U.S. patent application number 10/320629 was filed with the patent office on 2003-05-08 for surgical system for tissue fixation.
Invention is credited to Haers, Piet E., Happonen, Harri, Kaikkonen, Auvo, Karhi, Olli, Sailer, Hermann, Suuronen, Riitta, Tormala, Pertti, Waris, Timo.
Application Number | 20030088252 10/320629 |
Document ID | / |
Family ID | 23624076 |
Filed Date | 2003-05-08 |
United States Patent
Application |
20030088252 |
Kind Code |
A1 |
Kaikkonen, Auvo ; et
al. |
May 8, 2003 |
Surgical system for tissue fixation
Abstract
A surgical tissue fixation system is described, including: (1) a
bioabsorbable tissue fixation plate having optionally a plurality
of through-holes arranged in alternating relation along the plate;
(2) bioabsorbable fasteners adapted for insertion into the
through-holes to secure the plate to underlying bodily tissue or
bone; and (3) an installation instrument which triggers (strikes or
shoots) fasteners one after one, in rapid succession, into the
through-holes made through the plate and into the underlying bodily
tissue or bone, which also optionally includes drillholes.
Inventors: |
Kaikkonen, Auvo; (Tampere,
FI) ; Haers, Piet E.; (Surrey, GB) ; Sailer,
Hermann; (Zurich, CH) ; Happonen, Harri;
(Tampere, FI) ; Suuronen, Riitta; (Espoo, FI)
; Waris, Timo; (Helsinki, FI) ; Karhi, Olli;
(Oulu, FI) ; Tormala, Pertti; (Tampere,
FI) |
Correspondence
Address: |
KENYON & KENYON
1500 K STREET, N.W., SUITE 700
WASHINGTON
DC
20005
US
|
Family ID: |
23624076 |
Appl. No.: |
10/320629 |
Filed: |
December 17, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10320629 |
Dec 17, 2002 |
|
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09410288 |
Sep 30, 1999 |
|
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6533454 |
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Current U.S.
Class: |
606/76 ; 606/301;
606/321; 606/329; 606/331; 606/77; 606/908; 606/910 |
Current CPC
Class: |
A61B 17/92 20130101;
A61B 17/68 20130101 |
Class at
Publication: |
606/76 ; 606/72;
606/73; 606/77; 606/69 |
International
Class: |
A61B 017/58 |
Claims
What is claimed is:
1. A synthetic bioabsorbable drug-delivery material comprising: a
synthetic bioabsorbable polymeric matrix; an antibiotic phase
dispersed into said polymeric matrix; and antibacterial,
bioabsorbable, bioactive glass dispersed into said polymeric matrix
for the promotion of bone growth.
2. The drug delivery material of claim 1, wherein the material is
in the form of microspheres, spheres, capsules, tablets, pearls,
pearls in string, beads, membranes, films, fibers, filaments,
threads, cords or knitted or woven fiber fabrics.
3. The drug delivery material of claim 1, wherein said antibiotic
phase comprises from 1 to 20 weight percent of said material.
4. The drug delivery material of claim 1, wherein at least a
portion of said material is porous.
5. The drug delivery material of claim 4, wherein the surface of
said material is porous.
6. The drug delivery material of claim 1, wherein said antibiotic
phase is released from said material for a period of at least 4
weeks in in vivo conditions.
7. The drug delivery material of claim 6, wherein said bioactive
glass is released from said material for a period of at least 4
weeks in in vivo conditions.
8. The drug delivery material of claim 6 wherein said antibiotic
phase is released at a levelof at least 2 mg/l after 4 weeks in in
vivo conditions.
9. The drug delivery material of claim 6 wherein said antibiotic
phase is released at a level of at least 10 mg/l after 4 weeks in
in vivo conditions.
10. The drug delivery material of claim 1 wherein said bioactive
glass is in the form of fibers.
11. The drug delivery material of claim 10 wherein said fibers
reinforce said material.
12. The drug delivery material of claim 1, wherein the material is
self-reinforced through solid state deformation.
13. The drug delivery material of claim 9 wherein said antibiotic
phase comprises ciprofloxazine.
14. A surgical implant comprising the material of claim 1.
15. The implant of claim 14, wherein the implant is in the form of
a pin, screw, plate, tack, intramedullary nail, bolt, suture
anchor, tissue anchor, interference screw, arrow, or wedge.
16. The implant of claim 14, wherein said material is a coating on
the surface of said implant.
17. A method of treating osteomyelitis or bone infection in a bone
comprising: providing a synthetic bioabsorbable drug-delivery
material comprising: a synthetic bioabsorbable polymeric matrix; an
antibiotic phase dispersed into said polymeric matrix; and
antibacterial, bioabsorbable, bioactive glass dispersed into said
polymeric matrix for the promotion of bone growth; and applying
said material to said bone.
18. The method of claim 17 wherein said antibiotic phase comprises
from 1 to 20 weight percent of said material and said antibiotic
phase is released at a levelof at least 2 mg/l after 4 weeks in in
vivo conditions.
Description
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/410,288, filed Sep. 30, 1999, the
disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to surgical tissue
fixation equipment and systems and, more particularly, to
bioabsorbable fixation systems including bodily tissue fixation
hardware comprising biocompatible, bioabsorbable (resorbable)
polymeric or composite plates and fasteners for securing the plates
to bodily tissue for fixation thereof, and an installation
instrument which triggers (strikes) fasteners one after one into
through-bores (holes) made through the plate and into the
underlying bodily tissue.
BACKGROUND OF THE INVENTION
[0003] Traditional orthopedic and traumatological and
cranio-maxillo-facial fixation systems to facilitate bone fracture
healing (osteosynthesis) or soft tissue-to-bone healing typically
employ metallic hardware, e.g., plates, screws, rods and the like,
formed of biocompatible, corrosion resistant metals such as
titanium and stainless steel. Typical metallic plates are
described, e.g., in the book F. Sequin and R. Texhammar, AO/ASIF
Instrumentation, Springer-Verlag, Berlin, Heidelberg, 1981, p.
21-22, 55-79, 107-108, 117-122, the entire disclosure of which is
incorporated herein by way of this reference. While such systems
are generally effective for their intended purposes, they possess a
number of inherent shortcomings. For example, metal release to the
surrounding tissues (see, e.g., L.-E. Moberg et al. Int. J. Oral.
Maxillofac. Surg. 18 (1989) p. 311-314, the entire disclosure of
which is incorporated herein by reference) has been reported. Other
reported shortcomings are stress shielding (e.g., P. Paavolainen et
al., Clin Orthop. Rel. Res. 136 (1978) 287-293, the entire
disclosure of which is incorporated herein by reference) and growth
restriction in young individuals (e.g., K. Lin et al., Plast.
Reconstr. Surg. 87 (1991) 229-235, the entire disclosure of which
is incorporated herein by reference). In infants and young children
there is the risk that metallic plates and screws sink, as a
consequence of skull bone growth, into and below the cranial bone
threatening brain (J. Fearon et al., Plast. Reconstr. Surg. 4
(1995) 634-637, the entire disclosure of which is incorporated
herein by reference). Therefore, it is recommended generally that
non-functional implants should be removed, at least in growing
individuals (see, e.g., C. Lindqvist, Brit. J. Oral Maxillofac.
Surg. 33 (1995) p. 69-70, the entire disclosure of which is
incorporated herein by reference).
[0004] Especially in maxillofacial and in cranial surgery metallic
mini plates are popular (see, e.g., W. Muhlbauer et al., Clin.
Plast. Surg. 14 (1987) 101-111; A. Sadove and B. Eppleg, Ann.
Plast. Surg. 27 (1991) 36-43; R. Suuronen, Biodegradable
Self-reinforced Polylactide Plates and Screws in the Fixation of
Osteotomies in the Mandible, Doctoral Thesis, Helsinki University,
Helsinki, 1992, p. 16, the entire disclosures of which are
incorporated herein by reference; and see the references cited in
the previous references). Mini plates are small, thin, narrow
plates, which have holes for screw fixation. They are located
typically on bone perpendicularly over the fracture to fix the bone
mass on both sides of the fracture to each others. Typical
geometries of mini plates are described, e.g., in U.S. Pat. No.
5,290,281, in FIGS. 6A-6F, the entire disclosure of which is
incorporated herein by reference.
[0005] The main advantage of metallic plates, screws, etc. (like
titanium, stainless steel and cobalt chrome molybdenum plates or
screws), is that they are strong, and tough. Ductile metal plates
can be deformed or shaped (bent) at room temperature in an
operation room by hand or with special instruments to the shape of
a form that corresponds to the surface topography of the bone to be
fixed, so that the plate can be fixed flush on the bone surface to
which the plate is applied.
[0006] Because of the shortcomings of metallic plates,
bioabsorbable plates have been developed for fracture fixation.
Longitudinal, six-hole plates were developed by Eitenmuller et al.
for orthopaedic animal studies (European Congress on Biomaterials,
Abstracts, Instituto Rizzoli, Bologna, 1986, p. 94, the entire
disclosure of which is incorporated herein by reference). However,
because of inadequate strength, some of the plates were broken in
animal experiments involving fracture fixation.
[0007] A particular advantage of bioabsorbable plates is that they
can be provided with openings for the insertion of surgical
fasteners (like screws) therethrough, while also allowing means to
permit the formation of additional fastener openings therethrough
during a surgical procedure at the surgeon's discretion, as has
been described in European Patent specification EP 0 449 867 B1,
the entire disclosure of which is incorporated herein by
reference.
[0008] However, the main disadvantage of most prior art
bioabsorbable plates is that they can be deformed (bent)
permanently and safely only at elevated temperatures above the
glass transition temperature (T.sub.g) of the bioabsorbable
polymer, as has been described, e.g., in EP 0 449 867 B1, U.S. Pat.
No. 5,569,250 and U.S. Pat. No. 5,607,427, the entire disclosures
of which are incorporated herein by reference. Below the respective
glass transition temperatures of the bioabsorbable polymers from
which they are made, most prior art bioabsorbable plates are
brittle and break easily when deformed. Only at temperatures above
the T.sub.g of the bioabsorbable polymer from which a given plate
is made does the molecular structure of most prior art plates have
enough mobility to allow shaping and bending of the plate, without
the risk of breaking.
[0009] Because the thermal conductivity of most polymeric materials
is generally poor, both heating and cooling of bioabsorbable plates
are slow processes. Therefore, the clinical use of such prior art
plates is tedious, slow and complex, especially if the surgeon must
shape the plate several times to make it fit exactly to the form of
the bone to be fixed.
[0010] K. Bessho et al., J. Oral. Maxillofac. Surg. 55 (1997)
941-945, the entire disclosure of which is incorporated herein by
reference, describe a bioabsorbable poly-L-lactide miniplate and
screw system for osteosynthesis in oral and maxillofacial surgery.
The plates of that reference also must be heated by immersion in a
hot sterilized physiologic salt solution, or by the application of
hot air, until they become plastic, and only then can those plates
be fitted to the surface of the bone being repaired.
[0011] EP 0 449 867 B1, the entire disclosure of which is
incorporated herein by reference, describes a plate for fixation of
a bone fracture, osteotomy, arthrodesis, etc., said plate being
intended to be fixed on bone with at least one fixation device,
like a screw, rod, clamp or some other corresponding device. The
plates of that reference comprise at least two essentially
superimposed plates, so as to provide a multilayer plate
construction, so that the individual plates of said multilayer
plate construction are flexible to provide a change of form of said
multilayer plate construction to substantially assume the shape of
the bone surface under the operation conditions. That change of
form is accomplished by means of an external force, such as by hand
and/or by a bending instrument directed to said multilayer plate
construction, whereby each individual plate assumes the position of
its own with respect to other individual plates by differential
motion along the surfaces of the coinciding plates.
[0012] Although the above multilayer plate can fit the curved bone
surface without heating of the individual plates, the clinical use
of such multilayer plates is tedious, because the single plates
easily slip in relation to each other before fixation. Additionally
the thickness of multilayer plate system easily becomes too thick
for cranio maxillofacial applications, causing cosmetic disturbance
and increased risks of foreign body reaction.
[0013] To avoid the above mentioned shortcomings in the prior art
devices, U.S. patent application Ser. No. 09/036,259, the entire
disclosure of which is incorporated herein by reference, describes
strong and tough, uni- and/or biaxially oriented and/or
self-reinforced bioabsorbable plates, which are deformable at room
temperature, like in operation room conditions, prior to
implantation in a patient. The plates described in that application
retain their deformed (bent or shaped) form so well at body
temperature in tissue conditions (e.g., when implanted on a
patient's bone) that they keep the fixed bone fragments in the
desired position to facilitate bone fracture healing. When using
such plates surgically, the surgeon can bend (and rebend) the plate
easily in operation conditions, without needing the slow and
tedious heating--bending--cooling procedure of the prior art
plates.
[0014] While the clinical use of the bioabsorbable plates described
in U.S. patent application Ser. No. 09/036,259 significantly
reduces operation time in comparison to the clinical use of other
prior art bioabsorbable plates, the fixation of plates on tissue or
bone is still a slow and tedious process. Prior art fixation
techniques mainly use screws or screw-type fasteners for plate
fixation. However, turning of screws or screw-type fasteners into
drill holes is a slow process. For example, in a single
maxillo-cranio-facial operation, tens of screws may be used for
plate fixation and such an operation may demand hours to complete.
On the other hand, manual use of other types of fasteners, like
expansion bolts (pins), or plugs or rivets is also a slow and risky
process. For example, manual hammering of fasteners, like those
described in U.S. Pat. No. 5,261,914 or U.S. Pat. No. 5,607,427,
the entire disclosures of which are incorporated herein by
reference, can easily be done too strongly, so that the head of the
fastener and/or plate and/or underlying tissue(s) is (are)
damaged.
[0015] Two-component fasteners, like expansion bolts or plugs (such
as those described in H. Pihlajamki et al.,: A biodegradable
expansion plug for the fixation of fractures of the medial
malleolus, Ann Chir Gyn 83: 47-52, 1994, the entire disclosure of
which is incorporated herein by reference) or pop rivet-type
fasteners can be complicated and risky to use because strong
expansion of a part of such a fastener can cause extensive
compression to the surrounding bone, leading to bone necrosis.
[0016] A need, therefore, still exists for a surgical tissue
fixation system comprising (a) a bioabsorbable (bioresorbable or
biodegradable) plate, which is strong, tough and thin,
substantially rigid and deformable (either at room temperature or
at an elevated temperature); (b) a bioabsorbable fastener adapted
for insertion into through-bores (drill holes) in the bioabsorbable
plate, to secure the plate to underlying bodily tissue in a rapid
and safe manner; and (c) an installation instrument which installs
(e.g., by triggering or striking) the fasteners one after another
rapidly, securely and with a minimal trauma into the through-bores
made through the plate and into the underlying bodily tissue.
[0017] A need also exists for a surgical tissue fixation system
comprising a bioabsorbable plate, bioabsorbable fasteners and an
installation instrument, which triggers the fasteners one after
another into the drill holes made through the plate and optionally
also into the underlying bodily tissue, with a single strike or
with several consecutive strikes, without the need of turning the
fastener around its long axis during installation.
[0018] A need also exists for a surgical tissue fixation system
comprising a bioabsorbable plate, bioabsorbable fasteners and an
installation instrument, which triggers the fasteners one after
another precisely into the drill holes in plates, so that the lower
surface of the fastener head mates exactly with the upper surface
of the plate (or with the countersink surface in the upper part of
the drill hole in the plate).
[0019] A need also exists for a curved cannula for attaching to the
above fixation instrument, to allow application of the fasteners
onto bone in areas, e.g., such as the posterior mandible or
subcutaneous spaces, where there is no access with straight upright
instrumentation.
SUMMARY OF THE INVENTION
[0020] In accordance with the present invention, there is provided
a surgical tissue fixation system, including a bioabsorbable plate
and a bioabsorbable fastener to secure the plate to underlying
bodily tissue and an installation tool which triggers the fasteners
one after another through drill holes made through the plate and
into the underlying bodily tissue. The plate and fastener equipment
is particularly adapted for fixating fractured or severed bones, or
for affixing a ligament, tendon or connective tissue on a bone or
into a drillhole in a bone, to promote rapid and beneficial healing
of the treated bones and/or tissues.
[0021] In a preferred embodiment of the invention, the installation
instrument cooperates as part of a surgical system with one or more
specially configured plates, fabricated from bioabsorbable
polymeric or composite material, wherein the plates can be secured
by a surgeon via a plurality of fasteners to a bone, cartilage,
tendon, connective tissue or other bodily tissue being repaired.
Other details, objects and advantages of the present invention will
become apparent from the following description of the presently
preferred embodiments and presently preferred methods of practicing
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The invention will become more readily apparent from the
following description of preferred embodiments, which are shown, by
way of example only, in the accompanying drawings.
[0023] FIG. 1 is a schematic representation of a typical fastener
according to the present invention, for securing a bodily tissue
fixation plate to underlying bodily tissue, as seen as perspective
figures from different directions.
[0024] FIG. 2 is a perspective view illustrating a bioabsorbable
fixation (osteosynthesis) plate in combination with a fixation
fastener, positioned in a relatively elevated position inside of an
installation cannula of an installation instrument, for insertion
of the fastener within a fastener opening of a fixation plate.
[0025] FIG. 3 is a schematic cross-sectional representation of a
fixation system (a plate+fastener) according to the present
invention, a fastener being applied into a drillhole in a plate and
into a drillhole in the underlying bone tissue.
[0026] FIG. 4. is a schematic representation of a fastener
according to the present invention being applied to a drillhole
with a curved cannula in an area where no direct access could be
achieved.
[0027] FIG. 5 shows cross-sections of fasteners of the invention,
showing different protuberance geometries.
[0028] FIG. 6 shows schematically, in a cross-section, elastic
bending of a ridge of a fastener during insertion into a drill
hole.
[0029] FIG. 7 shows a surface of a fastener body with a ridge,
which has been cut with longitudinal grooves, including a side view
(A) and an upper view (B) of the stem and ridge.
[0030] FIG. 8 shows typical geometries of the head of the fastener
when seen from the upper side of the fastener in the direction of
the longitudinal axis of the fastener.
[0031] FIG. 9 shows schematically the tip of a cannula whose
diameter has been decreased by splitting it and pressing the split
parts to each other.
DETAILED DESCRIPTION OF THE INVENTION
[0032] According to the invention, the fastener(s) and plate(s) are
manufactured of bioabsorbable polymer, polymer alloy or composite
material, which is strong and tough and retains its strength in
vivo several weeks or months.
[0033] FIG. 1 shows a typical fastener (1) according the invention
comprising a proximal head (2), a stem (3), from which one or more
protuberances (4) emerge. Typical protuberances are ridges,
reaching at least partially around the stem (3), threads,
pyramid-like or half ball-shaped papillae, barbs, scales, etc. The
geometry of protuberances (4) is such, that it allows easy gliding
of the fastener into the drill hole in the plate (6 in FIG. 2) and
into the bone (7 in FIG. 2) or into an optional drillhole in the
bone (10 in FIG. 3), while still locking the fastener effectively
into its place, preventing its movements backwards after
installation. Finally, according to FIG. 1 the fastener comprises
the distal tip (5), which can be conical with a sharp or blunt or
rounded end (5a) to facilitate its installation into the drillhole
in the plate (and optionally into the drillhole in bone).
[0034] According to the invention, the presently preferred
bioabsorbable polymeric or composite materials forming the fixation
plates (the compositions of which will be later described in
greater detail) can be bent and shaped, in operation room
conditions or at an elevated temperature, typically at temperatures
ranging from about 15.degree. C. to 120.degree. C.
[0035] A number of geometries are useful for the plate, such as
those described in U.S. patent application Ser. No. 09/036,259. The
plate of the invention is desirably of a thickness of less than
about 2 mm and may include a plurality of spaced apart
through-bores adapted to accommodate fasteners. Fasteners also can
be formed from any suitable biocompatible and bioabsorbable
polymeric or composite material from the classes used for forming
the plates or from other acceptable materials of similar properties
and characteristics. Such materials have been described extensively
in prior art, e.g. in U.S. patent application Ser. No.
09/036,259.
[0036] FIG. 2 is a perspective view illustrating a fastener (1)
according to the present invention used for fastening of the plate
(6) to underlying bodily tissue, like bone (7) during a surgical
operation. As suggested herein above, fastener (1) may be formed of
any suitable bioabsorbable and biocompatible polymeric or composite
material; however, the material must be chosen from those materials
having sufficient strength and toughness and hardness whereby the
fastener head (2), stem (3) and fastener protuberances (4) and tip
(5) (see FIG. 1) do not fail upon the application of pressure to
the fastener head (2), which occurs when fastening the bodily
tissue fixation plate (6) to underlying bodily tissue (7). Such
pressure is applied by triggering the fastener (I) with the
installation instrument (8), whose cannula (8a) and piston or tool
(8b) are seen in FIG. 2, into a through-bore (9) in the plate and
into an optional drillhole (10 in FIG. 3) in tissue (7) under the
plate. In the perspective of FIG. 2, a fastener (1) is positioned
in a relatively elevated position inside of an installation cannula
(8a) (the cross-section of the cannula shows the fastener (1)
inside of the cannula) of an installation instrument (8) (not seen
totally in this Figure). The fastener (1) can be triggered (shot)
into a drillhole (bore) (9) in the plate (6) by pushing it rapidly
with the piston (8b) into the drillhole (9).
[0037] FIG. 3 shows a cross-sectional view of a fastener (1) after
having been triggered into a drillhole (9) in the plate (6) and
further into a drillhole (10) in the bone (7). The head (2) of
fastener (1) may optionally contain a tool receiving notch or
recess (11), which may be cylindrical or angular of its
cross-section. The notch or recess (11) is configured for receiving
the tip of the piston (tool) (8b) and for securing the grip of the
tip of the tool inside of the notch or recess with a frictional
grip. It is also possible, that the head of fastener (1) is smooth
and there is no frictional grip between the head (2) and the tip of
the piston (8b).
[0038] While the tool-receiving portion of fastener head may assume
any conventional socket configuration, it is preferred that the
head includes a socket shape adapted to minimize the likelihood of
inadvertent slippage of the tip of the triggering tool during
fastener installation. Moreover, the underside of the fastener head
(2) is desirably contoured as conical to mate (conform) to the
shape of a fastener head seat (12 in FIG. 3) formed at the upper
ends of through-bores (9) of plate (6), thus minimizing the height
of the fastener plate profile. It is preferred that the distal end
(5) of the stem (3) portion (with protuberances (4)) of the
fastener (1) be formed into a generally pointed configuration (5a),
as illustrated, so as to facilitate guidance and insertion of the
fastener into both its corresponding through-bore (9) and the
preformed receiving hole (10) that may be provided in the
underlying bodily tissue (7) being repaired.
[0039] The maximum outer diameter D.sub.1 between the protuberances
(see FIG. 5) of the fastener (1) of the present invention is
desirably less than about 3.0 mm. Indeed, according to presently
preferred embodiments of the invention, the outer diameter is
typically approximately 2.0 mm or less for normal service
requirements in surgery and up to about 2.5 mm for emergency
requirements, and the corresponding nominal bore diameter of
through-bores (9 and 10) is preferably about 1.8-1.9 mm or less.
Because of the very small diameters of the fasteners (1), they are
particularly well-suited for fixation of small and/or non-weight
bearing bones or other bodily tissues.
[0040] According to an advantageous embodiment of the invention,
the protuberances (e.g., scales, ridges or threads) on the fastener
have such a structure that they can deform at least partially
elastically during insertion of the fastener. FIG. 5 shows
schematically in a cross-section such protuberances, (like
horizontal ridges), which can deform (bend) elastically during
insertion. As shown in FIG. 6, when the maximum outer diameter
(D.sub.1) of the fastener (D.sub.1=the maximum distance between
protuberances on opposite sides of the fastener) is bigger than the
diameter (D.sub.2) of the drillhole in the plate (6) and in the
compact bone (7) below (see FIG. 6A), the protuberances can bend
temporarily inside the drillhole in the plate and in the compact
bone below the plate (see FIG. 6B), but widen again to almost their
original width when they have slipped into the soft tissue or void
space (13) below the compact bone. In such a case, the fixation of
the fastener is especially strong because the widened protuberances
effectively prevent the slippage of the fastener back from the
drillhole.
[0041] According to FIGS. 7A and 7B, the protuberance (ridge) (4)
on the surface of the fastener stem (3) of the invention, has been
split to several parts having longitudinal grooves (4a). Such
separate ridge parts bend elastically more easily than an intact
ridge on insertion of the fastener.
[0042] The head of the fastener of the invention also can have
different geometries. FIGS. 8A-E show different types of fastener
heads, as seen from above. FIG. 8A shows a rounded head. FIG. 8B
shows such a head equipped with a quadrangular tool-receiving notch
(14). FIG. 8C shows a flat head with a groove-like notch (15). FIG.
8D shows a cross-like head and 8E a triangular head. It is evident
that the form of the head of the fastener is not limited to those
forms expressly described here.
[0043] According to an advantageous embodiment, the fastener of the
invention can be cannulated, which means that inside of the
fastener there is a longitudinal hole which traverses the fastener.
Such a cannulated fastener can be pushed along a metallic
guide-wire into the tissue. The guide-wire can facilitate the
installation operation in certain cases, e.g. guide-wire(s) can be
used to keep the plate and/or damaged tissue in a proper place
before the installation of the fastener.
[0044] The installation instrument of this invention can be any
instrument which triggers (strikes or shoots) the fastener through
a cannula by means of a piston through the drillhole in a plate
into the underlying bodily tissue. Such instruments have been
described, e.g., in U.S. patent application Ser. No. 08/887,130 and
U.S. Pat. No. 6,010,513, the entire disclosures of which are
incorporated herein by reference. Accordingly, the installation
instrument has a conduit, such as a cannula, that may be easily
inserted into the patient and through which the fastener is
delivered to the patient. This conduit is aligned with a seat for
holding a fastener and a means for pushing a fastener, such as a
piston, so that the pushing means is capable of pushing a fastener
from its seat, through the conduit and into the patient. In a
preferred embodiment of the invention, the shape of the conduit
relatively exactly matches the shape of the cross-section of the
fastener so that the surgeon may more accurately direct the angle
and location at which the fastener enters the patient. In another
preferred embodiment, the pushing means may be made to slowly push
the fastener from its seat and through the conduit until the distal
end of the fastener contacts the drillhole of the plate at the end
of the conduit. At that time, the pushing means may be made to
accelerate rapidly, thereby inserting the fastener into the
drillhole of the plate and into the tissue being treated. An
advantage of this embodiment is that the fastener is less likely to
become jammed in the conduit while being pushed slowly through it.
Further, the conduit, piston, and fastener are subject to less
wear, which helps to ensure proper functioning of the instrument
during an operation.
[0045] The seat for holding fasteners is capable of holding a
magazine containing one or more fasteners. When inserted into the
seat, the magazine may be positioned so that a fastener is aligned
with the pushing means and the conduit leading to the patient. Once
a fastener has been inserted into the patient, the magazine may be
manually positioned so that another fastener is shifted into
position to be inserted. In one embodiment of this invention, the
magazine may have means, such as a spring, for automatically moving
a fastener into position for insertion once a first fastener has
been inserted.
[0046] The magazine may be easily removed from the seat during an
operation, so that it may be replaced with a magazine containing
one or more fasteners, without requiring the conduit to be removed
from the patient. Alternatively, the same magazine could be
removed, refilled with one or more additional fasteners, and
reinserted into the seat, without requiring the removal of the
conduit from the patient. In yet another embodiment of the
invention, when the magazine is positioned to allow the insertion
of one fastener into the patient, a portion of the magazine is
accessible to allow the insertion of one or more additional
fasteners into the magazine. In this fashion, additional fasteners
may be added to the magazine without requiring its removal from the
device or the removal of the conduit of the device from the
patient.
[0047] In a preferred embodiment of the invention, the conduit or
cannula of the instrument is easily removable from the rest of the
device. This allows the same instrument to be used during an
operation with differently shaped conduits, depending upon the
location and condition of the plate being fixed and tissue being
treated. Thus, for instance, during the same operation, the surgeon
could insert fasteners through a straight conduit (cannula), then
easily replace the straight conduit with a curved conduit and
continue the operation without the need for an entirely new
device.
[0048] In yet another preferred embodiment of this invention, the
device has a safety mechanism that helps prevent the surgeon from
inadvertently shooting the fastener into the patient until the
proper moment. This mechanism works in conjunction with the
triggering mechanism so that the means for propelling the fastener
into the patient cannot be actuated until both the triggering means
and the safety mechanism are actuated simultaneously.
[0049] FIG. 4 describes an installation device (8) with a curved
cannula (8c), inside of which is a fastener (1), which can be
triggered from the cannula with a flexible piston (8d) into a
tissue area where no direct access could be achieved.
[0050] Special attention must be directed to the relationship
between the fastener and the cannula and piston of the installation
instrument. The fastener must glide inside of the cannula easily
but it should not be allowed to drop out of the cannula end by its
own weight. The fastener should be capable of moving completely out
of the cannula only when the piston pushes (strikes) it out into
the drillhole in the plate and in the bodily tissue. Such behavior
is attained, e.g., when the head of the fastener has a notch (as is
described e.g. in FIG. 3 and in FIGS. 8B and C) into which the tip
of the piston can be pushed. When the geometries of the notch and
of the tip of the piston have been designed properly, a good
frictional grip between the fastener and the piston can be
achieved.
[0051] Another option is to make the dimensions of the fastener
head and/or protuberances in relation to the inner diameters of the
cannula such that a substantial friction exists between the
fastener head and/or protuberances and the inner surface of the
cannula, so that the fastener glides inside of the cannula only
when it is pushed forward by means of the piston.
[0052] According to an advantageous embodiment of the invention,
the diameter of the distal end of the instrument cannula is smaller
than the diameter of its proximal end. In such a case, the fastener
glides easily inside of the cannula, but cannot glide totally out
of the cannula without a substantial push of the piston. FIG. 9
shows such an embodiment, where the distal part of the cannula has
been split, e.g., by sawing to make grooves (16) which split the
distal part of cannula into two or several (in this case, four)
parts. These parts have been bent slightly so that the inner
diameter of the distal part of the cannula is smaller than the
diameter of the other parts of the cannula. The fastener can be
pushed easily to the end (tip) of the cannula, but the reduced end
of the cannula prevents the premature drop of the fastener out of
cannula. The tip of the fastener, which can protrude out of the
cannula, can be then located easily into the drillhole in the
plate, until the strike of the piston pushes the fastener totally
out of the cannula and into the drillhole.
[0053] The fixation fasteners and/or plates of the present
invention can be manufactured by known techniques from known
materials, such as thermoplastic bioabsorbable (resorbable or
biodegradable) polymers, copolymers, polymer alloys, or composites,
e.g., of poly-.alpha.-hydroxy acids and of other aliphatic
bioabsorbable polyesters, polyanhydrides, polyorthoesters,
polyorganophosphatzenes, tyrosine polymers and other bioabsorbable
polymers disclosed in numerous publications, e.g., in S. Vainionp
et al., Prog. Polym. Sci., 14 (1989) 679-716, FI Pat. No. 952884,
FI Pat. No. 955547 and WO-90/04982, EP 0449867 B1, U.S. Pat. No.
5,569,250, S. I. Ertel et al., J. Biomed. Mater. Res., 29 (1995)
1337-1348, the entire disclosures of which are incorporated herein
by reference, as well as in the reference publications mentioned in
the aforementioned publications.
[0054] Implants (plates and/or fasteners) in accordance with the
invention can be manufactured of biodegradable polymers by using
one polymer or a polymer alloy. The implants can also be reinforced
by reinforcing the material by fibers manufactured of a
bioabsorbable polymer or of a polymer alloy, or with biodegradable
glassfibers, such as tricalsiumphosphate fibers, bioactive
glassfibres or CaM fibers (as described in, e.g., EP146398, the
entire disclosure of which is incorporated herein by reference).
Ceramic powders can also be used as additives (fillers) in implants
to promote new bone formation.
[0055] Implants according to the invention can also contain layered
parts comprising, e.g., (a) a flexible outer layer as a surface
layer improving the toughness and/or operating as a hydrolysis
barrier and (b) a stiff inner layer. It is natural that the
materials and implants of the invention can also contain various
additives for facilitating the processability of the material (e.g.
stabilizers, antioxidants or plasticizers) or for changing its
properties (e.g. plasticizers or ceramic powder materials or
biostable fibers, such as carbon) or for facilitating its treatment
(e.g. colorants).
[0056] According to one advantageous embodiment, the implant of the
invention contains some bioactive agent or agents, such as
antibiotics, chemotherapeutic agents, agents activating healing of
wounds, growth factor(s), bone morphogenic protein(s),
anticoagulant (such as heparin) etc. Such bioactive implants are
particularly advantageous in clinical use, because they have, in
addition to their mechanical effect, also biochemical, medical and
other effects to facilitate tissue healing and/or regeneration.
[0057] Because the plates contemplated by the present invention can
be shaped (bent or twisted, etc.) in situ rapidly and at room
temperature, either manually or with special bending tools (like
forceps), the plates can be brought effectively into virtual
conformance with the underlying bodily tissue being repaired,
including damaged tissue having small radii of curvature, such as
cranial and facial bones, even those of a small child. Thereafter,
the plate can be fixed on bone rapidly and safely with fasteners of
the invention, using the installation system of the invention. As a
result, the bodily tissue on opposite sides of the severance or
fracture is rapidly and effectively restrained against relative
movement, whereby rapid, sturdy and non-disfiguring consolidation
and/or healing of the bodily tissue is achieved.
[0058] Because, according to an advantageous embodiment, the plate
shaping and fastener fixation procedures are done at room
temperature, there is no risk of heat-related damage to biological
tissue in the immediate vicinity of the treatment area, even in
rather deep biological incisions, while such risk is a reality when
using prior art plates which are shaped in situ by using heat.
[0059] Because the whole tissue fixation operation by using the
system of the invention is done much more rapidly than when using
prior art systems, surprising advantages are obtained: a shorter
operation time results in smaller risks of operation complications
and infections to the patient and considerable economic savings
and/or increases of efficacy of operation room facilities.
[0060] The principles of the present invention described broadly
above will now be described with reference to the following
specific example, without intending to restrict the scope of the
present invention.
EXAMPLE 1
[0061] A side of a fresh cadaver swine mandible was prepared by
removing soft tissue from the testing surface of the bone. A
bioresorbable bone fixation plate was then fixed to the bone with 4
bioabsorbable monocortical screws or fasteners of the
invention.
[0062] Fixation plates, screws and fasteners were made from
self-reinforced 70L/30DL PLA (Draw ration 3.5 to 5.5) (Manufacturer
of Polymer is Boehringer Ingelheim Pharma KG, BU Fine Chemicals, PM
Resomer, D-55216 Ingelheim, Germany, tel +49-(O)6132-77 2633, fax
+49(0)6132-77 4330, M.sub.w=i.v. 5.5 to 7.0 dl/g). The plates were
made with the method described in PCT/EP99/01438, the entire
disclosure of which is incorporated herein by reference, and the
screws and tacks were made according to PCT/FI 96/00511, the entire
disclosure of which is incorporated herein by reference. The tack
geometry was that of FIG. 1 of this invention. The Principal
dimensions of the 6-hole fixation plate were 5.5.times.39.times.1.2
mm. The screws had a diameter of 2.0 mm and a length of 6 mm. The
tack diameter was also 2.0 mm and length 6 mm.
[0063] Plate and Screw Fixation:
[0064] The fixation plate was laid on the bone. A screw hole of 1.5
mm diameter was drilled with an electric drilling machine into the
bone through the screw hole of the plate. The drilled hole was then
tapped with a tapping instrument of 2.0 mm diameter. The screw was
driven through the screw hole of the plate and into the tapped
screw hole with the manual screwdriver. The procedure was then
repeated for 4 screws, leaving the innermost 2 screwholes of the
6-hole plate intact. That space was left free for a pullout testing
jig.
[0065] Plate and Tack Fixation.
[0066] A fixation plate was laid on the bone as above. A hole of
2.0 mm diameter was drilled for the tack with the electric drilling
machine into the bone through the screw hole of the plate. A tack
was shot through the hole of the plate into the drillhole with the
tack insertion instrument of the invention. This procedure was
repeated for 4 tacks, leaving the innermost 2 holes of the 6-hole
plate intact. That space was left free for a pullout testing
jig.
[0067] The total time used for each of the above fixations was
measured with a stopwatch. The stopwatch was started before
drilling the first drillhole and ended when all four screws or
fasteners were inserted. Five parallel tests were performed for
both fixation methods, and an assistant was serving instruments and
implants to the operating surgeon.
[0068] Results
[0069] The total time used for inserting and fixing 4 screws in the
above plate varied from 124 to 178 seconds, with an average of 156
seconds. The total time used for inserting and fixing 4 tacks in
the above plate varied from 58 to 102 seconds, with an average of
76 seconds. This test showed that the time for fixation with the
method of this invention took only about 50% of the time for
fixation using the prior art method.
[0070] Although the invention has been described in detail for the
purpose of illustration, it is to be understood that such detail is
solely for that purpose and that variations can be made therein by
those skilled in the art without departing from the spirit and
scope of the invention except as it may be limited by the
claims.
* * * * *