Lateral Collateral Ligament (LCL) Injury of the Knee
Introduction: How LCL Knee Injuries Occur
A lateral collateral ligament (LCL) injury of the knee occurs when the ligament on the outside of the knee becomes stretched or torn (Figure 1). The LCL helps stabilize the knee and prevents it from bending outward too far (while the lower leg is bending inwards). These injuries usually occur when a force pushes the knee outward while the foot is planted, such as during football, soccer, skiing, or other sports. Direct blows to the inside of the knee are a common cause. LCL injuries are less common than medial collateral ligament (MCL) injuries but can be quite serious, especially in athletes and active individuals.
The Severity of LCL Injuries
The severity of an LCL injury can range from a mild stretch (Grade 1) to a complete tear (Grade 3). Patients often experience pain and tenderness along the outer side of the knee, swelling, and a feeling that the knee may “give way.” More severe injuries may involve other structures on the outer back corner of the knee, known as the posterolateral corner (PLC). These associated injuries are important because the PLC helps control rotational stability of the knee. In some cases, injuries to the anterior cruciate ligament (ACL) or posterior cruciate ligament (PCL) may also occur along with the LCL tear.
How Doctors Diagnose a Lateral Collateral Ligament Injury of the Knee
Doctors diagnose an LCL knee injury by reviewing the patient’s symptoms and performing a physical examination. The doctor may apply a gentle inward stress to the knee stretching the structures on the outside of the knee to determine whether the outer side of the knee opens abnormally, suggesting ligament damage. The amount of looseness helps determine the severity of the injury.
Imaging Studies
X-rays are often obtained to rule out fractures or bone injuries. The most useful imaging test is usually an MRI scan, which can show the LCL, other ligaments, cartilage, and surrounding soft tissues in detail. MRI is especially important if a more complex injury involving the posterolateral corner or cruciate ligaments is suspected.
Treatment of an LCL Injury of the Knee
Initial Treatment
Initial treatment for an LCL knee injury focuses on reducing pain and protecting the knee. This often includes rest, ice, compression, and elevation (RICE). Crutches may be used temporarily if walking is painful. Many patients are also placed into a knee brace to protect the ligament while it begins to heal. Anti-inflammatory medications may help reduce pain and swelling. Early gentle motion exercises are often encouraged to prevent stiffness.
Conservative Treatment of an LCL Injury of the Knee
Many mild or moderate LCL injuries can be treated conservatively without surgery. Grade 1 injuries and some Grade 2 injuries often heal well with bracing, physical therapy, and gradual return to activity. Rehabilitation focuses on restoring knee motion, strengthening the muscles around the knee and hip, and improving balance and stability. Most patients with mild injuries are able to return to sports within several weeks to a few months, depending on the severity of the injury and the demands of the activity.
Surgical Treatment of an LCL Injury of the Knee
Surgery is more commonly recommended for complete LCL tears (Grade 3 injuries), injuries involving the posterolateral corner, or cases where multiple ligaments are injured. Surgical treatment may involve repairing the torn ligament or reconstructing it using a tendon graft. If the posterolateral corner is also injured, these structures may need reconstruction as well. After surgery, patients usually wear a brace and follow a structured rehabilitation program. Recovery often takes several months, and return to high-level sports may require 6–12 months depending on the severity of the injury.
Prognosis and Potential Complications
The prognosis for LCL injuries is generally good when they are recognized and treated appropriately. Mild injuries often heal completely with conservative treatment. More severe injuries can also do well after surgery and rehabilitation. However, complications can occur if the injury is missed or not treated properly. Persistent knee instability, stiffness, weakness, or early arthritis may develop in some patients. Injuries involving the posterolateral corner are especially important to recognize because untreated instability can place extra stress on other knee ligaments and cartilage.
Summary
A lateral collateral ligament (LCL) knee injury is a sprain or tear of the ligament on the outside of the knee. It usually happens during sports or from a blow to the inside of the knee. Symptoms include pain, swelling, and a feeling that the knee may give way. Doctors use an examination and MRI scan to diagnose the injury. Mild injuries often heal with bracing and therapy, while severe injuries may require surgery. Most people recover well with proper treatment and rehabilitation.
Edited by Stephen Pinney MD, May 23, 2026.