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Collateral ligament injuries of the knee


The medial and lateral collateral ligaments are important stabilizers of the knee joint. Injury can occur in isolation or in concert with multiligamentous injuries and severe knee dislocations. The evaluation of collateral ligamentous integrity is essential following any knee injury, as damage to the collaterals can cause significant instability to varus and valgus stress. Furthermore, unrecognized collateral ligament injury can have a negative impact on the surgical outcomes of anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) reconstructions.

Medial collateral ligament (MCL) injuries are relatively common in isolation and in combination with ACL injuries. Lateral collateral ligament (LCL) injuries are extremely rare in isolation and are usually seen with posterolateral corner (PLC) injuries and multiligamentous knee injuries. For this reason, the majority of this chapter will deal with MCL injuries, with some discussion of the anatomy and function of the LCL.

Structure and function

The MCL provides stability to valgus stress and resists external rotation in concert with the ACL. The MCL is typically divided into separate superficial and deep structures.

  • The superficial MCL, also known as the tibial collateral ligament, attaches proximally to the medial femoral condyle and distally on the proximal metaphysis of the tibia. This distal insertion lies 4 to 5 cm distal to the pes anserine insertion. The superficial MCL contributes approximately 50% of medial knee stability at 5 degrees of flexion and increases to 80% of stability at 25 degrees of flexion.  The superficial MCL combines with the posteromedial bundle of the ACL to resist external rotator y forces.
  • The deep MCL, a thickening of the medial joint capsule, is subdivided into meniscotibial and meniscofemoral components. The deep MCL originates and inserts just proximal and distal to the joint line, respectively.  It is a secondary stabilizer in full extension only, with minimal contribution to stability with flexion. The posterior oblique ligament (POL), a separate structure from the MCL, is a fibrous extension of the semimembranosus muscle that blends with and reinforces the posteromedial joint capsule and plays an important role in medial stability. More severe injuries are associated with a combined tear of the MCL and POL.

The LCL is the primary static lateral restraint to a varus stress at the knee.  The femoral origin is normally found just posterior and proximal to the lateral epicondyle of the femur. Distally, the LCL inserts onto the anterolateral fibular head. The LCL provides varus stability throughout range of motion of the knee but is most significant at 30 degrees of flexion. The individual ultimate strength of the LCL is estimated at a force of 295 Newtons. Similar to the medial aspect of the knee, additional rotatory and dynamic soft tissue stabilizers are found laterally and include the IT band, popliteus, and popliteofibular ligaments.


The MCL is the most commonly injured knee ligament, with an incidence of 0.24 per 1,000 in the U.S. The majority of medial-sided injuries occur in isolation; however, MCL injuries are also found commonly with ACL injuries. MCL injuries are most commonly found in young individuals participating in athletics.

 As mentioned previously, isolated LCL tears are very rare. Combined LCL and posterolateral corner injuries are seen in severe knee dislocations and high energy trauma.

Clinical presentation

The mechanism of injury to the MCL and the POL typically involves a contact valgus force with or without external rotation. Localized pain, swelling, and ecchymosis along the medial aspect of the knee are typical of an isolated MCL injury. Rupture usually occurs at the proximal femoral aspect. A large knee effusion is not normally found with an isolated MCL tear, as the superficial MCL is extra-capsular.

Physical examination of the knee following an acute injury can be difficult due to patient guarding. Palpation of the origin and insertion of the MCL can reveal tenderness. A fully relaxed patient is essential to assess ligamentous integrity. A complete ligamentous exam to rule out concomitant injury is paramount as MCL tears are often associated with ACL injuries. To isolate the MCL on exam, the knee is flexed to 30 degrees and a valgus load is applied. The amount of medial opening as well as presence or absence of a hard endpoint is documented. The injury is graded based on the amount of opening:

  • Grade 1: < 5mm
  • Grade II: 5-10 mm
  • Grade III: >10 mm

A valgus load is also applied with the knee in full extension. This tests the integrity of the MCL and the POL. The contralateral knee is used for comparison.  A complete rupture has a "soft" endpoint.

Differential diagnosis

In any acutely injured knee, a thorough ligamentous exam should be performed if possible. The differential diagnosis includes:

  • Patella dislocation
  • Fracture
  • ACL/PCL injury
  • PLC injury
  • Medial meniscus tear
  • Extensor mechanism rupture

A large knee effusion should alert the examiner to the possibility of injury to the cruciate ligaments. Anterior drawer and Lachman’s exam are performed to evaluate the integrity of the ACL. Patella dislocation and subluxation can present with medial sided knee pain and an unclear history that may be difficult to differentiate from an MCL injury. Careful palpation of the attachment sites of the MCL should be performed. A patient with patella dislocation will have additional risk factors seen on exam and imaging. Mobility of the patella, patellar apprehension, and description of the injury mechanism can be used to assess for patellar dislocation. The patient should be able to perform a straight leg raise to rule out rupture of the extensor mechanism.

Objective evidence

Radiographs are indicated in any acutely painful, swollen knee to rule out fractures and bony pathology. A bony avulsion at either insertion site of the MCL is uncommon but may be seen on plain films. Stress views, not commonly peformed, can be ordered to verify the amount of medial or lateral opening. MRI is the key imaging study to assess integrity of the collateral ligaments as well as intra-articular ligamentous injury. Injury is indicated by high signal intensity on T2 sequences. Retraction of the ligament can be seen with complete rupture. Characteristic bone bruising on the lateral aspect of the femur and tibia may also be seen on T2 sequences.

Risk factors and prevention

Most Grade II and Grade III MCL injuries result from a valgus force applied laterally near the knee. Logically, this most commonly occurs in contact sports such as football, hockey, rugby, and soccer. Extreme rotation can also cause injury and is seen in skiers and snowboarders. The MCL is the only structure in the knee that has been shown in the literature to be protected by prophylactic bracing. This is the basis for prophylactic knee bracing seen in college and NFL lineman.

Treatment options

Isolated grade I and II MCL injuries do well with non-surgical treatment. This includes early protected motion and functional rehabilitation focusing on quadriceps strengthening. A hinged knee brace is used for stability. Proximal MCL injuries have better outcomes with conservative management than distal injuries. Acute grade III injuries are also usually given a trial of functional rehabilitation. Surgical treatment is indicated in cases of chronic MCL laxity that interferes with daily activities or sports participation. Surgical options include direct repair or reconstruction with augmentation and/or grafting. Early motion is imperative to prevent the formation of intra-articular adhesions.

MCL injuries found in combination with ACL injuries are also typically treated conservatively. Most authors advocate early ACL reconstruction followed by 6 weeks of bracing to protect the medial structures of the knee. Some authors advocate late ACL reconstruction to allow for some healing of the MCL, citing decreased rates of arthrofibrosis.


Most isolated MCL tears can be managed non-operatively with good outcomes. Patients generally return to activities and sport following an adequate rehabilitation protocol. Patients with residual laxity and/or pain do well with delayed surgical repair or reconstruction. Equivalent outcomes are seen with conservative and surgical management of the MCL in combined ACL/MCL injuries.


A Pelligrini-Stieda lesion is a calcification of the MCL seen on radiographs. This is associated with chronic MCL injury and may be symptomatic. The lesion can be treated with local anesthetic injection or open surgical resection.

Key terms

Collateral ligaments, varus/valgus stress, knee instability, multiligamentous knee injuries


  • Recognize a clinical history consistent with collateral ligament injury
  • Be able to perform full knee exam, including assessment of ligamentous integrity
  • Understand basic principles of both conservative and surgical interventions for collateral ligament injury

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