An LCL injury is a sprain or tear of the ligament on the OUTSIDE of your knee.
A mild or moderate LCL sprain on its own usually heals without surgery. Typical recovery is about 3 to 4 weeks for grade 1 and roughly 6 to 12 weeks for grade 2.
The catch: the LCL is rarely hurt alone.
It is part of the posterolateral corner, a group of structures at the back and outer side of the knee. A bad injury here usually comes with a torn ACL or PCL, and a complete posterolateral corner tear often needs surgery EARLY, ideally within 2 to 3 weeks.
So the first job after an outer knee injury is not rehab. It is getting the right diagnosis quickly.
What the LCL and posterolateral corner do
The lateral collateral ligament (LCL) runs down the outer side of the knee, from the thighbone to the top of the fibula, the thin bone on the outside of your lower leg. It stops the knee bowing outward.
The posterolateral corner (PLC) is the LCL plus several tendons and ligaments just behind it. Together they stop the knee bowing outward, twisting outward and bending backward too far.
- A blow to the inside of the knee, which pushes the knee outward, such as a tackle in football or rugby
- The knee forced backward, from landing on a straight leg or a hit to the front of the shin
- A twist with the foot planted, common in soccer, basketball and skiing
- Car crashes and falls from a height, which are more likely to tear several ligaments at once
An LCL tear on its own is uncommon. About 7 in 10 posterolateral corner injuries come with a torn cruciate ligament, the ACL or PCL inside the knee. See PCL injury.
Symptoms
- Pain and tenderness along the outer side of the knee
- Swelling and bruising, sometimes less than you would expect for how unstable the knee feels
- Giving way, especially when the knee is straight, on stairs, or when you twist and pivot
- A sideways lurch when you walk, where the knee bows outward each time you put weight through it
- Numbness on the top of the foot, or trouble lifting the foot and toes, which means a nerve has been hurt too
The three grades
- Grade 1: the ligament is stretched but not torn. The knee is sore but stable
- Grade 2: some fibers are torn. The outer knee opens a little when tested, but the ligament still holds
- Grade 3: the ligament is completely torn. The knee opens noticeably, and the rest of the posterolateral corner and other ligaments are usually damaged too
A doctor or physio tests the LCL by pushing the knee inward to open up the outer side, and checks the corner by turning the shin outward with the knee bent. An MRI is usually needed if the knee feels at all unstable, because what matters most is what ELSE is torn. Compare the inner-knee ligament in MCL injury.
A sprained LCL on its own usually heals. A torn posterolateral corner usually doesn’t, and the window to fix it well is short.
Why an isolated LCL heals and the corner often needs surgery
The outer side of the knee has less built-in stability than the inner side. The end of the thighbone and the top of the shinbone are both rounded on that side, so the joint depends on its ligaments rather than its bony shape. A complete tear there tends to heal long and loose rather than tight.
- Early repair works best: in the first 2 to 3 weeks, torn structures can often be stitched or reattached to bone. After that, scar tissue forms and the ends pull back, so a reconstruction using a tendon graft becomes the usual option
- It protects other repairs: a missed posterolateral corner injury is a well-known reason an ACL or PCL reconstruction later stretches out and fails. See ACL reconstruction recovery
- A loose outer knee wears badly: left alone, it can keep giving way and put extra load on the joint surfaces
Recovery without surgery
This applies to grade 1 and 2 LCL sprains with no other ligament torn. Your doctor may give you a different plan. Use theirs.
- First week: ice, elevation and crutches if you are limping badly. Your doctor may ask you to keep weight off the leg for a short time
- Brace: a hinged knee brace is common for about 3 to 6 weeks. It blocks the knee from bowing outward but still lets it bend and straighten
- Weeks 1 to 6: regain full bend and straightening, tighten the thigh muscle, use a stationary bike, then build hip and thigh strength and one-leg balance
- Return to sport: when the knee is stable when tested, strength is close to the other side, and you can run, hop and cut without pain. Grade 1 often takes about 3 to 4 weeks; grade 2 often takes 6 to 12
- Avoid for now: pivoting sports and snapping the knee back to straight
After surgery
- Crutches and brace: expect several weeks of limited weight on the leg while the repair or graft heals. See weight-bearing after surgery
- Motion comes back gradually, guided by your surgeon’s limits, while the thigh muscle is kept working
- Return to sport usually takes many months, often 6 months or longer, and longer again if a cruciate ligament was reconstructed at the same time
For a clear explanation of the grades and treatment options, see OrthoInfo’s guide to collateral ligament injuries.
Go to the emergency department if
- Your foot is numb, cold or pale after a knee injury
- You can’t lift your foot or toes up, so your foot drags or slaps when you walk (foot drop). The peroneal nerve, which wraps around the outer knee, is injured in somewhere between about 1 in 6 and 1 in 3 serious posterolateral corner injuries
- The knee looked out of place, even if it went back by itself. That can mean the knee dislocated, which can damage the main artery behind it
- Your calf becomes painful, swollen or warm
Get it checked within days if
- You hurt the outer knee and it feels unstable, especially if it buckles backward or sideways
- You heard a pop and the whole knee swelled within a few hours
- You can’t put weight on the leg
See your doctor or physio if
- The knee still gives way after 6 weeks of rehab
- You notice the knee bowing outward when you walk
- Pain and swelling aren’t improving week to week
A sprained outer knee needs time. A torn posterolateral corner needs a surgeon, and it needs one soon.