Lateral Collateral Ligament (LCL) Injuries

The LCL is a strong band of tissue that runs along the outside of the knee. It connects the thighbone (femur) to the smaller bone in the lower leg (fibula). Its main job is to stabilize the outer (lateral) side of the knee and prevent the joint from bending outward too far.

Unlike some other knee ligaments, the LCL is located outside the joint capsule. This position means it plays a key role in side-to-side stability, especially during activities that involve cutting, pivoting, or sudden changes in direction. When the LCL is injured, the knee may feel unstable, particularly when weight is placed on the leg.

An LCL injury occurs when the ligament is overstretched (sprained) or torn. These injuries are commonly graded based on severity:

• Grade 1: The ligament is stretched but not torn. There may be mild tenderness and discomfort, but the knee remains stable.
• Grade 2: The ligament is partially torn. Pain is more noticeable, and there may be some looseness in the knee.
• Grade 3: The ligament is completely torn. This can lead to significant instability and difficulty bearing weight.

LCL injuries can occur on their own, but they are often seen along with other knee injuries. In more severe trauma, the LCL may be injured along with structures such as the anterior cruciate ligament (ACL) or other components of the posterolateral corner of the knee. A thorough evaluation is essential to identify all involved structures.

Symptoms can vary depending on the severity of the injury. In general, patients may experience:

• Pain along the outside of the knee
• Swelling that develops over several hours
• Tenderness when pressing on the outer knee
• A feeling of looseness or instability
• Difficulty walking or bearing weight
• Stiffness or limited range of motion

In milder injuries, discomfort may only be noticeable during certain movements, such as pivoting or twisting. In more severe tears, the knee may feel like it could “give out,” especially when turning or walking on uneven ground.

Because symptoms can overlap with other knee injuries, it is important not to assume the problem is minor. Persistent pain or instability should be evaluated promptly.

LCL injuries most often occur from a direct blow to the inside of the knee. This force pushes the knee outward, stretching or tearing the ligament on the outside. Contact sports such as football and soccer are common settings for this type of injury.

Other causes include:

• Sudden twisting or pivoting movements
• Hyperextension of the knee
• Motor vehicle accidents
• Falls or high-impact trauma

Athletes who participate in sports that involve rapid direction changes are at higher risk. However, LCL injuries are not limited to athletes. Anyone who experiences significant force to the knee can sustain this type of injury.

In some cases, underlying instability or previous ligament injuries can increase the risk of future damage. Proper evaluation and rehabilitation are critical to restoring stability and reducing the chance of reinjury.

Diagnosis begins with a detailed history and physical examination. A provider will ask about how the injury occurred, the timing of symptoms, and whether the knee feels unstable. Understanding the mechanism of injury provides important clues.

During the physical exam, specific stress tests are performed to evaluate the LCL. One common test involves applying gentle pressure to the inside of the knee while the leg is slightly bent. If the outer side of the knee opens more than expected, it may indicate LCL damage.

Swelling, tenderness along the ligament, and changes in knee alignment are also assessed. Comparing the injured knee to the unaffected side helps determine the degree of instability.

Imaging studies are often used to confirm the diagnosis and assess the severity of the injury. X-rays can rule out fractures and evaluate overall alignment. Magnetic resonance imaging (MRI) is particularly useful because it provides detailed images of soft tissues, including ligaments, tendons, and cartilage. An MRI can show whether the LCL is stretched, partially torn, or completely ruptured, and whether other structures are involved.

Accurate diagnosis is essential because treatment decisions depend on the severity of the injury and whether additional ligaments are affected.

Ignoring knee instability can lead to ongoing problems. A knee that remains unstable is at higher risk for further injury, cartilage damage, and long-term joint degeneration. Even mild sprains benefit from appropriate guidance on activity modification and rehabilitation.