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Anterior Cruciate Ligament (ACL) Injury

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

Key Features

  • An injury involving an audible pop when the knee buckles

  • Acute swelling immediately (or within 4 hours)

  • Instability occurs with lateral movement activities and going down stairs

  • ACL tears are common with sporting injuries

  • Can result from both contact (valgus blow to the knee) and non-contact (jumping, pivoting, and deceleration) activities

Clinical Findings

  • Acute swelling of the knee, causing difficulty with motion

  • After the swelling has resolved, the patient can walk with a 'stiff-knee' gait or quadriceps avoidance gait because of the instability

  • Patients describe symptoms of instability while performing side-to-side maneuvers or descending stairs

Diagnosis

  • Stability tests assess the amount of laxity of the knee while performing side-to-side maneuvers or descending stairs

    • The Lachman test is performed with the patient lying supine and the knee flexed to 20–30 degrees (Table 41–7)

    • The anterior drawer test is performed with the patient lying supine and the knee flexed to 90 degrees (Table 41–7)

    • The pivot shift test is performed with the patient lying supine with the knee in full extension and is used to determine amount of rotational laxity of knee (Table 41–7)

  • Plain radiographs are usually negative in ACL tears but are useful to rule out fractures

  • MRI is the best method to diagnose ACL tears

Table 41–7.Knee examination.
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Table 41–7. Knee examination.

Maneuver

Description

Inspection

Examine for the alignment of the lower extremities (varus, valgus, knee recurvatum), ankle eversion and foot pronation, gait, SEADS.

Palpation

Include important landmarks: patellofemoral joint, medial and lateral joint lines (especially posterior aspects), pes anserine bursa, distal iliotibial band and Gerdy tubercle (iliotibial band insertion).

Range of motion testing

image

Check range of motion actively (patient performs) and passively (clinician performs), especially with flexion and extension of the knee normally 0–10 degrees of extension and 120–150 degrees of flexion.

Knee strength testing

Test resisted knee extension and knee flexion strength manually.

Ligament Stress Testing

Lachman test

image

Performed with the patient lying supine, and the knee flexed to 20–30 degrees. The examiner grasps the distal femur from the lateral side, and the proximal tibia with the other hand on the medial side. With the knee in neutral position, stabilize the femur, and pull the tibia anteriorly using a similar force to lifting a 10- to 15-pound weight. Excessive anterior translation of the tibia compared with the other side indicates injury to the anterior cruciate ligament.

Anterior drawer

image

Performed with the patient lying supine and the knee flexed to 90 degrees. The clinician stabilizes the patient’s foot by sitting on it and grasps the proximal tibia with both hands around the calf and pulls anteriorly. A positive test finds anterior cruciate ligament laxity compared with the unaffected ...

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