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  • ACL sprain
  • ACL partial Tear
  • ACL full-thickness tear

  • 844.2 Sprain of cruciate ligament of knee
  • 717.83 Old disruption of anterior cruciate ligament

  • S83.509A Sprain of unspecified cruciate ligament of unspecified knee, initial encounter
  • M23.50 Chronic instability of knee, unspecified knee


  • American Medical Association (AMA) has developed standard nomenclature for athletic injuries to ligamentous structures1
    • 1st degree sprain: minor tear of ligament fibers
    • 2nd degree sprain: partial tear of ligament structure
    • 3rd degree sprain: complete tear of ligament

Essentials of Diagnosis

  • Clinical diagnosis of a partial tear1
  • Medial and lateral menisci and medial collateral ligament (MCL) are commonly injured with the ACL2
  • History
    • Contact injuries: typically due to application of varus or valgus force to the knee imposing a shear force on the joint
    • Risk for injury increased by2
      • Sudden deceleration
      • Abrupt change in direction
      • Hyperextension of the knee
    • Non-contact injuries (70% of ACL injuries4) typically due to3
      • Deceleration and change in direction (cutting maneuvers)
      • Landing from a jump in full knee extension
      • Pivoting with planted foot and extended knee
      • Hyperextension/flexion of the knee

General Considerations

  • It is estimated that more than 250,000 ACL injuries occur in the United States each year2
  • 75,000–100,000 ACL reconstructions performed annually5


  • ACL injuries reported to be 2–9 times more likely in females than in males4,6

Signs and Symptoms

  • Feelings of instability in the knee7
  • Severe pain at the time of injury 7
  • Audible pop at the time of injury7
  • Immediate swelling at the time of injury (effusion)

Functional Implications

  • Instability of the knee during weight-bearing tasks
  • Ambulation distance
  • Squatting
  • Activities requiring single-leg stance (donning lower extremity clothing)
  • Mobility on uneven terrain

Possible Contributing Causes

  • Female sex
    • Tendency of females to land from a jump and change direction in a more erect posture, characterized with increased knee and hip extension3,8
    • Tendency of females to land with increased knee valgus3,8
    • Pelvic structure and lower-extremity alignment that result in a varied Q-angle9
    • More narrow intercondylar notch3,9
    • Smaller ACLs3,9
    • Increased estrogen levels and related increase in laxity.3 (This is controversial in research literature.)
  • Increased duration of activity and fatigue10
  • Athletic activities in dry-weather conditions or playing on artificial turf3
  • Increased Body Mass Index (BMI)
  • Decreased hamstring strength relative to quadriceps3
  • Decreased core ...

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