Anatomy (Lower Extremity, Histology, Embryology)
Lower extremity and foundational anatomy
The lower limb is organized into fascial compartments whose boundaries determine which vessels and nerves are vulnerable in trauma and compartment syndrome. Know the femoral triangle, adductor canal, popliteal fossa, tarsal tunnel, and the course of the tibial and common fibular nerves. The common fibular nerve wraps the fibular neck, so a proximal fibular fracture can cause foot drop. The anterior compartment is supplied by the deep fibular nerve; the lateral compartment by the superficial fibular nerve. In the leg, the posterior compartment contains the tibial nerve and posterior tibial vessels. In the foot, understand the medial and lateral plantar nerves, the plantar arterial arch, and the layers of intrinsic muscles.
Histology questions often test tissue recognition rather than rote location. Distinguish the four basic tissues, cartilage types, bone remodeling, and skin layers. Embryology questions favor limb bud outgrowth, somite-derived muscle, neural crest derivatives, and programmed cell death in digit separation.
Traps and worked rule
A common trap is confusing the femoral nerve with the femoral sheath contents. The femoral nerve lies outside the femoral sheath, lateral to the artery; within the sheath, the artery is lateral to the vein. A useful rule is NAVEL from lateral to medial in the femoral triangle: Nerve, Artery, Vein, Empty space/lymphatics. Remember the nerve is not in the sheath, so a femoral sheath hematoma does not directly compress the nerve in the same way it compresses the vessels.