Knee Injuries: Acl, Pcl, Mcl, Meniscus

Knee Injuries: Acl, Pcl, Mcl, Meniscus is a topic covered in the 5-Minute Emergency Consult.

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Basics

Description

  • Cruciate ligament injuries:
    • Anterior cruciate ligament (ACL):
      • From the posteromedial aspect of the lateral femoral condyle to the intraspinus area on the tibia
      • Prevents excessive anterior translation of the tibia, internal rotation of the tibia on the femur, or hyperextension of the knee.
    • Posterior cruciate ligament (PCL):
      • Twice as strong and twice as thick as the normal ACL, less commonly injured
      • From anterolateral aspect of medial femoral condyle to the posterior tibia
  • Meniscal tears:
    • Medial meniscus injury most common
      • More firmly attached to the joint capsule and less mobile than lateral meniscus
    • Tears are the result of tensile or compressive forces between the femoral and tibial condyles
    • Extension of meniscal tear may result in a free segment that may become displaced into the joint, resulting in a true locked joint.
  • Medial collateral ligament:
    • From the posterior aspect of medial femoral condyle to the tibia, distal to joint
    • Often accompanied by other injury:
      • Hyperextension with external rotation (ACL/PCL injured 1st)
      • Anterior stress (ACL injured 1st)

Epidemiology

Incidence and Prevalence Estimates
  • ACL:
    • Most commonly injured knee ligament
    • 200,000 ACL injuries annually in US
    • 2/3 of all ACL injuries are noncontact
    • Female gender: 3× greater risk
  • Associated injuries:
    • ∼50% ACL injuries are associated with meniscal tears
    • ACL injuries commonly have chondral and subchondral injuries
  • Meniscus:
    • Medial meniscus injury 10× more common than lateral
    • True locked joint in only 30%

Etiology

  • Cruciate ligament injuries:
    • ACL: Often deceleration with flexion and rotation, or hyperextension
      • Usually sports-related, especially skiing and football
      • Plant-and-pivot or stop-and-jump mechanism
    • PCL:
      • “Dashboard injury”: Flexed knee with posteriorly directed force to the anterior proximal tibia (motor vehicle crash or direct trauma)
      • Fall on flexed knee
  • Meniscus Injury:
    • Sudden rotary motion of knee associated with squatting, pivoting, turning, and bending
    • Common in sports with low stance positions (wrestling/football) or kneeling position (carpet installers, plumbers)
  • Medial collateral ligament injuries:
    • Direct trauma to lateral knee
    • Most common: Valgus stress with external rotation on flexed knee:
      • From catching a ski tip
      • Side tackle (football)

Pediatric Considerations
  • The ACL is the most frequently injured knee ligament in children.
  • Isolated MCL injury infrequent before growth plate closure (<14-yr old)

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Citation

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TY - ELEC T1 - Knee Injuries: Acl, Pcl, Mcl, Meniscus ID - 307647 Y1 - 2016 PB - 5-Minute Emergency Consult UR - https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307647/all/Knee_Injuries:_Acl__Pcl__Mcl__Meniscus ER -