ACL Tear

General Information

ACL (anterior cruciate ligament) tears are a type of knee trauma. ACL tears most commonly occur as a result of sports injuries.


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ACL injury

Description:

  • Knee trauma


Organs involved:

  • Anterior cruciate ligament (fortunately not essential to reasonable joint function)
    • Originates on posterior medial border of lateral femoral condyle, broad insertion anterior to tibial spine
    • Anteromedial, Posterolateral, and intermediate bundles
      • Anteromedial bundle tight with flexion
      • Posterolateral bundle tight during extension
    • Functions to check anterior displacement of tibia, hyperextension, also controls anterior medial or rotational instability and barrier to valgus instability


Incidence/Prevalence:

  • Uncommon but also underdiagnosed
  • Incidence of anterior cruciate ligament tears vary by gender and sport
    • Based on systematic review of 33 studies
    • Incidence of ACL tears per 1,000 practice sessions or games
      • 0.29 for female college basketball players
      • 0.08 for male college basketball players
      • 0.09 for female high school basketball players
      • 0.02 for male high school basketball players
      • 0.20 for female professional basketball players
      • 0.21 for male professional basketball players
      • 0.32 for female college soccer players
      • 0.12 for male college soccer players
      • 5.21 for female indoor soccer players
      • 1.88 for male indoor soccer players
      • 0.18 for female college lacrosse players
      • 0.17 for male college lacrosse players
      • 0.63 for recreational Alpine skiers
      • 0.03 for expert Alpine skiers
      • 0.08 for football players
    • Reference – Arthroscopy 2007 Dec;23(12):1320


Causes and Risk Factors

Causes:

  • Coming down hard on slightly flexed knee, twisting, externally applied force


Pathogenesis:

  • Resulting dysfunction depends on muscle tone, other injured structures, underlying joint laxity


Possible risk factors:

  • Phase of menstrual cycle may influence risk of ACL injury
    • Case-control study of female recreational alpine skiers with ACL rupture and age-matched control skiers
    • Alpine skiers in preovulatory phase of menstrual cycle significantly more likely to tear ACL than skiers in postovulatory phase, based on serum progesterone levels (odds ratio 3.22, p = 0.027) and menstrual history data (odds ratio 2.38, p = 0.086)
    • Reference – Am J Sports Med 2006 May;34(5):757


Complications and Associated Conditions

Complications:

  • Chronic ligamentous instability
  • Meniscal lesions
  • Degenerative joint disease
    • Knee osteoarthritis may be common following ACL injury; study of 103 Swedish female soccer players (mean age 31 years) with history of ACL injury 12 years earlier; 67 patients had weight-bearing knee radiography, 82% of injured knees (vs. 37% contralateral knees) had radiographic changes, 51% of injured knees had radiographic knee arthritis; 84 patients completed questionnaires, 75% reported symptoms affecting knee-related quality of life (Arthritis Rheum 2004 Oct;50(10):3145 in J Musculoskel Med 2004 Dec;21(12):650)


Associated conditions:

  • Often collateral ligament, capsular or cartilage injury