An LCL injury is damage to the lateral collateral ligament, a tough, cord-like band of tissue on the outer side of your knee. This ligament is the primary stabilizer preventing your knee from bowing outward, and it can be partially or completely torn by a forceful blow or awkward twist. Isolated LCL injuries are among the least common knee ligament injuries, but they can cause significant pain and instability when they do occur.
Where the LCL Is and What It Does
The LCL runs along the outside of the knee, connecting the bottom of the thighbone to the top of the smaller lower leg bone (the fibula). Its main job is resisting what orthopedic specialists call “varus stress,” which is any force that pushes the knee outward. At about 30 degrees of bend, the LCL is the single most important structure keeping the outer side of the knee stable.
Because the LCL works alongside several other structures in the back and outer corner of the knee (collectively called the posterolateral corner), a significant LCL tear often involves damage to those neighboring structures or even to the cruciate ligaments deeper inside the joint. Purely isolated LCL tears are less common than these combined injuries.
How LCL Injuries Happen
The classic mechanism is a direct blow to the inner side of the knee, which forces the outer side to gap open. Think of a football tackle that hits the inside of a planted leg, or a collision in soccer or ice hockey. The ligament can also tear during twisting injuries or when the knee hyperextends beyond its normal range.
Contact and collision sports carry the highest risk, but LCL injuries also show up in activities that generate high rotational forces around the knee, like skiing and ice skating. Isolated LCL tears are most commonly seen in gymnasts and tennis players, where sudden direction changes and landing forces can overload the ligament without a direct hit from another person.
Symptoms to Recognize
The hallmark symptoms of an LCL tear are pain and tenderness along the outer side of the knee, swelling, and bruising. Many people hear or feel a pop at the moment of injury. What often distinguishes an LCL tear from a simple bruise or strain is a feeling of instability: the knee may feel like it’s about to give out, buckle, or lock up when you try to stand or walk.
That unstable sensation can persist even after the initial pain and swelling improve. If you notice your knee wobbling or giving way during walking, or if you feel grinding, crunching, numbness, or tingling in the knee or lower leg, those are signs the injury may be more significant than a mild sprain.
Injury Grades
LCL injuries are classified into three grades based on the extent of damage to the ligament fibers:
- Grade I (mild sprain): The ligament is stretched but not torn. You’ll have pain and tenderness on the outer knee, but the joint still feels stable.
- Grade II (partial tear): Some of the ligament fibers are torn. There’s more swelling and pain, and you may notice mild looseness when the knee is stressed sideways.
- Grade III (complete tear): The ligament is fully ruptured. On MRI, this shows up as complete discontinuity of the ligament fibers. The knee feels noticeably unstable, and the outer side gaps open under stress.
An MRI is the standard tool for confirming the diagnosis and grading the tear. It also reveals whether nearby structures like the posterolateral corner or cruciate ligaments are involved, which significantly affects the treatment plan.
Treatment for Mild and Moderate Tears
Grade I and most Grade II injuries are typically managed without surgery. The rehab process follows a structured timeline that spans roughly four months:
During the first six weeks, you’ll wear a hinged knee brace locked in a straight position and use crutches to keep weight off the joint. The focus is on protecting the healing ligament while gently maintaining muscle tone in the surrounding leg muscles.
From about six to ten weeks, the brace is unlocked to allow increasing range of motion. Physical therapy ramps up with exercises targeting strength, balance, and controlled movement. Between ten and sixteen weeks, you’ll continue wearing the brace during activity while progressing to more dynamic exercises like light jogging and lateral movement drills. After sixteen weeks, most people transition to wearing the brace only during sports or high-demand activities, if at all.
When Surgery Is Needed
Complete LCL tears (Grade III), especially those involving damage to the posterolateral corner or cruciate ligaments, often require surgical repair or reconstruction. The reasoning is straightforward: a fully ruptured LCL on its own rarely heals tightly enough to restore stability, and when multiple structures are torn, the knee becomes too loose for rehab alone to fix.
Surgery may involve stitching the torn ligament back together (repair) or replacing it with a tissue graft (reconstruction), depending on the quality of the remaining tissue and how much time has passed since the injury. Surgical recovery is longer than conservative treatment, often requiring six months or more before returning to sports.
Recovery and Returning to Activity
For mild sprains treated conservatively, most people return to full activity within two to three months. Partial tears take closer to three to four months with consistent physical therapy. Complete tears treated surgically have the longest timeline, with return to sport generally falling in the six to nine month range depending on the complexity of the repair and whether other ligaments were involved.
Throughout recovery, the lingering sense of knee instability is often the last symptom to resolve. Strengthening the muscles around the knee, particularly the hamstrings and the muscles along the outer hip and thigh, plays a major role in compensating for any residual looseness in the ligament. Many athletes continue targeted strengthening exercises and wear a supportive brace during competition well beyond the point where they feel “healed” to reduce the risk of reinjury.