Knee Ligaments and Tears

Contributed by: Ali A. Qadeer, Baylor College of Medicine, 1 Baylor Plaza, Houston, Tx 77030
Overview
  • The knee is composed of two joints and includes a condyloid (hinge) joint formed by the articulation between the femur and tibia and a sellar (gliding) joint formed by the articulation between the patella and femur. The knee is inherently unstable and as such depends on several interosseous ligaments for its stability. Knee ligament tears are common in adults and can be the result of acute injury or chronic degeneration (arthritis).
Anatomy
  • Anterior Cruciate Ligament (ACL)
    • The ACL connects the posteromedial aspect of the lateral femoral condyle to the anterior tibial eminence. This important ligament prevents anterior translation of the tibia relative to the femur.
  • Posterior Cruciate Ligament (PCL):
    • The PCL connects the lateral aspect of the medial femoral condyle to the posterior proximal tibia. This ligament prevents posterior translation of the tibia relative to the femur.
  • Lateral (Fibular) Collateral Ligament (LCL)
    • The LCL connects the lateral femoral epicondyle to the fibular head and is the primary restraint against varus force at the knee.
  • Medial (Tibial) Collateral Ligament (MCL)
    • The MCL connects the medial femoral epicondyle to tibia and is the primary restraint against valgus force at the knee.
  • Medial/Lateral Meniscus
    • The menisci are fibrocartilage discs that are thickest at the periphery and thinnest at the center. They attach firmly at medial and lateral tibia plateau. The menisci function to transmit load and act in load shock absorption, ensure joint congruity and stability, as well as help lubricate the joint.
Injury Mechanisms and Diagnosis
  • ACL Tear
    • Clinical Manifestation
      • The ACL is the most commonly injured ligament in the knee and typically results from non-contact pivoting injuries due to sudden deceleration. Injury often manifests with an audible “pop” followed by pain and effusion due to immediate hemarthrosis.
      • The “Unhappy Triad” refers to a concomitant medial meniscus and MCL injury with an ACL tear. However, in acute ACL injury the lateral meniscus is more commonly torn.
    • Diagnosis
      • Lachman Test: At 30 degree flexion, one hand stabilizes the femur and other hand anteriorly translates the tibia. A positive test occurs when there is excessive laxity compared to the contralateral knee and a vague endpoint. This is the most sensitive examination for acute ACL injury.
      • Anterior Drawer Test: Performed with the knee flexed to 90 degrees. The proximal tibia is pulled anteriorly and a positive test occurs with anterior translation.
  • Meniscus Tear
    • Clinical Manifestation
      • This commonly occurs in younger adults acutely as a result of sports-related twisting injuries and in older patients insidiously secondary to degeneration. The medial meniscus tears more commonly than the lateral meniscus. Patients typically describe catching and locking in addition to pain.
    • Diagnosis
      • On physical exam there is typically medial/lateral joint line tenderness and a positive McMurray Test. In this test the examiner performs internal and external rotation of tibia while extending the knee starting from full flexion, resulting in pain or popping when there is a lateral or medial meniscus tear, respectively.
  • MCL Tear
    • MCL tears commonly occur as a contact injury where a valgus force is applied to the knee. On physical examination there is typically tenderness to palpation medially and laxity to valgus stress with the knee in slight flexion (about 30 degrees).
  • LCL Tear
    • This commonly occurs as a contact injury where a varus force is applied to the knee. On physical examination there is typically tenderness to palpation laterally and laxity to varus stress with the knee in slight flexion (about 30 degrees).
Further Reading
  • Miller, Mark D., Stephen R. Thompson, and Jennifer Hart. Review of orthopaedics. Elsevier Health Sciences, 2012.
  • Thompson, Jon C. Netter's concise orthopaedic anatomy. Elsevier Health Sciences, 2009.
  • Miyasaka, K. C., et al. "The incidence of knee ligament injuries in the general population." Am J Knee Surg 4.1 (1991): 3-8.


To cite this article
Qadeer, AA, “Knee Ligaments and Tears” in Pathway Medicine: An Introduction to Clinical Medicine", PathwayMedicine.org (2015).