The use of humeral nails for femoral subtrochanteric fractures is rarely reported. We present a case in which a humeral nail was employed for a subtrochanteric femur fracture alongside contralateral prophylactic stabilization of the femoral neck and shaft. A 29-year-old female patient with a history of bilateral varus-producing proximal femoral osteotomies, complicated by symptomatic hardware indicating bilateral removal, sustained a subtrochanteric fracture. Given her 98-degree neck-shaft angle, a humeral nail was selected for right femur fixation. She also underwent prophylactic stabilization of the contralateral proximal femur with a humeral nail. There are limited options for addressing subtrochanteric femur fractures in patients with anatomy variations that preclude using standard femoral nails. This case demonstrates the successful off-label use of a humeral nail for subtrochanteric femur fracture when a traditional femoral nail is impossible.