The hip joint is a ball-and-socket structure where the rounded top of the thigh bone (femoral head) fits into the cup-shaped socket in the pelvis (acetabulum). When the joint is severely damaged, a hip replacement may be necessary to restore function and relieve pain. A total hip replacement replaces both the ball and the socket with artificial components. A partial hip replacement, or hemiarthroplasty, is a targeted procedure that addresses only one part of the damaged joint.
Understanding Hemiarthroplasty
Hemiarthroplasty involves replacing the “ball” (femoral head) of the hip joint while leaving the natural “socket” (acetabulum) untouched. The surgeon removes the damaged femoral head and replaces it with a metal or ceramic prosthetic component.
This artificial ball is attached to a stem secured inside the hollow center of the femur. Prosthetic options include a unipolar design (a single ball component) or a bipolar design (a smaller head rotating within a larger metallic head). Because the acetabulum remains intact, this procedure is less complex than a total hip replacement, often resulting in less blood loss and shorter surgical time.
Surgical Selection Criteria
The decision between a partial and a total hip replacement hinges on the condition of the patient’s acetabulum. If the cartilage lining the socket is healthy and shows no signs of significant wear or arthritis, hemiarthroplasty is the preferred option. Preserving the undamaged natural socket can lead to a less invasive surgery and potentially a faster recovery.
If imaging reveals the acetabulum is damaged by chronic conditions like advanced osteoarthritis or rheumatoid arthritis, a total hip replacement is necessary. In those cases, both the ball and the socket must be replaced with prosthetic components. While hemiarthroplasty is less extensive, using a prosthetic ball against the natural cartilage carries a risk of future socket erosion. This erosion can lead to pain and potentially require a second surgery years later to convert it to a total replacement.
Specific Indications for Partial Replacement
A partial hip replacement is most commonly performed as an emergency procedure following an acute fracture of the femoral neck. This fracture occurs in the area connecting the ball of the femur to the shaft of the thigh bone and is common in older adults, often resulting from a low-energy fall.
A displaced femoral neck fracture can severely compromise the blood supply to the femoral head, leading to avascular necrosis, where the bone tissue dies. Since the bone cannot heal properly, replacing the damaged head with a prosthesis is the most reliable way to restore mobility quickly. Total hip replacement is typically indicated for patients suffering from long-term, degenerative conditions that have caused widespread damage, such as severe arthritis. For a patient with a clean fracture but a healthy socket, hemiarthroplasty offers a direct solution.
Post-Operative Expectations and Rehabilitation
Recovery begins almost immediately after the procedure, aiming to get the patient safely mobile as soon as possible. Most patients are encouraged to begin standing and walking with assistance, such as a walker, within 24 hours of surgery. The typical hospital stay for a hemiarthroplasty is short, often ranging from two to four days, depending on the patient’s progress.
Physical therapy starts in the hospital and focuses on strengthening the muscles around the hip and restoring a normal walking pattern. Patients are advised to follow specific movement precautions to prevent the prosthetic joint from dislocating, such as avoiding bending the hip past a 90-degree angle. While a return to daily activities is often achieved within several weeks, a full functional recovery can take anywhere from three to six months.