Tibial Plateau Leveling Osteotomy for Cranial Cruciate Tear
Cranial cruciate ligament rupture is one of the most common orthopedic injuries in the dog. The primary cause of rupture is degeneration of the ligament and rarely just trauma. About 40-60% of dogs that tear one cruciate ligament will tear the other within 1 to 2 years of the first injury.
The cranial cruciate ligament is the primary stabilizer of the knee. Once it ruptures the dog will become acutely lame due to severe inflammation that occurs within the joint. This will generally improve within the first few days if the dog is placed on anti-inflammatory medications. The chronic lameness is associated with the instability within the stifle joint. This chronic lameness is caused by the tibial plateau angle.
In the dog, the tibial plateau (the joint surface or top of the tibial is a hill sloping backward) slopes caudally. When the dog bears weight the femur hits the top of the tibia and slips backward down the tibial plateau (this is tibial thrust). When this occurs chronically, the immobile medial meniscus can be crushed and torn. When the meniscus tears this is a very painful event.
Cranial cruciate ligament injury leads to a cascade of events including progressive osteoarthritis and medial meniscal tears. The instability results in synovitis (inflammation of the joint capsule), articular cartilage degeneration, periarticular osteophyte formation and capsular fibrosis (arthritis).
Progressive osteoarthritis continues even after stabilization of the knee regardless of the procedure used for stabilization. There are studies to support early stabilization with a tibial plateau leveling osteotomy slows the progression or severity of osteoarthritis.
Tibial Plateau Leveling Osteotomy (TPLO)
The tibial plateau leveling osteotomy is chosen by most surgeons for both small and large breed active dogs. This choice is made over concerns for larger heavier dogs damaging an extra- capsular repair resulting in chronic lameness. This can also occur in smaller breed dogs that are young and active. Dogs having a TPLO are immediately stable after surgery and return to function earlier than other procedures. Another reason to choose this procedure is for dogs with bilateral disease to get them walking as soon as possible. There is some evidence that choosing a TPLO over another procedure will result in less osteoarthritis over the life of your pet.
The tibial plateau leveling osteotomy changes the biomechanics to the canine stifle (knee). Normally the knee is stabilized both passively (cruciate ligament, menisci, joint capsule) and actively (muscles & tendons). The cranial cruciate is a passive constraint to cranial tibial translation as well as internal rotation. The cranial tibial translation is tested by cranial tibial thrust test. The severity of cranial tibial thrust is related to the slope of the tibia. The premise of the TPLO is that if you reduce cranial tibial thrust to neutral the pain associated with cranial tibial translation will resolve.
The tibial plateau leveling osteotomy requires well positioned radiographs that allow the surgeon to measure the slope of the tibial plateau. The slope angle is then converted to millimeters depending on the size of the osteotomy. The procedure incorporates the release of meniscus and debridement of remaining cruciate ligament. A curved saw blade is utilized to make the osteotomy. The osteotomy is then rotated a specified number of millimeters. The osteotomy is then stabilized by a bone plate. Once this is completed cranial tibial thrust should be eliminated.
The tibial plateau leveling osteotomy takes approximately 8 weeks to heal. The osteotomy must go through the process of bone healing just like a fracture. During the healing period your dog should have only controlled exercise. This procedure requires radiographs at the 8 week after surgery to determine if healing is sufficient to allow release back to normal activity.
With any surgery there is the potential for complications. The TPLO procedure has an 11.4% rate of both major and minor complications. The major complication rate is about 3% and minor is about 8%.
The most common complications are swelling at the incision site, seroma along the incision, premature staple/suture removal by dog. These complications are fairly easily dealt with. If the dog removes his staples or sutures the incision should be flushed and closed and he should be placed on antibiotics. Swelling can be minimized by icing the incision 3 times a day. Seroma is a benign build up of fluid in the space between the skin and the fascia. Seromas tend to be self limiting but if they are very big they should be drained and the dog should be placed in a bandage. The concern with draining them is that you can introduce bacteria into the surgical site. Most of the time hot packing and time resolves the problem.
Infection is a potential problem with any surgery. It can occur for no reason just because of having surgery this happens in less than 1% of the cases. Infection most often occurs secondary to licking or chewing at the incision. This can be minimized by the use of an e-collar. If the infection is severe surgery may be necessary to flush the joint and obtain cultures.
The most concerning problem is implant failure and migration. Reported complications are tibial tuberosity fracture, fibular fracture, screw loosing or screw fracture. The most common reason for these types of complications is an event that traumatizes the surgical repair, overactivity, falling, running, jumping etc. They have however been reported not in association with a traumatic event. These complications require revision surgeries to stabilize and repair damage.
Meniscal tears are fairly frequent in association with cranial cruciate tears. If the meniscus is not torn we release it from its caudal attachment. Subsequent meniscal tears occur in 6.3% of the cases.