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Condition/Disorder Synonyms

  • ACL sprain

  • ACL partial Tear

  • ACL full-thickness tear

ICD-9-CM Code

  • 844.2 Sprain of cruciate ligament of knee

  • 717.83 Old disruption of anterior cruciate ligament

ICD-10-CM Code

  • S83.509A Sprain of unspecified cruciate ligament of unspecified knee, initial encounter

  • M23.50 Chronic instability of knee, unspecified knee

Preferred Practice Pattern

Key Features


  • 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

    • Asymmetric Lachman test

    • Negative pivot-shift test

    • KT-1000 arthrometer test ≤ 3mm

    • Confirming arthroscopic observation

  • 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

Clinical Findings

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 ...

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