Updated: 11/30/2019

Anterior Cruciate Ligament (ACL) Injury

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  • Snapshot
    • 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.
  • Introduction
    • Clinical definition
      • injury in the form of tear or rupture affecting the anterior cruciate ligament (ACL) in the knee
    • 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
  • 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
  • ETIOLOGY
    • Pathoanatomy
      • 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
      • 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
  • Presentation
    • 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
  • 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
  • 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
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Questions (1)

(M2.OR.17.4799) A 25-year-old male presents to his primary care physician for pain in his knee. The patient was in a wrestling match when his legs were grabbed from behind and he was taken to the floor. The patient states that the moment this impact happened, he felt a snapping and sudden pain in his knee. When the match ended and he stood back up, his knee felt unstable. Minutes later, his knee was swollen and painful. Since then, the patient claims that he has felt unstable bearing weight on the leg. The patient has no significant past medical history, and is currently taking a multivitamin and protein supplements. On physical exam you note a tender right knee, with erythema and an effusion. Which of the following is the most likely physical exam finding in this patient?

QID: 109202
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Laxity to valgus stress

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Laxity to varus stress

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Clicking and locking of the joint with motion

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Anterior translation of the tibia relative to the femur

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Posterior translation of the tibia relative to the femur

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