• A 21-year-old man presents to the emergency department for severe pain in the right knee. A few hours prior to presentation, an opposing football player hits his leg from his right side. Afterwards, he felt a "pop" sound that was followed by severe knee pain and a sensation of knee instability. On physical exam, there is anterior translation of the proximal tibia when pulled as the patient has the knee flexed at 90° and supine. Ice is applied to the knee and ibuprofen is prescribed. Orthopedic surgery is consulted to evaluate if ligamental reconstruction is needed. 
  • 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
  • Symptoms 
    • feeling a "pop" in the knee
      • thereafter, there is acute swelling and pain
    • instability 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
  • Magnetic resonance imaging (MRI)
    • indication
      • an imaging modality that can confirm the diagnosis
      • if reconstruction is a possibility or to identify concomitant knee pathology
  • Making the diagnosis
    • can be made based on typical clinical presentation alone
    • can be confirmed by MRI or knee arthroscopy
  • 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
  • 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)
  • Osteoarthritis
  • Arthrosis
  • Sports disability


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