Anterior Cruciate Ligament (ACL) Injury

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

• Meniscal tear
  • differentiating factor
    • patients can have a positive
      • Thessaly test 
      • McMurray test 
      • Apley test 
• Posterior collateral ligament (PCL) injury 
  • differentiating factor
    • patients can have a positive posterior drawer test
    • trauma is typically due to
      • a motor vehicle accident leading to “dashboard injury”
      • falling on a flexed knee while the foot is plantarflexed
• direct trauma to the proximal tibia

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

• Osteoarthritis
• Arthrosis
• Sports disability