The posterior cruciate ligament is a structure that supports the knee during all of its ranges of motion. Primarily it is useful for preventing backward movement of the tibia in relation to the femur. The femur is the upper thigh bone, making up the top of the knee, and the tibia is the lower leg or shin bone that makes up the bottom portion of the knee. PCL injuries occur either as isolated injuries or in conjunction with other torn structures in the knee. Treatment can be either surgical or nonsurgical for injuries. Treatment decisions depend on the extent of the injury to the PCL, whether other knee structures are also injured, and specific factors about the patient including other medical issues and functional levels.
Anatomy of the PCL
The posterior cruciate ligament, or PCL, is the main structure responsible for preventing posterior movement of the tibia in relation to the femur. The PCL originates on the femur and attaches to the to tibia.
There are two distinct components of the PCL with differing functions. The anterolateral bundle is more taught in flexion and lax in extension. The posteromedial bundle is more taught in extension and lax in flexion. The anterolateral bundle is larger, stronger, and stiffer than the posteromedial component. The large ligamentous insertion sites and asymmetrical fibers within the PCL make the anatomical and biomechanical properties difficult to recreate surgically. For this reason, surgical reconstructions of the PCL for isolated PCL rupture have generally not produced improved functional outcomes when compared to conservative management.
Isolated PCL Injury
An isolated PCL injury typically occurs by the means of either a "dashboard" injury or during hyperflexion or hyperextension. A dashboard injury typically occurs during a motor vehicle accident in which the patient hits a flexed knee against the dashboard. Falling on a bent knee can mimic this mechanism. This mechanism forces the tibia backward in relation to the lower leg, stressing the PCL. With enough force, the PCL can rupture. A hyperflexion injury can occur without a distinct traumatic episode. A hyperextension injury usually occurs with poor form on landing from a jump, in which the knee is forced into hyperextension, which stresses the PCL. A PCL injury can be found based on clinical exam or through the use of imaging. An X-ray can show malalignment of the bones or bony fragments. An MRI can directly visualize the injured ligament.
Isolated PCL Injury Treatment
Generally it is believed that an isolated PCL injury can be treated non-operatively. If the ligament pulls a piece of bone off--a condition known as a bony avulsion--it is recommended that surgery be performed to repair the bone and the PCL. The non-operative treatment consists of rehabilitation of the knee with stretching and strengthening exercises. A brace can also be used to limit the posterior translation of the tibia when performing activities. Essentially the brace acts externally on the knee as the posterior restraint. If instability exists after rehabilitation, a surgical repair may be indicated for an isolated PCL injury. If surgery is performed, the surgeon will use a cadaver graft or often harvest a graft from the patient's patellar tendon, quadriceps tendon, Achilles tendon, or hamstring.
Posterolateral Corner Injury
The posterolateral corner refers to injuries to lateral structures of the knee. These structures include the popliteus tendon, arcuate ligament complex, and lateral collateral ligament/lateral capsule. There is often an associated anterior cruciate ligament or PCL injury. Often the posterolateral corner is injured in knee dislocations.
These injuries occur with or without trauma. Non-traumatic causes can include chronic ligamentous laxity usually associated with a bowed, or varus,knee, chronic changes from an injured ACL or PCL, and if there is significant external rotation of the lateral tibial plateau when there is an intact PCL.
Traumatic posterolateral corner injuries occur with hyperextension and a varus stress. A varus stress refers to the leg being hit so that the femur and the tibia move in such a way that the knee is forced into a bowed leg stress. This varus stress puts deforming forces on the lateral collateral ligament.
An MRI is the best way to non-invasively assess the posterolateral corner structures due to the MRI sensitivity for detecting soft tissue injuries. It is also useful for operative planning.
Posterolateral Corner Injury Treatment
The goal of treatment for any injury of the posterolateral corner is to reduce the laxity associated with the injury. Low grade injuries can be treated with rehabilitation and bracing. Higher grade injuries and those injuries that fail rehabilitation should undergo operative management.
All surgical repairs are aimed at either reconstructing or replacing the ligaments and tendons with grafts or reattaching torn entities to their normal attachment sites. This can be done arthroscopically or with an open incision.
Combined ACL/PCL Injury
Multiligament knee injuries are most commonly caused by high energy trauma usually resulting in a dislocation of the knee. Neurovascular compromise needs to be assessed in any multiligamentous injury. Treatments can either be nonsurgical or surgical.
Nonsurgical indications are typically limited to the elderly and other low-demand patients. Occasionally the knee will not be too unstable and non-operative options can be tried in some select patients. Treatment is aimed at protecting the range of motion and placing the knee in a brace for stability.
Surgery is generally performed for most multiligament knee injuries. Surgery is aimed at restoring joint stability by reconstructing the damaged ligaments and soft tissue structures. Grafts are typically used to create new ligamentous supports most commonly for the ACL and PCL. Rehabilitation and bracing is performed post-operatively.
References
- Wheeless' Textbook of Orthopaedics: Posterior Cruciate Ligament
- "AAOS Comprehensive Orthopaedic Review"; Jay Lieberman; 2009.
- "Current Diagnosis and Treatment in Orthopaedics"; Harry Skinner; 2006.
