Pet Talk: ACL injuries in dogs
The anterior cruciate ligament, or ACL, otherwise known as the cranial cruciate ligament, or CCL, when referring to pets, is a vital support structure of the knee, and its function and anatomy is very similar to the human ACL. Since most of us in the High Country are very familiar with the term ACL, it will be used in this article in place of the specific CCL term used in veterinary medicine. This ligament’s primary role is to provide and maintain stability to the knee.
The knee’s anatomy contains two cruciate ligaments that cross inside the knee joint and provide stability of the upper femur and lower tibia while cartilage cushions called medial and lateral menisci rest between the tibia and femur to create a soft barrier between the two bones.
A support bone called the fabellae flanks the tibia on the side while the knee cap or patella slides up and down the front of the knee during flexion and extension. The anterior cruciate ligament prevents the tibia from sliding forward out from under the femur.
How does a dog injure ITS ACL?
The most common cause of cruciate ligament rupture is excessive internal rotation of the tibia when the joint is partially flexed. This can be the result of trauma or running and planting the hind limbs while the momentum of the body continues to move forward.
What factors increase the chance of an ACL injury?
Conformational deformities of the knee such as patella laxation contribute to repeated stress on the ACL. Obesity increases the stress on support structures, and animals over 5 years of age demonstrate a decrease in strength and stiffness of these structures.
Animals that have ruptured one ACL are more inclined to rupture the opposite side in one to three years. Finally, immune mediated diseases may weaken and eventually lead to complete failure of one or both ACLs.
Recent studies have also identified specific breeds that appear to be more predisposed than other breeds to ACL injuries, such as mastiffs, Newfoundlands, Akitas, St. Bernards, Rottweilers, Chesapeake Bay retrievers, American Staffordshire terriers and Labrador retrievers.
signs of an ACL tear
A ruptured ACL has quickly become the most common orthopedic injury seen in dogs today; in fact, in most cases a sudden lameness of the hind limb tends to be a ruptured cruciate until proven otherwise.
The most common signs include sudden pain of the hind limb, swelling of the knee, instability of the knee or hind-limb weakness.
The key to diagnosis of a ruptured cruciate ligament is the presence of a type of knee instability called a cranial drawer sign. This is where the tibia moves forward on palpation from the femur like the motion of a drawer being opened.
Often in large dogs that are experiencing pain, this test is best performed when the dog is sedated to allow for the knee to completely relax. Other important supportive diagnostics used may include radiographs, MRI and arthroscopic surgery.
How to treat a ruptured ACL and when to act?
Rupture of the cruciate ligament results in progressive and degenerative changes within and around the joint, therefore surgery is the most proven and consistent way to treat a ruptured ACL. Historical data also demonstrate that dogs that start with a partial ACL tear almost always result in a full ACL tear in a matter of weeks or a few months. Early surgical repair has demonstrated a more complete and quicker recovery with less chances of progressive cartilage damage or weakening of the opposite leg’s cruciate ligament.
Surgeries that are commonly performed can be divided into intra-articular versus extra-articular and arthroscopy versus arthrotomy.
Most common surgical techniques include extracapsular repair (used almost exclusively in small dogs), tibial plateau leveling osteotomy and tibial tuberosity advancement (most commonly used in medium- to large-breed dogs). Typically dogs that have undergone surgery are supporting weight within 10 days and full function is achieved in three to four months.
Early detection and treatment of a ruptured ACL will heal better and more quickly, with less chance of debilitating arthritis in the future or tearing of the adjacent ACL.
Factors to identify early that may predispose your pet to an ACL injury are conformational deformities, obesity, animals older 5 years of age, immune mediated diseases, specific breeds and a history of a previous ACL tear. Remember, however, that an ACL tear can occur in any dog.
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