Anterior Cruciate Ligament (ACL) disease is the single most common orthopedic problem of dogs. Injury to this ligament necessitates orthopedic surgery for more patients than all other bone and joint problems combined. That’s really quite impressive. The Cruciatus Curse beats Everything Else by a factor of two to one. It’s easy to imagine JK Rowling’s inspiration for the famous curse: The Knee-Who-Must-Not-Be-Named is cursed with cruciate ligament disease.
The cruciate ligaments (anterior and posterior) are two important (dare I say, crucial?) ligaments that cross deep inside the knee joint. The ACL attaches in a more forward (hence ‘anterior’) location than its partner, and prevents both forward motion and inward rotation of the lower leg. This doesn’t sound like a big job, but a knee with a non-functional ACL is unstable and can’t bear weight reliably. The knee becomes inflamed, painful and swollen, and then quickly degenerates. Inflammation damages the articular cartilages and the body creates spurs of arthritic bone in an attempt to widen and stabilize the joint. The fibrous tissue of the knee thickens so the normal range of motion is progressively lost. Deep inside the knee, the medial meniscus - a cartilaginous pillow that cushions the femur (thigh bone) from contact with the tibia (ankle bone) – degenerates and often tears, leading to still more pain, more inflammation, and more degradation of the sensitive cartilages of the joint. Before long, an ACL-deficient knee degenerates into a scared wreck that can never be restored to normal.
It gets worse: Dogs who suffer from predisposing factors for cruciate disease have a very high risk of breaking both ACLs, particularly after the first ACL breaks. The previously unaffected leg degenerates rapidly when it must support the animal’s weight alone. After the second ACL ruptures, the patient is left with two minimally functional knees and a lifetime of pain. ACL disease is, in a word, “crippling.”
Who develops cruciate disease? Large breed dogs, typically those who are thinness-challenged and live less-than-athletic lifestyles. Small dogs and cats also suffer from cruciate ligament disease, but tolerate it much better and require surgery less frequently. The disease has a genetic basis. Some knees are conformed in a geometry that results in constant micro-strain of the ACL. Because ligaments contain no internal blood vessels, they have extremely limited ability to heal after an injury. Poor knee joint conformation coupled with excessive ligament strain due to obesity can sometimes bring about ACL rupture in dogs aged two years and younger, but most patients suffer ACL problems in their middle years.
What must be done? Once broken, a cruciate ligament cannot be regrown. Even relatively mild injuries to this ligament often begin a cascade of degenerative changes that lead to its ultimate rupture. Prevention, in the form of careful breeding, weight control and regular exercise is the best preventive treatment, but once the ligament is ruptured, early surgery (before degeneration creates permanent damage to the knee) is the most effective treatment option, particularly in larger dogs.
There are three common surgical procedures for correcting ACL disease. All of these share certain characteristics. Typically, the affected knee joint is opened and explored. The shredded ends of the broken ACL are removed and the medial meniscus is inspected. Damage to the meniscus is the most common problem requiring a second knee surgery, and a damaged meniscus may need to be trimmed or completely removed, after which the joint is thoroughly flushed. Some surgeons fill the joint with local anesthetic or narcotic pain relievers or both to control post-surgical pain, after which the joint cavity is sutured closed. The degree to which a particular joint needs to be opened and internally repaired varies considerably from patient to patient (and from surgeon to surgeon).
Correction of the functional deficiency in the knee can be accomplished in several ways. The Tibial Tuberosity Advancement (TTA) and Tibial Plateau Leveling Osteotomy (TPLO) surgeries are more recently developed methods for restoring stability of the knee that was lost when its ACL ruptured. Lateral Stabilization is a much older method of replacing the function of the ACL and can be accomplished using any of several different procedures. We’ll talk about the differences between the various ACL repair techniques in next month’s column.