Anterior Cruciate Ligament – the ACL

Anterior Cruciate Ligament – the ACL

By Dr. Ed Mapes
Stonebridge Animal Hospital
McKinney, Tx

Injury to the Anterior Cruciate Ligament (ACL) is the most common cause of lameness in companion animals, and comprises the bulk of orthopedic surgeries done at our hospital. We’ve made this diagnosis in dogs ranging from toys to working breeds, and even in the rare feline case; but young, active, large breed dogs are the most commonly affected.
As seen in Figure 1, the anterior cruciate pairs with the posterior cruciate ligament inside the knee joint. Together, they assist other structures to hold the tibia in proper alignment with the femur bone. Though both ligaments are prone to injury, damage to the ACL is far more common.

Figure 1:  normal anterior cruciate ligament

Figure 1: normal anterior cruciate ligament

Figure 1 a normal anterior cruciate ligament (also referred to as the cranial cruciate ligament) is seen, along with other important structures of the knee joint. Notice the meniscus, a pad that separates femur from tibia, which is often torn along with the ACL.

Any damage to components of this vital joint results in pain, restricted motion, and lameness. A torn ACL allows for abnormal motion within the joint, causing bone surfaces to degenerate, erode, and develop arthritic changes. This process continues until the joint becomes chronically painful and the animal resorts to using only three legs to walk (Figure 2).

Traumatic injury is usually thought to be responsible for acute clinical signs, but in fact natural deterioration of the ligaments often contributes to ruptures in adult or senior patients. This accounts for the presence of arthritic changes in the knee during surgery on acutely lame animals, and explains the fact that patients sometimes rupture the ACL in their other leg at some point after we repair the original knee.

Figure 2:  Arthritis evident in this 6-year old patient

Figure 2: Arthritis evident in this 6-year old patient

Figure 2 arthritis is already evident in this 6-year old patient that had limped on his left rear leg for two years. The damaged ligament allowed abnormal joint motion that led to the arthritis; the ligament finally ruptured totally after slow deterioration. We resect damaged material from the joint, remove arthritic bone spurs, and stabilize these knees at surgery.

Patients brought to the hospital are commonly non weight-bearing on the affected leg. These usually represent cases of acute ACL tears, and we can also find joint swelling, varying degrees of pain on manipulation, and excessive motion between the major bones.
Some cases though are partially weight-bearing – placing reduced weight on the leg – with altered gait and pain. They have often suffered incomplete ligament tears or had previous total ruptures and have learned to adapt to the abnormality. The lameness in these dogs can improve over several months, but the animal never returns to full function without recurring lameness. Over time, even a partially ruptured ACL degenerates and eventually tears completely, leading to even more pain and abnormal joint motion.
In the majority of cases, surgery is the only measure that can return the patient to acceptable levels of function.

Figure 3

Figure 3

Figure 3 Jasmine is seen on her four day post-op examination. The protective bandage will be removed today, and she’ll begin a course of range of motion exercises and controlled leash walking as the leg heals.

Surgery to stabilize the bony structures, remove torn sections of meniscus, and debride arthritic growths are the best chance in most patients to regain acceptable levels of limb use and patient comfort. The pain resulting from ligament rupture is alleviated right away, and improved stability greatly reduces future arthritis. A range of surgical techniques are available; surgeons consider the circumstances of each case to select the most viable surgical options.
We incorporate four treatments with the laser therapy unit after surgery as an important aid in healing. The laser decreases swelling, pain, and inflammation and has proven to help our patients heal faster. The first treatment is done immediately after surgery; followed by another on the next morning. Two more sessions are scheduled within the next week.
I make it a point to advise clients, however, that whenever a joint structure has been damaged and we enter the capsule to make repairs, the joint will never be perfect again. It is inevitable that, just as in human knee surgeries, the pet may experience some discomfort after vigorous activity, and some degree of arthritic changes will occur over time. It is unrealistic to expect complete restoration to the pre-injury joint.
We recommend joint supportive medications after surgery – canine preparations of glucosamine, chondroitin, and methylsulfonylmethane – and weight restriction in overweight patients as additional measures to assure success after surgery.

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