Knee
Core concepts
Know ACL, PCL, and multiligament injuries; meniscal tears and repair principles; patellar instability and MPFL injury; osteochondral lesions and OCD; extensor mechanism injuries; and knee dislocation. Understand the pivot shift, Lachman, posterior drawer, dial test, and patellar apprehension tests. Meniscal tear patterns, red-zone vascularity, and root tears influence repair versus debridement. In acute hemarthrosis, consider ACL tear, patellar dislocation, and osteochondral fracture. Knee dislocation is a limb-threatening injury because of popliteal artery and peroneal nerve injury.
Traps
A Segond fracture signals an ACL tear and possible anterolateral complex injury. Do not dismiss a locked knee with a displaced bucket-handle meniscus as a simple sprain. In knee dislocation, a normal pulse does not exclude intimal arterial injury; check ankle-brachial index and obtain CT angiography when indicated. Patellar instability questions often mislabel a medial patellofemoral ligament tear as a meniscal tear. In a child, OCD of the femoral condyle may present with vague activity-related knee pain.
Worked example
A 24-year-old football player has a knee dislocation reduced on the field, a warm foot, and an ankle-brachial index of 0.7. Rule of thumb: an ABI below 0.9 after knee dislocation mandates urgent vascular evaluation with CT angiography. Do not rely on palpable pulses alone, and document peroneal nerve function before and after reduction.