Posterior Cruciate Ligament

Original Editor -

Top Contributors - Rania Nasr and Kim Jackson

Description

The posterior cruciate ligament (PCL) is the strongest and largest intra-articular ligament in human knee and the primary posterior stabilizer of the knee. It comprises of 2 functional bundles: the larger anterolateral bundle (ALB) and the smaller posteromedial bundle (PMB). The size of the femoral attachment of the ALB is nearly twice the size of its tibial attachment.

Origin

The PCL originates from the anterolateral aspect of the medial femoral condyle within the notch.

Insertion

The PCL inserts along the posterior aspect of the tibial plateau, approximately 1 cm distal to the joint line. The average surface area of the PCL attachments to the femur and tibia was studied by Voos et al. It was found the area of the femoral footprint to be 209 mm2 and tibial footprint to be 243 mm2. Thus, the PCL insertion sites are roughly three times larger than its mid-substance.

Vascular supply

The middle geniculate artery perforates the posterior capsule running parallel to the superior edge of the synovial septum. It has branches to the synovium around the PCL forming a plexus of vessels supplying the PCL. There is also a potential supply from a branch of the inferior geniculate artery.

Nerve Supply

The tibial and obturator nerve has posterior articular branches to the posterior capsule. These branches perforate the posterior capsule to reach the PCL.

Function

The PCL functions as one of the main stabilizers of the knee joint and serves primarily to resist excessive posterior translation of the tibia relative to the femur. The PCL also acts as a secondary stabilizer of the knee preventing excessive rotation specifically between 90° and 120° of knee flexion. The two bundles of PCL, ALB and PMB function synergistically.

Clinical relevance

Posterior cruciate ligament (PCL) tears comprise 3% of outpatient knee injuries and 38% of acute traumatic knee hemarthroses. These injuries rarely occur in isolation, and up to 95% of PCL tears occur in combination with other ligament tears.PCL tears are increasingly being recognized as source of morbidity and reduced function because of persistent instability, pain, impaired function and development of degenerative joint disease.

PCL tears are typically produced by external trauma such as the classic “dashboard injury” resulting from a posteriorly directed force on the anterior aspect of the proximal tibia with the knee flexed. In athletics, the typical mechanism of isolated PCL tears is a direct blow to the anterior tibia or a fall onto the knee with the foot in a plantar flexed position. Football, soccer, rugby and skiing are among the sports with highest incidence of PCL tears.

Symptoms depend upon the injury mechanism (high vs low-energy) as well as chronicity. Stiffness, swelling and pain on the posterior aspect of the knee are typical symptoms, while anterior knee pain and instability when descending stairs are more often associated with chronic isolated tears.

Assessment

A careful vascular examination of the lower extremities is essential because a PCL injury can be accompanied by a popliteal artery injury. If the pulses are weak or the ankle-brachial index is ≤0.8, an intimal tear should be suspected and arteriography should be performed. Acute PCL injuries present with joint swelling and about 10° to 20° of restriction in further flexion due to pain. Chronic PCL injuries may present with limited activity such as having difficulty in climbing slopes due to lethargy and pain in the anterior and medial areas of the knee rather than instability.

Special test

The posterior drawer test is the most accurate test for PCL injuries. At 90° of knee flexion, posterior sagging of the tibia is observed on the affected side. If the tibia is pulled forward or the quadriceps is contracted with the knee flexed to 90° (quadriceps active test), anteroposterior instability of the knee is noted.