9.14 Knee Sprain

agk’s Library of Common Simple Emergencies

Presentation

An athlete may have planted the foot while decelerating, torn the anterior cruciate ligament allowing the tibia to dislocate anteriorly, fallen to the ground where it spontaneously relocated, and not been able to get up. Alternatively, he may have been clipped on the lateral knee, causing a valgus deformity which tore the medical collateral ligament and perhaps the medial meniscus and anterior cruciate as well. An adolescent girl may have dislocated her patella laterally, tearing the medial retinaculum. These sorts of injury tend to come to the ED within an hour or two, in pain, holding the knee flexed ten to twenty degrees, with a tense joint effusion and quadriceps spasm which prevents detailed diagnosis by physical examination.

What to do:

• If the patient has not already done so, ice and elevate the injury.
• Load with anti-inflammatory analgesics like ketorolac (Toradol) 60mg im or ibuprofen (Mortin) 800mg po.
• Examine as permitted by pain. Clear the back and pelvis. Check hip flexion, extension, and rotation. Thump the sole of the foot as an axial loading clue to a tibia or femur fracture. Document any effusion, discoloration, heat, deformity, loss of function, circulation, sensation, movement.
• Document the range of motion, then carry out the rest of the exam with the knee slightly flexed, always comparing to the uninjured knee. Palpate the medial and lateral collateral ligament and test them with varus and valgus stress. Palpate the joint line anteriorly to assess the menisci and tibial plateaux. Drawer the tibia anterior and posterior to test the cruciates (the Lachman test).
• Obtain x rays.
• Aspirate the joint only if you need to rule out infection or obtain a few hours of mobility.
• Discharge the patient with the knee immobilized in a splint or Jones dressing, crutches, a prescription for NSAIDs, and an appointment for orthopedic re-evaluation in 3-4 days.

Discussion

Chronic injuries can also be treated with NSAIDS, immobilization, and crutches. Examples include meniscal tears and joint mice, which may present with a history of the knee catching or giving way, and even flareups of osteoarthritis, degenerative joint disease, and pseudogout.

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