Ligament Injuries of the Knee

There are multiple ligaments that give mechanical support to the knee joint. Major structures include the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and the lateral collateral ligament (LCL) in conjunction with the posterolateral corner. Injuries to these ligaments are commonly seen in athletes as well as active adults and children.

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Diagramatic example of knee anatomy and ligaments

Compromise of the ligamentous supports of the knee can result in instability, pain, and the development of early arthritis. Diagnosis of these injuries is made by clinical examination and often magnetic resonance imaging (MRI).  Treatment depends of the nature of the injury, the activity demands of the patient, and the baseline condition of the knee joint. Options include physical therapy, bracing, direct anatomic repair, and ligament reconstruction.

ACL Injuries

The ACL rupture is one of the most common ligament injuries seen in athletes. The ACL provides the knee with anterior and rotation stability. When torn, the ACL will not heal. In an ACL-deficient knee, athletes often have trouble with cutting and shifting exercises. ACL injuries may occur in isolation or in conjunction with other knee injuries. Commonly associated injuries are MCL ruptures, posterlateral corner tears, and meniscal tears. Treatment for ACL ruptures is personalized to each patient.

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Arthroscopic image of ruptured ACL

Surgery for ACL ruptures involves drilling tunnels in both the tibia and the femur to anatomically restore the ACL. The new ligament is pulled into these tunnels and fixed to “reconstruct” the ligament. After surgery the patient starts physical therapy immediately to work on knee range of motion and muscle rehabilitation.

The patient is fit for a functional ACL brace which is worn during rehab and sometimes during early return to athletic competition. Return to unrestricted athletic activity is allowed as soon as knee strength is normal and ACL graft has integrated into the body. Aggressive sports-based physical therapy can speed return to play.

PCL Injuries

Injuries to the PCL are much less common than that of the ACL. The PCL provides posterior and rotational stability to the knee. Although possible, athletes rarely tear the PCL in isolation. Most often this occurs in conjunction with other knee ligament injuries. Unlike the ACL, many PCL injuries will often heal with conservative treatment. Most injuries are managed initially with bracing and physical therapy.

For severe injuries or multiple ligament injuries PCL reconstruction can be necessary. This is performed in similar fashion to ACL reconstruction. Tissue is either harvested from the patient or cadaveric tissue is utilized. Drill holes are made in the bone to anatomically reconstruct the PCL. The new graft is pulled into place and fixed thereby “reconstructing” the ligament. Post-operative therapy is of critical importance to rehabilitate knee motion and strength.

MCL Injuries

The MCL of the knee provides support to the inner or medial aspect of the knee. When an athlete sustains a blow to the outside of the knee it is the MCL that prevents the knee from buckling inward. The MCL is crucial to normal knee function. MCL injuries are common among athletes.

Fortunately most of these injuries will heal with non-operative treatment and leave little functional deficit. The MCL consists of two distinct structures. These are the deep MCL and superficial MCL. When injury to the MCL occurs either one of both of these stuctures can be damaged.

Injuries are graded from I-III with I being a mild partial injury and III being the complete rupture of the ligament. Treatment of MCL injury is based upon the severity of rupture, concomitant knee injuries, and the functional demands of the patient. In isolated cases of severe trauma with complete rupture primary repair of the MCL may be indicated.

This may be beneficial in very high demand athletes. In the vast majority of cases MCL injuries are managed non-operatively with bracing and physical therapy. The MCL clearly has the capacity to heal with conservative non-operative treatment.

Lateral Ligament Injuries

The lateral aspect of the knee is supported by multiple structures. The main ligamentous structure is the LCL. The posterolateral corner of the knee also consists of the lateral joint capsule, the popliteus, and the iliotibial band. The structures function to provide lateral support to the knee.

When an athlete sustains a varus (outwardly directed) force to the knee it is the LCL and posterolateral structures that prevent the knee from buckling outward. These structures also assist with the rotational stability of the knee.

Injuries to the LCL and posterolateral corner can be treated either conservatively or operatively. Partial injuries in lower demand patients can be treated with bracing and physical therapy with excellent results.

Complete ruptures, especially those in conjunction with cruciate ligament injuries, are often treated with surgery. If the athlete presents immediately after injury then often the injured structures can be repaired directly. If the injury is chronic then surgery is often aimed at reconstructing the injured structures.

Reconstruction can be performed using the patient’s own tissues or cadaveric grafts. When a lateral ligament injury occurs in the setting of ACL rupture it is imperative that the injury is recognized and treated along with the ACL. Failure to do so can severely compromise the treatment of the ACL injury.

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