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

Key Features

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

  • Pain and instability in the affected area

  • Limited range of motion

  • The medial collateral ligament is commonly injured with acute anterior cruciate ligament (ACL) injuries

  • The lateral collateral ligament (LCL) is less commonly injured, but this 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

Clinical Findings

  • Pain along the course of the ligaments

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

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


  • Varus and valgus stress tests (Table 41–7) are best methods to assess injuries; results are categorized into grades

    • Grade 1: Patient has pain with varus/valgus stress test but no instability

    • Grade 2: Patient has pain, and the knee shows instability at 30 degrees of knee flexion

    • Grade 3: Patient has marked instability but not much pain; knee is often unstable at both 30 degrees and 0 degrees of knee flexion

  • Radiographs

    • Usually nondiagnostic except for avulsion injuries

    • However, should be used to rule out fractures

  • MRI

    • Not required for isolated medial collateral ligament injuries

    • Should be used to evaluate possible associated cruciate ligament injuries

    • Should be used in LCL or posterolateral corner injuries to exclude associated injuries and to determine their significance

Table 41–7.Knee examination.

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