What is your diagnosis?

Isolated medial collateral ligament (MCL) tear. 

• Pearl: Isolated MCL tears are usually seen with a valgus force applied to an already flexed knee without rotational forces. 

• Pearl: When rotational forces are applied to the knee, it more commonly results in multiple ligament injuries, such as those seen in the unhappy knee triad (MCL tear, medial meniscus injury, and ACL tear).

•  In the absence of a knee effusion; multiligamentous injury, ACL tear, patellar dislocation, or meniscal injury are much less likely.

What do you expect on the physical exam?

Increased laxity with valgus stress test as compared to the other side. Normal anterior drawer/Lachman, normal varus stress testing. Minimal to no joint effusion.

• Pearl: In MCL tears, there will be increased laxity when valgus stress is applied due to the ligament compromise. MCL tears are graded according to the degree of knee flexion at which valgus laxity can be reproduced. Grade I: no laxity, Grade II: laxity at 30º flexion, Grade III: laxity at 30º and 0º flexion.

What imaging modality could be used to aid in diagnosis in the ED?

Ultrasound and plain films

Figure 2 (same as above). AP and lateral plain films showing soft tissue swelling and edema. No fracture or dislocation seen. Author’s own images.

Figure 3A. Ultrasound imaging of the affected knee showing increased laxity of the MCL when valgus stress is applied as compared to the unaffected knee (Figure 3B). Author’s own media.

Figure 3B. Ultrasound images of the asymptomatic knee with valgus stress being applied. Imaging shows no medial laxity of the MCL ligament. Author’s own media.

• Pearl: With bedside ultrasound modalities, it is possible to evaluate the valgus laxity of the affected knee in a dynamic manner and to compare it with the unaffected knee. The extensor mechanism of the knee as well as the joint space can be evaluated to look for effusion or associated injuries. 

Plain radiographs are needed in order to rule out fracture or avulsion injury. Can use Ottawa Knee rules to decide on appropriate imaging in ED.

What do you do in the ED?

Stabilize the knee with hinged knee brace to protect from further valgus stress. 

• Pearl: If hinged knee brace is not available in the ED and high grade injury suspected, a knee immobilizer may be applied until the patient can obtain a hinged knee brace on an outpatient basis. Due to complications associated with knee immobilizer use (e.g. skin ulcerations), can consider ACE wrap with non weight bearing precautions and crutches.

When do you call Orthopaedics?

Emergent operative treatment is generally not needed for isolated MCL injuries, but close follow up should be obtained with either orthopaedics or sports medicine to evaluate healing and presence of persistent laxity. Orthopaedics should be consulted for any open fracture, suspected knee dislocation, or presence of neurovascular deficit. 

• Pearl: Operative treatment is indicated if there is a persistent inability to tolerate valgus laxity or if there are any bony avulsions seen on plain films. Distal MCL injuries have lower healing rates than proximal injuries.