Knee Injury
Basics
Description
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
- Anterior cruciate ligament (ACL):
- 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 meniscus injury most common:
- Medial collateral ligament (MCL):
- 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 first)
- Anterior stress (ACL injured first)
Epidemiology
Incidence and Prevalence EstimatesEpidemiology
- ACL:
- Most commonly injured knee ligament
- 200,000 ACL injuries annually in the U.S.
- 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
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
- ACL: Often deceleration with flexion and rotation, or hyperextension:
- 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)
- MCL 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
Schaider, Jeffrey J., et al., editors. "Knee Injury." 5-Minute Emergency Consult, 6th ed., Lippincott Williams & Wilkins, 2020. Emergency Central, emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307714/all/Knee_Injury.
Knee Injury. In: Schaider JJJ, Barkin RMR, Hayden SRS, et al, eds. 5-Minute Emergency Consult. Lippincott Williams & Wilkins; 2020. https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307714/all/Knee_Injury. Accessed October 9, 2024.
Knee Injury. (2020). In Schaider, J. J., Barkin, R. M., Hayden, S. R., Wolfe, R. E., Barkin, A. Z., Shayne, P., & Rosen, P. (Eds.), 5-Minute Emergency Consult (6th ed.). Lippincott Williams & Wilkins. https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307714/all/Knee_Injury
Knee Injury [Internet]. In: Schaider JJJ, Barkin RMR, Hayden SRS, Wolfe RER, Barkin AZA, Shayne PP, Rosen PP, editors. 5-Minute Emergency Consult. Lippincott Williams & Wilkins; 2020. [cited 2024 October 09]. Available from: https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307714/all/Knee_Injury.
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