Lateral Collateral Ligament Knee Injuries

Continuing Education Activity

The lateral collateral ligament (LCL), also known as the fibular ligament serves as one of the key stabilizers of the knee joint. Originating on the lateral epicondyle of the femur and inserting on the fibular head, the lateral collateral ligament's primary purpose is to prevent excess varus stress and posterior-lateral rotation of the knee. This activity reviews the anatomy, evaluation, and treatment of lateral collateral ligament knee injuries, and highlights the role of an interprofessional team in improving care for these patients.


  • Identify the etiology of lateral collateral ligament knee injuries medical conditions and emergencies.
  • Review the appropriate evaluation of lateral collateral ligament knee injuries.
  • Outline the management options available for lateral collateral ligament knee injuries.
  • Describe the interprofessional team strategies for improving care coordination and communication to advance lateral collateral ligament knee injuries treatment and improve outcomes.


The lateral collateral ligament (LCL), also known as the fibular ligament serves as one of the key stabilizers of the knee joint. Originating on the lateral epicondyle of the femur and inserting on the fibular head, the lateral collateral ligament's primary purpose is to prevent excess varus stress and posterior-lateral rotation of the knee. Although the least frequent of all knee injuries, high suspicion is warranted for both lateral collateral ligament and posterior-lateral corner (PLC) injuries on all knee exams. The goal of this article is to review the anatomy, etiology, history and physical, diagnosis, and treatment of such injuries.


Origin and Insertion: Originating 1.4 mm proximal and 3.1 mm posterior to the lateral epicondyle of the femur, the LCL runs approximately 0.69 mm along the lateral portion of the knee. It inserts 28.4 mm distal to the fibular styloid tip, where it there inhabits nearly 38% of the fibular head.[1] 

Anatomic differences from the MCL: The LCL differs from the medial collateral ligament (MCL), in the fact that it is known to be more cord-like, rather than the fan-like, and does not attach to a meniscus or joint capsule.[2]

Nerve/Blood Supply: Nerve supply to the LCL stems from the common fibular nerve. Blood supply ultimately arises from the popliteal artery, primarily from branches of the superior and inferior lateral genicular arteries.[3]

Surrounding Structures: Deep to the LCL, lays the popliteus tendon (PLT), which measures, on average, 55mm in length. Superficial to the LCL is the iliotibial band (ITB), which inserts along the anterolateral portion of the knee at Gerdy's tubercle.[4]


The LCL is the primary resistor of varus stress in all degrees of knee flexion, with the popliteus tendon, cruciate ligaments, iliotibial band, biceps tendon, and lateral gastrocnemius tendon assisting as secondary varus stabilizers.[1] It also plays a significant role in providing posterolateral stability to the knee, primarily preventing medial translation of the tibia.[5]

The LCL and PLT make up the primary resistors of external tibial rotation of the knee in 0-30 degrees of knee flexion. As knee flexion increases past 60 degrees, studies show that the popliteofibular ligament (PFL) provides resistance to external tibial rotation.[6]

Although not primary stabilizers, studies show that the LCL and posterior-lateral corner structures play a minor role in stabilizing anterior and posterior tibial translation when the cruciate ligaments are torn.[7]


The most common mechanism of injury is seen via a high-energy blow to the anteromedial knee, combining hyperextension and extreme varus force.[1] Noncontact hyperextension and noncontact varus stressors have also been reported to cause LCL injuries. 


Frequency of Condition

Due to its close association with the PLC, PCL, and ACL, the LCL is rarely ever injured in isolation. Studies show that isolated LCL injuries in high school athletes are second to last in incidence at 7.9%. PCL injuries are the least common, at 2.4%.[8] Reportedly, 40% of PLC and LCL injuries are due to contact sports. Other instances are due to trauma, motor vehicle accidents, and falls.

Risk Factors

Although there have been few studies completed on isolated LCL injuries, reports show that female gender, high contact sports, and sports that require high velocity pivoting and jumping increase the likelihood of injury. These same studies show that while soccer has the highest likelihood of overall knee injury, tennis and gymnastics are most specific for isolated LCL injury. A United States military study has shown that prior knee, ankle, or hip injury predisposes soldiers to increased rates of lateral knee injuries.[9]

History and Physical


Patients tend to present with a history of an acute event consistent with a medial blow to the knee while fully extended, or extreme noncontact varus bending. They will complain of sudden onset lateral knee pain, swelling, and ecchymosis after the injury. the patient may also report thrust gait, where they will complain of the foot kicking in mid-stance.[10] Patients may complain of paresthesias over the lateral lower extremity as well as weakness and/or a foot-drop.[7]

It is imperative to gain a complete history with regards to these patients, including but not limited to, bleeding/clot disorders, previous surgeries, occupation, gait, ambulation-assisted devices, living situation (stairs at home).

Physical Exam

A comprehensive full range of motion knee exam is imperative for all patients. Attention should focus on tenderness to palpation of the lateral knee, the most common exam finding; this may also be evident along the infrapatellar bursa, Gerdy's tubercle, and the patellar tendon attachment. Ecchymosis, swelling, and warmth may be present. Gait, when possible, should be examined for the classical "varus thrust" finding.

Special Testing

  • Varus Stress Test: Studies show that this is the most useful test to assess LCL injury. The test is performed with the examiner's hand stabilizing the femur (monitoring the lateral joint line) while placing a varus force on the ankle. The test is first performed at 30 degrees. Any lateral compartment gaping is a positive indicator for LCL and potential PLC injury. The test is then done in full knee extension. If there is increased stability when tested in full extension, then it is positive for an isolated LCL injury. If instability persists when tested in full extension, then the test is positive for LCL and PLC injury.
  • External Rotation Recurvatum Test: This test measures the posterolateral rotary stability of the knee. The patient lies in the supine position. The examiner places a downward force through the suprapatellar region while lifting the big toe off the table and externally rotating the tibia with the other hand. Excess hyperextension, compared to the uninjured knee, illustrates a positive exam. It is important to note that this exam is less than 10% accurate in identifying PLC injuries, but is more accurate in diagnosing associated ACL injuries.
  • Posterolateral Drawer Test: Similar to the posterior drawer test, the patient lies in the prone position with the knee flexed to 90 degrees and externally rotated 15 degrees. The examiner grips the femoral condyles and directs a posterior force. Any excess posterolateral translation on the injured leg suggests a PLC injury.
  • Reverse Pivot Shift: This test is performed in the same position as the posterolateral drawer test. The examiner monitors the lateral joint line and slowly extends the knee while applying a valgus and external rotating force. At 30 degrees, the ITB transitions from a flexion vector to an extension vector, and reduces the previously subluxated lateral tibial plateau seen at 90 degrees. The test is positive if there is an audible "clank" heard at 30-degrees. It is important to compare results bilaterally, as a large percentage of noninjured knees may show false-positive results.[11]
  • Dial Test: This test, which measures the external rotation of the femur, is useful in confirming PLC injury. The patient lies prone. The examiner places one hand, stabilizing the thigh, and uses the other hand to rotate the ankle and leg externally. This test is performed at 30 and 90 degrees of knee flexion bilaterally. Ten degrees or more of external rotation on the injured leg confirms PLC injury.

Due to the increased likelihood of associated ligamentous, meniscal, or soft tissue injuries, an examination should be thorough and must include all structures of the knee. Anterior and posterior drawer tests are necessary to rule out possible ACL or PCL injuries, respectively. The patella requires assessment for accompanying subluxation or dislocation.


Plain Radiograph:

Plain AP and Lateral knee radiographs will not reveal any changes to the LCL; however, X-rays are imperative to rule out associated structural injuries. Frequently seen radiographical changes include fibular head fractures/avulsions (arcuate sign), tibial spine avulsions, or lateral tibial plateau (i.e., Segond fracture). Arcuate sign (avulsion of the styloid of the proximal fibula) and Segond fractures are both pathognomonic for PLC injury, and should immediately warrant further workup for LCL injury. In elderly patients, with chronic lateral knee pain, plain radiographs can be beneficial in ruling out underlying arthritic changes.

Varus and kneeling posterior stress radiographs are also necessary. Both have shown the ability to distinguish the severity of LCL and PLC injury; however, they have high user reliability.[12]

Magnetic Resonance Imaging:

MRI is the gold standard to diagnose structural LCL and PLC injuries. Coronal and sagittal T1 and T2 weighted series have the highest sensitivity and specificity for LCL injury (approximately 90%). MRI alone does not correlate with determining the need for surgery. Radiographs and proper physical examination are a requirement.

Musculoskeletal Ultrasound:  When available, ultrasound can be a useful tool in the rapid diagnosis of LCL injuries. Imaging will show a thickened and hypoechoic LCL. A complete tear may show edema, dynamic laxity, or lack of LCL fiber continuity.

Classification of Injury: LCL injuries classify into three grades depending on severity.

  • Grade 1: Mild Sprain - Diagnosed with localized lateral knee tenderness. No instability or mechanical symptoms are present.
  • Grade 2: Partial Tear – Diagnosed with more severe localized lateral and posterolateral knee pain, as well as swelling. 5 to 10 mm of laxity may be observed, but there is a fixed endpoint of the ligament.
  • Grade 3: Complete Tear – Pain and swelling vary in patients. It is usually associated with PLC and other related injuries. >10mm of laxity, as well as mechanical symptoms, are noted.

Treatment / Management

Treatment options are highly dependent on the grade of LCL injury and if associated injuries are present; therefore, it is imperative to gather definitive imaging promptly. Acutely, all grades of injury can be treated with: rest, compression, NSAIDs, and ice. Ice should not be applied for longer than 15 minutes at a time to the lateral knee to help prevent cold injury to the common peroneal nerve.

Grade 1 and 2: Usually, nonoperative treatment the therapeutic approach. Patients should be non-weight-bearing and use crutches for one week for better pain control. For the next 3 to 6 weeks, the patient should be placed in a hinged knee brace to stabilize the medial and lateral aspects of the joint while performing functional rehabilitation. 

Grade 3:

Recent studies show that in terms of grade 3 isolated LCL injuries, both knee range of motion and pain reduction was highest in those who underwent surgical treatment.[13] Intrasubstance LCL repairs have proven unsuccessful; therefore, recent literature recommends reconstructive surgeries instead. In isolated LCL injuries, reconstruction is preferable, using a semitendinosus autograft. It is imperative to note the common peroneal nerve, and ACL, to avoid potential complications.

Differential Diagnosis

Lateral knee injuries should be examined closely due to the large differential.

  1. ACL/PCL tears: often confused with LCL injury do to the common nonspecific features of swelling, acute onset pain, and instability. Tests such as anterior/posterior drawer tests should help differentiate the injuries.
  2. Lateral Meniscus tear: often confused with LCL injury do to the common nonspecific features of swelling, bucking, and lateral joint line pain. A lateral meniscus tear can be differentiated by a positive McMurray test, not seen in LCL tears.
  3. Popliteal injury: a proper history is essential. Popliteal tendinopathy commonly presents as posterolateral knee pain (distal to lateral femoral epicondyle) worse with downhill walking. Popliteal pain can be differentiated by a positive Garrick test (flex knee and externally rotate the tibia as the patient resists), which is not present in LCL injury.
  4. Bone contusion: often, these injuries, depending on location, may present as LCL tear. It is imperative to palpate the lateral joint line and stress the knee. Varus stress will not affect lateral bone contusion pain.
  5. IT band syndrome: diagnosis is made via history. IT band presents as a gradually developing chronic pain at the lateral distal femoral epicondyle. Pain should not be reproducible via varus stress.


Undiagnosed LCL and PLC injuries often have several long-term complications. The most common complications are continued knee instability and chronic pain. Reports also show that approximately 35% of PLC injuries may have an associated peroneal nerve palsy. This comorbidity is likely due to the proximity of the peroneal nerve to the LCL. Patients may develop long term foot drop, as well as lower extremity weakness and decreased sensation. In those patients treated with surgical intervention, common postoperative complications include hardware irritation and stiffness. 

Postoperative and Rehabilitation Care

Healing and protecting the ligaments is vital in all grades of injury. Recommendations include:

Grade 1 & 2: Passive and active prone knee flexion should be initiated in the immediate weeks following injury to help prevent stiffness or contracture. Around six weeks post-injury, the hinged knee brace is removed, and the patient should begin physical therapy. Patients may return to sports only when meeting the following criteria: full, painless knee motion, complete reduction of lateral knee tenderness, and complete resolution of ligamentous laxity. In general, return to sports is approximately four weeks for grade 1 injuries, and ten weeks for grade 2 injuries.

Grade 3: Patients should be non-weight bearing in a knee immobilizer for six weeks after surgical interventions. Like grade 1 and 2 injuries, quadriceps strengthening is imperative throughout recovery. Hamstring strengthening should be avoided for at least four months to prevent damage to the reconstruction. Sport-specific therapy may commence after four months postoperatively.

Deterrence and Patient Education

Patients experiencing acute traumatic knee pain should consult their PCP or present to an urgent care. Rest, ice, compression, and elevation can be useful early on. Depending on the history of injury and physical exam, your physician may want to order an MRI of the knee. Depending on the severity of the injury, patients may need to be immobile for several weeks. In severe cases, LCL reconstruction surgery is advised, with approximately a 6-month rehabilitation process.

Pearls and Other Issues

Although one of the least common knee injuries, physicians should maintain a high index of suspicion in diagnosing LCL and PLC injuries to treat symptoms and prevent complications properly. If LCL injury is suspected, a thorough physical examination is necessary, and an MRI of the knee ordered. “RICE” therapy and immobilization of the knee should start early in the treatment process. Patients should receive a referral to an orthopedic surgeon for possible surgical intervention.

Enhancing Healthcare Team Outcomes

An interprofessional team, including; an emergency department physician, orthopedic surgeon, nurse practitioner, and a physical therapist, are essential in the diagnosis and management of LCL injuries. Initial treatment of LCL injuries is always RICE therapy. A proper history and physical, along with an MRI, when indicated,  is the gold standard in diagnosing this injury. Depending on the severity, LCL injuries are manageable nonoperatively or operatively. With appropriate treatment, the prognosis for LCL or PLC injuries are good, but recovery time may exceed four months in high-grade injuries.

Article Details

Article Author

Reed Yaras

Article Author

Nicholas O'Neill

Article Editor:

Amjad Yaish


5/4/2021 10:28:39 AM



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