Lateral collateral ligament injury of the knee

Last revised by Joachim Feger on 21 Jan 2023

Lateral collateral ligament injuries of the knee are rare in isolation and usually occur in the context of a posterolateral corner injury or in association with other ligamentous or meniscal injuries.

A lateral collateral ligament injury of the knee is also referred to as the fibular collateral ligament injury and comprises a spectrum of injuries ranging from ‘sprain’ over ‘tear’ to ‘rupture’.

Lateral collateral ligament injuries usually occur in conjunction with other knee ligament injuries, but are rare in isolation and comprise <2% of all knee injuries 1.

Activities that increase the likelihood of developing a lateral collateral ligament injury of the knee are 2:

  • football (soccer)

  • rugby / American football

  • wrestling

  • skiing

Clinical conditions associated with a lateral collateral ligament injury include the following 2-4:

History often reveals a varus stress injury or an anteromedial blow. Complaints are lateral knee pain and swelling after acute trauma, instability of the knee near knee extension and difficulties climbing stairs. On physical exam, soft tissue swelling and discolouration, as well as a joint laxity on varus stress, are indicative of a lateral collateral ligament injury. A perceived opening at 30° of flexion only might indicate an isolated tear whereas joint laxity in full extension points toward a more severe injury including fibular collateral ligament rupture with concomitant posterolateral corner and possibly posterior cruciate ligament injury 2.

Lateral collateral ligament injury can lead to the following conditions 2:

  • persistent varus instability or hyperextension laxity

  • rotatory instability

  • increased insufficiency of the anterior cruciate ligament

  • peroneal nerve injury

  • stiffness

  • osteoarthritis of the knee

  • physeal arrest

Lateral collateral ligament injuries can range from a minor sprain, over a partial tear to complete disruption. They can be located at mid-substance or the femoral and fibular insertion sites 2-4.

Isolated lateral collateral ligament injury is usually due to a lower velocity injury mechanism and the following 2,3:

  • external rotation stress in full extension

  • varus force in extension or mild to moderate flexion

  • posterolaterally directed blow to the anteromedial aspect of the tibia in knee extension

Higher varus impact injuries such as a dashboard injury usually result in a concomitant injury of other posterolateral corner structures and/or cruciate ligament injury.

Plain radiographs are of limited value, especially in the setting of an isolated injury. Stress radiographs might show increased opening 5. An arcuate sign/fracture can be seen in case of an avulsion injury of the fibular tip 2-4.

MRI allows for the localization of the injury and injury grading. Fibular collateral ligament injuries can be best depicted in coronal and axial views 2. Furthermore, it is the modality of choice for the workup of concomitant ligamentous and meniscal injuries.

Lateral collateral ligament injuries will display different findings depending on the extent of the injury:

  • grade 1: fluid surrounding the lateral collateral ligament

  • grade 2: partial discontinuity of the ligament fibers

  • grade 3: complete disruption of the fibers

The radiological report should include a description of the following 3:

Treatment options include non-surgical and surgical approaches and will mainly depend on the presence of associated injuries and the grade of the injury 2-4.

Isolated lateral collateral ligament sprains and partial tears can be treated conservatively with an initial resting period and other conservative measures as the application of ice, compression and elevation (RICE) followed up with range of motion exercises and functional rehabilitation 2-4.

Lateral collateral ligament disruption can be managed conservatively if isolated or operatively with repair or reconstruction (e.g. semitendinosus graft), the latter showing better outcomes, especially in more chronic states 2,6.

High-grade lateral collateral ligament injuries with concomitant injuries of other posterolateral corner structures and/or cruciate ligament injuries benefit from ligament reconstruction, in particular, if they are associated with rotatory instability or posterolateral instability.

Conditions that can mimic the presentation and/or the appearance of a lateral collateral ligament injury include:

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Cases and figures

  • Case 1: rupture
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  • Case 2: chronic sprain
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  • Case 3: sprain associated with ACL and meniscal tears
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  • Case 4
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