ACL Injuries

What is the ACL?

ACL stands for anterior cruciate ligament of the knee. The knee is the largest and most complex joint in the body. It depends on four ligaments and other muscles and tendons to function properly. There are two ligaments on the sides of the knee: the medial collateral ligament (MCL) and the lateral collateral ligament (LCL), and two crossed ligaments in the center of the joint, the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL). The ACL prevents the tibia from sliding forward under the thigh bone.

How is the ACL injured?

One of the common ways for the ACL to be injured is by a direct blow to the outer side of the knee such as in football. In this case, the knee is forced into an abnormal position that results in tearing of one or more knee ligaments. However, most ACL tears happen without any contact. The most common non-contact injuries happen when the athlete is planting the foot and cutting, landing on a straight leg, or when making a sudden stop. These mechanisms of injury are common in basketball, soccer and volleyball.

What are the signs of an ACL tear?

In many cases you will feel a "pop" when the ligament tears. There is usually a significant amount of pain, but surprisingly the injured warrior tries to return to play only to have the knee "give away" again. Over the next 12 hours, the knee swells, stiffens up, and walking becomes difficult. The swelling and limited range of motion usually begin to subside after 48 hours, and the knee gradually begins to feel better.

How is an ACL tear diagnosed?

ACL tears usually cause enough concern for the patient to seek medical evaluation. A physician who is experienced in sports medicine will usually be able to tell which ligaments have been injured if he gets an opportunity to examine a fresh injury. It becomes more difficult to examine once the swelling and stiffness have set in. Other tests such as x-rays, an MRI, or possibly diagnostic arthroscopy may be necessary.

Will I need surgery?

The most frequently asked question after an ACL injury is, will I need surgery? The answer is difficult, and varies from person to person. Many factors must be considered before making the decision. These factors include age, activity level, expectations of the patient, other associated injuries such as meniscal cartilage tears, and whether there is any underlying abnormal joint laxity. A young patient, who desires to return to competitive jumping and pivoting sports is more likely to need surgery for a satisfactory outcome than an older patient who only wants to return to light jogging and golf. If surgery is not indicated or chosen, an aggressive rehabilitation program should be started to regain motion and strength. A return to sports, with or without a brace, should not be considered until appropriate strength, balance, and coordination have returned.

Many different surgical techniques have been tried to restore ACL function through the years. Repair by stitching the injured ACL back together has not proven to give a consistently good result. Most current procedures use a "graft" to replace the injured ligament. Sources for the graft include the patients own tissue ( patellar tendon or hamstring tendon) and cadaver structures. The reconstruction is done via the arthroscope, and as an outpatient. Over a period of time the newly grafted ACL regains a blood supply, and is securely anchored to the bone.

Rehabilitation of the post op knee requires time and hard work. Most patients are allowed to bear weight immediately, with crutches only needed for a week to 10 days. Time off work depends upon your job, with desk jockeys usually missing less than a week, students 7-10 days, and steel workers may be off for as long as 4-5 months. The overall success rate is excellent and reproducible. Most large series show that over 90% of the patients return to sports without symptoms of instability.

Authored by: William D. Ferris MD 6/8/99