The Lateral Collateral Ligament (LCL) is a strong, cord-like band of tissue that maintains the mechanical stability of the knee joint. It is one of the four main ligaments connecting the femur (thigh bone) to the lower leg bones, acting as a tether to restrict excessive side-to-side movement. The LCL’s location on the outer side of the knee makes it particularly susceptible to certain types of forceful impacts, which can lead to discomfort and instability.
Anatomy and Primary Function of the Lateral Collateral Ligament
The Lateral Collateral Ligament is a distinct, fibrous structure that originates on the lateral femoral epicondyle (a bony bump on the outer side of the thigh bone). It extends downward and attaches to the head of the fibula. Unlike the Medial Collateral Ligament (MCL), the LCL is situated entirely outside the joint capsule, classifying it as an extracapsular ligament.
This positioning gives the LCL a unique, rope-like shape, separate from the lateral meniscus. The LCL’s primary biomechanical function is to act as the main restraint against varus stress—a force that pushes the knee inward and causes the outer side of the joint to open. It provides a significant portion of this restraint at both 5 degrees and 30 degrees of knee flexion.
The ligament also contributes to the knee’s overall rotational stability, particularly against excessive posterolateral rotation. Because the LCL is located behind the axis of knee rotation, it becomes taut when the knee is straightened (extended) and more relaxed when the knee is fully bent (flexed). The LCL is considered a component of the posterolateral corner (PLC) of the knee, which includes several other ligaments and tendons that provide complex stability.
Common Mechanisms of LCL Injury
LCL injuries are less common than those affecting the MCL because the forces required to cause a tear are substantial. The most frequent mechanism involves a high-energy blow to the inside (medial side) of the knee while the foot is planted, generating an extreme varus force. This force pushes the knee joint inward, stretching the LCL on the outer side past its limit.
LCL damage can also result from severe hyperextension or a significant twisting motion. Isolated LCL tears, where only the LCL is damaged, are rare, occurring in less than 2% of all knee injuries. It is far more common for an LCL tear to be accompanied by damage to other structures, such as the Anterior Cruciate Ligament (ACL), Posterior Cruciate Ligament (PCL), or other parts of the posterolateral corner.
The presence of concomitant injuries makes the overall trauma more complex and often impacts the treatment approach. Athletes involved in contact sports, such as football or rugby, are at a higher risk due to collisions that deliver a powerful blow to the side of the knee.
Recognizing and Grading LCL Injuries
Following an injury, patients typically experience acute pain and tenderness over the outer side of the knee joint. Swelling is often localized to the lateral side, though it can sometimes be more generalized depending on the extent of the damage. A prominent symptom is the feeling of instability or the knee “giving way,” particularly when attempting to pivot or bear weight on the injured leg.
Diagnosis begins with a physical examination, which includes the Varus stress test, performed by a healthcare provider to assess the degree of joint laxity. The test involves applying a force to the inner knee while it is slightly bent, checking for excessive lateral opening compared to the uninjured knee. Magnetic Resonance Imaging (MRI) is the preferred method for confirming the diagnosis and determining the extent of the ligament damage.
LCL injuries are classified using a three-grade system that guides the management strategy. A Grade I sprain is the mildest form, involving only stretching of the ligament fibers with minimal pain and no noticeable instability. A Grade II injury is a moderate, partial tear, characterized by more severe pain, swelling, and minor instability, often showing 5 to 10 millimeters of laxity upon stress testing. The most severe is a Grade III injury, which represents a complete rupture of the LCL, resulting in significant pain, substantial swelling, and pronounced joint laxity or instability, often exceeding 10 millimeters.
Treatment and Rehabilitation Protocols
The course of treatment for an LCL injury depends on the grade of the tear and whether other knee structures were also damaged.
Non-Surgical Management
Grades I and II LCL sprains are typically managed conservatively without surgery. Initial treatment follows the R.I.C.E. protocol (Rest, Ice, Compression, and Elevation) to control pain and swelling. This non-surgical approach often includes the use of a hinged knee brace and a structured physical therapy program. Rehabilitation focuses on regaining full range of motion and progressively strengthening the muscles surrounding the knee. Athletes with Grade I or II tears can often return to sport within four to eight weeks, depending on their progress and the severity of the initial injury.
Surgical Management
In contrast, Grade III tears, especially those involving other major knee ligaments or structures in the posterolateral corner, frequently require surgical intervention. Unlike the MCL, the LCL does not heal reliably on its own due to its cord-like structure and relatively poor blood supply. Surgery typically involves repairing the torn ends of the ligament or reconstructing it using a tissue graft, such as a hamstring tendon.
Following surgery, rehabilitation is a lengthy process that can take six to nine months before a full return to high-level activity is advised. The early phases prioritize protecting the surgical repair with bracing and restricted weight-bearing. Later phases concentrate on advanced strengthening, balance training, and sport-specific drills to restore full functional stability. Consistent adherence to the rehabilitation protocol is necessary to ensure the best possible long-term outcome.