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Total Knee Replacement – Dogs
A prosthesis and instrumentation for canine total knee
replacement (TKR) is now available for clinical trials. Treatment options
for advanced knee osteoarthritis (OA) and irreparable traumatic injuries
have historically been limited to conservative medical management,
arthrodesis, or amputation. TKR is a common procedure in humans with over
400,000 performed annually in the United States1,2.
Osteoarthritis of the canine knee is a common problem and frequently is a
consequence of cranial cruciate ligament (CCL) injury. Some dogs with a CCL
injury have OA that is too advanced as seen on radiographs (Figure 1) or
arthroscopically to anticipate acceptable results following
reconstructive knee surgery and some dogs with CCL surgery have progression
of OA in spite of the highest standard of surgical treatment. Dogs can
benefit from knee replacement surgery when the
indications for surgery are present.
Development of the TKR System is a comprehensive multifaceted project
including the prosthesis design, instrumentation design, surgical technique
evolution, rehabilitation effort, objective follow-up data collection, and
education to train surgeons.
The profile of the femoral and tibial prosthesis is based on anthropomorphic
study. The geometry is based on functional analysis of the canine knee. A
femoral condyle (femoral component) (Figure 2) articulates with a tibial
bearing surface (tibial component) (Figure 3). Currently, the patella is not
resurfaced. Materials used to manufacture the prototype components are
cobalt chrome stainless steel and ultra high molecular weight polyethylene.
Other material may be used in future generations. Multiple sizes are
available for dogs ranging from about 12 kg and more.
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Figure 2 and 3: The femoral
condyle (left) and the tibial component (right) implants
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Total knee replacement results in a joint that is
replaced with the femoral condyle prosthesis on the end of the femur and the
tibial component on the top of the tibia. This mimics joint function and
joint motion as close as possible to normal standing, normal standing on
rear legs, and normal sitting. The metal femoral component is visible on the
post-operative radiographs, but the polyethylene tibial component is not
(Figure 4)
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Figure 4:
Post-operative radiographs of a dog that received a TKR |
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Instrumentation for implanting the prosthesis is
designed specifically for the dog and the newly designed prosthesis.
Instrumentation design considerations include ease of understanding and
simplification of the surgical technique. Guide systems reference off of
radiographic and surgical anatomical landmarks to insure proper placement of
the implants.
The surgical technique has improved as upgrades have been made to the system
and with surgeon experience. Everything starts with the preoperative
examination and preoperative care.
Rehabilitation begins immediately after surgery. A systemic and local pain
management protocol is used to allow early return to function. Postoperative
care is important. Dog owners receive instructions at the time of release
from the hospital after surgery. Instructions include the home exercise
program. Passive range of motion exercises help to maintain the minimum of
155 degrees of extension to 40 degrees of flexion. Progressive, more active,
exercise begins at 6 weeks after surgery with introduction to the underwater
treadmill.
Objective data to evaluate patient progress is collected before surgery, at
6 weeks, 3 months, 6 months, and 1 year after surgery. At the minimum,
specific information is collated. Radiographs are in digital format. Video
imaging preserves and facilitates clinical subjective evaluations for
comparison to subjective evaluations.
Computerized gait analysis provides a
graph from limb function objective data. Range of motion, muscle
extensibility, and limb measurements add to, and either support or deny, the
entire objective information data bank.
Preliminary results indicate the implants closely mimic original anatomy to
allow normal range of motion of a normal intact ligament stable knee.
Radiographic evidence suggests that the bone-cement-implant interfaces are
acceptable after 1 year follow-up. A rehabilitation program is recommended
since it appears to accelerate limb usage. Gait analysis documents improved
limb function, and it confirms the clinical impression that the dog is
“better” from the standpoint of pain relief and limb usage.
Preoperatively, dogs typically have disuse atrophy as a result of chronic
end-stage OA, and they are often weight bearing lame over an extended period
prior to their TKR surgery. Most dogs are weight bearing 2 weeks after
surgery.
Based on early experiences, it appears that canine total knee replacement
may become an even more viable treatment option in future for dogs with knee
arthritis. In order to make this surgery available for large numbers of dogs
of various sizes and breeds, implant design and materials will continue to
evolve, instrumentation will continue to be perfected for precision during
surgery, reliable methods to secure (cemented and cementless) implants to
the bone bed will be confirmed, the surgical technique will improve with
experience, objective data will be evaluated, and more surgeons will be
trained. It will take 5-10 years before more details are known about the
long term function of the TKR in dogs. Until then, dog owners should
understand the options and seek advice from surgeons who have experience
with this procedure.
Reference:1. 2003 National Hospital Discharge Survey, Advance Data
No. 359, July 8, 2005, Table 8, Page 14. U.S.
Department of Health and Human Services, Centers for Disease Control and
Prevention, National
Center for Health
Statistics.2. 2003 National Hospital Discharge Survey, Advance Data
No. 359, July 8, 2005, Table 10, Page 16. U.S.
Department of Health and Human Services, Centers for Disease Control and
Prevention, National
Center for Health
Statistics.
The Specialists at Gulf Coast Veterinary Surgery, Orthopedics
& Neurology are available to
consult with your veterinarian.
Please call if you have any questions:
Phone: 713-693-1122
Fax: 713- 693-1110
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