Injuries to the Anterior Cruciate Ligament

Everybody had heard of famous athletes who have “blown out” their knees, never to return to their pre-injury level of performance — athletes like Leslie Frazier of the Bears and Billy Sims of the Lions.

For the majority of these athletes their injury consists of a tear of the anterior cruciate ligament (ACL). But, this injury is not limited to football, or even to professional athletes. It commonly occurs in recreational athletes from skiers to basketball players and, with modern reconstructive surgical technique, need not signal the end of a career.

The ACL is the most important ligament in the knee. It connects the thigh bone (femur) to the shinbone (tibia) and stabilizes the knee, keeping the bones from slipping out of joint. When the tibia slides too far forward, the ACL can tear. This most frequently happens when an athlete is running at, or near, full speed and plants his foot to cut.

It may also happen when landing from a powerful jump or in a skiing fall in which the bindings fail to release. Without an ACL, the knee becomes unstable. The athlete is unable to plan and cut without the buckling or giving way. The extra motion between the bones also increases the risk that a cartilage (meniscus) can get caught and torn.

When ligaments on the outside of the knee are torn, they heal on their own with bracing and therapy. Because the ACL is on the inside of the knee, it is bathed in joint fluid which prevents healing even if the torn ends are surgically repaired. For this reason, the ACL must be reconstructed. This means a piece of tissue from elsewhere in the body must be substituted for the torn ligament.

Although sports medicine surgeons disagree on the best tissue to replace the ACL, the most commonly used is a piece of the patellar tendon. This is the thick tendon that connects the kneecap (patella) to the tibia. A one centimeter strip of this tendon is taken as a graft and inserted arthroscopically into the knee, reconstructing the torn ACL.

Over time the body incorporates this substitute ligament and it begins to simulate the function of the ACL. Although it can never be as good as the natural ligament, for most athletes it provides sufficient stability to return to their sport.

As important as the surgery is the rehabilitation following ACL reconstruction. It begins immediately after surgery with a continuous passive motion (CPM) machine which moves the knee for the athlete. Weight bearing is begun the next morning and controlled exercises are performed daily to strengthen the leg muscles. By six weeks, stationary biking is added and activity is progressively advanced for nine to twelve months, at which time the athlete is finally ready to return to play.

For those with the drive and persistence to endure the long months of rehabilitation, the reward is a chance to regain their former performance level. Athletes such a Bernard King, who returned from ACL surgery to become an NBA All-Star, have been an inspiration to the thousands of athletes who injure their ACL each year. Although no athlete is ever quite the same after tearing his ACL, modern surgery and rehabilitation techniques have dramatically changed the prognosis of this once career-ending injury.