The anterior and posterior cruciate ligaments crossover within the stifle to provide the major stabilization against forward and backward stressors. Unfortunately, many dogs and some cats seem prone to injuring the anterior ligament portion. Increasingly, newer studies suggest that underlying conformational stressors predispose to ACL injuries, rather than them being strictly a result of an injury. Partial tears may mimic a "sprain" which resolves with time, but the majority will eventually become totally ruptured. When this occurs, it results in significant pain, often causing a non-weight bearing lameness.

When we examine these patients, sedation may be required to examine the knee due to its tenderness. The ACL rupture is diagnosed when a characteristic "forward drawer" motion is palpable due to the stifle's instability. X-rays are taken to check for concurrent injuries or other radiographic findings which may influence our treatment options.

Once diagnosed, treatment options need to be individualized depending upon the age and size of our patient. Left untreated, the ligament will not heal. Over several weeks, the surrounding tissues will tighten and some (but not all) of the instability will resolve. With time, varying degrees of weight bearing will return; however, arthritis will develop due to the instability. In some small-breed dogs and many cats, this may be so slow in developing that in older animals non-surgical conservative treatment may be a viable option.

For the majority of pets, surgery needs to be performed. Traditional surgical repair reduces the instability within the joint, and thereby less arthritis develops. By speeding up the time to which pets are weight bearing under controlled conditions, less muscle wasting occurs, thus aiding the healing process. Surgery should be seen as an important "start" to the healing process, since exercise restrictions and controlled weight bearing on the leg for the first 8 to 12 weeks post-operatively are also critical for longterm successful outcomes. For most pets, surgery first involves exploration of the joint to ensure no damage to the menisci, or "shock absorbers" within the knee, which may require removal of the loose or damaged portions. Following this, the joint is usually stabilized with special long-lasting sutures tightened just enough to remove the instablity. More recently, a radically different surgical approach can be considered, through referral to a surgical specialist. In this approach, rather than knee-stabilizers being used, very precise cuts are made in the surrounding bone and re-alignments are performed to change how forces are transmitted through the knee when weight bearing. This surgery appears to be especially beneficial to very large and/or obese animals. Regardless of repair, owners need to be aware that a significant percentage of these dogs may suffer a similar injury to the ACL in the other leg within a few years. Thank goodness they don't have ACL's in the front legs too!


As with most injuries, prevention is best! Although these problems may not be completely avoided, keeping our pets at their ideal weight and minimizing excessive jumping can lower the risk.