Anterior Cruciate Ligament Rupture

The most common cause of rearlimb lameness in the dog is rupture of the anterior cruciate ligament. This injury allows degenerative changes to occur in the stifle (knee) joint, which must be limited before permanent cartilage and bony changes occur and result in irreversible arthritis.

The stifle is a hinge joint which allows a wide range of motion of the tibia on the femur. To maintain stability through this range of motion there are two cruciate ligaments. These ligaments cross each other (hence the name cruciate) to provide a major role in stifle stability. The anterior cruciate ligament also prevents forward displacement of the tibia on the femur (anterior drawer motion). See Fig.1.

The anterior cruciate ligament acts as a constraint against the tibia moving forward on the femur (see Fig. 2). The most common mechanism for anterior cruciate rupture is sudden rotation of the stifle when the joint is in flexion (i.e. a sudden right turn on the weightbearing right rear pivot limb). The ligament also can rupture when a dog jumps, if his or her knee is hit from the front (as when a football player is hit from the front), or if he or she steps in a hole. Degenerative changes in the stifle joint from obesity, conformational deformities, patellar luxations, or from repeated minor stresses can result in progressive deterioration of the cruciate ligament. When the anterior cruciate ligament ruptures, the compensatory stress placed upon the opposite rear limb may predispose it to ligament rupture. Weight reduction and immediate repair of the damaged leg to minimize the risk to the unaffected limb are therefore of critical importance.

Symptoms

The clinical signs of anterior cruciate rupture can vary depending on the extent and chronicity of the injury. Animals with an acute rupture present with a non weightbearing lameness, joint effusion, palpable pain in the stifle, and joint instability. Those with more chronic injuries generally exhibit an intermittent weightbearing lameness, muscle atrophy, thickening of the joint capsule with palpable bone spurs present, and joint instability with a frequent meniscal click associated with a torn medial meniscus.

Menisci have been described as elastic, movable washers which aid in the lubrication of the joint and also act as shock absorbers. The most common meniscal injury occurs in the medial meniscus and is associated with rupture of the anterior cruciate ligament. In some cases, the meniscus is crushed between the femur and the tibia. In others, the meniscus may undergo a longitudinal tear. With this type of lesion, the meniscus may fold itself during the abnormal sliding motion of the unstable joint. This type of lesion frequently exhibits a clicking or snapping sound as the meniscus unfolds (see Fig. 3).

Treatment

Surgical stabilization of the stifle is recommended for all anterior cruciate ruptures. (If your dog is over forty pounds, please refer to the article entitled Tibial Plateau Leveling Osteotomy on this website for information regarding surgical treatment.) Surgical techniques can be divided into extracapsular or intracapsular. The extracapsular techniques alter the tissues outside the joint to tighten and stabilize the knee. They include heavy sutures placed outside of the joint (i.e. modified Flo imbrication technique) and the manipulation of ligaments adjacent to the joint to stabilize the knee (fibular head transposition). Intracapsular techniques generally utilize a graft from an adjacent tissue in the knee to replace the anterior cruciate ligament. In either case, any damaged portion of the meniscus and all remnants of the ruptured cruciate ligament are removed or repaired at the time of corrective surgery (see Fig. 4).

Postoperative Care

Postoperative care is critical to long term success. The most critical element is confinement of the dog to a small area. After surgery, the knee is bandaged in a stable walking configuration for one to two weeks. After that time, the bandage and sutures are removed and passive physical therapy is started at home. This physical therapy requires only a few minutes three to four times daily. Swimming therapy and short walks gradually increasing in length over six to eight weeks will be started several weeks after surgery. Again, complete confinement to a small room, pen, or cage when not working on physical therapy is mandatory. Avoid slick floors, jumping, running, stair climbing, and all acrobatics until recovery is complete.