The lateral collateral ligament (LCL) is a strong band of tissue located on the outside of the knee joint that maintains stability. An LCL injury, often called a sprain or tear, occurs when this ligament is stretched or damaged due to excessive force. These injuries vary widely in severity, ranging from minor overstretches to complete ruptures. Since the knee is a complex joint that manages the body’s weight, damage to the LCL can result in pain and functional limitations. Understanding the nature of this injury is important for anyone experiencing lateral knee pain.
Anatomy and Function of the Lateral Collateral Ligament
The lateral collateral ligament is a cord-like structure that runs along the outer aspect of the knee. It originates on the lateral femoral epicondyle (the prominence on the end of the femur) and attaches to the head of the fibula, the smaller bone in the lower leg. The LCL is sometimes referred to as the fibular collateral ligament (FCL).
The LCL’s primary function is to resist varus stress—a force that attempts to push the knee joint outward, opening the lateral side of the knee. It acts as a primary stabilizer against this outward movement and also helps control the knee’s posterolateral rotation. Unlike its counterpart on the inside of the knee, the LCL does not attach directly to the meniscus or the joint capsule. This ligament’s integrity ensures the knee moves in a stable, hinge-like manner.
Mechanisms of Injury and Immediate Symptoms
LCL injuries most commonly occur from a high-energy blow to the inside, or medial, side of the knee. This forceful impact drives the knee outward, placing excessive varus stress on the LCL and causing it to stretch or tear. Non-contact mechanisms, such as a sharp change in direction, sudden twisting, or hyperextension of the knee, can also strain the ligament. Athletes in sports involving frequent pivoting, cutting, or direct collisions, like soccer, football, and skiing, are at an elevated risk for this trauma.
The immediate onset of symptoms is often sharp and localized to the outside of the knee. Individuals frequently report hearing or feeling a “pop” at the moment of injury, followed by pain and tenderness over the ligament’s path. Localized swelling and bruising on the lateral side of the knee are common signs that develop shortly after the trauma. A defining symptom of an LCL tear is a feeling of instability or “looseness,” where the knee feels like it will give out, especially when attempting to bear weight or pivot.
Grading the Injury and Diagnostic Procedures
LCL injuries are classified into three grades based on the degree of ligament damage and resulting joint instability. A Grade I injury is a mild sprain, involving overstretching of the fibers but no loss of joint stability. Grade II is a moderate injury representing a partial tear of the ligament, leading to noticeable instability or gapping of the joint when physically tested. A Grade III injury is the most severe, indicating a complete rupture of the ligament, which results in marked joint instability.
Diagnosis begins with a thorough medical history and a physical examination focused on assessing the knee’s stability. The physician performs the varus stress test, which involves applying an outward force to the knee while it is slightly bent to check for excessive lateral joint gapping. The amount of gapping helps determine the injury grade; gapping of more than 10 millimeters suggests a complete tear. While X-rays rule out associated bone fractures, a Magnetic Resonance Imaging (MRI) scan is the preferred imaging technique. The MRI confirms the extent of the LCL tear and identifies any other associated injuries to the knee’s internal structures.
Treatment Modalities and Rehabilitation Timelines
Treatment for an LCL injury is determined by the grade of the tear and whether other structures in the knee are also damaged. Most isolated Grade I and Grade II injuries are managed non-surgically, focusing on reducing pain and inflammation. This conservative approach begins with rest, ice application, compression, and elevation (RICE), along with temporary use of crutches to limit weight-bearing. Physical therapy is then initiated to restore range of motion and strengthen the surrounding muscles.
A hinged knee brace is often worn for several weeks to provide stability and protect the healing ligament from sideways forces. Patients with Grade I tears may return to activity within three to four weeks, while Grade II tears require a longer period of rehabilitation, often taking eight to twelve weeks for a safe return. In contrast, a Grade III tear, especially one involving other ligaments or structures in the posterolateral corner, frequently necessitates surgical repair or reconstruction. Surgical intervention aims to reattach the torn ligament or replace it with a graft to restore long-term stability. Recovery from surgery is significantly longer, involving a structured physical therapy program that can extend the rehabilitation timeline to six to nine months before a full return to demanding activities.