The femoral shaft (diaphysis) is the cylindrical long bone segment between the lesser trochanter and the femoral condyles. Its cross-section is roughly circular with a slight anterior bow (femoral anteversion axis). The linea aspera runs along the posterior surface as a roughened longitudinal ridge providing attachment for adductors, vastus medialis, vastus lateralis, biceps femoris short head, and the nutrient artery foramen. The femoral shaft is the strongest bone in the body.
Femoral shaft fractures are high-energy injuries in young adults (road traffic accidents, falls from height) and pathological fractures in the elderly from metastatic disease or osteoporosis. Intramedullary nailing is the gold standard treatment, providing load-sharing fixation aligned with the mechanical axis. The femoral anterior bow must be matched by the nail curvature to avoid anterior cortex perforation. Stress fractures occur in the medial femoral cortex (compression side, relatively safe) and lateral cortex (tension side, high risk of complete fracture requiring prophylactic nailing).
High-energy transverse, oblique, comminuted, or segmental fractures of the femoral shaft produce marked thigh swelling, shortening, and deformity with blood loss of 1-2 litres into the thigh, managed by intramedullary nailing with reduction of blood loss, early mobilisation, and restoration of limb length and alignment.
Repetitive loading in distance runners and military recruits causes fatigue stress fractures, most dangerous on the lateral (tension) femoral cortex where incomplete fractures can rapidly propagate to complete displaced fractures; identified by MRI and managed by prophylactic intramedullary nailing for lateral cortex involvement.
