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The medial collateral ligament (MCL) and lateral collateral ligament (LCL) serve as stabilizers of the knee, providing both mediolateral stability as well as some degree of rotational stability. Injury to a ligament occurs when external forces applied to the knee overwhelm its integrity, either in isolation or in combination with other structures (i.e., other ligaments, bone, or menisci).


MCL injuries occur as a result of an excessive valgus load and/or external tibial rotation. The femoral attachment experiences the greatest stress with valgus loads. Isolated LCL injuries result from an excessive varus load to the knee. At 30 degrees of knee flexion, the LCL serves as the primary stabilizer against varus stress. Both MCL and LCL injuries typically occur in contact, cutting, and collision sports (i.e., football and soccer) or in sports where high torque forces can be generated about the knee (i.e., skiing and ice skating).

Epidemiology including risk factors and primary prevention

Ligament sprains are the most common type of knee injury.1 The MCL and anterior cruciate ligament (ACL) are the most commonly sprained knee ligaments. The MCL is injured in at least 42% of ligamentous knee injuries, with isolated MCL injuries accounting for 29% of these injuries alone.1 In the U.S. population, the incidence of MCL injury is 0.24/1000 people or 74,000 injuries annually.2 MCL sprain is the most common knee injury in high school athletes.  In young athletes, one study found that females have a higher rate of MCL injury at the high school level, while males have a higher rate of MCL injury at the college level. However, there is no significant sport-specific sex disparity with MCL injuries in a given sport.3 MCL injuries tend to occur with higher rates in contact sports such as American football, soccer, hockey, and rugby. Although not a contact sport, skiing has marked prevalence as well, with 60% of all skiing-related injuries linked to MCL and LCL injuries.4

MCL injuries are more common than LCL injuries. Isolated LCL injuries are rare, accounting for only 2% of knee ligament injuries.1 LCL injuries are more commonly associated with a more profound injury to the knee, often involving the posterolateral corner structures in adults.

Prophylactic knee orthoses, which implement a lateral knee guard to support the MCL from valgus stress, have been commonly used in contact sports, including American football.5 Some studies suggest reduced MCL injury rates with the use of prophylactic knee bracing; however, high quality evidence is lacking.6    


The MCL is composed of a superficial layer and a deep layer. Proximally, the superficial layer attaches just posterior to the medial femoral epicondyle while its distal attachment is approximately 6 cm beyond the medial tibial plateau. The deep layer is a thickening of the joint capsule itself; it is composed of the meniscofemoral and meniscotibial components. Isolated MCL injuries typically involve the proximal fibers of the superficial layer. Because the MCL is extra-articular, isolated MCL injuries may have medial knee swelling without intra-articular effusion.

The LCL originates proximally just posterior to the lateral femoral condyle and attaches distally to the proximal portion of the fibula in a conjoined fashion with the biceps femoris tendon. Isolated LCL sprains occur as a result of excessive varus loading of the knee. Avulsion of the LCL off the fibula usually signifies a concomitant posterolateral corner injury.

Collateral ligament sprains are graded:

  • Grade 1: pain along ligament, no instability or gapping of joint with stress testing
  • Grade 2: partial gapping (5-10 mm) of joint with stress testing at 30 degrees of knee flexion
  • Grade 3: wide gapping (>10 mm) of joint at 30 degrees of knee flexion (no end feel)

Disease progression including natural history, disease phases or stages, disease trajectory (clinical features and presentation over time)

The prognosis of an isolated MCL or LCL injury is typically good; both injuries can generally be treated non-operatively though research has shown that the LCL does not heal quite as well as the MCL.7 Initially the knee may be swollen and painful, which may limit range of motion. The quadriceps muscle may become inhibited secondary to pain and swelling. During the sub-acute phase, pain and swelling resolve and ligamentous laxity improves. Progression through the rehabilitation process will parallel these improvements. Return to play can be estimated as follows: grade 1 (approx. 10 days), grade 2 (approx. 20 days), grade 3 (approx. 60 days).8 In a cohort study of athletes with isolated MCL sprains, the average amount of time lost per injury was 23.2 days.4

Grade 1 and 2 MCL injuries are usually treated conservatively unless another co-occurring injury is present that is more severe and warrants surgery. Recovery for grade 1 and 2 MCL injuries undergoing conservative management is typically effective. Surgical repair of an isolated MCL injury is indicated in grade 3 tears with valgus instability, MCL entrapment over pes anserinus, intra-articular or bony avulsion, or failed conservative treatment. Surgical repair may be indicated acutely in the case of an avulsed ligament or with a grade 3 isolated LCL injury with persistent varus instability despite conservative treatment.

Specific secondary or associated conditions and complications

Collateral ligament injuries can be associated with cruciate ligament sprains or tears, meniscal tears, capsular avulsion injuries, fractures or bony contusions, patellar or tibiofemoral knee dislocations, and complex multi-structure injuries occurring along the corners of the knee. Combined injuries may require operative repair to stabilize the knee. Failure to recognize these more complex injuries can lead to chronic instability, weakness, repeated soft tissue injury, and, ultimately, post-traumatic arthritis.

Essentials of Assessment


  • Mechanism of injury: Did the injury occur with twisting or      cutting or with a direct blow to the knee? Location of impact?
  • Ability to continue with participation in activity immediately after injury
  • Location of swelling and/or bruising and time course of swelling.
  • Exacerbating and alleviating factors
  • Mechanical symptoms, such as instability or a locked joint
  • Neurovascular symptoms

Physical examination

  • Observation and inspection of joint for obvious deformity
  • Inspection and palpation of joint: assess effusion and tenderness
  • Active and passive range of motion of hip, knee, and ankle
  • Valgus and varus stress testing of the knee at 30 degrees to isolate stress to collateral ligaments
    • grade 1 injury: firm end point
    • grade 2 injury: firm end point with minor opening of joint
    • grade 3 injury: soft/no end point with significant opening of joint
  • Valgus and varus stress testing at 0 degrees: lack of a firm end point in this position indicates injury to the collateral ligament plus additional ligamentous structures such as cruciate ligament or corner injury.
  • Neurovascular examination of lower extremities
  • Gait: ability to bear weight

Functional assessment

Acutely after injury, ambulation may be limited secondary to pain and swelling. The patient may also report knee instability with ambulation. As the condition improves, the range of motion and gait normalize.


Radiographs (A-P, lateral, and sunrise views) are generally ordered to assess for fractures. In chronic MCL tears, there may be evidence of a calcification of the proximal MCL (Pellegrini-Stieda Syndrome). Stress radiograph may be obtained to evaluate for instability. Stress radiographs for an MCL injury may be completed with valgus stress at 20 degrees of flexion to help visualize a gap that can help with ligament grading9

  • < 3.2 mm = no injury or grade 1-2 injury
  • 3.2-9.8 mm = grade 3 superficial MCL tear
  • > 9.8mm = complete tear of both MCL layers and the posterior oblique ligament
  • >27.6 mm = complete medial knee injury with both cruciate ligament tears

Others have suggested utilizing the Ottawa knee rules to guide the decision to obtain radiographs in a suspected MCL or LCL injury. According to these rules, a radiographic knee series is only indicated if one or more of the five criteria below are met.10    

  • Patient age ≥ 55 years
  • Isolated tenderness of the patella
  • Tenderness at the head of the fibula
  • Inability to flex knee to 90o
  • Inability to bear weight both immediately and in the emergency department for 4 steps

Magnetic resonance imaging (MRI) may be used for confirmation of the injury, its location and severity, and concomitant injuries. MRI has an 86.4% sensitivity in identifying an MCL injury; however, MRI is generally not necessary unless there is concern for associated injuries or surgical repair is being considered.11 For lateral knee injuries, identification of involved posterolateral corner structures is generally difficult. Thus, MRI is often used to assist in identifying the injured structures. However, this comes with its own limitations as some studies have shown that MRI has only a 55% sensitivity for identifying LCL injuries.12

Recently, ultrasonography has become a popular tool deployed in clinical practice for its quick and cost-effective approach for assessing the collateral ligaments of the knee. Under direct visualization the ligaments can be stressed at 30 degrees of knee flexion. Medial joint line opening can be objectively measured to aid in grading injury: 0-5mm = grade 1; 6-10mm = grade 2; >10mm = grade 3.13 Notably, ultrasound evaluation of the collateral ligaments does have limitations as some studies have suggested that ultrasonography has sensitivity of 52.5% and specificity of 84.15% for identifying MCL and LCL injuries. It is also important to note that diagnostic ultrasound is dependent on the sonographer’s skills which can impact its clinical utility.14

Supplemental assessment tools

Utilizing functional measures of the knee that include strength, hop, and quality of movement testing can assist with deciding if the knee has fully recovered. Functional measures may include isokinetic testing, functional movement screening, Y-balance test, triple-hop test, and landing error scoring system.15 There is no standard for return to play testing for collateral ligament injury; however, some measures such as strength, hop, and quality of movement testing have been validated specifically for post-ACL reconstruction rehabilitation.16    

Early predictions of outcomes

Isolated collateral ligament injuries generally have a good natural history with non-operative management, allowing for full return to participation in the majority of cases. Lower grade injuries are associated with quicker recovery periods. Multi-structure injuries may warrant additional investigative studies (i.e., MRI) and potential need for operative intervention.

Although most medial collateral ligament injuries are treated non-operatively, it is important to be aware of special situations involving complete disruption that may require operative intervention.  Indications for operative treatment include17

  • A large bony avulsion
  • A concomitant tibial plateau fracture
  • Associated cruciate ligament injury
  • Intra-articular entrapment of the end of ligament.


Collateral ligament injuries typically occur in contact and collision sports such as American football, soccer, and ice hockey where the participant is vulnerable to sudden unexpected blows to the knee. Sports such as skiing may expose the knee to excessive rotation forces, injuring portions of the MCL via a non-contact mechanism.

Social role and social support system

Isolated collateral ligament injuries rarely result in long-term disability. If chronic instability and pain result, the patient may not be able to resume prior level of sports/activity or employment. In these instances, referral to psychology for adjustment and/or vocational rehabilitation may be warranted.

Professional issues

Isolated knee collateral ligament injuries generally heal with non-operative management over a course of weeks to months. During the recovery period the patient will need to be removed from the offending activity to allow the ligament to adequately heal. Length of recovery is generally related to the severity of the ligament injury.

Rehabilitation Management and Treatments

Available or current treatment guidelines

Acute injuries are generally managed with weight bearing as tolerated. Bracing of the joint may be performed initially, depending on degree of instability or presence of valgus/varus angulation of the knee joint. P.R.I.C.E (Protect, Rest, Ice, Compression, Elevation) principles are employed initially along with early restoration of joint motion. Non-steroidal anti-inflammatory drugs (NSAIDs) can be used as well to help control pain and inflammation.

Quadriceps and hamstring strengthening exercises are progressed from open chain isometric to isotonic exercises as tolerated. Aerobic exercise is resumed as soon as tolerated, often starting with stationary bike and progressing to other single plane low impact exercises and eventually straight line jogging. Once pain is reduced and strength is 80% of the contralateral side, closed chain strengthening exercises are initiated. As joint stability normalizes, neuromuscular/agility training is initiated in preparation for return to play/activity.8

At different disease stages

Isolated collateral ligament injuries regardless of grade generally heal and patients can expect to resume their prior level of activity. Questions still remain regarding the need for bracing upon return to sports/activity. Studies reveal that off-the-shelf knee braces can reduce loading of the MCL and rate of injury among certain positions in football4; however, prophylactic bracing is controversial given the concern for compromised athletic performance when wearing the brace.18 Commonly after a MCL injury is sustained, patients are prescribed a functional or rehabilitative knee orthosis. Grade 1 MCL injuries can be treated without knee bracing; however, grade 2 and 3 MCL injuries typically benefit from wearing a brace for 3 to 6 weeks.19

Patients with ongoing pain, swelling, or mechanical symptoms may have associated injuries such as meniscal tears or other ligamentous injuries. These cases may warrant further evaluation to identify the source of their ongoing impairment. In the case of an acute multi-ligament injured knee or a chronically unstable knee with persistent medial laxity, surgical repair of the collateral ligaments may be indicated. For multi-ligament injuries involving both the ACL and MCL, early ACL reconstruction and MCL repair are recommended when there is increased medial joint space opening with valgus stress in extension, a significant meniscotibial deep MCL injury, or a displaced tibial-sided superficial MCL avulsion.20    

Coordination of care

A detailed rehabilitation protocol should be developed and effectively communicated to the treating physical therapist or athletic trainer. Follow-up visits with the patient should occur during transition periods within the protocol to ensure that the patient is progressing as expected.

Patient & family education

The patient and family should be advised that the natural history of isolated collateral ligament(s) injury is good. However, premature resumption of sports/activity may stress the healing ligament too soon and lead to chronic instability and pain. The patient should return to sports when laxity has resolved, and sport/activity specific maneuvers can be performed without pain or instability.

Emerging/unique interventions

Patient outcomes can be measured with the Tegner Lysholm Knee Scoring Scale. This scoring system assesses pain, instability symptoms, and functional limitations.21 This measurement outcome can be used clinically or for research purposes. Return to play/activity is empirically driven and based on reduction in pain, resolution of ligamentous laxity, and presence of full joint range of motion and strength. Functional assessment prior to returning an athlete to play should be performed by a physical therapist and/or athletic trainer to ensure sport/activity-related maneuvers can be performed without pain or instability.

Translation into practice: practice “pearls”/performance improvement in practice (PIPs)/changes in clinical practice behaviors and skills

Early initiation of a rehabilitation protocol focusing on restoration of motion, weight bearing as tolerated, and a graduated strength and condition program lead to more efficient recovery and return to sport/activity. Newer animal studies show evidence that NSAIDs may impair the healing of ligamentous tissue; as a result, one should consider limited use of these medications.22

Cutting Edge/Emerging and Unique Concepts and Practice

Regenerative medicine techniques, including prolotherapy and protein-rich plasma (PRP), are being used to enhance healing of ligamentous structures through direct injection of substances into an injured ligament. Unfortunately, there is no robust evidence to support these techniques in medial collateral ligament and lateral collateral ligament injuries of the knee.

Prolotherapy or proliferative therapy consists of injection of substances such as dextrose, Sarapin, procaine, and lidocaine. A single case study using prolotherapy treatment showed improvement in a rugby player’s grade 2 MCL sprain in just 3 weeks, at which time he was pain free and with full range of motion. Injections of 15% dextrose and 0.2% lidocaine were used. This three-week recovery was compared to a typical four to eight week recovery for grade 2 MCL sprain.23

PRP studies in animal models have shown mixed results with regards to early MCL injury healing over the first three to six weeks post-injury.24,25 Clinical studies using PRP for ligament injuries have shown some positive outcomes including improved pain and function.26 In one case report, a football player with an isolated Grade 3 MCL injury received three injections of LR-PRP with 1-week intervals and was followed for 16 months. The football player resumed sports activities at day 18, and full competition at day 25.27 A similar case report consisted of a football player with a proximal grade 3 MCL injury who returned to sport at 31 days following a similar protocol.28 In a recent case report29 and a case series of three subjects,30 PRP was used for treatment of persistently painful chronic MCL injuries and resulted in successful return to physical activity and evidence of healing documented on MRI. Separately, there is even less exploration of PRP injections for LCL injuries. A single case report demonstrated significant positive outcomes in an active duty military male officer.31

Gaps in the Evidence-Based Knowledge

  • Can braces be developed that protect against knee injuries?
  • Can exercise interventions and educational programs reduce the rate of knee injuries?
  • Is there a role for regenerative therapies in the treatment of ligament injuries?
  • Is reconstruction of the MCL necessary in the treatment of a multi-ligament knee injury?


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  13. Jacobson JA. Fundamentals of Musculoskeletal Ultrasound. Philadelphia: Saunders; 2007.
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  26. Taylor DW, Petrera M, Hendry M, and Theodoropoulos JS. A systematic review of the use of platelet-rich plasma in sports medicine as a new treatment for tendon and ligament injuries. Clinical Journal of Sport Medicine. 2011; 21(4): 344-352. doi:10.1097/JSM.0b013e31821d0f65.
  27. Eirale C, Mauri E, and Hamilton B. Use of platelet rich plasma in an isolated complete medial collateral ligament lesion in a professional football (soccer) player: A case report. Asian J Sports Med. 2012;4(2):158-162. doi:10.5812/asjsm.34517.
  28. Bagwell MS, Wilk KE, Colberg RE, Dugas JR. The use of serial platelet rich plasma injections with early rehabilitation to expedite grade III medial collateral ligament injury in a professional athlete: a case report. Int J Sports Phys Ther. 2018 Jun;13(3):520-525. PMID: 30038838; PMCID: PMC6044600.
  29. Zou G, Zheng M, Chen W, He X, Cang D. Autologous platelet-rich plasma therapy for refractory pain after low-grade medial collateral ligament injury.
  30. Yoshida M, Marumo K. An autologous leukocyte-reduced platelet-rich plasma therapy for chronic injury of the medial collateral ligament in the knee: a report of 3 successful cases. Clin J Sport Med. 2019;29(1):e4-e6.
  31. Castle CD, Dunderdale CM, Patzkowski JC, Carius BM. Platelet-Rich Plasma Improves Strength and Speed of Recovery in an Active-Duty Soldier with Isolated Injury to the Lateral Collateral Ligament of the Knee: A Case Report. Med J (Ft Sam Houst Tex). 2023 Apr-Jun;(Per 23-4/5/6):17-19. PMID: 37042501.

Original Version of the Topic

Robert Irwin, MD, Michelle D. Francavilla, MD. Medial and lateral collateral ligament injuries. 12/28/2012

Previous Revisions of the Topic:

Daniel Herman, MD, Justin Weppner, DO, Sara Raiser, MD. Medial and lateral collateral ligament injuries. 8/16/2016

Sara Raiser, MD, Daniel Herman, MD, PhD, Justin Weppner, DO. Medial and lateral collateral ligament injuries. 3/11/2021

Author Disclosures

Sara Raiser, MD
Nothing to Disclose

Kevin Mesina, MD
Nothing to Disclose

Alaric Gee, DO
Nothing to Disclose

Justin Weppner, DO
Nothing to Disclose

Daniel Herman, MD, PhD
Nothing to Disclose