Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2001-01-30
2002-03-12
Smith, Jeffrey A. (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
C606S060000, C606S064000
Reexamination Certificate
active
06355041
ABSTRACT:
This invention pertains to a surgical implant and method to stabilize equine fetlock joints with a bone pin-plate that inserts into the third metacarpal bone and attaches to the tension surface of the first phalanx.
Horses, like humans, are susceptible to injuries sustained through physical exercise. The most common injuries sustained by horses are bone and joint fractures. While horses are usually capable of a complete recovery from minor bone fractures, a breakdown fracture in the ankle area, referred to as the fetlock joint or metacarpophalangeal joint, is usually catastrophic. Breakdown fractures can occur when the supporting structures of the fetlock joint give way under stress. Without the use of this supporting structure, a horse cannot satisfactorily support its own body weight.
Horses with catastrophic injuries to the fetlock supporting structure usually do not have an athletic future. Therefore, the goal of treatment is usually to salvage a horse for breeding by stabilizing the fetlock joint through arthrodesis. “Arthrodesis” is the surgically-induced fusion of the bones of a joint. Complications often follow arthrodesis, including support limb laminitis, infection, implant failure, and cast sores. Such complications often mean that the treatment is ultimately unsuccessful.
The angles of the fetlock joint and the position of surrounding soft tissue make surgical stabilization of the fetlock supporting structure difficult. Surgical fixation with a bone plate is a method used for stabilization. However, the bone plate usually experiences fatigue failure due to cycling when placed on the compression side (dorsal side) of the third metacarpal bone, because the plate acts as the load carrying member. See M. Muller et al.,
Manual of Internal Fixation: Techniques Recommended by the AO Group,
(2
nd
ed., Springer-Verlag, 1979) pp. 42, 58. As illustrated in
FIG. 2
, the compression side
28
of the third metacarpal bone is the side that experiences compression when weight is applied to the fetlock joint.
Unfortunately, the tension band side (palmar surface) of the horse's fetlock joint lies beneath important supporting soft tissues. As illustrated in
FIG. 2
, the tension band side
26
of the fetlock joint
10
is the side that experiences expansion as weight is applied to the fetlock joint
10
. See R. Kainer, “Functional Anatomy of Equine Locomotor Organs.” in: Stashak, T.S.,
Adams' Lameness in Horses
(Philadelphia, Lea & Febiger, 1987), pp. 10-18. Equine surgeons have generally considered surgical approaches through these soft tissue structures too risky. Rather than risk damage to the soft tissues, surgeons have avoided the tension band side by placing the bone plate on the compression surface because the dorsal side is easier to access.
To minimize cyclic fatigue of the bone plate, most surgeons arthrodese (fuse) the fetlock joint into an unnatural straight line, resulting in an extended limb length. Horses usually adapt to the fusing of their fetlock joints in this unnatural position. However, unnatural fusion of the joints often causes a horse to overload its pastern and coffin joints because of uneven leg lengths, eventually causing secondary degenerative joint disease and pastern joint subluxation. See L. Bramlage, “An Initial Report on a Surgical Technique for Arthrodesis of the Metacarpophalangeal Joint in the Horse,”
Proceedings of the American Association of Equine Practitioners,
vol. 27, pp. 257-261 (1982); and G. Crawley et al., “A Modified Cloward's Technique For Arthrodesis of the Normal Metacarpophalangeal Joint in the Horse,”
Veterinary Surgery,
vol. 17, pp. 117-127 (1988).
Currently, there are four fundamentally different surgical devices to arthrodese horses' fetlock joints.
FIG. 1
illustrates a front plan view of one embodiment of an external skeletal fixation device. The device comprises transfixation pins
2
, an external frame having a foot plate
4
, and ascending vertical bars
6
placed on both sides of the third metacarpal bone
14
. The transfixation pins
2
are inserted through the third metacarpal bone
14
and attached to the vertical bars
6
. The foot plate
4
is attached to the hoof
8
. However, this external fixation device is prone to infections and stress concentration around the pin-bone interfaces. See D. Richardson et al., “Use of an External Skeletal Fixation Device and Bone Graft For Arthrodesis of the Metacarpophalangeal Joint in Horses,”
Journal of the American Veterinary Medical Association,
vol. 191, pp. 316-321 (1987).
FIG. 2
illustrates a perspective view of one embodiment of a modified Cloward device. Two holes are drilled through the fetlock joint
10
and a steel basket
12
, packed with autogenous porous bone, is driven into each hole. However, the stainless steel baskets
12
can induce stresses and have caused fractures emanating from the baskets into the proximal phalanx and the third metacarpal bone. See Crawley et al., 1988.
FIG. 3
illustrates a perspective view of one embodiment of an interlocking intramedullary nail device. A hole is drilled through the third carpal bone (not shown) into the medullary canal of the third metacarpal bone
14
and the first phalanx
16
. An interlocking nail
18
is inserted through the third carpal bone, the metacarpal bone
14
, and the first phalanx
16
. Screws
20
are inserted through the interlocking nail
18
, along the longitudinal axis of the first phalanx
16
and the metacarpal bone
14
. See D. Herthel, “Application of the Interlocking Intramedullary Nail.” in: Nixon, A. J.,
Equine Fracture Repair,
(Pennsylvania, W. B. Saunders Company, 1996), pp. 371-376. However, clinical experience has shown that the interlocking nail method requires the fetlock joint be placed in an unnatural, completely straight position.
The most commonly used device today is the plate and tension-band wire device.
FIG. 4
illustrates a side plan view of one embodiment of a plate and tension-band wire device. A plate
22
having one end contoured to fit the top surface of the first phalanx
16
is attached to the first phalanx
16
using screws
20
, while the second end extends along the longitudinal axis of the third metacarpal bone
14
. A figure eight tension-band wire
24
is placed on the tension surface through holes drilled transversely through the first phalanx
16
and third metacarpus
14
to absorb some of the cyclic load. After tightening the tension-band wire
24
, screws
20
are inserted through the plate
22
and into the third metacarpal bone
14
to secure the fetlock joint
10
. See H. Valdez et al., “Arthrodesis of the Fetlock Joint With Dynamic Compression Plates,”
Journal of Equine Medicine and Surgery,
vol.3, pp. 421-427 (1979); and L. Bramlage, “Fetlock Arthrodesis.” in: Nixon, A. J.,
Equine Fracture Repair,
(Pennsylvania, W.B. Saunders Company, 1996), pp. 172-178. Nevertheless, a significant number of patients must be euthanatized (19 out of 43 cases in one study), usually because of support limb laminitis. See L. Bramlage, “Arthrodesis of the Metacarpophalangeal Joint—Results in
43
Horses,(Abstract)”
Veterinary Surgery,
vol. 14, p. 49 (1985).
Support limb laminitis results from persistent, severe lameness arising from the inability of a horse to support all of its body weight on one leg. Asymmetric limb loading causes mechanical failure of the attachments between the hoof and the bone in the hoof. Horses treated with the tension-band wire technique will likely remain lame because the fixation is not optimally stable. Unstable fixations result in movement between the bone ends, causing pain, slower healing, and prolonged unilateral weight bearing. See Muller et al., 1979. All of these factors increase the probability of support limb laminitis.
I have discovered a bone pin-plate and a surgical method that promote bone fusion of a fetlock joint breakdown by supporting and stabilizing the limb. The device is a bone pin-plate combination capable of being implanted and attached to the tension band surface (rear surface) of the fi
Board of Supervisors of Louisiana State University and Agricultu
Porter André J.
Runnels John H.
Smith Jeffrey A.
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