Key diagnostic factors

presence of risk factors (common)

• Risk factors include participation in activities involving valgus stress at the knee joint, age 20 to 35 years (most likely to engage in high-risk athletic pursuits), and age 55 to 70 years (more prone to MCL injuries during falls).

injury due to excessive or repetitive valgus loading of MCL (common)

• Lower-grade MCL injuries frequently occur with non-contact valgus and external rotation injuries (e.g., twisting injuries during ski accidents).
• More severe injuries are usually associated with a blow to the lateral side of the knee.

medial knee pain (common)

• MCL injury is associated with pain on the medial side of the knee along the length of the ligament, both above and below the joint line.
• Paradoxically, higher-grade MCL injuries are usually associated with less pain, perhaps because there is little or no tension on the injured ligament. [13]

joint effusion (common)

• The location of joint effusion has been shown to correlate with the injury site in the superficial MCL 64% of the time. [13]
• Absence of joint effusion may indicate a severe tear: grade III injuries result in tearing of the joint capsule, allowing fluid to escape to surrounding soft tissues.
• Speed of onset of swelling provides clues to the pathology involved. An acute effusion, within 2 hours of injury, suggests haemarthrosis. Swelling 12 to 24 hours after injury usually indicates a synovial effusion. [16]
• Haemarthrosis, while uncommon, is suspicious for injury to the anterior cruciate ligament.

tenderness (common)

• Usually occurs at the adductor tubercle or proximal tibia. In 76% of cases, the site of tenderness corresponds with the site of injury in the superficial MCL. [13] Medial meniscal tears have tenderness limited to the joint line.

laxity on valgus stress testing (common)

• The abduction stress test (i.e., applying a valgus load to the knee) at 30° flexion is an excellent diagnostic tool. View image Pain and disproportionate laxity imply stretching or tearing of the MCL.
• Pain and laxity with valgus stress in a fully extended knee suggest coexistent anterior cruciate ligament tear. [16]

Other diagnostic factors

ecchymosis (common)

• Ecchymosis over the MCL often develops 1 to 3 days after injury.

audible pop or tearing sensation at time of injury (uncommon)

• Suggests grade III MCL injury or cruciate ligament injury.

difficulty walking (uncommon)

• Most patients are able to continue walking after an acute injury. In one study, even with grade III MCL injuries, 76% of patients were able to walk into a surgery unaided by external support. [13]

instability symptoms of knee (uncommon)

• Most MCL injuries are not associated with instability symptoms ("giving way"). The rare exception is injury to the posterior oblique portion of the deep MCL, which can result in anteromedial instability.
• If instability is a prominent feature, ACL or PCL injury is likely.

mechanical knee symptoms (uncommon)

• Symptoms such as catching, locking, giving way, and popping are not usually associated with MCL injuries. Concomitant meniscus tear or cruciate ligament injury should be suspected.

knee deformity (uncommon)

• May signify patellar subluxation or dislocation.

positive anterior drawer test (uncommon)

• Test is performed with the foot in external rotation and knee flexed at 90°.
• Any anteromedial instability evident during test View image suggests that the deep MCL may be damaged, specifically the posterior oblique portion.

positive posterior drawer test (uncommon)

• Test is performed the same way as an anterior drawer test but with a push on the tibia.
• Any laxity indicates injury to the posterior cruciate ligament.

positive Lachman's test (uncommon)

• The best diagnostic test for anterior cruciate ligament (ACL) injury. View image
• The patient's knee is put in 20° to 30° of flexion. One hand is placed on the patient's thigh and the other behind the tibia (with the thumb on the tibial tuberosity). The tibia is pulled anteriorly.
• The incidence of ACL tears has been found to be 20% when there is no valgus laxity on clinical examination, 53% with valgus laxity in 30° of flexion, and 78% with valgus laxity in full knee extension. [4]

positive pivot shift test (uncommon)

• Used in conjunction with the Lachman's test for diagnosing anterior cruciate ligament (ACL) injury.
• An internal rotation and valgus stress is applied on the knee while taking it from 20° to 40° of flexion. In an ACL-deficient knee, the tibia will anterolaterally sublux in the initial phase of flexion and then reduce with further flexion.

joint line tenderness (uncommon)

• Although not the most sensitive or specific sign for meniscal injury, [22] joint line tenderness may indicate potential meniscus pathology.

chronic pain (uncommon)

• Knowing when the patient injured his or her knee helps to distinguish acute MCL injuries from chronic ones. Chronic is usually defined as having an MCL injury 3 or more months previously. [3]