Knee ligament injuries

Last updated: June 27, 2022

Summarytoggle arrow icon

Knee ligament injuries are often the result of rotational movement of the knee joint (e.g., cutting and pivoting movements in sports). Injuries to the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL) result in knee pain and instability. Various maneuvers aid in demonstrating knee instability and are usually sufficient for the diagnosis of collateral ligament tears. An MRI is the best confirmatory test for cruciate ligament tears. Isolated ligament injuries are usually treated conservatively, but surgery is recommended for complex injuries, severe knee instability, and patients with physically demanding occupations.


Mechanism of injury

  • Low-energy noncontact: sports injuries with a twisting mechanism, e.g., football, soccer, basketball, baseball, alpine skiing, and gymnastics [3]
  • High-velocity contact injuries (less common): direct blows to the knee causing forced hyperextension or valgus deformity of the knee

Clinical features

  • History: Patients often report a popping sound shortly before the onset of symptoms.
  • Physical examination findings
    • Knee swelling (e.g., due to hemarthrosis), pain, and instability
    • Positive Lachman test (most sensitive test)
    • Positive anterior drawer test
    • Positive pivot shift test
      • With full extension of the knee joint, the examiner slowly flexes the knee while applying valgus stress with one hand and internally rotating the tibia with the other.
      • If the ACL is torn, the tibial plateau jerks backward at 30° of knee flexion.
  • Commonly associated injuries




  • Mechanism of injury
    • Noncontact injury involving hyperflexion of the knee with a plantarflexed foot (seen in athletes)
    • Direct posterior blow to a flexed knee, seen in motor vehicle accidents (dashboard injury) or athletic contact injury
    • Rotational injury involving hyperextension of the knee (rare)
  • Clinical features
    • Initially vague symptoms: minimal (or absent) posterior knee pain, swelling, decreased functional range of motion
    • Positive posterior drawer test
    • Positive posterior sag sign
      • The patient lies down with both hips and knees flexed and aligned together.
      • In this position, the tibia on the side of the torn PCL will appear to fall backwards under the influence of gravity.
    • Positive quadriceps active test
      • The patient is placed in supine position with the knee flexed at 90° with the foot flat on the bed.
      • The patient is asked to contract the quadriceps which, if there is PCL injury, should move the tibia forward.
      • If the tibia moves forward by more than 2 mm, then the test is positive.
    • Positive posterolateral drawer test
      • The patient is sitting on the edge of the examining table (thighs supported) with the legs hanging over the floor.
      • A posterior drawer test is performed which moves the lateral tibial plateau posteriorly around the axis of the PCL.
  • Diagnostics
  • Treatment

Overview of collateral ligament injuries
Medial collateral ligament injury Lateral collateral ligament injury
Mechanism of injury
Associated injuries
Clinical features
  • Conservative (functional brace and physical therapy) for isolated tears
  • Surgery if associated injuries are present.

MCL injuries are more common than LCL injuries.

Knee dislocations are frequently associated with severe neurovascular injuries and should be treated immediately.


  1. Mohseni M, Simon LV. Knee Dislocation. StatPearls. 2021 .
  2. Mall NA, Chalmers PN, Moric M, et al. Incidence and Trends of Anterior Cruciate Ligament Reconstruction in the United States. Am J Sports Med. 2014; 42 (10): p.2363-2370. doi: 10.1177/0363546514542796 . | Open in Read by QxMD
  3. Musahl V, Karlsson J. Anterior Cruciate Ligament Tear. N Engl J Med. 2019; 380 (24): p.2341-2348. doi: 10.1056/nejmcp1805931 . | Open in Read by QxMD
  4. Dordevic M, Hirschmann MT. Injury Mechanisms of ACL Tear. Springer Berlin Heidelberg ; 2014 : p. 49-53
  5. Bousquet BA, O'Brien L, Singleton S, Beggs M. POST-OPERATIVE CRITERION BASED REHABILITATION OF ACL REPAIRS: A CLINICAL COMMENTARY.. International journal of sports physical therapy. 2018; 13 (2): p.293-305.
  6. Phisitkul P, James SL, Wolf BR, Amendola A. MCL injuries of the knee: current concepts review.. Iowa Orthop J. 2006; 26 : p.77-90.

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