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United States Patent |
6,093,189
|
Sellers
|
July 25, 2000
|
Orthopedic system having detachable bone anchors
Abstract
The present invention provides an improved orthopedic system in which the
part of the device that attaches to the bone is detachable from the parts
of the device which provide the bone stabilization, distraction, etc. In a
preferred embodiment, the system includes a proximal bone plate and
associated proximal fastener, and a distal bone plate and associated
distal fastener. The bone plates are affixed to the bone on opposing sides
of the bone repair site, which may be an osteotomy. The fasteners serve to
mechanically couple the orthopedic device, which may be a distractor,
through the bone plates, to the bone. The fasteners are releasably
mechanically coupled to the bone plates. This releasability permits the
distractor and fasteners to be removed after the orthopedic procedure is
complete, leaving only the bone plates in the patient. The bone plates may
be made with a low profile, such that they may be left permanently in the
patient. In a preferred embodiment, the bone plates are made from a
resorbable material, such that they will be absorbed by the patient's
body. Methods for using this novel orthopedic system are also disclosed.
Inventors:
|
Sellers; Timothy M. (Wayne, PA)
|
Assignee:
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Synthes (USA) (Paoli, PA)
|
Appl. No.:
|
274698 |
Filed:
|
March 23, 1999 |
Intern'l Class: |
A61B 017/56 |
Field of Search: |
606/69,70,71,77,57,105
|
References Cited
U.S. Patent Documents
4550449 | Nov., 1985 | Tunc | 623/16.
|
5013315 | May., 1991 | Barrows | 606/71.
|
5147358 | Sep., 1992 | Remmler | 606/57.
|
5152687 | Oct., 1992 | Amino | 433/173.
|
5201733 | Apr., 1993 | Etheredge, III | 606/53.
|
5275601 | Jan., 1994 | Gogolewski et al. | 606/72.
|
5364396 | Nov., 1994 | Robinson et al. | 606/53.
|
5470334 | Nov., 1995 | Ross et al. | 606/72.
|
5484439 | Jan., 1996 | Olson et al. | 606/65.
|
5522817 | Jun., 1996 | Sander et al. | 606/72.
|
5540687 | Jul., 1996 | Fairley et al. | 606/60.
|
5713903 | Feb., 1998 | Sander et al. | 606/72.
|
5827286 | Oct., 1998 | Incavo et al. | 606/71.
|
5855580 | Jan., 1999 | Kreidler et al. | 606/71.
|
Foreign Patent Documents |
0390613 A1 | Oct., 1990 | EP | .
|
0530585 A2 | Mar., 1993 | EP | .
|
0815878 A2 | Jan., 1998 | EP | .
|
0818183 A2 | Jan., 1998 | EP | .
|
Primary Examiner: Buiz; Michael
Assistant Examiner: Woo; Julian W.
Attorney, Agent or Firm: Pennie & Edmonds LLP
Claims
What is claimed is:
1. An orthopedic system comprising:
at least two bone anchors for anchoring the system to a patient's bone,
each anchor having a bone-contacting surface and a fastener-connecting
portion;
a fastener associated with each of the bone anchors, each fastener having a
device-connecting portion and an anchor-connecting portion, the
anchor-connecting portion and the fastener-connecting portion of the
associated bone anchor providing a releasable mechanical coupling of the
fastener to the bone anchor; and
an orthopedic device coupled to the device-connecting portions of each
fastener;
whereby after an orthopedic procedure is complete, the mechanical coupling
of the bone anchors to the fasteners can be released, allowing the
fasteners and orthopedic device to be removed from the patient without
removal of the bone anchors.
2. The orthopedic system of claim 1, wherein the bone anchors are made of a
bio-absorbable material.
3. The orthopedic system of claim 1, wherein the bone anchors are bone
plates, each plate having at least one screw hole adapted to receive a
bone screw to anchor the plate to the bone.
4. The orthopedic system of claim 3, wherein the bone plates are made of a
bio-absorbable material.
5. The orthopedic system of claim 4, further comprising bone screws made of
a bio-absorbable material which takes at least as long as the bone plates
to be absorbed in the patient.
6. The orthopedic system of claim 3, wherein the orthopedic device is a
distractor.
7. The orthopedic system of claim 1, wherein the releasable coupling of at
least one of the bone anchors and the associated fastener comprises a
detent mechanism, the release of the detent mechanism being prevented when
the orthopedic device is substantially fully coupled to the
device-connecting portion of that fastener and release of the detent
mechanism being permitted when the orthopedic device is at least partially
uncoupled from the device-connecting portion of that fastener.
8. The orthopedic system of claim 1, wherein the anchor-connecting portion
of at least one fastener comprises a shoe, and the fastener-connecting
portion of the bone anchor associated with that at least one fastener
comprises an engagement cavity; wherein the shoe is sized and shaped to be
slidingly received by the engagement cavity.
9. The orthopedic system of claim 8, wherein the shoe and the associated
engagement cavity have a corresponding substantially rectangular shape;
whereby the releasable mechanical coupling is a slip lock.
10. The orthopedic system of claim 8, wherein the shoe and the associated
engagement cavity have a corresponding substantially tapered shape;
whereby the releasable mechanical coupling is a frictional lock.
11. An orthopedic distraction system for distracting first and second
osteotomically separated bone sections of a patient, the system
comprising:
a distal bone plate for subcutaneous implantation and attachment to the
first bone section, the distal bone plate having screw holes adapted to
receive bone screws, a bone-contacting surface, and a first engagement
cavity having a substantially rectangular shape;
a distal fastener associated with the distal bone plate and having a
device-connecting portion and a shoe, the shoe being shaped and sized to
correspond to the first engagement cavity; whereby the shoe is slidingly
accepted by the first engagement cavity producing a slip lock of the
distal fastener to the distal bone plate;
a proximal bone plate for subcutaneous implantation and attachment to the
second bone section, the proximal bone plate having screw holes adapted to
receive bone screws, a bone-contacting surface, and a second engagement
cavity;
a proximal fastener associated with the proximal bone plate and having a
device-connecting portion and a anchor-connecting portion, wherein
proximal bone plate and proximal fastener are releasably coupled by a
detent mechanism,
an orthopedic device coupled to the device-connecting portions of each
fastener;
wherein the release of the detent mechanism is prevented when the
orthopedic device is at least substantially fully coupled to the
device-connecting portion of the proximal fastener, and release of the
detent mechanism is permitted when the orthopedic device is at least
partially uncoupled from the device-connecting portion of the proximal
fastener, and further wherein both fasteners can be released from their
corresponding bone plates, allowing the fasteners and distraction device
to be removed from the patient without removal of the bone plates.
12. The orthopedic system of claim 11, wherein the bone plates are made of
a bio-absorbable material.
13. The orthopedic system of claim 12, further comprising bone screws made
of a bio-absorbable material which takes at least as long as the bone
plates to be absorbed in the patient.
14. A method for treating a bone repair site in a patient comprising the
steps of:
making an incision for access to the bone repair site;
attaching separate bone anchors to the bone on each side of the bone repair
site;
releasably mechanically coupling a fastener to each of the bone anchors;
coupling an orthopedic device to the fasteners;
performing an orthopedic procedure using the orthopedic device;
removing the orthopedic device and fasteners from the patient; and
closing the incision, without detaching the bone anchors from the bone.
15. The method of claim 14, which further comprises making the bone anchors
of a bio-absorbable material.
16. The method of claim 15, which further comprises providing bone anchors
in the form of bone plates, with each plate having at least one screw hole
adapted to receive a bone screw.
17. The method of claim 16, which further comprises providing bone plates
made of a bio-absorbable material.
18. The method of claim 17, which further comprises providing bone screws
made of a bio-absorbable material which takes at least as long as the bone
plates to be absorbed by the patient.
19. The method of claim 16, which further comprises providing a distractor
as the orthopedic device.
20. The method of claim 14, which further comprises providing at least one
of the bone anchors with an engagement cavity, providing the associated
fastener with a shoe adapted to be slidingly received by the engagement
cavity, and wherein the step of releasably mechanically coupling said
anchor and said fastener comprises sliding said shoe into said engagement
cavity.
21. The method of claim 20, wherein the step of providing at least one of
the bone anchors with an engagement cavity comprises providing said bone
anchor with a substantially rectangular cavity, the step of providing the
associated fastener with a shoe adapted to be slidingly received by the
engagement cavity comprises providing said associated fastener with a shoe
having a shape substantially corresponding to the rectangular cavity, and
the step of releasably mechanically coupling said anchor and said fastener
further comprises slip locking said anchor and said fastener.
22. The method of claim 20, wherein the step of providing at least one of
the bone anchors with an engagement cavity comprises providing said bone
anchor with a cavity having a substantially tapered shape, the step of
providing the associated fastener with a shoe adapted to be slidingly
received by the engagement cavity comprises providing said associated
fastener with a shoe having a shape substantially corresponding to the
cavity having a substantially tapered shape, and the step of releasably
mechanically coupling said anchor and said fastener further comprises
friction locking said anchor and said fastener.
23. The method of claim 14, which further comprises providing the
releasable coupling as a detent mechanism, with the release of the detent
mechanism being prevented when the orthopedic device is substantially
fully coupled to the device-connecting portion of that fastener and the
release of the detent mechanism being permitted when the orthopedic device
is at least partially uncoupled from the device-connecting portion of that
fastener.
Description
TECHNICAL FIELD
The present invention relates to an orthopedic system and, more
particularly, to an improved orthopedic system wherein the part of the
device that attaches to the bone is detachable from the parts of the
system which provide the bone fixation, reduction, distraction, etc.
BACKGROUND OF THE INVENTION
A variety of orthopedic devices, including bone fixation, reduction, and
distraction devices, are known in the art. Fixation devices, or fixators,
are used to stabilize bone segments and to facilitate the healing of bones
at a bone repair site. As used herein "bone repair site" refers to any
bone region which is bounded on opposing sides by relatively healthy bone
regions to which orthopedic devices can be secured, such as an osteotomy
or a fracture. Reduction and distraction devices (commonly referred to as
reducers and distractors), are used to gradually adjust the relative
orientation and spacing of the bone parts on opposing sides of a bone
repair site.
Fixators generally consist of transcutaneous pins or screws secured in the
bone on either side of the bone repair site. An adjustable external
fixation mechanism is attached to the pins, allowing the relative
positions of the pins to be adjusted, thus aligning the bone regions
across the bone repair site. When the desired alignment is achieved, the
fixation mechanism is locked in place to maintain the alignment. After the
bone repair site has healed, the fixator is removed from the patient.
Reducers and distractors typically have structure similar to fixators,
except that they additionally include a mechanism which allows controlled
incremental adjustment of the distance between parts of the device on
opposing sides of the bone repair site. Typically, distractors are used to
perform distraction osteogenesis. This procedure was perfected by the
Russian orthopedic doctor, Gavriel Ilizarov. A typical procedure of this
type involves at most an osteotomy completely separating the bone into two
segments, or at least an incision of the cortical portion of the bone.
Then, the bone segments on either side of the osteotomy (or the medullary
or cancellous portion of the bone on either side of the incision) may be
expanded. This gradual separation allows new bone to form in the osteotomy
void. The distraction phase is followed by a consolidation phase, during
which the distractor is held fixed, and the new bone growth gains
strength. Following the consolidation phase, the distractor is removed
from the patient.
The design of the early fixators and distractors, which used bone pins and
screws to attach the device to the bone are known to have certain
problems. For example, numerous pins are needed to attach a single device;
at a minimum, two pins are required, but typically, many more are used.
Each pin involves a transcutaneous incision, thus multiplying the risk of
infection to the patient. Furthermore, a pin clamp or coupling is required
to join the fixation/distraction mechanism to the pins, and the design and
operation of these couplings are complicated by the difficulty in aligning
the pins accurately when they are inserted into the bone. Finally, because
the pins extend in a generally perpendicular direction from the insertion
site, they cause the resultant overall device to stick out quite far from
the patient's body (i.e., the device has a high profile), and the device
is unsightly. A high-profile device is more subject to bumps and snags
than one which is completely located close to the patient's body. Such
seemingly aesthetic considerations are also important because a
high-profile device may be rejected by prospective patients, especially
children.
Accordingly, more recent devices have been designed not to use
transcutaneous pins for attachment to the bone, but rather to use more
low-profile bone anchors, such as plates with screw holes, as part of a
low-profile overall device. This improved prior art is exemplified by U.S.
Pat. No. 5,364,396 to Robinson et al. ("the Robinson patent"), which
discloses an implantable bone distraction device which includes low
profile blocks for attachment to osteotomically separated bone sections.
The entire device can be implanted subcutaneously, except for a
transcutaneous actuator assembly which is linked to the implanted
distraction assembly, and allows adjustment of the distraction distance
from outside the patient's body.
However, modern low-profile fixation/distraction systems such as that
disclosed in the Robinson patent suffer from the drawback that their use
necessitates two substantial, invasive, surgical procedures: one to
implant the device, and another to remove it after the
fixation/distraction procedure is complete. Unnecessary surgical
procedures are of course undesirable, based on both considerations of
health care costs and the medical risks associated with surgery.
Accordingly, there is a need in the art to provide a low-profile
fixator/distractor that does not require a second surgical procedure to
remove the device after the fixation/distraction procedure is complete.
Indeed, there is a need in the orthopedic device art more generally, to
provide a device that does not require a second surgical procedure to
remove the device after the orthopedic procedure is complete.
SUMMARY OF THE INVENTION
The present invention addresses the need in the art by providing an
orthopedic device, such as a bone fixator, reducer, or distractor, with
detachable bone anchors, such that after the completion of the orthopedic
process, the orthopedic device can be remotely disengaged, from outside
the patient, from the subcutaneous bone anchors, leaving only the
subcutaneous bone anchors implanted in the patient.
The orthopedic system of the present invention includes at least two bone
anchors. Each of these anchors has a bone-contacting surface and
fastener-connecting portion. There is a fastener associated with each bone
anchor; the fastener includes a device-connecting portion for connection
to an orthopedic device (such as a distractor), and a anchor-connecting
portion for establishing a releasable mechanical coupling with the
fastener-connecting portion of the associated anchor. An orthopedic
device, such as a distractor, is coupled to the device-connecting portions
of each fastener in order to perform the desired procedure. After the
orthopedic procedure involving the orthopedic device is complete, the
mechanical couplings of the fasteners to the bone anchors can be released,
allowing the fasteners and device to be easily removed from the patient
without requiring the removal of the bone anchors.
The bone anchors may be in the form of bone plates, and may be made in full
or in part from any appropriate bio-compatible material, such as a
bio-absorbable (resorbable) material. When formed as bone plate, the
anchors may have one or more screw holes adapted to receive a bone screw.
The bone screws may also comprise a bio-absorbable material, in which case
the material selected for the screws should be such that the screws will
take at least as long to be absorbed by the patient's body as the bone
plates.
The releasable coupling of at least one of the bone anchors and fastener
may comprise a detent mechanism. Preferably, the release of the detent
mechanism is prevented when the orthopedic device is substantially fully
coupled to the device-connecting portion of that fastener; this avoids
undesired release of the system while it is in use. Release of the detent
mechanism is permitted when the orthopedic device is at least partially
uncoupled from the device-connecting portion of that fastener, such that
the system can be disassembled when desired.
One of the fasteners may have an anchor-connecting portion comprising a
shoe; in this embodiment, the bone anchor associated with that fastener
will have a fastener-connecting portion comprising an engagement cavity.
The shoe and cavity are sized and shaped to allow the shoe to be slidingly
received by the cavity. The shoe and engagement cavity may have a
corresponding substantially rectangular shape, in which case the
releasable mechanical coupling of the fastener to the bone anchor is a
slip lock. Alternatively, the shoe and the associated engagement cavity
have a corresponding substantially tapered shape, in which case the
releasable mechanical coupling of the fastener to the bone anchor is a
frictional lock.
An orthopedic distraction system for distracting first and second
osteotomically separated bone sections according to the present invention
may comprise a distal bone plate, a distal fastener, a proximal bone
plate, a proximal fastener, and a distraction device. The distal bone
plate is designed to be subcutaneously implanted and attached to the first
bone section, and is provided with screw holes adapted to receive bone
screws, a bone-contacting surface, and a first engagement cavity having a
substantially rectangular shape.
The distal fastener associated with the distal bone plate has a
device-connecting portion and a shoe. The shoe is shaped and sized to
correspond to the first engagement cavity. In this way, when the shoe is
slidingly accepted by the first engagement cavity, a slip lock of the
distal fastener to the distal bone plate is produced.
The proximal bone plate is also designed to be subcutaneously implanted,
and is attached to the second bone section. The proximal bone plate has
screw holes adapted to receive bone screws, a bone-contacting surface, and
a second engagement cavity. A proximal fastener is provided, to be
associated with the proximal bone plate; this proximal fastener has a
device-connecting portion and a anchor-connecting portion. The releasable
coupling of the proximal bone plate and proximal fastener comprises a
detent mechanism. Release of the detent mechanism is prevented when a
distraction device is fully coupled to the device-connecting portion of
the proximal fastener, but release of the detent mechanism is permitted
when the orthopedic device is at least partially uncoupled from the
device-connecting portion of the proximal fastener. In use, the
distraction device is coupled to the device-connecting portions of each
fastener. According to the novel orthopedic system of the present
invention, when desired, both fasteners can be released from their
corresponding bone plates, allowing the fasteners and distraction device
to be easily removed from the patient without requiring the removal of the
bone plates.
Also disclosed is a method for treating bone sections on either side of a
bone repair site. Bone anchors are attached to the bone on each side of
the bone repair site, and fasteners are releasably coupled to each of the
bone anchors an orthopedic device is coupled to the fasteners, either
before or after the fasteners are coupled to the anchors. The orthopedic
procedure is performed using the orthopedic device, and the orthopedic
device and fasteners may be removed. The removal of the orthopedic device
and fasteners may be performed in any order. The method disclosed is
compatible for use with all of the various embodiments of the novel
distraction system described herein.
The method for treating a bone repair site according to the present
invention generally comprises the following steps. An incision is made,
for access to the bone repair site. One bone anchor is attached to the
bone on each side of the bone repair site, and a fastener is releasably
mechanically coupled to each of the bone anchors. An orthopedic device is
mechanically coupled to the fasteners and is used in performing the
desired orthopedic procedure. When the procedure is complete, the
orthopedic device and fasteners are removed, in any order, from the
patient. The incision is then closed, leaving the bone anchors attached to
the bone.
More specifically, the method for treating a bone repair site on a patient
according to the present invention comprises the following steps. An
incision is made, for access to the bone repair site. A distal bone plate
is subcutaneously attached to the bone; this distal bone plate has screw
holes adapted to receive bone screws, a bone-contacting surface, and a
first engagement cavity having a substantially rectangular shape. A distal
fastener is releasably coupled to the distal bone plate, this distal
fastener having a device-connecting portion and a first shoe, the shoe
being shaped and sized to correspond to the first engagement cavity. The
shoe is slidingly accepted by the first engagement cavity, producing a
slip lock of the distal fastener to the distal bone plate. A proximal bone
plate is subcutaneously attached to the bone, this proximal bone plate has
a bone-contacting surface, a second engagement cavity, and screw holes
adapted to receive bone screws. A proximal fastener is releasably
mechanically coupled to the proximal bone plate; this proximal fastener
has a device-connecting portion and a anchor-connecting portion. The
releasable coupling of the proximal fastener to the proximal bone plate
comprises a detent mechanism. An orthopedic device, such as a distractor,
is coupled to the device-connecting portions of both fasteners, and is
used to perform the desired orthopedic procedure. After the procedure is
complete, the distal fastener is uncoupled from the distal bone plate and
the proximal fastener is uncoupled from the proximal bone plate, allowing
the fasteners and orthopedic device to be removed from the patient.
Finally, the incision is closed, leaving the bone plates in the patient.
BRIEF DESCRIPTION OF THE DRAWINGS
The features and advantages of the present invention will become more
readily apparent from the following detailed description of the invention
in which like elements are labeled similarly and in which:
FIG. 1 is a perspective view of an embodiment of the present orthopedic
system adapted for use on the mandible, illustrating a distractor attached
to osteotomically separated portions of a mandible;
FIG. 2 is a top plan view of the system illustrated in FIG. 1;
FIG. 3 is a sectional side view of the system illustrated in FIG. 1 taken
along line 3--3 in FIG. 2;
FIGS. 4A and 4B are a top plan view and a side elevation view,
respectively, of the proximal foot plate of the system illustrated in FIG.
1;
FIGS. 5A and 5B are a top plan view and a side elevation view,
respectively, of the distal foot plate of the system illustrated in FIG.
1;
FIGS. 6A and 6B are a side elevation view and a bottom plan view,
respectively, of the proximal fastener of the system illustrated in FIG.
1;
FIGS. 7A and 7B are a side elevation view and a bottom plan view,
respectively, of the distal fastener of the system illustrated in FIG. 1;
FIGS. 8A and 8B are a side elevation view of a distal foot plate and a
bottom plan view of a distal fastener, respectively, in another embodiment
of the system illustrated in FIG. 1;
FIG. 9 is a perspective view of the proximal footplate and the proximal
fastener which illustrates the fastener partially engaged with the plate;
and
FIG. 10 is a perspective view of the distal foot plate and the distal
fastener which illustrates the fastener partially engaged with the plate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The orthopedic device of the present invention is discussed herein with
reference to a preferred embodiment adapted to be used in a linear
distraction of a mandible. However, it will be clear that the invention is
not limited to mandibular distraction, or indeed to distraction generally,
but rather finds general application for use with any orthopedic device
that involves anchoring devices to bone.
As seen in FIGS. 1-3, the orthopedic system 10 generally consists of
distraction assembly 12, proximal and distal foot plates (or bone plates)
14 and 16, respectively, and proximal and distal fasteners 18 and 20,
respectively. The distraction assembly 12 has a proximal, or adjustment
end 22, and a distal end 24. The orthopedic system 10 is affixed to
mandible 5 by bone screws 8 which are inserted through screw-holes in foot
plates 14 and 16. In use, the entire orthopedic system 10 is implanted
subcutaneously, except for the adjustment end 22 of the distraction
assembly 12, which extends subcutaneously through a small incision in the
skin. It will be understood that with reference to the various elements of
the present invention, the term proximal is used to refer to the end of
the device associated with the proximal end of the distraction assembly
that extends outwards transcutaneously, and the term distal is used to
refer to the other end of the device.
Turning now to the details of the orthopedic system 10 as best illustrated
in FIGS. 2 and 3, the distraction assembly 12 generally consists of a lead
screw 102, an outer sleeve 202, and an inner sleeve 302. As described in
detail below, lead screw 102 is journaled within in outer sleeve 202, such
that screw 102 can rotate, but not translate axially, relative to sleeve
202. Inner sleeve 302 has internal threading which interacts with the
external threading 106 on screw 102. Thus, in the assembled distraction
assembly 12, rotation of screw 102 is translated to linear motion of the
inner sleeve 302, like a nut being driven on a bolt, causing telescopic
expansion or contraction of the overall assembly 12.
Lead screw 102 has a distal shaft portion 104 provided with external screw
threading 106, an enlarged-diameter intermediate portion 108, a proximal
shaft portion 110, and a proximal, or adjustment end 112. Adjustment end
112 is provided with a tool interface 114, such as a hexagonal surface
which can be driven a standard hexagonal driving tool. The outer sleeve
202 has two different inside cavity portions. The proximal cavity portion
206 has an inside diameter sized so as to slidably accept the proximal
shaft portion 110 of the screw 102. The distal cavity portion 208 has an
inside diameter sized so as to slidably accept the inner sleeve 302. Inner
sleeve 302 is provided with internal threading that matches the external
threading 106 on screw 102, and an exterior surface 306 which is generally
smooth except for longitudinal slot 308. Slot 308 extends from the
proximal end 310 of the sleeve towards the distal end 312.
The proximal fastener 18 is best understood by reference to FIGS. 6A and
6B. It has a device-connecting portion comprising an internally-threaded
bore 188 which accepts the external threading on the distal end of the
outer sleeve 202. The proximal fastener also has a bone anchor-connecting
portion comprising shoe 182. The shoe may have a rectangular shape, as
shown in FIG. 6B, or may have a tapered shape, depending on the shape
selected for the cavity 142 in proximal bone plate 14. This shoe 182 is
provided with a sprung arm 184, on the end of which is a projection 186.
The operation of the sprung arm and projection in forming a detent
mechanism coupling the fastener 18 to the plate 14 is discussed in detail
below. FIG. 9 shows the fastener 18 in an intermediate stage of being
releasably mechanically coupled or uncoupled from plate 14.
The distal fastener 20 is best understood by reference to FIGS. 7A and 7B.
It has a device-connecting portion comprising a bore 28 which accepts the
distal end of the inner sleeve 302. The distal fastener also has a bone
anchor-connecting portion comprising shoe 220. The shoe may have a
substantially rectangular shape, as shown in FIG. 8B, or a substantially
tapered shape, as shown in FIG. 7B. The shape of the shoe is selected to
correspond to the shape of the cavity 162 in the plate 16. FIG. 10 shows
the fastener 20 in an intermediate stage of being releasably mechanically
coupled or uncoupled from plate 16.
The proximal shaft portion 112 of lead screw 102 is slideably received
within the proximal cavity portion 206 of outer sleeve 202, such that
screw 102 is free to rotate relative to the outer sleeve 202. A region of
the proximal shaft portion 110, and the adjustment end 112 of screw 102
extend out from the proximal end 204 of the sleeve. A collar 116 is
attached to the screw on the extending region of the proximal shaft
portion by pin 118. The collar 116 and the enlarged-diameter intermediate
shaft portion 108 prevent axial translation of the screw 102 relative to
outer sleeve 202. In this way, screw 120 is effectively journaled within
the outer sleeve 202.
The internal threading of inner sleeve 302 interacts with the external
screw threading 106 of lead screw 102, while at the same time the smooth
exterior surface 306 of the inner sleeve is in sliding relation with the
smooth inner surface of the proximal cavity portion 208 of outer sleeve
202. In this way, inner sleeve 302 is in sliding, telescoping relation
with outer sleeve 202.
Guide pin 210 is press-fit into a hole which extends through the thickness
of the outer sleeve 202. The end of the guide pin which extends inwards
projects sufficiently beyond the inner surface of the outer sleeve so as
to interact with the longitudinal slot 308 provided on the exterior
surface of the inner sleeve 302. Thus, it will be appreciated that the
interaction of longitudinal slot 308 and guide pin 210 form a keyway which
prevents relative rotation of the sleeves about the longitudinal axis X-X
of the device (designated X-X in FIG. 3).
Foot plates 14 and 16 serve as the bone anchors, and can be made from any
biocompatible material such as metal, plastic, or composites. In a
preferred embodiment, the foot plates are bone plates made of a titanium
alloy. In an alternative embodiment discussed in more detail below, the
foot plates can be made from a bio-absorbable material. The choice of
material from which to construct the foot plates is a routine design
matter which depends purely on the particular medical application in which
the system according to this invention is used.
As shown in FIG. 1, the foot plates are provided with screw holes 9 to
accept the bone screws 8 which affix the device to the bone on either side
of the patient's bone repair site. These holes are preferably countersunk
to reduce the height of projection of the screw heads above the foot plate
surface after the device is fully implanted. The foot plates have a
bottom, or bone-contacting surface 15 which may be flat or may be shaped
to conform to the contours of the bone to which it is being attached.
The distal foot plate 16 is provided with a fastener-connecting portion
comprising the slot-like engagement cavity 162 which accepts the shoe 220
of the distal fastener. The engagement cavity may have a substantially
rectangular shape. In this case, the side walls 166 of the cavity are
parallel with the longitudinal axis X-X of the device, as shown in FIG.
8A, and the shoe 220 has a substantially rectangular shape corresponding
to the shape of the cavity 162. The shape and size of the shoe is selected
to allow the shoe 220 to be slidingly received by the cavity 162, creating
a slip lock of the fastener 20 to foot plate 16. The slip lock is a
releasable mechanical coupling which is easily released by the application
of a force separating the fastener 20 from foot plate 16.
In an alternate embodiment, the engagement cavity may have a substantially
tapered shape, in which case side walls 166 are tapered relative to the
longitudinal axis X-X of the device, as shown in FIG. 5A. The shoe 220 in
this embodiment has a substantially tapered shape corresponding to the
shape of cavity 162. The shape and size of the shoe in this embodiment
creates a frictional lock of the fastener 20 to the foot plate 16. The
frictional lock is a releasable mechanical coupling, but requires more
separating force to achieve the release than does the coupling in the slip
lock embodiment described above.
If the device is to be used in the standard distraction procedure (i.e., a
procedure in which the device is to apply a tensile force to the bone
repair site), then the foot plate is mounted with the open end of the
cavity facing the bone repair site, that is, the orientation shown in FIG.
1. In this way, as the distraction device is activated, the distraction
force will tend to drive the shoe 220 of the distal fastener 20 into the
engagement cavity 162, resulting in a releasable mechanical coupling of
the fastener 20 and plate 16 resulting from the interaction of the shoe
220 with the cavity 162. Conversely, if the device were to be used in a
compression mode, the foot plate could be mounted with the open end of the
cavity facing away from the bone repair site, such that the compression
force would tend to produce the above-described coupling.
As shown in FIG. 5A, the screw holes of plate 16 are located around the
cavity 162. This geometry has been found to provide a good combination of
accessibility to the screws and holding strength when the device of the
present invention is used in the distraction of a mandible. However, it is
to be understood that the location of the screw holes and the contoured
shape of the plate 16 as seen in FIG. 5A is not a critical aspect of the
present invention; other screw hole placements and plate shapes could be
used without departing from the spirit or scope of the present invention.
The proximal foot plate 14 is also provided with a fastener-connecting
portion comprising an engagement cavity 142. This engagement cavity may
utilize the tapered wall geometry similar to that of the cavity 162 as
described above and shown in FIG. 5A, in which case the proximal fastener
18 would have a wedge-shaped shoe similar to that of fastener 20, as shown
in FIG. 7B. The activation force applied to the device would then result
in a frictional lock providing a releasable mechanical coupling of the
fastener 18 to the plate 14. In a preferred embodiment, however, the
cavity 142 will utilize side walls 144 which are parallel to the
longitudinal axis X-X of the device, and the releasable mechanical
coupling will be a slip lock.
This detent mechanism is comprised of parts of the proximal foot plate 14,
proximal fastener 18, and also sleeve 202. The bottom surface 145 of the
cavity is provided with a depression 147, which may be in the form of a
truncated spherical volume section. The shoe 182 of proximal fastener 18
is provided with a naturally sprung arm 184. Arm 184 is provided on its
bottom surface with a "bump" or projection 186 complementary to the shape
of depression 147. When the shoe 182 is slid into the cavity 142, the
projection 186 and depression 147 operate as a detent mechanism to prevent
axial separation of fastener 18 from plate 14.
As can be understood from FIG. 6A, when the sleeve 202 is not threaded into
the bore 188, the spring arm 184 may deflect upwards such that the
projection 186 becomes disengaged from depression 147, thus disengaging
the detent mechanism. The force provided by spring arm 184 alone can serve
to hold the detent mechanism in the engaged position under low forces.
Furthermore, when sleeve 202 is threaded into bore 188, it completely
prevents upwards motion of arm 184, thus preventing disengagement of the
detent mechanism even when subjected to substantial forces, such as those
generated during when the device is removed from the patient. Only when
the sleeve 202 is sufficiently unthreaded from bore 188 can the arm 184
again deflect upward sufficiently to allow the detent mechanism to be
disengaged, which in turn permits the shoe 182 to slide out of cavity 142.
In other words, when the sleeve is screwed into the fastener, it locks the
fastener to be plate 14.
As shown in FIG. 4A, the screw holes of plate 14 are offset both to one
side of axial centerline X-X of the device, and are placed such that the
plate as a whole takes on the shape similar to an upper case "Y". This
geometry has been found to provide a good combination of accessibility to
the screws and holding strength when the device of the present invention
is used in the distraction of a mandible. However, it is to be understood
that the location of the screw holes and the contoured shape of the plate
14 as seen in FIG. 4A is not a necessary part of the present invention;
other screw hole placements and plate shapes could be used without
departing from the spirit or scope of the present invention.
It is important to note that the fasteners and foot plates of the system of
the present invention are separate parts, as opposed to being integrally
formed. Furthermore, due to the way in which they are mechanically joined
in an conveniently releaseable locked way, they are capable of being
separated after the device has served its purpose in the orthopedic
procedure--the fasteners and foot plates are not permanently joined, for
example by welding, nor are they joined by some other means which would
make their separation difficult or inconvenient. Furthermore, the
mechanical coupling of the fasteners and foot plates of the present
invention does not require any additional parts to achieve the coupling.
In order to use the device of the present invention in a typical
distraction procedure, the surgeon makes an incision, performs the
distraction, permits consolidation, then removes the distraction assembly,
leaving the foot plates affixed to the bone, and closes the incision.
To assemble the system, the lead screw 102 is first inserted into the outer
sleeve 202, after the sleeve has first been provided with guide pin 210.
The collar 116 is installed on the region of the proximal shaft portion
112 which extends out from the proximal end 204 of the outer sleeve 202.
The collar 116 is captivated on the shaft by pressing a pin through
matching holes in the collar and proximal shaft portion. The outer sleeve
202 is then threaded into the proximal fastener 18, after the fastener has
first been slid into, and lockingly engaged with, foot plate 14 (using the
detent mechanism described above). The lead screw 102 is then threaded
into inner sleeve 302, care being taken that the longitudinal slot on
sleeve 302 is properly engaging with guide pin 210. The distal fastener 20
is then pressed and pinned onto the distal end of the inner sleeve 302,
and finally, is engaged with the distal foot plate 16.
To implant the device, a small incision is made of appropriate size to
permit access to the bone necessary to attach the foot plates, and in a
location appropriately offset from the bone repair site bearing in mind
that only the proximal end of the distraction device will extend
percutaneously through the incision once implanted. The assembled system
is carefully guided into the percutaneous opening and positioned relative
to the bone repair site. The foot plates are then affixed to the bone
using bone screws, and the incision is closed, with only the proximal end
of the device extending percutaneously.
The distraction osteogenesis procedure is performed by turning the lead
screw using the tool interface 114. Counter-clockwise rotation of the
screw will result in axial lengthening of the device, resulting in a
distraction force being communicated to the bones through the foot plates.
After the distraction and consolidation phase of the procedure is complete,
the device is removed, or disengaged, by reversing the direction of
rotation of the lead screw 102. The amount of reverse (i.e., clockwise)
rotation depends on the thread pitch of the lead screw, but typically, at
least ten full clockwise rotations will be required to cause the distal
fastener 20 to disengage from the distal foot plate 16. The sleeve 202 is
unthreaded from fastener 18 sufficiently to allow sprung arm 184 to flex,
such that when the device is now pushed towards the bone surface, the
detent mechanism holding proximal fastener 18 to corresponding proximal
foot plate 14 is released, unseating the device from the proximal foot
plate. The entire activation portion of the device (lead screw, sleeves,
and fasteners) is now disengaged from the patient, and can now be gently
removed through the percutaneous port, leaving only the foot plates (and
associated bone screws) in the patient. As a final step, the percutaneous
port is closed using standard surgical procedures.
In one embodiment of the present invention, the foot plates 14 and 16 may
be formed of a bio-absorbable material. Any bio-absorbable material may be
used, either natural or synthetic (for example polylactides,
polyglycolides, or polyesteramides). By forming the foot plates from a
bio-absorbable material, the foot plates may be left in situ after the
completion of the distraction osteogenesis. By appropriate selection of
the bio-absorbable materials, the foot plates will begin to absorb after
their mechanical strength is no longer required for the procedure, and
over time the foot plates will substantially or totally be resorbed by the
body. By eliminating the need for a second surgical procedure to remove
the foot plates, this invention advantageously reduces health care costs
as well as the medical risks associated with even the most carefully
performed surgery.
In addition, the bone screws 8 used to affix the foot plates to the bone
may also be made of bio-absorbable material, either the same material as
the foot plates, or a different material. In this case, it may be
desirable to select the bio-absorbable materials such that the screws are
not absorbed until after the foot plates are substantially absorbed. If
the screws were to be absorbed first, this would create the undesirable
situation of the foot plates coming loose from the attachment site and
being free to migrate subcutaneously.
It should be emphasized that the above described embodiment of the present
invention is merely one specific example adapted for a specific
application in the human skeletal system. The modifications appropriate
for other applications may readily be realized by those who are skilled in
the art and who have been equipped with the understanding of the structure
and operation of the present invention as set forth in the above
description.
For example, the particular linear distractor embodiment shown in FIG. 1
could be used, without any structural modifications, in well-known
orthopedic applications other than mandibular distraction; for example it
is entirely appropriate for use in the distraction of long bones. In
addition, it is evident that various other well-known distraction and
fixation assemblies could be substituted for the distraction assembly 12
described above, without departing from the spirit or scope of the present
invention. For example, instead of a simple linear distraction assembly,
an assembly providing both linear and angular distraction could be
provided to bridge the bone repair site and mechanically link the foot
plates. Accordingly, it should be understood that the embodiment herein is
merely illustrative of the principles of the invention. Various
modifications may be made by those skilled in the art which will embody
the principles of the invention and fall within the spirit and the scope
thereof.
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