The lateral collateral ligament, often called the LCL, is an important stabilizing ligament on the outer side of the knee. In my practice, I often explain to patients that this ligament helps prevent the knee from opening outward too much under varus stress and also contributes to stability during twisting and turning movements [1][2].

Many Bangladeshi patients are more familiar with ACL injuries than LCL injuries, but pain on the outer side of the knee should never be ignored, especially after trauma, sports injury, or a forceful twist. An LCL injury can range from a mild sprain to a complete tear. In more serious cases, it may occur together with posterolateral corner injury or other ligament damage, which changes the treatment plan significantly [1][2][3].

This article explains what the lateral collateral ligament does, how LCL injuries happen, how they are diagnosed, and when treatment may be non-surgical or surgical.

What Is the Lateral Collateral Ligament?

The lateral collateral ligament is on the outer side of the knee. It runs from the outer part of the femur to the fibular head [2]. Unlike the medial collateral ligament, it is more cord-like and does not attach directly to the meniscus or joint capsule [2].

What does the LCL do?

The LCL helps:

• resist outward opening of the knee
• control side-to-side stability
• support the knee during twisting and directional change
• contribute to posterolateral stability along with nearby structures [2][3]

This is why patients with LCL injury may complain not only of pain, but also of looseness or the sense that the knee does not feel safe.

How LCL Injuries Happen

AAOS explains that collateral ligament injuries usually happen when a force pushes the knee sideways. For the LCL specifically, a blow to the inside of the knee that pushes the knee outward can injure the ligament [1].

Common causes I see in practice

• football injuries
• cricket fielding or twisting injuries
• motorcycle or road traffic accidents
• falls with awkward knee twisting
• gym and fitness injuries
• higher-energy trauma causing multiligament injury

In some patients, the injury is isolated. In others, especially after stronger trauma, the LCL injury is part of a larger injury involving the posterolateral corner, ACL, or PCL. That distinction is extremely important.

Symptoms of an LCL Injury

The symptoms depend on severity, but common complaints include:

• pain on the outer side of the knee
• swelling around the injury site
• tenderness over the lateral ligament
• stiffness
• difficulty walking normally
• instability or giving way

AAOS lists pain on the side of the knee, swelling, and instability as key symptoms of collateral ligament injury, with LCL pain typically felt on the outer side [1].

One important point I want Bangladeshi patients to understand is that even if swelling is not very dramatic, a feeling of side-to-side looseness after trauma is a warning sign that deserves proper orthopedic evaluation.

Grading of LCL Injuries

Like other ligament sprains, LCL injuries are commonly described by grade.

Grade I

This is a mild sprain. The ligament is stretched but not completely torn. Pain is present, but the knee is usually still fairly stable.

Grade II

This is a partial tear. There is more tenderness and looseness, but some ligament continuity remains.

Grade III

This is a complete tear. There is significant instability and the ligament may be torn through or avulsed from its attachment [1][2].

Grade matters because it influences treatment. A mild sprain is very different from a complete tear that has avulsed off the bone or is part of a posterolateral corner injury.

Why the LCL Is Not Always an “Isolated” Problem

This is one of the most important issues in lateral knee injuries.

The posterolateral corner connection

The LCL is closely related to the posterolateral corner, or PLC, of the knee. StatPearls notes that the LCL is part of this posterolateral complex, along with structures such as the popliteus and popliteofibular ligament [2].

That means a serious LCL injury may not be “just an LCL tear.” It may represent a broader instability pattern. Review articles on PLC injuries repeatedly emphasize that the fibular collateral ligament is one of the main stabilizers in this region [3].

Why this matters

If a patient has a combined LCL and posterolateral corner injury, simple rest may not be enough. Missing the full injury pattern can lead to persistent instability and poor long-term knee function.

How I Evaluate an LCL Injury

When I evaluate patients with suspected LCL injury, I do not look only at the area that hurts. I assess the whole knee.

History and examination

I usually ask:

• Was there a direct blow?
• Was the knee forced inward or outward?
• Did the patient feel a pop?
• Is the knee giving way?
• Is there difficulty walking or using stairs?
• Was the injury sport-related or from a road traffic event?

On examination, I assess: