PARTIAL HIP REPLACEMENT (Hemiarthroplasty)
A hip hemiarthroplasty is similar to a hip replacement but only one half of the hip joint is replaced. In a hip hemiarthroplasty the top of the thigh bone (femur) is replaced by a metal implant.
The hip joint is a ball and socket joint. The socket is formed by a cup in the pelvis, known as the acetabulum. The ball of the joint is formed by the head of the thigh bone (femur). The top part of the thighbone, just below the head, is called the neck of the femur.
A hip hemiarthroplasty may be required if the neck of the femur has been fractured, particularly if the break is close to the hip joint. If the fracture is very close to the hip joint, the blood supply to the head of the femur may be disrupted. In this case, even if the fracture healed, the head of the femur will just crumble away due to lack of blood supply.
When the hip is fractured, the socket portion (the acetabulum) is usually not injured. If the cartilage of the hip socket is in good health, the metal ball of the hemiarthroplasty can glide against the cartilage without damaging the surface. This operation is easier to do than replacing both the ball and the socket (total hip replacement), and it allows patients to begin moving soon after the surgery. This helps prevent complications that can arise due to long periods of bed rest.
Hemiarthroplasties are favored as treatment for hip fractures in the following situations:
• the fracture has disrupted the blood supply to the femoral head: in this case even if the fracture heals, the head of the femur will crumble. This is known as avascular necrosis and will lead to the hip joint failing.
• severe osteoporosis: if the bone is too brittle, other methods of fracture treatment will not be successful
• a fracture that has been present for several days
Hemiarthroplasties CAN NOT be performed if there is:
• osteoarthritis of the acetabulum: if the hip socket (or acetabulum) is worn out or damaged due to osteoarthritis, then a hemiarthroplasty will not succeed. In this case a total hip replacement may be required.
• a pre-existing infection: if there is an infection in or around a hip, then a hemiarthroplasty can not be performed