Anterior Cruciate Ligament (ACL) Injury - MSK

Overview

Snapshot

A 27-year-old woman presents to the emergency department for severe pain in the right knee. A few hours prior to presentation, an opposing soccer player strikes her leg from her right side while her foot was planted to the ground. Afterwards, she felt a "pop" sound that was followed by severe knee pain and swelling. After the swelling improved, she feels that her right knee is unstable. On physical exam, the patient has a positive Lachman test. The patient is asked to rest, place ice and compress the knee, and elevate the affected leg. Given her sport demands, a conversation is made on the necessity of surgical reconstruction of the anterior cruciate ligament.

Introduction

Clinical definition
- injury in the form of tear or rupture affecting the anterior cruciate ligament (ACL) in the knee
Epidemiology
- incidence
  - non-contact ACL injuries are more common
- demographics
  - more common in female athletes
- risk factors
  - sports (e.g., football, soccer, skiers, and basketball)
  - motor vehicle accidents
Pathoanatomy
- normal anatomy
  - the ACL course
    - originates in the posteromedial aspect of the lateral femoral condyle
    - reaches the anteromedial aspect of the tibia
  - the ACL plays an important role in knee stability
    - it controls anterior translation of the tibia
      - it also restrains against tibial rotation, varus, and valgus stress
- pathology
  - contact mechanisms
    - injury that causes hyperextension or valgus deformation of the knee
      - e.g., football injury
    - high-speed motor vehicle accident
  - non-contact mechanisms
    - changing direction, pivoting, or landing that leads to rotation or valgus stress of the knee after sudden deceleration
Associated conditions
- unhappy triad which consists of injury to the
  - ACL
  - medial collateral ligament
  - medial meniscus
Prognosis
- the majority of athletes are able to return to their sports activities with ACL reconstruction

Presentation

Symptoms
- feeling a "pop" in the knee
  - thereafter, there is acute swelling and pain
- unstable or "giving out" knee
Physical exam
- anterior drawer test
  - the proximal tibia is anteriorly pulled while the patient is supine and the knee is flexed at 90 degrees
    - if there is anterior translation then the test is positive
- Lachman test
  - the proximal tibia is anteriorly pulled with one hand, while the other hand stabilizes the distal femur while the knee is flexed at 30 degrees
- hemarthrosis

Imaging

Magnetic resonance imaging (MRI)
- indication
  - an imaging modality that can confirm the diagnosis
  - if reconstruction is a possibility or to identify concomitant knee pathology

Studies

Making the diagnosis
- can be made based on typical clinical presentation alone
- can be confirmed by MRI or knee arthroscopy

Differential

Treatment

Conservative
- rest, ice, compression, and elevation (RICE) therapy
  - indication
    - management to reduce pain, edema, and hemarthrosis in the acute stage of the injury
      - nonsteroidal anti-inflammatory drugs are typically added
Operative
- surgical reconstruction
  - indications
    - performed in
      - young and active patients with high demand sports or jobs
      - significant knee instability
        
        such as injuries affecting multiple knee structures (e.g., unhappy triad)

Complications