Quick Medical Diagnosis & Treatment 2025

Anterior Cruciate Ligament (ACL) Injury

For further information, see CMDT Part 43-06: Musculoskeletal Injuries of the Knee

KEY FEATURES

Essentials of Diagnosis

An injury involving an audible pop when the knee buckles
Acute swelling immediately (or within 2 hours)
Instability occurs with lateral movement activities and going down stairs

General Considerations

ACL tears are common with sporting injuries among young adolescents and middle-aged patients
Can result from both contact (valgus blow to the knee) and non-contact (jumping, pivoting, and deceleration) activities
Prepubertal and older patients usually sustain fractures instead of ligamentous injuries

CLINICAL FINDINGS

Acute swelling of the knee, causing difficulty with motion
Difficulty with weight bearing
Instability of the knee during side-to-side maneuvers or while descending stairs
After the swelling has resolved, the patient can walk with a "stiff-knee" gait or quadriceps avoidance gait because of the instability
Stability tests to assess the amount of laxity of the knee (Table 43–8)
- Pivot shift test
- Lachman test is 84–87% sensitive for ACL laxity compared with the other side
- Anterior drawer test is 48% sensitive and 87% specific for ACL laxity compared with the other side

Table 43–8.Knee examination.

View Table||Download (.pdf)

Table 43–8. Knee examination.

Maneuver

Description

Inspection

Examine for the alignment of the lower extremities (varus, valgus, knee recurvatum), ankle eversion and foot pronation, gait, and “SEADS” (swelling, erythema, atrophy, deformity, surgical scars).

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

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

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 lift a 10- to 15-pound weight.

Positive test: Excessive anterior translation of the tibia compared with the other side indicates injury to the anterior cruciate ligament.

Anterior drawer

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.

Positive test: There is anterior cruciate ligament laxity compared with the unaffected side.

Pivot shift

Used to determine the amount of rotational laxity of the knee. The patient is examined while lying supine with the ...

Get Free Access Through Your Institution

Learn how to see if your library subscribes to McGraw Hill Medical products.

Subscribe: Institutional or Individual

Sign In

Username

Password

Forgot Password? Forgot Username?

Download the Access App: iOS | Android

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.