The LCL (lateral collateral ligament) is on the outside of your knee. “Lateral” means “away from the midline of the body,” so the name itself tells you where it sits. It runs along the outer edge of the knee joint, connecting your thighbone to the smaller bone in your lower leg.
Where Exactly the LCL Attaches
The LCL starts at a small bony depression just behind the bump on the outer side of your thighbone (the lateral epicondyle of the femur). From there, it courses downward and attaches to the head of the fibula, the thin bone that runs alongside your shinbone on the outside of your lower leg. The attachment covers roughly 38% of the fibular head’s surface.
This ligament is part of a group of structures called the posterolateral corner, a collection of ligaments and tendons that together stabilize the back and outer portion of the knee.
How It Differs From the MCL
Your knee has two collateral ligaments, one on each side. The MCL (medial collateral ligament) is on the inside of the knee, connecting your thighbone to your shinbone. The LCL is on the outside, connecting your thighbone to your fibula. The two ligaments are also shaped differently: the MCL is wide and flat, while the LCL is thinner and rounder, more like a cord.
An easy way to remember the difference: “medial” means toward the middle of your body (inner knee), and “lateral” means away from the middle (outer knee).
What the LCL Does
The LCL’s primary job is to prevent your knee from bowing outward. When a force pushes your lower leg away from the midline of your body (called varus stress), the LCL resists that motion. It handles about 55% of that stabilizing work when the knee is nearly straight and up to 69% when the knee is bent to about 30 degrees. Without a functioning LCL, the outer side of the knee joint would gap open under stress.
How LCL Injuries Happen
LCL injuries typically result from a direct blow to the inside of the knee, which forces the outer side of the joint to stretch open. Contact sports, car accidents, and awkward landings can all deliver this type of impact. Compared to ACL and MCL injuries, isolated LCL tears are relatively uncommon. When they do occur, they often involve damage to neighboring structures in the posterolateral corner as well.
Symptoms of an LCL Injury
Because the LCL sits on the outer knee, that’s where you’ll feel the symptoms. Pain, swelling, tenderness, and bruising concentrate along the outside of the joint. Many people report a popping sensation at the moment of injury, followed by a feeling that the knee might give out, buckle, or lock up. The instability is most noticeable when you try to change direction or bear weight on the leg.
How an LCL Injury Is Diagnosed
The standard hands-on test is called a varus stress test. Your provider places pressure on the inner side of your knee while stabilizing your ankle, pushing the lower leg outward. If the outer side of the joint gaps open more than normal, or you feel pain during the maneuver, the test is considered positive. This test alone isn’t definitive, so imaging (usually an MRI) typically follows to confirm the tear and check for damage to surrounding structures.
Recovery After an LCL Tear
LCL injuries are graded on a three-point scale. A grade 1 sprain means the ligament is stretched but intact, and recovery usually involves rest, bracing, and physical therapy over a few weeks. A grade 2 tear is a partial rupture with more instability, requiring a longer course of rehabilitation. Grade 3 injuries are complete tears, and these often need surgical reconstruction, especially when other posterolateral corner structures are also damaged. Full recovery from surgery can take several months, with a structured rehab program to restore strength and stability before returning to sport or heavy activity.