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

Key Features

Essentials of Diagnosis

  • Caused by a valgus or varus blow or stress to the knee

  • Pain and instability in the affected area

  • Limited range of motion

General Considerations

  • The medial collateral ligament (MCL)

    • Most commonly injured ligament in the knee

    • Usually injured with a valgus stress to the partially flexed knee

    • Can also occur with a blow to the lateral leg

    • Commonly injured with acute anterior cruciate ligament (ACL) injuries

  • The lateral collateral ligament (LCL)

    • Less commonly injured

    • Can occur with a medial blow to the knee

  • Since both collateral ligaments are extra-articular, injuries to these ligaments may not lead to any intra-articular effusion

  • Affected patients may have difficulty walking initially, but this can improve when the swelling decreases

Clinical Findings

Symptoms and Signs

  • Pain along the course of the ligaments

  • Limited range of motion due to pain, especially during the first 2 weeks following the injury



  • Radiographs

    • Usually nondiagnostic except for avulsion injuries

    • Should be used to rule out fractures that can occur with collateral ligament injuries

  • MRI

    • Usually not needed for isolated MCL injuries

    • Should be used to evaluate possible associated cruciate ligament injuries

    • Should be done for LCL or posterolateral corner injuries to exclude associated injuries and to determine their significance

Diagnostic Procedures

  • Varus and valgus stress tests are best methods to assess the collateral ligaments (Table 41–6)

Table 41–6.Knee examination.

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