 326 only intersect with
surface of rotation 401 along a curve, and therefore are not
coincident with surface of rotation 401 over a significant area. As
shown, projected surface area 402 is less than 20% of the total
projected area 404 of helicoid surfaces 326, where total projected
area 404 is the area of a circle with a diameter corresponding to
thread major diameter 327. As a result, when orthopedic screw
device 300 contacts bone material (such as cancellous bone 156)
with cortex climbing thread 350, orthopedic screw device 300 will
not simply spin in place. Instead, cortex climbing thread 350 will
positively engage the bony material and advance into the bony
material without the need for high axial force.
[0053] The pitch and phase of the cortex climbing thread 350 may be
substantially the same as or different from the pitch of the body
thread of the orthopedic device. In some embodiments, the cortex
climbing thread 350 may have a double lead thread within the
spatial domain of the cone, each of the leads may have the same
pitch.
[0054] The purpose of avoiding surface of revolution at the tip is
that the surface of revolution will tend to spin against cancellous
bone and not penetrate. With surface of revolution surface
geometry, as a crest 410 of the cortex climbing thread 350 spins
against the bone, there is no relief angle immediately behind the
leading crest 410 of the cortex climbing thread 350. If, on the
other hand, the tip surface facing the bone is a helicoid, then
crest 410 of the cortex climbing thread 350 has a relief behind the
crest 410 that allows the cortex climbing thread 350 to draw
directly into bone. For purposes of illustration, a threaded
portion of a screw tip that has significant tip surfaces that do
coincide with a surface of rotation will now be described.
[0055] FIG. 5 is a side view of a screw tip 500 that includes a
significant surface area that is coincident with a surface of
rotation 501, according to an embodiment of the present disclosure.
FIG. 5 further includes a projected surface area 502 of surfaces
526 that are coincident with surface of rotation 501. Surface of
revolution 501 includes a curved portion 511 that is coincident
with a rounded tip 525 of screw tip 500 and a cone-like portion 512
that is coincident with multiple surfaces 526 of a thread 530. As
shown, a projected surface area 502 is more than 20% of the total
projected area 504 multiple surfaces 526. The high projected
surface area 502 that is coincident with surface of rotation 501
indicates that contact with a bony material by screw tip 500 while
screw tip 500 is rotating can result in screw tip 500 spinning in
place against the bony material, rather than actively engaging and
entering the bony material.
[0056] Thus, the helicoid surface geometry of cortex climbing
thread 350 (shown in FIG. 3A) enhances the lead, or entry, into
cancellous bone. If, however, cone 345 is of a high aperture angle,
for example 90.degree., the lead into hard cortical bone is
inhibited. The geometry of the spiral helix of cortex climbing
thread 350 may be viewed as a sort of spiral wedding cake or as a
Tower of Babel as it is represented in illustrations. The walkway
on the Tower of Babel is that facing toward the tip of the tower or
the tip of the screw. That walkway is one form of a helicoid
surface. The edges of the walkway may contact a conical surface or
other converging surface of revolution, but the surface of the
walkway or the surface of the helicoid is not part of the surface
of the cone.
[0057] The aperture angle of the cone of the tip defines the
incidence angle of orthopedic screw device 300 against the surface
of cortical bone at which it tends to climb rather than penetrate.
The aperture angle of the cone may be as great as 120.degree., or
as little as 60.degree.. For example, if the cone aperture angle of
cone 345 is 90.degree., and orthopedic screw device 300 impinges
against the inner sidewall of the far cortex at less than
45.degree., the base of the cone at the full diameter of body
thread 323 will contact the sidewall of the cortex, before tip 325
contacts the sidewall of the cortex. Rotation of the orthopedic
device will then cause the cortex climbing thread 350 to climb
along the cortical wall toward the desired final location of
orthopedic screw device 300. Yet, the helicoid geometry of the
cortex climbing thread 350 of orthopedic screw device 300 will
promote penetration into the cancellous bone at the other end of
the canal when tip 325 arrives at that location.
[0058] The core diameter of cortex climbing thread 350 is reduced
at locations within cone 345, relative to thread core diameter 328
of body thread 323 of orthopedic screw device 300. The core
diameter of the cortex climbing thread 350 may approach zero near
apex 346 of cone 345, i.e., near tip 325. The core diameter of the
cortex climbing thread 350 may also be reduced in areas of the body
thread that are adjacent to the cortex climbing thread 350.
[0059] The orthopedic screw device 300, such as a flexible bone
screw with a cortex climbing thread 350, may also be described as
follows. The thread at the tip is helicoid convergent on the tip of
the screw, with the margin of the helicoid being tangent to, or
touching, a surface of revolution. The surface of revolution has
its widest dimension where its surface intersects the cylinder or
other surface of revolution that is defining the outer diameter of
the main thread body. The smallest transverse dimension (i.e.,
perpendicular to axis 347) of the surface of revolution is zero, at
the tip of the screw. Thus, in some embodiments, between the
intersection of the main thread body (body region 321) and the
surface of revolution and the tip of the screw, the helicoid (tip
region 322) is contained within or is tangent to a right circular
cone (cone 345), having diameter 2r at the base, and height h from
the base to the apex. The cone may also be defined according to the
aperture angle, where the aperture angle is 2.theta., where .theta.
is the angle between the cone axis and the side of the cone. A
portion of the helicoid forms a surface of tip thread 324 that is
visualized in the end-on projection of the tip. Specifically, when
viewed from the tip end, the surface visualized does not form more
than 10% or 20% of a surface of revolution, and the surface viewed
is primarily a helicoid surface. In some embodiments, the point of
tip 325 is rounded, and in such embodiments, the rounded portion of
tip 325 does form a surface of revolution with small surface area.
The helicoid surface shown as 326, makes an angle with axis 347.
This angle may be as high as 90.degree., or may be less than
90.degree. but greater than 80.degree., or may be greater than
70.degree., or may be greater than 60.degree.. Alternatively this
angle may be greater than 50.degree. and up to 60.degree..
[0060] In operation, a hole is made in the side of a bone during
the course of orthopedic surgery. The hole maybe made oblique by
tilting the entry tool drilling device. The orthopedic device with
the cortex climbing thread 350 at the tip is inserted into the
hole, to a depth where the shaft of the orthopedic device is
resting in the hole. The shaft diameter is less than the hole
diameter, and this will allow for added obliquity of the orthopedic
device with respect to the axis of the bone. The orthopedic device
is inserted at an angle such that it impinges against the opposite
cortex at an angle which is less than one half of the cone aperture
angle. In the case of the prior example, that would be an angle of
less than 45.degree.. The orthopedic device is spun and advanced.
Mild forward pressure is applied. The thread at the base of the
cone geometry touches the wall of cortex, and the cortex climbing
thread 350 of the orthopedic device climbs up the wall. If the
orthopedic device is the flexible bone screw, then climbing up the
wall is associated with elastic bending of the shaft of the
flexible bone screw, and as the flexible bone screw progresses up
the intramedullary canal, it becomes an axial intramedullary
device. As the tip of the orthopedic device encounters cancellous
bone at the far end of the canal, there is no cortical wall to walk
on, and it penetrates directly straight into the cancellous
bone.
[0061] The tip of the orthopedic screw device 300 is designed with
a cortex climbing thread 350, which can also penetrate cancellous
bone without a pilot hole and yet avoids penetration into the far
cortex of the cortical bone.
[0062] The thread at the tip combines uniquely with the helicoid
thread geometry, that reduced surface area of rotation at the tip
of the screw, and conical aperture of greater than 90.degree.. The
conical aperture angle enables the screw to climb the far cortex
with an incidence angle of less than 45.degree., without cortical
bone penetration, and the helicoid thread at the blunt tip allows
the tip to penetrate straight into cancellous bone. The reduced
surface area of a surface of rotation at the tip further
facilitates entry into cancellous bone, so that the tip does not
act as a drill. These features combine uniquely to make the
flexible bone screw effective.
[0063] In some embodiments, a threaded orthopedic device comprises
a flexible shaft and a threaded portion that is disposed on one end
of the shaft. The threaded portion includes a tip region with a tip
thread, a body portion with a body thread that has a major diameter
that is equal to or greater than the largest major diameter of the
tip thread, and a transition point disposed where an edge surface
of the tip thread meets an edge surface of the body thread. The tip
region is disposed within a cone that is 1) centered on a
longitudinal axis of the shaft and 2) passes through the transition
point. In some embodiments, a projected area of a portion of the
surfaces of the tip thread that are coincident with a second
surface of revolution, which is symmetrically positioned around a
longitudinal axis of the shaft, is no more than 30% of the total
projected area of the surfaces of the tip thread. In some
embodiments, the projected area of the portion of the surfaces of
the tip thread that are coincident with the second surface of
revolution is no more than 10% of the total projected area of the
surfaces of the tip thread. In some embodiments, the projected area
of the portion of the surfaces of the tip thread that are
coincident with the second surface of revolution is no more than 5%
of the total projected area of the surfaces of the tip thread.
[0064] In some embodiments, the tip thread of the threaded
orthopedic device is configured as a decreasing radius helicoid. In
some embodiments, the tip thread is disposed within and does not
extend beyond a cone having an aperture angle of 90.degree. or
greater and symmetrically positioned around a longitudinal axis of
the shaft. In some embodiments, the cone contacts the tip thread
where the tip thread meets the body thread. In some embodiments,
the cone also contacts the tip thread closest to the tip of the tip
thread, and the contact in these two locations defines the angle of
the cone. In some embodiments, the cone is an example of a surface
of revolution about the longitudinal axis of the shaft. In some
embodiments, different surfaces of revolution than a cone can be
employed to define the dimensional limits of the converging thread
of the tip thread. For example, in such embodiments, the tip region
could be defined (i.e., reside within) a sphere.
[0065] In some embodiments, the tip thread converges from the body
thread of the screw so that a minimized area of the tip thread is
coincident with any surface of revolution centered on the axis of
the shaft and including the transition point. In such embodiments,
a crest of the tip thread may touch the conical surface of
revolution that defines the tip thread, with our sharing surface
area. In some embodiments, the tip thread has a geometry that
preserves a helicoid surface facing the tip end of the screw, and
thereby avoids having substantial surface area that is coincident
with any possible surface of revolution.
[0066] In some embodiments, the point of the screw is rounded to
avoid excessive sharpness. In such embodiments, this rounded point
may be a surface of revolution that is included in the sum fraction
of the tip thread surface that is coincident with a surface of
revolution. In some embodiments, the tip thread is defined as the
thread that is between the screw point and the substantially
constant diameter body thread. In some embodiments, the purpose of
the helicoid geometry of the tip thread is to facilitate entry into
cancellous bone in the axial direction. In some embodiments,
multiple different thread profiles can be employed that provide a
helicoid surface facing the tip end of the screw and avoiding
surfaces of rotation.
[0067] In some embodiments, a flexible bone screw comprises a
threaded tip configured for climbing the far cortex of bone,
wherein as seen from the threaded tip end, the projected tip
surface area is coincident with less than 30% a surface of
revolution. In some embodiments, the projected tip surface of the
flexible bone screw is at least 70% helicoid. In some embodiments,
the projected tip surface of the flexible bone screw is at least
85% helicoid. In some embodiments, the projected tip surface of the
flexible bone screw is at least 15% helicoid.
Fluted Entry Tool
[0068] FIG. 6 depicts multiple views of a tip 612 of a fluted entry
tool 610 according to the present disclosure.
[0069] The fluted entry tool 610 is generally used for making holes
through a single cortex in bone from an exterior surface thereof.
The fluted entry tool 610 is designed to avoid plunging through the
bone and making a hole in the far side of the cortex. The fluted
entry tool 610 is also designed to allow a moderate amount of side
cutting when the shaft is tilted sideways in the hole. This is an
important added capability compared to commonly used trocar points.
It has a sharp point to prevent it from walking along the surface
of a bone as the fluted entry tool 610 is rotated after initial
contact with the exterior surface of the cortex, to initiate
penetration of the bone at exactly the desired location, and also
to prevent slipping off the side of the bone and injuring a
neurovascular structure. The tip of this fluted entry tool 610 has
a very short length of irregular side profile and flutes, e.g.,
less than about 2 cm, to prevent capturing and winding of soft
tissues around the shaft as it is rotated. It is anticipated that
in most cases this fluted entry tool 610 will not require the use
of a tissue protector, saving additional required assistance in
executing the surgical procedure.
[0070] The fluted entry tool 610 is generally a substantially
cylindrical drilling tool, with drilling features at the very tip.
The sides of the fluted entry tool 610, which are away from the
tip, are smooth to prevent winding up soft tissues. This compares
to the usual drill with spiral flutes, and flutes extending greater
than 2.5 or 5 cm from the tip of the tool. The fluted entry tool
610 has features to allow drilling, typically a trocar point, with
three facets located 120.degree. apart, but it may also have
greater than three facets, or another configuration that allows
drilling. The facets trocar-type points have a plane angle relative
to tool axis angle of typically less than 20.degree., and typically
more than 8.degree.. The facets converge to a sharp point. The
facets may be surfaces that are planar as well as surfaces other
than planar surfaces. There are generally one or more flutes
beginning several millimeters (mm), for example 5 mm, from the tip,
and extending to a position proximal to the facets, but less than
30 mm from the tip. There may be relief cuts or grooves that are
ground on the side of the tool, adjacent to the flutes, to enhance
the side-cutting action.
[0071] One example of a method of operation of the fluted entry
tool 610 is as follows. A skin incision may be made, exposing the
surface of a bone 630 to be penetrated. The fluted entry tool 610
is mounted onto a powered drilling apparatus (not shown). The tip
of the fluted entry tool 610 is placed against the surface of bone
630 and spinning of the fluted entry tool 610 is initiated. Tip 612
does not walk along the surface of the bone and does not slip off
to possibly cause injury to adjacent neurovascular structures.
Further, pressure is applied to advance the fluted entry tool 610
in an approximately orthogonal direction to the surface of the
bone, as shown in FIG. 7. As penetration into the bone is achieved,
the fluted entry tool 610 is then tilted to initiate oblique entry
into the bone, as shown in FIG. 8. As the surgeon notices
penetration of the inside of the cortex, less forward force may be
applied, and further tilting of the drill may be initiated. The
fluted entry tool 610 is then advanced into the cortex to create an
oblique hole. The diameter, or maximum transverse dimension, of the
oblique hole may be larger than the diameter of the fluted entry
tool 610. The fluted entry tool 610 may further include relief
surfaces adjacent to the one or more flutes such that a distance
from a surface to an axis is less than a distance from a margin of
one of the one or more flutes to the axis.
[0072] One benefit of the fluted entry tool 610 is the trocar,
which prevents or reduces walking along the surface of the bone.
The trocar combined with flutes allows clearance of chip, or
drilling debris, reducing the heating action of the tool as it
drills past the midlength of the facet, and allows some full
diameter cutting action that is normally not allowed by a trocar
point. Additionally, the taper of the tip is at a relatively low
angle, so the tip of the point passes through the inside wall of
the cortex before the full diameter of the hole is made in the
cortex. In this way, decreased required drilling force is noted by
the surgeon, so that the surgeon knows that the cortex has been
penetrated. The surgeon then reduces forward drilling force, such
that the drilling tool does not plunge suddenly through the cortex.
This prevents making an unwanted hole on the far side of the
intramedullary canal, and allows a very controlled formation of the
hole with controlled forward forced and tilting of the drill-tool
unit. Additionally, tilting of the drill creates an oblique entry
hole.
[0073] In some embodiments, a fluted entry tool comprises a trocar
with three facets, each of the three facets being spaced 120
degrees apart; a trocar pointed tip at a point of convergence of
the three facets, wherein the trocar pointed tip is configured to
penetrate a surface of a bone; and one or more flutes beginning
about 5 millimeters from the trocar pointed tip and extending to a
position proximal to the three facets, but less than 30 millimeters
from the tip. In some embodiments, a fluted entry tool comprises a
trocar-type point having three or more facets, each of the three or
more facets being spaced approximately an equal number of degrees
apart; a trocar pointed tip at a point of convergence of the three
or more facets, wherein the trocar pointed tip is configured to
penetrate a surface of a bone; and one or more flutes beginning
about 5 millimeters from the trocar pointed tip and extending to a
position proximal to the three or more facets, but less than 30
millimeters from the tip. In some embodiments, the fluted entry
tool further comprises relief surfaces adjacent to the one or more
flutes, wherein a distance from a surface to an axis is less than a
distance from a maximum radius margin of one of the one or more
flutes to the axis. In some embodiments, the three or more facets
are at an angle between 20 degrees and 8 degrees to the axis.
Pin Directing Device
[0074] FIG. 9 includes multiple views of a pin directing device
900, according to embodiments of the present disclosure. FIG. 9
includes a front view 910 and a side view 920 of pin directing
device 900. In addition, FIG. 9 includes a magnified front view 930
and a magnified side view 940 of a tip 902 of pin directing device
900.
[0075] The pin directing device 900 is generally used to direct an
orthopedic device such as an intramedullary implant during
orthopedic surgery. The orthopedic device may be, for example, a
flexible bone screw or pin. The present disclosure will refer to
direction of flexible bone screws, as an example, however other
examples of orthopedic devices such as other intramedullary
implants are also contemplated. A potential problem with the
flexible bone screws is that, when multiple flexible bone screws
are installed from the same entry hole, the threaded ends of the
various flexible bone screws tend to cluster in a location dictated
by the elasticity of the flexible bone screws and the anatomic
shape of the intramedullary canal.
[0076] The pin directing device 900 is generally elongate, thin,
flexible and curved. The pin directing device 900 is approximately
the length of the flexible bone screw, or other orthopedic device,
which is to be directed inside the intramedullary canal. There is a
hole 903 (or eyelet) at the tip 902 of the pin directing device
900. The passage length of the hole at the tip 902 may be very
small or large relative to the length of the pin directing device
900. The hole at the tip 902 allows passage of the shaft of the
flexible bone screw to be controlled and directed by moving the pin
directing device 900. In one example, the hole at the tip 902 is
formed through a very short segment of the far end of the pin
directing device 900, forming an eyelet, and that far end is bent,
such that after the shaft of the flexible bone screw passes through
the small hole at the tip 902. More particularly, the hole at the
tip 902 may be made with wire, such as 1.6 mm stainless steel wire,
which is flatted at the tip and then either cold or hot forged to
create an eyelet in the flattened portion. Alternatively, the tip
is made by welding or brazing a separate loop of wire onto the tip
of the pin directing device. This increases the strength and
reduces fragility of the loop or eyelet, compared to an eyelet
created by flattening the wire of the pin directing device, and
then drilling a hole through this flat portion. See magnified side
view 940. Additionally, bends in the pin directing device 900 may
be created. For example, the pin directing device 900 may have a
bend 911 adjacent to the hole in the tip allowing the shaft of the
flexible bone screw to lie alongside of the adjacent shaft of the
pin directing device 900. The pin directing device may also or
alternatively have a bend 912 between 1 cm and 7 cm from the eyelet
903. The shaft of the flexible bone screw can lie substantially
parallel to the shaft of the pin directing device 900, especially
in the portion of the pin directing device shaft adjacent to the
entry hole, as shown in FIG. 10. Generally, the first bend is
located very close to the tip 902 of the pin directing device 900,
for example within about 0 mm and 3 mm from the hole. There is a
second bend approximately 1 to 7 cm from the far end hole or eyelet
at the tip 902. This second bend serves as a fulcrum, so that the
pin directing device 900 can lift the shaft of the flexible bone
screw away from the far side of the intramedullary canal, and with
twisting of the pin directing device shaft, the flexible bone screw
can be manipulated into various locations within the intramedullary
canal, as shown in FIG. 11. The near end of the pin directing
device 900 projects from the entry hole in the bone, and the pin
directing device 900 may be advanced into the hole or pulled back
out of the hole. The near end may also be twisted clockwise or
counterclockwise manipulating the position of the hole of the pin
directing device 900 and the shaft of the flexible bone screw while
observed under fluoroscopy. This allows the flexible bone screw to
be efficiently and accurately directed. A handle (or other manual
control means) 904 is placed on the near end of the pin directing
device 900, so that the surgeon may grasp the handle 904 to
facilitate advancing or withdrawing the pin directing device 900
from the intramedullary canal, and twisting the pin directing
device 900.
[0077] One example of a method of operation of the pin directing
device 900 is as follows. A hole is made in the cortex of a bone
930 with a bone entry tool such as a fluted trocar, an example of
which is discussed below, or other drilling device. The pin
directing device 900 is slipped onto the shaft end of the flexible
bone screw and the hole and the tip 902 of the pin directing device
900 is slid all the way up against the wider thread end of the
flexible bone screw, as shown in FIG. 10. The shaft of the pin
directing device 900 is then tilted, such that the shaft of the pin
directing device 900 adjacent to the tip 902 is lying parallel to
the shaft of the flexible bone screw. As shown in FIG. 11, the
flexible bone screw and pin directing device 900 are then passed
through the hole in the cortex of the bone into the intramedullary
space of the bone. Generally the transverse dimension of the hole
or eyelet at the tip 902 of the pin directing device 900 is chosen
to be smaller than the entry hole into the bone, or smaller than
the thread major diameter at the tip of the flexible bone screw.
The flexible bone screw is then advanced up the canal of the bone,
e.g., by rotating it using a drill that is attached to the proximal
end of the flexible bone screw, and the pin directing device 900 is
pushed to follow immediately behind it. The flexible bone screw is
advanced up the bone, into the zone of cancellous bone near the end
of the bone, and at this time the pin directing device 900 is
manipulated to steer the tip of the flexible bone screw, so that
the threaded tip of the flexible bone screw enters the cancellous
bone 1101 in a preferred location. This is observed and directed
under fluoroscopy. The flexible bone screw is then twisted and
threadedly advanced into the cancellous bone in the location
targeted under fluoroscopic imaging, without pushing the pin
directing device 900 behind it. The pin directing device 900 is now
extracted from the intramedullary cavity by pulling on it and
twisting. The twisting, by for example 1/2 turn, may be necessary
to extract the pin directing device 900, especially as it is
sliding over the shaft of the flexible bone screw, where the shaft
is coming out of the hole in the side of the bone. The pin
directing device 900 may be twisted such that the shaft of the pin
directing device 900 is sitting on top of the shaft of the flexible
bone screw and nearly parallel to the flexible bone screw, facing
the surgeon, and it is pulled out of the cortex hole in this
rotational position. This allows the pin directing device 900 to
act as a sled against the cortical bone, and prevents the hole or
eyelet at the tip 902 of the pin directing device 900 from becoming
hooked against the cortex at the hole in the bone. If the hole of
the pin directing device 900 does become hooked against the
cortical bone at the entry hole, the pin directing device 900 maybe
twisted and pulled harder, and this will result in breakage of the
hole through a notch 906 (shown in FIG. 9) at the most distal
extent of the hole or eyelet, as shown in FIG. 1D. The hole at the
tip 902 of the pin directing device 900 may also become hooked at
other sites inside the bone as well. The breakage of the hole at
the tip 902 occurs in a controlled and planned fashion at the
frangible notch 906. The notch 906 is preferably at the most distal
extent of the hole at the tip 902, allowing the hole to open at the
frangible notch in the ring of the hole at the tip 902, with
spreading of both sides of the hole or eyelet. This allows
spreading and opening of the ring of the hole, and extraction of
the pin directing device 900 out of the intramedullary space, allow
without leaving a small fragment of metal from the pin directing
device 900. In another example, the hole may not include a notch
906.
[0078] The pin directing device 900, which includes a steering
handle 904, an elongate shaft, and a tip 902 having a hole
therethrough, allows a user, such as a doctor, to direct and
control the movement of a flexible bone screw, or other orthopedic
device, through the cavity of a bone while the flexible bone screw
is steered and advanced through the length of the bone by a motor
drill unit. Additionally, the frangible notch 906 of the pin
directing device 900 allows extraction from the bone without
sliding the pin directing device 900 off the shaft of the flexible
bone screw, even if the hole in the tip 902 becomes hooked within
the bone.
[0079] In some embodiments, a pin directing device comprises an
elongated shaft; a tip at a distal end of the elongated shaft
having a hole therein for engaging a flexible bone screw; and a
handle at a proximal end of the elongated shaft configured to be
rotated to advance, retract, or steer the flexible bone screw
through an intramedullary cavity. In some embodiment, the hole at
the tip of the distal end is an eyelet. In some embodiments, the
pin directing device has first a bend adjacent to the eyelet
allowing a shaft of the flexible bone screw to lie alongside of an
adjacent shaft of the pin directing device. In some embodiments,
the pin directing device has a second bend between about 1 cm and
about 7 cm from the eyelet. In some embodiments, the elongated
shaft is thin such that a diameter of the elongated shaft is less
than an entry hole diameter minus a diameter of the shaft of the
flexible bone screw.
Flexible Bone Screw with a Rotary Position Marker
[0080] After insertion of a flexible bone screw, or other
orthopedic device, into a bone canal, it is difficult to know the
rotary position of the tip of the flexible bone screw which is
inside the bone canal without viewing it using fluoroscopic
imaging. Even with fluoroscopy, however, the determined rotary
position of the tip is not always accurate.
[0081] FIG. 12 is a flexible bone screw 1220 with a rotary position
marker 1222 according to the present disclosure. The flexible bone
screw 1220 is configured for management of proximal humerus
fractures. The flexible bone screw 1220 includes a shaft 1224, a
threaded portion 1226, and a tool engagement portion 1228. In some
embodiments, tool engagement portion 1228 may be any suitable
length that is less than approximately half the length of shaft
1224. Thus, in some embodiments, tool engagement portion 1228 can
extend beyond
[0082] In one example, the rotary position marker 1222 may be a
groove or mark 1222 milled onto the side of the shaft 1224, for
example, in the 25% terminal portion of the shaft 1224. In another
example, the rotary position marker 1222 may be a laser etched mark
on the side of the shaft 1224, for example, in the extent of the
shaft 1224 25% from the end. In another example, the rotary
position marker 1222 may be a surface ground onto the side of the
shaft 1224 at a similar position near the end. In yet another
example, the rotary position marker 1222 may be a cold forged mark
on the side of the shaft 1224, for example, in the terminal 25% of
the shaft 1224. In yet other examples, the rotary position marker
1222 may be a non-axisymmetric grind on the end of the shaft, or a
small bend at the end of the shaft.
[0083] In operation, a flexible bone screw 1220 is used to
stabilize a fracture. Then, on intraoperative radiographic images,
it may be noted that the fracture site is angulated in an
unacceptable way. The angulation is in one direction, for example,
apex medial. The flexible bone screw 1220 is withdrawn from the
bone, and at the level of the fracture, the shaft 1224 of the
flexible bone screw 1220 is bent to an angle necessary to correct
the improper angulation of the fracture. The user may reference the
rotary position marker 1222 on the shaft 1224 for the direction of
the apex of the bend. The flexible bone screw 1220 is then
re-inserted, and advanced up the bone until the rotary position
marker 1222 is directed laterally, thereby correcting the apex
medial angulation.
[0084] The rotary position marker 1222 may be used to determine the
rotary position of the tip of the flexible bone screw 1220 that is
inside the bone without relying completely on fluoroscopy or other
intraoperative imaging. One occasion when rotary position of the
tip is important is when there is a bend in the shaft of the
flexible bone screw 1220. A bend in the shaft may be introduced to
correct for angular position of a fracture that the shaft of the
flexible bone screw is crossing over. Decreased imaging radiation
may be achieved using the flexible bone screw 1220 with a rotary
position marker 1222 without use of fluoroscopy.
[0085] In some embodiments, a flexible bone screw comprises an
elongated shaft that is configured for elastic bending having a
rotational position marker positioned thereon at a terminal
twenty-five percent of the shaft; and a threaded portion at one end
of the shaft for engagement with a bone, the threaded portion
having an outer diameter that is larger than a diameter of the
shaft.
Side Application Bending Clamp
[0086] After insertion of a flexible bone screw, or other
orthopedic device, into a bone, it is often either desirable, or
necessary to cut off the extra length of the proximal end of the
flexible bone screw that projects out of the bone. The cut end of
the flexible bone screw may be sharp and palpable under the skin
after the wound is closed. It is therefore desirable to have a
technique by which the flexible bone screw that has been cut off
can be bent over so that there is a smooth knuckle under the skin
and the sharp end of the flexible bone screw does not poke against
the skin. It is known that short ends of stiff metal bone screws
and shafts of bone screws are bent with considerable difficulty
using standard operating room instruments. Standard plate and pin
bending irons do not work well because they have difficulty
grabbing a short bone screw, and they spin and rotate while trying
to bend.
[0087] FIG. 13A is a view of one bending tool 1310 of a pair of
bending tools that make up a pin bending clamp, according to
embodiments of the present disclosure. FIG. 13B is a close-up view
of tips 1301 of one bending tool 1310 according to embodiments of
the present disclosure. FIG. 13C is a view of one bending tool 1310
of pin bending clamp 1300 holding a shaft 1320 of a flexible bone
screw, according to embodiments of the present disclosure. FIG. 13D
is a view of pin bending clamp 1300 being used to bend a shaft 1330
of a flexible bone screw, according to embodiments of the present
disclosure.
[0088] The pin bending clamp 1300 may include a pair of bending
tools 1310, each having a transverse hole 1322 (shown in FIGS. 13A
and 13B) near tips 1301. Each transverse hole 1322 is located in
bending tool 1310 to intersect with the inner surface of the
bending tool 1310. Thus, when the bending too 1310 is open, the
hole space is open. The bending tool 1301 closes with closure of
jaws 1323, which are located opposite a hinge 1335 from handles
1334. The transverse holes 1322 are generally approximately equal
to the diameter of the shaft of the flexible bone screw to be bent.
Each of the bending tools has handles 1334 which, when moved apart,
open the jaws of the bending tool 1301, and allow the shaft of the
flexible bone screw to be placed into the transverse hole 1322 in
jaws 1323 of the bending tool 1301. Thus, the shaft of the flexible
bone screw may be engaged by opening jaws 1323, approaching from
the side, and then closing over the shaft, achieving a firm hold
onto the shaft.
[0089] In operation, as shown in FIGS. 13C and 13D, a proximal end
of the flexible bone screw, before or after cutting, is grasped by
a bending clamp 1310. The handle 1334 is locked in the clamped
position. The handle 1334 is then moved in the plane shared by the
bending clamp and the shaft, introducing a bend in the shaft. This
procedure may be performed with a pair of bending tools 1310
side-by-side, moving the bending tool 1301 that is closer to the
shaft end, introducing a bend at a location in the shaft between
the two bending tools 1301. Generally the shaft end is bent in a
direction away from the skin surface, providing a smooth knuckle of
wire under the skin that is not aggravating to a patient with such
an orthopedic device.
[0090] While the foregoing is directed to implementations with
flexible bone screws in several examples, other orthopedic devices
and applications, such as pins or other screws or other screws, may
be devised without departing from the basic scope thereof.
[0091] In some embodiments, a pin bending device comprises a clamp
comprising a hinged instrument with two handles, a hinge, and two
jaws located opposite the hinge from the handles. In some
embodiments, the pin bending device comprises a handle that is
disposed at a proximal end of each of the bending tools. In some
embodiments, a recess in the jaws of the clamp receives the shaft
of the flexible bone screw, said recess communicating with the
closing surface of the jaws.
Bone Screw Application Kit
[0092] A kit for application of the flexible bone screw is further
developed. The kit consists of multiple flexible bone screws and at
least an entry tool. The it may include three, four, or five
flexible bone screws. Additionally it may include a Bending Clamp.
Additionally it may also include a steering device.
[0093] The method of application of the flexible bone screw
includes first making an entry hole in the side of the bone with
the entry tool. Optionally at this time the shaft of the flexible
bone screw may be inserted through the eyelet of the steering
device. The flexible bone screw is then mounted in a motorized
driver, and inserted into the entry hole in the bone. The threaded
tip of the flexible screw is then run with motorized rotation
against the far cortex, allowing it to climb the far cortex and
bend, moving along the intramedullary canal. The fracture is
reduced under fluoroscopic imaging, and then the flexible bone
screw is run across the fracture, with or without guidance from the
steering device, and into the cancellous bone of the opposing bone
fragment. This process is repeated with additional screws as
needed, until sufficient stability of the fracture has been
achieved. The excess length of the shafts may then be cut off, and
the ends of the shafts protruding from the bone may be bent with
the bending clamp.
[0094] In some embodiments, a bone fracture repair device comprises
a flexible bone screw having an elongated shaft that is configured
for elastic bending with a thread at one end; and a cortex climbing
thread portion at one end of the flexible bone screw, wherein the
cortex climbing thread portion is substantially helicoid and an
aperture angle of a cone containing the cortex climbing thread
portion is 90 degrees or more, wherein the cortex climbing thread
portion has an end view surface area less than 20 percent being
part of a surface of revolution, and wherein the cortex climbing
thread portion is configured to rotationally climb up an inside of
a tubular bone cortex and penetrate cancellous bone.
[0095] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
* * * * *