Knee ligament injuries

Last updated: September 18, 2023

Summarytoggle arrow icon

Knee ligament injuries are often the result of rotational movement of the knee joint or direct trauma. 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 can be used to evaluate the stability of the joint and usually suffice to diagnose collateral ligament tears. An MRI is the best confirmatory test for cruciate ligament tears. Isolated ligament injuries are usually treated conservatively, while surgery is recommended for complex injuries, severe knee instability, and patients with physically demanding occupations.

Tibiofemoral joint dislocation is usually caused by high-energy trauma and is considered an orthopedic emergency. Immediate reduction is indicated to prevent neurovascular damage. Following reduction, a full neurovascular assessment must be performed in all patients, which includes a detailed neurovascular exam, measurement of the ankle-brachial index, and, if vascular injury is suspected, a CT angiogram.

Anatomical overviewtoggle arrow icon

Acute internal knee derangementtoggle arrow icon

Description [1]

Initial management [1][2][3]

Empiric management is often necessary as the clinical diagnosis of specific knee ligament injuries is limited acutely. The initial goal is to identify and treat potentially disabling or limb-threatening injuries.

All patients

Acute pain and swelling can make ligamentous and/or meniscal injury difficult to identify clinically. Repeat examination and confirmatory testing (e.g., MRI) in follow-up settings is typically appropriate. [3]

Specific injury suspected

Avoid knee immobilizers in isolated ligamentous injuries, as these can negatively affect treatment outcomes by decreasing quadriceps strength. Instead, use an unlocked hinged knee brace. [3]

Ottawa knee rules [4][5]

This clinical decision rule can be used to help determine when knee x-rays are indicated for emergency department (ED) patients with knee injuries. [3]

  • Inclusion criteria: nonpregnant adults ≥ 18 years of age with acute knee pain ≤ 7 days after injury
  • Exclusion criteria
  • Risk features: Any of the following is an indication for a full knee x-ray series.
    • Age ≥ 55 years
    • Fibular head or isolated patellar tenderness
    • Inability to flex knee to ≤ 90 degrees
    • Inability to weight bear for 4 steps immediately after injury and in the ED

Cruciate ligament injuriestoggle arrow icon

Overview [3]

Both ACL injury and PCL injury may present initially as acute internal knee derangement, reducing the yield of physical examination maneuvers. The diagnosis is typically confirmed via MRI, which can have variable findings depending on the mechanism and associated injuries.

Comparison of ACL and PCL injury [3]
ACL injury PCL injury
Relative frequency
  • More common
  • Less common
Classic mechanism
Distinguishing clinical features
  • Popping sound
  • Knee pain
  • Decreased ability to bear weight
Positive physical examination maneuvers
Definitive treatment
  • Conservative treatment: suitable for patients with mild instability, older age, or a sedentary lifestyle
  • Surgical treatment: appropriate for competitive athletes, concomitant meniscal or collateral ligament injury, or chronic knee instability
  • Conservative treatment: used for isolated injury; most common treatment pathway
  • Surgical treatment: appropriate for multiligament injury, chronic knee instability, or competitive athletes

Complications of cruciate ligament injuries [6][7]

  • Chronic knee instability
  • Meniscal degeneration
  • Osteoarthritis
  • Functional limitation
  • Postoperatively: graft failure, graft impingement

Anterior cruciate ligament injurytoggle arrow icon


Mechanism of injury [3]

  • Low-energy noncontact: sports injuries with a twisting mechanism, e.g., football, soccer, basketball, baseball, alpine skiing, and gymnastics [10]
  • High-velocity contact injuries (less common): direct blows to the knee causing forced hyperextension or valgus deformity of the knee

Clinical features [3]

  • History
    • Popping sound: commonly heard shortly before the onset of symptoms
    • Knee buckling: episodic giving out and loss of ability to bear weight
    • Difficulty getting up and moving
  • Physical examination findings
    • Knee swelling (e.g., due to hemarthrosis), pain, and instability [3]
    • Positive Lachman test (most sensitive test)
    • Positive anterior drawer test
    • Positive pivot shift test [11]
      • 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 anteriorly subluxed lateral tibial plateau jerks backward at 30° of knee flexion.
  • Commonly associated injuries

Consider deferring physical examination maneuvers in the acute setting as pain and swelling may limit their usefulness. [2]

Diagnostics [3][9]

If MRI is not readily available, a provisional clinical diagnosis of ACL injury can be made if physical examination maneuvers are feasible and reliable.

Treatment [3][6][12]

For immediate management following injury, see “Acute internal knee derangement.”


See “Complications of cruciate ligament injuries.”

Posterior cruciate ligament injurytoggle arrow icon

Mechanism of injury [14]

Clinical features [3][14]

Consider deferring physical examination maneuvers in the acute setting as pain and swelling may limit their usefulness. [2]

Diagnostics [3][14]

If MRI is not readily available, a provisional clinical diagnosis of PCL injury can be made if physical examination maneuvers are feasible and reliable.

Treatment [3][14]

For immediate treatment following injury, see “Acute internal knee derangement.”


See “Complications of cruciate ligament injuries.”

Collateral ligament injurytoggle arrow icon


Overview of collateral ligament injuries [3]

Medial collateral ligament injury Lateral collateral ligament injury

Mechanism of injury

Associated injuries
Distinguishing clinical features

MCL injuries are more common than LCL injuries.

Clinical features [3]


The degree of joint laxity is graded based on the estimated size of lateral joint space during the valgus stress test or varus stress test. [15]

  • Grade I: 3–5 mm (mild instability)
  • Grade II: 6–10 mm (moderate instability)
  • Grade III: > 10 mm (severe instability; other knee ligaments may be injured)

Diagnostics [3]

Treatment [3]

For immediate management, see “Acute internal knee derangement.”

Tibiofemoral joint dislocationtoggle arrow icon

Mechanism of injury [3]

Usually caused by high-energy trauma (e.g., dashboard injury, fall from a height)

Clinical features [3]

Maintain a high level of suspicion for vascular injury, as popliteal artery injury may be present despite palpable pulses. [3]

Management [3]

See also “Acute internal knee derangement” for the approach to an undifferentiated knee injury.

Knee dislocation is an orthopedic emergency requiring immediate reduction to prevent limb-threatening neurovascular injury. [3]

Knee dislocations frequently reduce spontaneously before presentation to the emergency department. Neurovascular evaluation is mandatory in all patients with a relevant lower extremity injury mechanism (see “Mechanism of injury”). [3]

Complications [18]

Referencestoggle arrow icon

  1. Walls R, Hockberger R, Gausche-Hill M, Erickson TB, Wilcox SR. Rosen's Emergency Medicine 10th edition- Concepts and Clinical Practice E-Book. Elsevier Health Sciences ; 2022
  2. Micheo W, Hernández L, Seda C. Evaluation, Management, Rehabilitation, and Prevention of Anterior Cruciate Ligament Injury: Current Concepts. PM&R. 2010; 2 (10): p.935-944.doi: 10.1016/j.pmrj.2010.06.014 . | Open in Read by QxMD
  3. Sepúlveda F, Sánchez L, Amy E, Micheo W. Anterior Cruciate Ligament Injury. Curr Sports Med Rep. 2017; 16 (3): p.172-178.doi: 10.1249/jsr.0000000000000356 . | Open in Read by QxMD
  4. Reckling FW, Peltier LF. Acute Knee Dislocations and Their Complications. Clin Orthop Relat Res. 2004; 422: p.135-141.doi: 10.1097/01.blo.0000131737.72363.7e . | Open in Read by QxMD
  5. Walker REA, McDougall D, Patel S, Grant JA, Longino PD, Mohtadi NG. Radiologic Review of Knee Dislocation: From Diagnosis to Repair. American Journal of Roentgenology. 2013; 201 (3): p.483-495.doi: 10.2214/ajr.12.10221 . | Open in Read by QxMD
  6. Peskun CJ, Levy BA, Fanelli GC, et al. Diagnosis and Management of Knee Dislocations. Phys Sportsmed. 2010; 38 (4): p.101-111.doi: 10.3810/psm.2010.12.1832 . | Open in Read by QxMD
  7. Pache S, Aman ZS, Kennedy M, et al. Posterior Cruciate Ligament: Current Concepts Review.. The archives of bone and joint surgery. 2018; 6 (1): p.8-18.
  8. Bunt CW, Jonas CE, Chang JG. Knee Pain in Adults and Adolescents: The Initial Evaluation. Am Fam Physician. 2018; 98 (9): p.576-585.
  9. 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
  10. 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
  11. Dordevic M, Hirschmann MT. Injury Mechanisms of ACL Tear. Springer Berlin Heidelberg ; 2014: p. 49-53
  12. Benjaminse A, Gokeler A, van der Schans CP. Clinical Diagnosis of an Anterior Cruciate Ligament Rupture: A Meta-analysis. Journal of Orthopaedic & Sports Physical Therapy. 2006; 36 (5): p.267-288.doi: 10.2519/jospt.2006.2011 . | Open in Read by QxMD
  13. Cimino F, Volk BS, Setter D. Anterior cruciate ligament injury: diagnosis, management, and prevention.. Am Fam Physician. 2010; 82 (8): p.917-22.
  14. 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.
  15. Phisitkul P, James SL, Wolf BR, Amendola A. MCL injuries of the knee: current concepts review.. Iowa Orthop J. 2006; 26: p.77-90.
  16. Grover M. Evaluating acutely injured patients for internal derangement of the knee.. Am Fam Physician. 2012; 85 (3): p.247-52.
  17. Stiell IG, Greenberg GH, Wells GA, et al. Derivation of a Decision Rule for the Use of Radiography in Acute Knee Injuries. Ann Emerg Med. 1995; 26 (4): p.405-413.doi: 10.1016/s0196-0644(95)70106-0 . | Open in Read by QxMD
  18. Sims JI, Chau MT, Davies JR. Diagnostic accuracy of the Ottawa Knee Rule in adult acute knee injuries: a systematic review and meta-analysis. Eur Radiol. 2020; 30 (8): p.4438-4446.doi: 10.1007/s00330-020-06804-x . | Open in Read by QxMD

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