Posterior cruciate ligament (PCL) tears are less common than anterior cruciate ligament tears.
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Epidemiology
Posterior cruciate ligament tears account for ~10% (range 2-23%) of all knee injuries 2.
Associations
Posterior cruciate ligament injuries are isolated in only 30% of cases and are thus commonly associated with other injuries 1,2.4:
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ligamentous injury (~40%)
bone contusion (80%) or avulsion fracture (<10%)
knee joint effusion
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
Radiographic features
MRI
Features of posterior cruciate ligament tears include 1,2:
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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
posterior tibial translation of >2-3 mm measured in the mid medial compartment 6,7
Treatment and prognosis
Posterior cruciate ligament tears may result in chronic instability and early degenerative change 2.
Differential diagnosis
meniscofemoral ligaments can mimic a PCL tear
Practical points
posterior cruciate ligament tears can spontaneously heal and commonly demonstrate fiber continuity on MRI, however, these fibers may heal in a non-functional, lax, elongated position, which can result in knee joint degeneration 7,8
posterior tibial translation on kneeling posterior stress radiographs of >5 mm 9 or >2-3 mm on MRI are signs of chronic posterior cruciate ligament (PCL) or PCL graft tears 6,7
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