The femoral head is attached to the femoral shaft by the femoral neck. The head is approximately spherical in shape, allowing it to act as the ball within the ball-and-socket hip joint. It is covered by articular cartilage that provides a tough, smooth surface for joint movement. The femoral head articulates with the acetabulum, which is also covered with articular cartilage. The entire joint is encased within the synovial membrane, which is in turn encased in the articular capsule. The membrane secretes synovial fluid to lubricate the joint, resulting in extremely low friction. Coefficients of static friction are reported as ms = 0.01 and coefficients of kinetic friction are reported as ms = 0.003.
The surface of the femoral head can be damaged by injury or disease, including labral tear, arthritis, pinched nerves, and cancer. The recommended treatment plan will depend on the diagnosis. In cases of significant joint degeneration, a total hip replacement is commonly offered. This is a surgical procedure in which the entire femoral head and neck is replaced by an implant. A mating implant, typically made of high-density plastic, is placed in the pelvis to replace the acetabulum.
The femoral neck transmits forces between the weight-bearing head and the femoral shaft. These high forces can fracture the neck, especially when the bone is weakened, as with osteoporosis. Fractures in the femoral neck are typically treated by open reduction and internal fixation (ORIF) surgery using screws, plates, and/or wires.
