Cruciate ligament tears are painful soft tissue injuries that happen commonly in the knee joint of dogs. The cranial cruciate ligament is more commonly affected than the caudal cruciate ligament in dogs; it is analogous to the human anterior cruciate ligament, or ACL. These injuries are common in both active, athletic dogs as well as older more sedentary dogs and may require surgery in order to prevent the development of long term side effects like osteoarthritis.
The cruciate ligaments are stabilizers of the knee joint in the dog. Together the cranial cruciate ligament and the caudal cruciate ligament form an X-shape as they cross each other inside the joint. The X formed by the cruciate ligaments connects the thigh bone to the shin bone from inside the knee and reduces the amount of front to back movement of the knee while a dog is running and making tight turns. While humans are most likely to severely injure their cruciate ligament suddenly during exercise, dogs tend to have a slower degeneration of the cruciate ligament resulting in partial damage at first. Dogs may still completely rupture their cruciate ligaments as time goes on, because the chronic degeneration and irritation they experience will weaken it and make it prone to rupture. The most commonly injured cruciate ligament in the dog is the cranial cruciate ligament. Approximately half of the dogs that damage the cruciate ligament in one knee will experience a problem with the ligament in the other knee at a future time.
Since the cranial cruciate ligament is an important stabilizer of the knee joint, damage to its fibers results in instability of the knee. This is painful because it causes other soft tissue structures to be stressed when the dog tries to use the joint. The cranial cruciate ligament is also attached to the medial meniscus in the dog -- the medial and lateral menisci sit between the bottom of the thigh bone and the top of the shin bone inside the knee and act as cushions to absorb the the weight of the dog as he loads his joint. Frequently when the cruciate ligament is torn, there is also damage to the medial meniscus. Both instability from the damaged cranial cruciate ligament as well as decreased cushioning from the medial meniscus can lead the bones of the knee joint to rub against each other. The end result of the inflammation of the ligament and meniscus, along with bone-on-bone contact, is the degeneration of the cartilage inside the joint and development of osteoarthritis. Osteoarthritis is a permanent condition that will cause pain and discomfort for your dog and limit her ability to run and play freely.
There are many treatment options available for cruciate ligament injuries in dogs, and factors such as breed, temperament, activity level, age, and severity of the injury will play a role in deciding which treatment to choose. The first choice to make is between medical treatment or surgical treatment. Medical treatment involves resting your dog by confining her to a crate for at least 30 days and only allowing her to go on short leash walks to go to the bathroom. She can also be treated with anti-inflammatory medications to control the pain and discomfort. This rest period gives a partially injured ligament a chance to heal without being re-inflamed, while anti-inflammatory medications make her feel better during the process. This method can be successful in small dogs without a lot of instability in the knee, but is less successful for larger dogs, or dogs with significant joint instability. In dogs with more serious ligament damage, the anti-inflammatory medications only mask the pain, and symptoms return when the medication is stopped.
Surgical treatment is a more definitive treatment for cruciate ligament injury in dogs and there are multiple surgical options available. The choice of surgery will depend on the degree of instability of the joint as well as the size of the patient. For small dogs, or dogs with partial tears, a procedure known as a "lateral suture" is available. This is the simplest surgery available and it involves using a piece of heavy gauge suture to secure the knee joint from the outside by anchoring the shin bone to the femur bone. In large or very active dogs this technique may fail, however, resulting in the same consequences as not doing surgery at all, namely joint instability and arthritis.
For dogs that are poor candidates for a lateral suture, one of two other surgical techniques are available -- the tibial plateau leveling osteotomy (TPLO) or the tibial tuberosity advancement (TTA) surgery. Both of these surgical techniques involve making a cut into the shin bone (the tibia) and using a metal plate or pin to change the angle of the knee so that it is stable even without a cranial cruciate ligament to hold it in place. Both of these surgical techniques are technically more demanding than the lateral suture and require specialized equipment and training by the surgeon performing the procedure. They offer superior results for large, active dogs however.
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