The most common cause of rear limb lameness in the dog is the Rupture of the Cranial Cruciate Ligament (RCCL) in the stifle (knee). This injury accounts for greater than 90% of knee problems in dogs over the age of 2 years. The CCL in is analogous to the Anterior Cruciate Ligament (the ACL ligament) of people. The anatomy of the ligament is the same in humans and animals and performs the same function — prevents forward and backward motion of the tibia (lower leg) relative the femur (upper leg). If the ligament is ruptured, painful inflammation and instability occur in the knee.
There are many contributing factors to CCL injury but the absolute underlying cause of the injury is not known. Traumatic injuries can damage the ligament but we also see injuries occur when dogs are doing normal movements. The injuries that occur under normal circumstances cannot be clearly explained. It is known that there are many underlying factors such as obesity, ongoing degenerative disease in the joint, mechanical/angular abnormalities, genetics, and the influence of sex hormones. There does appear to be a strong breed disposition to this injury as Labrador Retrievers, Newfoundlands, Rottweilers, and West Highland White Terriers are over-represented.
Dogs with RCCL usually present with either an acute or chronic historical complaint. The acute injury is usually a dog that was playing/running/jumping/walking, then vocalized and now will not bear any weight on the affected leg. The chronic injury is usually a dog that has a history of weeks to months of intermittent lameness. The acute injury usually is characterized by a non-weight bearing or “toe touching” lameness that shows no improvement in 7-10 days and may be a complete tear of the CCL. The chronic presentation is usually a partial tear of the ligament that gradually progresses to a complete tear.
Your veterinarian can make a tentative diagnosis by reviewing the history, observing your dog’s ambulation (movements), and by completing a thorough exam. In most instances, the gold standard to definitively diagnose a RCCL is sedation, manipulation of the joint and radiographs. When under sedation your pet will not consciously hold the joint tight, allowing an evaluation of the joint in a relaxed state. The two most common tests of instability in the knee are the “Cranial Drawer” test and the “Tibial Thrust”. Both tests are an evaluation of the forward and backward movement of the lower leg (tibia) relative to the upper leg (femur). Some movement of the tibia relative to the femur is normal but anything greater than 2mm is considered instability and confirms at least a partial tear of the ligament.
Once a diagnosis of a Ruptured Cranial Cruciate Ligament is confirmed, a discussion of treatment options follows. The immediate plan is pain management (Tramadol, Buprenorphine, or other opiods), anti-inflammatories (Rimadyl, Previcoxx, etc), and rest. These approaches help with immediate comfort and pain but do not address long term stability of the joint.
Surgical correction is the best option to return normal range of motion and normal activity. There are 3 primary surgical corrections that are common today: Tibial Plateau Leveling Osteotomy (TPLO), Tibial Tuberosity Advancement(TTA), and Extracapsular Stifle Stabilization (Lateral Suture). All three techniques have their merits and drawbacks and your veterinarian can discuss these options with you. If surgical correction is not pursued, substantial degenerative changes will occur in the joint and your dog will never regain full use of the limb. Over time, scar tissue will provide some stability and some usage of the limb is usually achieved but there is usually a chronic persistent lameness, especially after exercise. Dogs that have a surgical correction usually will regain full normal use of the limb without persistent lameness.
If you believe your dog has a Ruptured Cranial Cruciate Ligament, please contact your veterinarian for an evaluation and to discuss a diagnostic and treatment plan.