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.
