Both are ligaments on the side of the knee, both are sprained by a sideways force, and both are graded 1 to 3. The MCL runs down the inner side of the knee and resists the knee being pushed inward. The LCL is a thinner cord on the outer side and resists the knee being pushed outward. Where it hurts and how the injury happened help tell them apart. The exam then checks which ligament is injured and whether anything else is involved. The MCL is the knee ligament injured most often. An LCL injury is less common and can be part of a larger injury to the outer and back corner of the knee, so the exam checks for that as well.
The MCL is the medial collateral ligament. The LCL is the lateral collateral ligament, also called the fibular collateral ligament.
Written by Kareem Hassanein, Registered Physiotherapist. Burlington, Ontario. This is a guide, not a diagnosis. An in-person exam usually narrows it down, though the two can overlap and some cases need imaging or a second look.
When to see a doctor firstOther ComparisonsThe patterns that separate MCL sprain from LCL sprain in clinic. Read across each row and compare.
| Aspect | MCL sprain | LCL sprain |
|---|---|---|
| Where it hurts | Along the inner side of the knee, often tender at one spot near the thigh-bone or shin-bone end of the ligament. | Along the outer side of the knee, often tender over a cord you can feel when the leg is crossed in a figure-four position. |
| How it usually happens | A blow to the outside of the knee, or the knee collapsing inward during a cut, a ski fall or a tackle. | A blow to the inside of the knee, or the knee being forced outward, often with the knee close to straight. |
| Swelling | Often local, along the inner side. A large swelling inside the joint suggests something else may be injured as well. | Often local, on the outer side. Marked swelling or bruising toward the back of the knee raises the question of a larger injury. |
| The test that stresses it | Gentle inward stress on the knee (valgus stress) at about 30 degrees of bend. | Gentle outward stress on the knee (varus stress) at about 30 degrees of bend. |
| What can be injured with it | The ACL, either meniscus and, in more severe injuries, other knee ligaments. | The outer and back corner of the knee, the cruciate ligaments, and the nerve that runs around the outside of the knee. |
| Usual management | Grade 1 and 2 sprains, and many grade 3 sprains without other injuries, are managed without surgery. Rehabilitation includes protection from sideways stress, movement as tolerated and progressive strengthening exercises. | Lower-grade sprains of the LCL alone are usually managed without surgery. Marked looseness or a suspected combined injury needs prompt medical assessment. A complete injury to the outer and back corner of the knee is most often treated surgically. |
Along the inner side of the knee, often tender at one spot near the thigh-bone or shin-bone end of the ligament.
Along the outer side of the knee, often tender over a cord you can feel when the leg is crossed in a figure-four position.
A blow to the outside of the knee, or the knee collapsing inward during a cut, a ski fall or a tackle.
A blow to the inside of the knee, or the knee being forced outward, often with the knee close to straight.
Often local, along the inner side. A large swelling inside the joint suggests something else may be injured as well.
Often local, on the outer side. Marked swelling or bruising toward the back of the knee raises the question of a larger injury.
Gentle inward stress on the knee (valgus stress) at about 30 degrees of bend.
Gentle outward stress on the knee (varus stress) at about 30 degrees of bend.
The ACL, either meniscus and, in more severe injuries, other knee ligaments.
The outer and back corner of the knee, the cruciate ligaments, and the nerve that runs around the outside of the knee.
Grade 1 and 2 sprains, and many grade 3 sprains without other injuries, are managed without surgery. Rehabilitation includes protection from sideways stress, movement as tolerated and progressive strengthening exercises.
Lower-grade sprains of the LCL alone are usually managed without surgery. Marked looseness or a suspected combined injury needs prompt medical assessment. A complete injury to the outer and back corner of the knee is most often treated surgically.
These are the tests I use at the first visit. You cannot do them all on yourself reliably, but knowing what each one looks for helps explain how an in-person exam narrows things down.
I press along each ligament from end to end. A single sore spot on one side of the knee is a useful pointer to which ligament is involved.
With your knee bent to about 30 degrees, I apply a gentle sideways stress in each direction and compare it with the other knee. I am looking at how far the joint opens and whether it comes to a firm stop.
Increased opening compared with the other knee when the leg is fully straight suggests a more extensive injury. If I find that, I refer you on.
A side ligament sprain after a bigger injury can come with other injuries, so I also screen the cruciate ligaments and the menisci.
With an injury on the outer side of the knee, I check the nerve that lifts the foot and supplies feeling to the outer shin and the top of the foot.
This is not a diagnosis. Symptoms can overlap, and the descriptions below are a starting point.
Your pattern more closely matches an MCL sprain if the pain is on the inner side, the knee was struck from the outside or collapsed inward, and it is tender along the inner ligament. Turning and cutting often feel worse than walking in a straight line.
Read the MCL sprain pageYour pattern more closely matches an LCL sprain if the pain is on the outer side, the knee was forced outward or struck from the inside, and it is tender over the cord on the outer side.
Read the LCL sprain pageLocation alone can mislead. The outer side of the knee also holds the IT band, the outer meniscus and a hamstring tendon, and the inner side holds the inner meniscus and a group of tendons just below the joint. An in-person exam usually narrows it down. Either injury can make the knee feel unstable, and pain and swelling can limit some tests in the first days, so I may repeat them at a later visit. If I find marked looseness, increased opening with the knee straight, or signs that more than one structure is injured, I flag it to your family doctor or a sports medicine doctor and refer you. Imaging can be arranged there when it would change the plan.
A single sideways blow opens one side of the knee and compresses the other, so it is unusual for one blow to sprain both. Both can be injured in a higher-energy injury, usually together with a cruciate ligament, and that knee needs a medical assessment.
Neither is worse by name; the grade and what else is injured matter more. Many MCL sprains recover without surgery. An LCL injury with marked looseness, or with damage to the outer and back corner of the knee, needs prompt medical assessment.
It depends on the grade, on what else is injured, and on what you are returning to. A mild sprain of either ligament often settles in weeks, while a higher-grade sprain can take months. I set expectations after the exam. Return to sport depends on how the knee tests and feels, alongside the time the ligament needs to heal.
Not always. Many lower-grade sprains are assessed and managed on the exam alone. I cannot order imaging. When imaging would change the plan, I flag it to your family doctor or specialist and refer you.
A hinged brace is sometimes used to limit sideways stress while the ligament heals, particularly when the knee is less stable. Studies of MCL rehabilitation vary in whether a brace is used and for how long. Whether a brace makes sense for you, and for how long, depends on the injury and the exam.
Often, in a modified way. Straight-line work is usually tolerated before cutting, pivoting and contact. I set the progression from how the knee responds.
The main sources behind this comparison.
Describes the medial collateral ligament as the most commonly injured ligament in the knee, and reports that isolated grade I and II tears and most grade III tears can be treated without surgery with a supervised, functional rehabilitation program.
Giannotti BF, Rudy T, Graziano J. "The non-surgical management of isolated medial collateral ligament injuries of the knee." Sports Medicine and Arthroscopy Review 2006; 14(2): 74-77.
A systematic review of 26 reports on non-operative treatment of isolated MCL injuries found that rehabilitation used strengthening exercises with poorly reported details, and that the use of a brace and how long it was worn were reported inconsistently.
Svantesson J, Piussi R, Weissglas E, et al. "Shedding light on the non-operative treatment of the forgotten side of the knee: rehabilitation of medial collateral ligament injuries, a systematic review." BMJ Open Sport & Exercise Medicine 2024; 10(2): e001750.
A review of injuries to the outer and back corner of the knee, which includes the lateral collateral ligament, reports that complete injuries rarely heal with non-operative treatment and are most often treated surgically, and that these injuries can be missed without a careful exam.
Chahla J, Moatshe G, Dean CS, LaPrade RF. "Posterolateral Corner of the Knee: Current Concepts." Archives of Bone and Joint Surgery 2016; 4(2): 97-103.
I assess and treat these conditions at Endorphins Health & Wellness Centre in Burlington. Direct insurance billing is available, and a physician referral is not required.
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