A lateral collateral ligament injury of the knee is less common than injuries to the medial ligament. But when it occurs, it can be equally serious for athletes. An LCL injury typically results from trauma, twisting, or a force that drives the knee inward. Recognising and treating these injuries promptly is essential for athletes who want to return to their sport safely. How do we diagnose and manage an LCL tear? 

Anatomy of the LCL

The lateral collateral ligament runs along the outside of the knee, connecting the femur to the fibula. Unlike the MCL, the LCL does not attach to the joint capsule or meniscus, making it a distinct stabiliser of the lateral knee. Its primary role is to resist inward knee forces and provide stability during side-to-side movements.

The LCL is part of the posterolateral corner (PLC), a complex structure that also includes the popliteus tendon, popliteofibular ligament, arcuate ligament, and lateral capsule. This anatomy is vital because severe LCL tears are often associated with PLC injuries, which significantly affect prognosis.

Another vital structure nearby is the common peroneal nerve, which wraps around the fibular neck. This nerve is at risk during severe lateral collateral ligament injuries or surgery. 

Causes of an LCL Injury

  • Direct blow to the inside of the knee during sport (e.g. football tackle)

  • Sudden twisting with the foot planted

  • Hyperextension with inward force 

  • High-energy trauma, such as skiing accidents or contact sports collisions

Symptoms of LCL Injury

lcl injury diagram

Patients with an LCL sprain or LCL tear usually report:

  • Sharp pain on the outer side of the knee

  • Tenderness and swelling along the lateral ligament

  • Instability or “giving way” when changing direction

  • Difficulty with weight-bearing in more severe injuries

Clinical Assessment LCL Injury

Assessment of an LCL injury includes careful inspection and palpation:

  • Tenderness over the ligament between the femoral epicondyle and fibular head

  • Varus stress test: At 30° knee flexion, pain or laxity suggests isolated LCL involvement. At full extension, laxity indicates additional injury to the cruciate ligaments or the PLC. We perform other tests for posterolateral corner injuries, such as external recurvatum and dial tests.

  • Joint line tenderness: May suggest associated meniscal injury.

  • Neurovascular assessment: The peroneal nerve should always be tested (touch sensation over the front of the foot and ankle dorsiflexion strength).

Associated Injuries

An isolated LCL sprain is possible, particularly in lower-grade injuries, but higher-grade trauma often leads to associated damage. Commonly linked injuries include:

Identifying these associated injuries is critical, as management and prognosis change significantly when the PLC or cruciate ligaments are involved.

Imaging of LCL Tears

  • MRI is the gold standard for diagnosing an LCL tear and assessing for PLC  or PCL involvement.

  • Ultrasound can provide a dynamic assessment of ligament integrity.

  • X-rays are often used to exclude fractures at the fibular head or the femur. 

Treatment of LCL Injury

Conservative Management

We treat most isolated Grade I and II LCL sprains non-operatively:

  • Rest, ice, compression, elevation (RICE) in the acute phase

  • Knee brace for 2–6 weeks to protect against varus stress, starting with full knee extension and increasing flexion over time. 

  • Physiotherapy focused on restoring range of motion, progressive strengthening, and proprioceptive training.

  • Return to sport when we restore pain-free stability and function.

Injection Therapy

In selected cases of low-grade lateral collateral ligament injury with persistent pain:

  • PRP (platelet-rich plasma) injections may promote healing of partial tears

Surgical Management

  • Grade III LCL tears usually require surgical repair (if acute) or reconstruction with a graft.

  • Combined injuries involving the PLC, ACL, or PCL almost always need surgery.

  • We also consider surgery if chronic instability persists despite rehabilitation.

Prognosis and Return to Sport

  • Grade I LCL sprain: Return within 2–3 weeks

  • Grade II LCL tear: Recovery typically 6–8 weeks with structured rehab

  • Grade III LCL tear with or without PLC involvement: Surgical recovery 4–6 months or longer, depending on associated ligament repair

Final Word from Sportdoctorlondon about an LCL injury

An LCL injury is less common than MCL injuries, but should not be underestimated. Accurate assessment of an LCL sprain or LCL tear is essential, not only to grade the injury but also to identify associated damage to the cruciate ligaments or posterolateral corner. Most isolated lateral collateral ligament injuries respond well to conservative treatment and rehabilitation. Still, high-grade tears often require surgical reconstruction to restore stability and allow athletes to return safely to sport.

Related conditions:

Dr Masci is a specialist sports doctor in London. 

He specialises in muscle, tendon and joint injuries.