Hemiarthroplasty is a surgical procedure that involves replacing only one part of a joint with an artificial implant. The term is derived from the Greek word “hemi,” meaning half, and “arthroplasty,” meaning joint replacement. This procedure is most commonly performed in the hip, replacing the ball of the ball-and-socket joint. While the hip is the most frequent site, hemiarthroplasty can also be used in other joints, such as the shoulder, when only one surface is damaged.
Indications for Hemiarthroplasty and Differentiation
The primary reason for hemiarthroplasty is to treat acute, displaced fractures of the femoral neck, the bone connecting the hip joint ball to the thigh bone. These fractures are common in older patients, often resulting from a low-energy fall. Damage to the blood supply in these cases creates a high risk of avascular necrosis (bone death) if the fracture is only fixed with screws.
Choosing hemiarthroplasty over a total hip arthroplasty (TJA) depends on the condition of the hip socket (acetabulum) and the patient’s expected activity level. In hemiarthroplasty, the prosthetic ball is seated directly into the patient’s native acetabulum. This procedure is only suitable if the socket cartilage is healthy and free of severe arthritis.
A total hip replacement, in contrast, replaces both the femoral head and lines the acetabulum with an artificial cup. Hemiarthroplasty is generally quicker and less invasive, which is preferable for elderly patients with lower functional demands and other existing medical conditions. While TJA may offer better long-term function for younger, active individuals, the partial replacement is often the deciding factor for older patients with acute fractures.
The Surgical Procedure and Implants
The procedure begins with the patient under anesthesia, and the surgeon makes an incision to access the hip joint, often using a posterior or lateral approach. Once exposed, the damaged femoral head is removed from the top of the femur. The medullary canal (the hollow interior of the femur) is then prepared to accept the implant’s stem component.
A metallic stem is inserted down the shaft of the femur, secured either with bone cement or by press-fitting a textured stem that allows for bone ingrowth. Bone cement is often preferred in older patients with softer, osteoporotic bone, as it provides immediate fixation and allows for earlier weight-bearing. Once the stem is secure, the new prosthetic ball (hemi-head) is attached.
Hemiarthroplasty implants are categorized into two main types: unipolar and bipolar. A unipolar implant is a single, fixed piece where the prosthetic head and stem are one unit, meaning movement occurs only between the prosthetic head and the natural acetabulum. A bipolar implant features two moving parts, with a small inner bearing that allows the prosthetic head to swivel independently of the stem. This design aims to reduce wear on the natural socket.
Recovery Timeline and Rehabilitation
Following surgery, pain management is a top priority to facilitate early mobilization. Patients are encouraged to stand and walk with assistance, such as a walker or crutches, as early as the first day after the operation. The average hospital stay is short, often lasting only a few days, depending on the patient’s overall health and mobility progress.
Physical therapy (PT) begins immediately and is crucial for restoring function and strength. The rehabilitation program focuses on range-of-motion exercises and strengthening the hip muscles, including the abductors and extensors. Patients must adhere to specific “hip precautions,” which limit movements—such as avoiding bending the hip past 90 degrees—to prevent the prosthetic ball from dislocating.
Recovery varies based on individual factors, but patients typically use a walking aid for at least six weeks. Most people return to walking without assistance and resume daily activities, such as driving, between three and six months after the procedure. Risks during the recovery phase include infection, blood clots, and the possibility of prosthetic dislocation, which the medical team monitors.