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For further information, see CMDT Part 41-06: Musculoskeletal Injuries of the Knee

Key Features

Essentials of Diagnosis

  • Usually follows anterior trauma to the tibia, such as a dashboard injury from a motor vehicle accident

  • The knee may freely dislocate and reduce

  • One-third of multi-ligament injuries involving the PCL have neurovascular injuries

General Considerations

  • The PCL is the strongest ligament in the knee

  • PCL injuries usually represent significant trauma and are highly associated with multi-ligament injuries and knee dislocations

  • More than 70–90% of PCL injuries have associated injuries to the posterolateral corner, medial collateral ligament (MCL), and anterior cruciate ligament (ACL)

  • Neurovascular injuries occur in up to one-third of all knee dislocations or PCL injuries

Clinical Findings

  • Ambulation is difficult in most patients with acute injuries

  • Patients with chronic PCL injuries

    • Can ambulate without gross instability

    • However, they may complain of subjective "looseness" and often report pain and dysfunction, especially with bending

  • Clinical examinations of PCL injuries include the "sag sign"

    • Patient is placed supine and both hips and knees are flexed to 90 degrees

    • Because of gravity, the knee with the PCL injury will have an obvious set-off at the anterior tibia that is "sagging" posteriorly

  • A PCL injury is sometimes mistaken for an ACL injury during the anterior drawer test, since the tibia is subluxed posteriorly in a sagged position and can be abnormally translated forward, yielding a false-positive test for an ACL injury

  • Pain, swelling, pallor, and numbness in the affected extremity may suggest a knee dislocation with possible injury to the popliteal artery

Diagnosis

Imaging

  • Radiographs are often nondiagnostic but are required to diagnose any fractures

  • MRI is used to diagnose PCL and other associated injuries

Diagnostic Procedures

  • The posterior drawer test

    • Patient is placed supine with the knee flexed to 90 degrees

    • In a normal knee, the anterior tibia should be positioned about 10 mm anterior to the femoral condyle

    • The clinician can grasp the proximal tibia with both hands and push the tibia posteriorly

    • The movement, indicating laxity and possible tear of the PCL, is compared with the uninjured knee (90% sensitivity and 99% specificity)

  • Varus stress testing (Table 41–6)

    • If the lateral knee is unstable, the patient should be assessed for a posterolateral corner, which consists of injuries to the lateral collateral ligament, popliteus tendon, and popliteofibular ligament

    • Injuries to the posterolateral corner usually requires urgent surgical treatment

Treatment

  • Isolated PCL injuries can be treated nonoperatively

  • Acute injuries are usually immobilized using a knee brace with the knee extension; the patient uses crutches for ambulation

  • Physical therapy can help achieve increased range of motion and improved ambulation

  • Many PCL injuries are ...

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