An LCL injury is a sprain or tear of the lateral collateral ligament, a tough band of tissue on the outer side of your knee that keeps the joint from bowing outward. It’s less common than injuries to the ACL or MCL, but it can cause significant pain, swelling, and instability along the outside of the knee. LCL injuries range from mild stretches to complete tears, and treatment depends heavily on which end of that spectrum you’re on.
What the LCL Does
The lateral collateral ligament runs along the outside of your knee, connecting the bottom of your thighbone (femur) to the top of the smaller lower leg bone (fibula). Its main job is resisting varus stress, which is the force that would push your knee outward into a bowlegged position. It does this across all degrees of knee bending.
The LCL also helps prevent your lower leg from rotating too far outward and from sliding backward, particularly when your knee is near full extension or only slightly bent (up to about 30 degrees). Several other structures on the outer and back part of the knee assist the LCL in these jobs, but the LCL is the primary stabilizer against that outward-bowing force.
How LCL Injuries Happen
The classic mechanism is a direct blow to the inside of the knee that forces the joint outward. Think of a football tackle hitting the inner knee, or a collision in soccer where your knee gets pushed laterally. This creates the varus force the LCL is designed to resist, and if the force exceeds what the ligament can handle, fibers stretch or tear.
Non-contact injuries are also possible. A sudden change of direction, an awkward landing, or hyperextension of the knee can all stress the LCL beyond its limits. Sports that involve cutting, pivoting, or direct contact carry the highest risk. Because the LCL rarely tears in isolation, injuries often involve damage to other structures on the outer and back part of the knee, sometimes including the cruciate ligaments.
Symptoms to Watch For
The hallmark symptoms are pain, swelling, and tenderness concentrated along the outer side of the knee. You may also notice stiffness and bruising in the area. Many people describe a feeling that the knee is loose or about to give way, especially when putting weight on it or changing direction. This sense of instability can persist even after initial pain and swelling improve.
More severe tears can cause numbness or weakness in the foot. This happens when the peroneal nerve, which runs close to the LCL near the top of the fibula, gets stretched during the injury or compressed by swelling afterward. If you notice any foot drop or tingling below the knee, that’s a sign of a more serious injury.
Injury Grades and What They Mean
LCL injuries are classified into three grades based on how much damage the ligament fibers have sustained. The grading matters because it largely determines whether you’ll need surgery and how long recovery will take.
- Grade 1: The ligament fibers are stretched but intact. On MRI, there’s abnormal signal within the ligament, but its overall structure and continuity are preserved. When a clinician tests the knee for looseness by pushing outward, there’s 5 mm or less of excess joint opening compared to the uninjured side.
- Grade 2: A partial tear. Some fibers are disrupted, but the ligament still holds together as a continuous structure. MRI shows partial loss of the normal fiber pattern. The varus stress test reveals 5 to 10 mm of excess opening.
- Grade 3: A complete tear. The ligament has lost both its fiber architecture and its continuity. Varus stress testing shows more than 10 mm of excess joint opening, and the knee feels markedly unstable.
How It’s Diagnosed
Diagnosis starts with a physical exam. The key test is the varus stress test: you lie on your back, and the examiner applies pressure just above your knee, pushing outward (away from your body). This is typically done twice, once with the knee straight and once with it slightly bent at about 30 degrees. If the examiner feels the outer side of the joint gap open more than normal, the test is positive. The amount of opening helps determine the grade.
MRI is the imaging tool of choice for confirming the diagnosis and seeing exactly where the damage is. Tears can occur at the upper attachment near the thighbone, in the middle of the ligament, or at the lower attachment on the fibula. MRI also reveals associated injuries. One telltale sign of a posterolateral corner injury is a bone bruise on the inner front part of the thighbone, sometimes paired with a bruise on the shinbone. An avulsion fracture at the top of the fibula, sometimes called the “arcuate sign,” can indicate that the LCL or nearby structures have pulled a small chip of bone away from its attachment.
Non-Surgical Treatment
Grade 1 and most grade 2 LCL injuries heal well without surgery. The standard approach involves a hinged knee brace, initially locked in a straight position for about two weeks to let early healing occur. After that, the brace is unlocked and the range of motion is gradually increased over the following six to eight weeks, with the flexion-extension arc expanding incrementally.
Weight bearing is typically restricted for the first two weeks, then progressively resumed. Physical therapy begins once the initial protected period ends, focusing on restoring range of motion, rebuilding strength in the muscles that support the outer knee, and retraining balance and stability. In a study of elite athletes with clinically diagnosed grade 1 and 2 LCL injuries, none required surgery, suggesting that the conservative approach works reliably for partial injuries.
About 70% of patients with grade 2 injuries and virtually all patients with grade 3 injuries use bracing for an average of four weeks, though the total rehabilitation timeline extends well beyond that.
When Surgery Is Needed
Complete grade 3 tears, especially those involving other ligaments or structures on the back and outer corner of the knee, are the primary candidates for surgery. If the knee remains unstable after a trial of bracing and rehabilitation, or if the LCL tear accompanies a cruciate ligament injury, surgical repair or reconstruction is typically recommended.
The procedure depends on the nature of the tear. If the ligament has pulled cleanly off the bone (sometimes with a bone fragment), it can often be reattached. Mid-substance tears where the tissue is too damaged to repair may require reconstruction using a tendon graft. Surgery is generally performed within the first few weeks after injury when possible, before scar tissue complicates the repair.
Recovery Timelines
Grade 1 injuries are the fastest to heal, with most people returning to normal activities within two to four weeks. Grade 2 injuries typically require six to eight weeks of structured rehabilitation before you’re back to full activity, though some athletes take longer depending on the demands of their sport.
Grade 3 injuries, whether managed surgically or not, involve the longest recovery. Post-surgical rehabilitation follows a phased approach: protected weight bearing and limited motion in the early weeks, progressive strengthening over the following months, and sport-specific training before full return. Total recovery from a grade 3 tear or surgical reconstruction commonly takes four to six months. One thing many people notice is that the sensation of knee instability can linger even after pain and swelling have resolved, particularly during activities that stress the outer knee. Rebuilding confidence in the joint is often the final phase of rehab.