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Knee Ligament Injuries (MCL, ACL, Unhappy Triad)
General Notes
MCL and ACL are the most common knee ligament injuries. Meniscus injury and repair is also a very common knee operation.
Clinical exam is often sufficient for diagnosis but when imaging is necessary MRI is the preferred modality.
Generally, conservative treatment for ligament injury involves rest, ice, compression, stabilization (knee brace), and elevation (knee above heart for optimal venous return), and pain meds as appropriate. If severe or associated with major trauma or other ligament injuries, refer to ER/Orthopedics as appropriate.
Medial Collateral Ligament (MCL) (aka Tibial Collateral Ligament)
General
This is arguably the most common knee ligament injury; however, it is often mild and is treated conservatively (thus it's underreported compared to ACL injury). It occurs due to sudden valgus (inward) bend movement to the knee.
Physical Exam
Physical examination demonstrates medial knee pain and variable valgus laxity.
- Grade 1: Pain and NO valgus laxity when flexed.
- Grade 2: Pain and valgus laxity when flexed to 30 degrees.
- Grade 3: Pain and valgus laxity at rest and when flexed to 30 degrees
Anterior Cruciate Ligament (ACL)
General
The most common knee ligament injury to require surgery. Often occurs due to sudden opposing rotational movements of the femur and tibia, due to sudden pivoting movement.
Physical Exam
The Lachman maneuver and anterior drawer maneuver are the two most common/reliable physical exam tests to evaluate ACL integrity.
Posterior Cruciate Ligament (PCL)
General
Typically occurs in the setting of other knee ligament injuries. When isolated, it may occur due to a direct blow to the anterior tibia (causing hyperextension of the knee).
Physical Exam
The posterior drawer test is used to evaluate joint stability.
Lateral Collateral Ligament (LCL) (aka Fibular Collateral Ligament)
General
This is a rare form of knee ligament injury.
Physical Exam
Look for any associated peroneal nerve injury.
Unhappy Triad ("Blown Knee")
Injury to the ACL, MCL, and medial meniscus. Severe injury that is often due to forceful impact to the lateral leg, causing a valgus (inward) bend to the knee, on a planted foot.
Meniscus Injury
A common knee surgery is meniscus repair. The McMurray test is a physical exam test used to assess knee meniscus integrity.
Detailed Knee Anatomy
See Knee Anatomy for detailed anatomy of the knee.