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. Many 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. We believe 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 slopes caudally. When the dog bears weight the femur hits the top of the tibia and slips backward down the tibial plateau. When this occurs chronically, the immobile medial meniscus can be crushed and torn.
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 no studies supporting one method over another with respect to the progression of arthritis.
Many believe there are reasons to choose the tibial plateau leveling osteotomy over the traditional extra-capsular repair utilizing nylon. This procedure is primarily chosen for large breed dogs weighing 70 pounds or more. It is increasingly becoming the procedure of choice for animals of any size for many surgeons. I believe that extra-capsular repair is very effective in dogs weighing less than 70 pounds and cats. There may be a gray area in dogs with very steep tibial plateau and dogs with bilateral disease than cannot walk. Unfortunately many cannot choose the TPLO or TTA for reasons of expense. A lateral suture or extra-capsular repair can be effective in dogs up to 100 pounds. The chances of instability do increase with the weight of the dog.
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