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Hamstring tendon graft for anterior cruciate ligament reconstruction - Home Study Program

AORN Journal, Oct, 2002 by Deborah M. Boni, George E. Herriott

The incidence of sports injuries is on the rise as more teenagers and adults become involved with sports activities. Anterior cruciate ligament (ACL) tears are becoming more common among adults and female teenagers because of their increased participation in contact sports, especially with the increase in female soccer players. Although the medial collateral ligament (MCL) is the most commonly injured ligament of the knee, the ACL is the most commonly injured ligament that causes abnormal knee joint laxity. (1) Injury to the ACL without injury to other ligaments occurs in approximately 60% of ACL injuries. The classic history of an ACL tear is a sudden twisting of the knee at which time the patient hears a pop or snap. The patient also may complain of a feeling that the knee is giving away. During the initial injury, the ACL may not be the only stability structure torn. For example, a common triad of injuries includes the torn ACL, a medial meniscus tear, and a partial or complete MCL tear.

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NORMAL ANATOMY

The knee joint is one of the largest and most complex joints in the body. It consists of

* the femur, which meets the tibia to form the main knee joint;

* the patella, a triangular-shaped bone embedded in the tendon of the quadriceps muscle, which is anterior to the knee joint in the intercondylar groove of the distal femur; and

* the patellofemoral joint, which is where the femur joins the patella.

The main knee joint has a medial and lateral compartment surrounded by a joint capsule that is attached proximally to the femoral condyles and distally to the tibial condyles and upper end of the fibula.

Ligaments are bundles of collagen fibers that provide stability and strength to the knee joint. The collateral ligaments (ie, medial, lateral) strap the outside of the joint and cruciate ligaments (ie, anterior, posterior) cross within the joint. The term cruciate comes from the word crux or cross and the word crucial. The cruciate ligaments consist of two fibrous bands that extend from the intercondylar fossa of the femur to attachments anteriorly and posteriorly in the intercondylar eminence of the tibia. They crisscross over one another to form an "X" inside the knee. The ACL connects the anterior surface of the tibia to the posterior surface of the femur and is crucial for preventing the knee from sliding forward. The posterior cruciate ligament (PCL) provides opposing support by passing anteriorly and medially (Figure 1). The capsule also is reinforced in front by the patellar and quadriceps tendons and posteriorly by the popliteus and gastrocnemius muscles.

[FIGURE 1 OMITTED]

The menisci (ie, thickened cartilage pads) are inserted between the femoral and tibial condyles and attached to the joint capsule. Menisci are almost totally avascular; therefore, degenerative changes usually are permanent. The suprapatellar bursa is situated between the tendon of the quadriceps femoris muscle and the anterior surface of the lower segment of the femoral portion of the knee joint. Synovial membrane (ie, a sheet of flattened connective tissue cells) lines the capsule of the joint and covers the infrapatellar fat pad, parts of the cruciate ligaments, and portions of the femur and tibia. (2)

Functional Anatomy

Normally, the knee flexes to a maximum of 135 degrees and extends to zero degrees. The two joints formed by the femur and tibia have a meniscus between them that acts as a smooth surface on which the joint can move. Bursa (ie, fluid-filled sacs) surround the knee joint to provide a gliding surface to reduce friction of the tendons, such as friction of the patellar tendon that attaches to the front of the tibia below the kneecap. Large blood vessels pass through the popliteal space behind the knee. The quadriceps muscle extends the knee joint, and the hamstring muscle flexes the knee joint.

The average adult ACL is approximately 3.5 cm long. It has a semicircular attachment at the posterior portion of the medial aspect of the lateral femoral condyle. The ACL lies in an anteromedial and distal direction, making an outward spiral and inserting near the anterior spine of the tibial plateau. The tibial attachment usually is 1.5 cm posterior to the anterior articular surface of the tibial plateau. The ACL, like the PCL, is an extrasynovial structure, and yet it is located intra-articularly.

The ACL provides a primary restraint to anterior tibial translation on the femur and acts as the major secondary restraint to medial tibial displacement. It provides stabilization to valgus and varus opening, as well as to internal and external rotation.

MECHANISM OF INJURY

The most common method of injuring the ACL happens without the knee coming in contact with another object. This kind of noncontact injury usually happens when the person changes direction rapidly so that, with the knee in full extension, the femur is rotated externally on a fixed tibia. Landing on a straight leg or attempting to make an abrupt stop also can torque the knee in this manner, causing an ACL injury. These kinds of injuries are common in basketball, football, volleyball, and soccer. Skiers and snow boarders also can experience this kind of injury because the foot and ankle is locked into a boot preventing the person from relieving the sudden torque on the knee. Also, the ACL often is injured by a direct blow of excessive lateral force to the knee. This valgus stress forces the knee into an abnormal position, tearing the ACL and other knee structures.

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Hamstring tendon graft for anterior cruciate ligament reconstruction - Home Study Program

AORN Journal, Oct, 2002 by Deborah M. Boni, George E. Herriott

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