Note: Descriptions are shown in the official language in which they were submitted.
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This disclosure re!a+es to a surgical procedure for fusing a bone joint
formed by opposed bony s~lrfaces surrounded by ligaments which resist
expansion of the joint.
This invention was developed specifically for the correction of Wobbler
syndrome in horses, which is a form of progressive ataxia due to
instability of the cervical spine creating encroachment on the spinal cord
(equine cervical vertebral malformation). Earlier attempts by $he inveneor
to surgically stabilize the spine in horses utilized placement of a precut
bone dowel within a prepared hole centered over the disk and partially cut
into the vertebral end plates both above and below the disk.
One difficulty posed by this earlier work related to the inherent
biological problems in using allogTafts (tissues transplanted between
individuals that are members of the same species but are not genetically
identical) or xenografts (tissues transferred between different species).
While the fusion technique using dowels has been successfully applied to
humans by using bone taken from a remote area of the body, this is
impractical when the technique is applied to horses. Removal of bone from
the leg of a horse, as an example, would seriously affect the running
ability of the horse. In addition, in all applications, dowels produced as
autografts (tissues transplanted from one site to another site in the same
individual) involve two separate surgical operations,` with resulting
increases in the lil~elihood of complications.
It is well known that autogenous tissues are considered to be the
most biologically suitable graft material. Histocompatibility differences
2 5 between donor and recipient do not exist, and there is no possibility of
transmitting disease from one individual to another. The potential
disadvantages of autografts include the need to sacrifice normal structures
elsewhere in the body, morbîdity associa$ed with a second surgical site or
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extended primaI ~- incision, and limitations in the size, shape, and quality
of avclilable autogenous tissues.
The instant method of bone-to-bone fusion not only immediately
stabil;zes the joint, as does the dowel technique when successful, but also
promotes bone growth across the joint by use of readily available
autogenous tissue in the form of bone fragments removed during
preparation of the joint. No additional surgery or bone removal is
required. This invention further answers the need for perfect cylindrical
bone dowels implant, which are impossible to meet when using natural
bone.
A preferred embodiment of the invention is illustrated in the
flccompanying drawingsl in which:
Fig. 1 is an exploded isometric view of the bone basket;
Fig. 2 is a side view;
Fig. 3 is an end view;
Yig. 4 is an opposite end view;
Fig. 5 is a sectional view taken along line 5-5 in Fig. 3;
Fig. 6 is a side view of an implanting tool;
Fig. 7 is an illustration of the implanting step; and
2 0 Fig . 8 is a partial sectional view of a spine, showing the implanted
bone basket.
The process described below is applicable to any human or animal
joint formed by opposed contiguous bony surfaces which are covered and
separated by intervening cartilage and are surrounded by ligaments which
2s resist expansion of the joint. Specific examples of such joints are a spinal
joint between adjacent vertebrae or the ankle joint. The process was
developed to immediately stabilize the joint and to further promote ultimate
bone-to-bone fusion~ It eliminates the need for the additional surgery
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previously required to Itil;~e autogenous bone grafts or dowels. It
provides a strong, rigid cylinder for implantation in a transverse position
centered across a joint. The implanted structure is in the form of a
perforated cylindrical bone basket which can be filled with bone frngments
produced during the preparation of the joint. These bone fragments
provide autogenous tissue to promote bone growth throlgh the basket, as
well as around it.
The process involves the initial steps of surgically accessing the joint
and removing intervening cartilage located between the contiguous bony
surfaces. A transverse cylindrical opening is then bored across the
contiguous bony surfaces. Immediate stabilization is achieved by driving
into the cylindrical opening a hollow basl~et having a rigid perforated
cylindrical wall whose outside diameter is slightly greater than the inside
diameter of the cylindrical opening. The implanting of the basket spreads
the bony surfaces apart in opposition to the resistance to expansion of the
joint provided by the surrounding ligaments. The basket is subsequently
filled with bone fragments produced by the boring step. The bone
fragments located within the basket promote bone growth abGut the basket
and through its perforated cylindrical wall while the joint is maintained in
a stabilized condition by the implanted basket. The surgical procedure is
completed by closing the wound. The basket remains permanently within
the fused joint and no secondary surgical procedure is required to later
remove it.
The rigid basket implant provides immediate and prolonged stability in
2 5 the joint and serves as a matrix for bony fusion across the joint area.
The controllable size, shape and strength of the rigid basket makes
surgical implantation more efficient and the results more predictable. The
implant, which is slightly larger than the implant hole, provides
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e~pansion-compressior~ of the joint, in contrast to direct compression for
implants used for arthrodesis and fracture treatment.
Expansion-compression is limited to special anatomical regions where
separation of the bones ;s restricted by soft tissue structures. The
vertebrae are good examples of such joint structure, since the annulus
fibrosus of the disk functions to limit the amount of bony distraction.
By implanting a cylindrical Figid basket bet~veen prepared contiguous
bony surfaces across a joint, immediate stability of the joint can be
achieved. The underlying principle is one of expansion-compression (or
distraction-compression). The expansion occurs due to the slightly
greater diameter of the cylindrical basket in relation to the diameter of the
hole within which it is implanted. The compression occurs due to the
tensioning of the surrounding ligaments attached to the bones forming the
joint. The basket is held in place between the bones by the compressive
forces exerted on the bones (and basket) by the ligaments which resist
expansion of the joint. The basket takes up all slack in the surrounding
ligaments created by the decreased thickness of the intervening cartilage
(disk) which creates the problem being corrected.
The basket 10 includes a rigid perforated cylindrical wall 11. The
2 0 basket might be made of stainless steel or other material suitable for
implantation purposes. Its cylindrical wall 11 must have greater
compressive strength than the bone structure into which it is implanted.
A first end 12 of the cylindrical wall 11 includes a beveled outer
surface 13 to facilitate its insertion between the contiguous bony surfaces
2 5 of the joint . A threaded circular end cap at the end 12 has an open
central aperture 17 formed through it, providing limited access to the
interior of the basket 10. The opposite end 14 of the basket 10 is
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substantic~ly closed, and has three apertures 15 formed through it for
cooperation with an installingr tool discussed below.
The cylindrical wall 11 is provided with a continuous array of
perforations formed through it. These perforations are indicated generally
by the reference numeral 23. They can be of varying sizes~ It has heen
found particularly useful to include a pair of diametrically opposed
enlarged openings through the wall 11 which can be aligned across the
joint to permit an enlarged bone ingrowth structure in alignment with the
joint (see Fig. 9).
The installing tool 16 shown in Figs. 6 and 7 includes an outer end
18 and a connecting shaft 19 leading to a basket support 28 having
inwardly movable prongs 21 adapted to releasably fit within the apertures
15 formed through end 14 of the basket. Shaft 19 is surrounded by a
slidable cylinder 20.
Fig. 7 generally illustrates implantation of the basket 10 between
adjacent vertebrae. After first anesthetizing the patient, an incision is
m~de to surgically access the location of the joint, As shown, the incision
is made through the skin surfaces 24 as indicated by numeral 25. The
surrounding tissues are held apart from the operational area by
conventional clamps 22.
The first step in preparing the joint for implantation is the boring of
a cylindrical opening centered across the contiguous bony surfaces of the
joint. The hole 29 is bored between two adjacent vertebrae 26. Before
boring the hole, it is necessary to remove any intervening cartilage located
between the contiguous bony surfaces. The hole 29 is positioned across the
transverse center of the joint. The cylindrical opening is defined by
opposing semi-cylindrical inner surfaces produced across the opposed
bones at the joint. The hole can be bored by conventional surgical tools.
.
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As indicated at 30 ~Fig. 8), bony extensions in the intended path of the
hole must be removed duFing the boring step.
The dialr eter of the hole 29 is selected to be slightly smaller than the
diameter of the basket 10. As an example, the cylindrical inside diameter
of hole 29 might be approximately two millimeters less than the cylindrical
outside diameter of basket 10. The diameter difference should be chosen
to match the physical dimensions of the specific joint being fused. More
particularly, this difference shoukl be chosen so as to assure that the
joint expansion achieved by implantation of the basket will fully take up all
slack in the surrounding ligaments that resist joint expansion.
The bone chips that are produced during the boring of the hole 29
are retained for later filling of the basket 10. E~asket 10 can be filled
with bone chips prior to its insertion. By providing basket 10 with a
threadably removable end cover at 14, one can alternately fill the basket
after its implantation between the bones of the joint.
After preparation of hol~ 29, basket 10 is attached to the installing
tool 16 by attaching the prongs 21 within the complementary apertures 15.
The basket 10 is driven between the bones in the prepared joint. Its
tapered end surfaces 13 assist in centering the basket coaxially within hole
29 and wedge the two bones slightly apart as the basket is driven between
them .
As is evident in Fig. 8, the axial length of the basket 10 is selected
so as to be substantially equal to the transverse width of the joint across
which the opening 29 is bored. The outer ends of the basket 10 should
not protrude beyond the surrounding bone.
After initially positioning the basket in hole 29, it is implanted by
impacting the outer end 18 of the installing tool 16. Impact forces can be
provided by engagement with a hammer, mallet or any equivalent device.
, .
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After instc~ tiorl of the basket 10, the installing tool 16 is detached.
In the specific e~.lbodiment shown, the prongs 21 are compressed and
released from the recei~ing apertures 15 by sliding cylinder 20 toward the
joint. The surgical process is then completed by removing clamps 22 and
closing the incision 25.
One significant advantage of this procedure, when compared to other
fusion techniques, is that the a~jacent bones ~re immediately stabilized and
the joint is maintained in an immobile condition. Stabili~ation occurs due
to the joint expansion that results from implanting within the hole 29 a
cylinder having a slightly larger diameter. The resilience of the bone
structure permits the interior surfaces of the cylindrical opening to spread
slightly to accommodate the difference in diameter of the basket.
However, the diameter difference occurring longitudinally through the
joint, which tends to spread the two bones apart, is resisted by the
strong, tough and basically inextensile nature of the surrounding ligaments
attached to the bone, schematically illustrated by the attached annulas
fibrosis 33. Since these ligaments do not readily yield, they oppose the
physical expansion of the joint. The resulting expansion/contraction
~orces are concentrated through the axial center of the basket. The
2 0 reaction forces exerted on the vertebrae 26 due to the strength and
rigidity of the cylindrical wall 11 about basket 10 are balanced by tensile
forces in the surrounding ligaments.
Permanent fusion of the bones at the joint occurs due to the
promotion of osteogenesis by ingrowth of bone tissue through and about
the basket 10. The expansive/compressive forces exerted on the bones by
implanting of basket 10 encourages bone healing~ and growth by applying
physical load to the live bone cells. The provision of bone fragments or
chips within basket 10 further encourages bone ingrowth and eventual
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fusion. The basket serves as a matrix for fusion across the joint, ancl is
permanently embedded within the resulting bone structure as a physical
reinforcement. The permanent interlocking of the bone and basket, which
results due to its perforated structure, provides a permanently fused joint
in areas such as the spine, where immobilization of the joint for fusion is
otherwise very difficult to achieve.
This procedure can be applied to any anatomical joint region where
separation of the contiguous bone surfaces is restricted by surrounding
soft tissue structures, such as ligaments. The vertebrae are good
examples, since the annulus fibrosus of the disk functions to limit the
amount of bony distraction. Another example of a suitable joint is the
ankle .
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