Collateral Ligament Injuries of the Knee
MCL and LCL Injuries picture album Several images illustrating the anatomy and mechanisms of injury of the collateral ligaments of the knee.
The knee joint is formed where the femur (the thigh bone)  meets the tibia (the shin bone).  Ligaments are band- like  structures that hold bones together.  The femur and tibia are  held together by four main ligaments.   The ligaments on the side of the knee are known as the  collateral ligaments.  They keep the knee from bending too  far to the side. The ligaments on the inside of the knee joint are known as  the cruciate ligaments because they cross.   The anterior cruciate ligament, or ACL, keeps the tibia from  gliding too far forward in relation to the femur.  The posterior  cruciate ligament, or PCL, keeps the tibia from gliding too far  backward in relation to the femur.  The cruciate ligaments  also contribute to rotational stability. The lateral collateral ligament keeps the knee from bending  too far to the inside. LCL injuries occur when an inward bending force (varus  force) is applied to the knee.  For example, the knee may be  struck from the inside with the foot planted, causing it to  bend inward. Sprains are injuries to ligaments.  They are graded from 1 to  3.  Grade 1 sprains occur when the ligament (such as the  LCL) is stretched but not grossly torn.  Grade 2 sprains are  partial tears.  Grade 3 sprains are complete tears. Lateral collateral ligament injuries are usually diagnosed  based on how the injury occured, symptoms, and a physical  exam.  A varus stress (inward bending force) may be applied  to the knee to check for instability.  This would indicate a  complete tear. X-rays may be obtained to look for fractures (broken bones).   Magnetic resonance imaging (MRI) may be used to confirm  that there is a lateral collateral injury and to rule out other  injuries.  LCL injuries often occur with other injuries such as  meniscus tears or posterolateral corner injuries.  Treatment for LCL injuries depends on whether the LCL is  completely torn and whether there are other injuries present. Grade 1 and 2 sprains are usually treated with rest, ice, and  bracing.  The brace is locked in extension or with the knee  slightly bent.  This puts the LCL at rest so it can heal.  Partial  weightbearing with crutches is permitted for a few weeks.   After this period of immobilization, range-of-motion and  weightbearing are gradually increased. Grade 3 sprains may also be treated with bracing, but  sometimes require surgical repair or reconstruction.  “Repair”  means that the torn ends of the ligament are sewn back  together.  This is usually only possible within 2-3 weeks of  the injury.  “Reconstruction” means that a graft is used to  replace the torn LCL. Recovery after an LCL injury depends on the severity of the  tear and the presence of other injuries.  Mild grade 1 sprains  may heal within a few weeks (2-4 weeks).  Grade 2 sprains  take longer (6-8 weeks).  Following surgery for grade 3  strains, several weeks of rehabilitation are necessary.