Posterior cruciate ligament tear

Posterior cruciate ligament (PCL) tears are less common than anterior cruciate ligament tears. 

Epidemiology

Posterior cruciate ligament tears account for ~10% (range 2-23%) of all knee injuries ². 

Clinical presentation

Sports injuries and car accidents (dashboard injury) are equally responsible for these injuries ¹. Many patients will be asymptomatic and their clinical examination is unremarkable. However, some patients may have knee instability or posterior sag sign.

Pathology

Three mechanisms of injury have been proposed ²:

• posterior tibial displacement in a flexed knee
• hyperextension
• rotation with an abduction or adduction force

Associations

PCL injuries are isolated in only 30% of cases and are thus commonly associated with other injuries ^1,2.4:

• ligamentous injury (~40%)
  • anterior cruciate ligament
  • medial collateral ligament
  • lateral collateral ligament
• meniscal tears
• posterolateral corner injury ⁵
• bone contusion (80%) or avulsion fracture (<10%)
• knee joint effusion

Radiographic features

MRI

Features of posterior ligament tears include ^1,2: 

• PCL usually remains contiguous (~70%) although there may be complete or partial ligamentous disruption
  • absent PCL replaced by high T1 and T2 signal
• enlarged and swollen PCL: >7 mm AP diameter of the vertical portion on sagittal imaging is indicative of a tear

Treatment and prognosis

PCL tears may result in chronic instability and early degenerative change ². 

Differential diagnosis

• mucoid degeneration ³
• meniscofemoral ligaments can mimic a PCL tear