A partial hip replacement, medically known as a hemiarthroplasty, is a specialized orthopedic procedure designed to restore function to a damaged hip joint. The hip is a complex ball-and-socket joint where the head of the thigh bone, or femur, fits into the socket of the pelvis, known as the acetabulum. When trauma or disease compromises the integrity of the ball portion, this targeted surgery provides an intervention to alleviate pain and restore mobility.
Understanding Partial Hip Replacement
A partial hip replacement involves the surgical removal of the damaged femoral head and neck, replacing it with a prosthetic implant. This implant consists of a metal stem that is inserted down the center of the thigh bone and a metallic or ceramic ball at the top. The artificial ball then articulates with the patient’s own natural, preserved hip socket.
The procedure leaves the acetabulum, the cup-shaped part of the pelvis, completely untouched. There are two main types of prosthetic heads used: unipolar and bipolar. A unipolar implant uses a single, fixed prosthetic ball that rotates directly inside the natural socket. A bipolar implant features a smaller prosthetic ball that swivels within a larger metal shell, which then moves inside the patient’s socket.
How it Differs from a Total Replacement
The difference between a partial hip replacement and a total hip replacement (total hip arthroplasty) lies in the extent of the anatomical structures replaced. In a partial replacement, only the femoral head and neck are substituted with a prosthetic component, retaining the patient’s natural acetabulum. A total hip replacement is a more comprehensive procedure that replaces both sides of the joint.
The surgeon replaces the damaged femoral head and neck and also resurfaces the acetabulum. The socket is lined with a prosthetic cup to provide an entirely artificial, smooth articulating surface for the new prosthetic ball. The difference in scope has implications for joint mechanics and long-term stability. While a partial replacement is generally a shorter operation with less surgical trauma, the friction of the artificial ball against the natural cartilage of the socket can potentially lead to wear and pain over time, known as acetabular erosion. A total hip replacement offers a more durable, low-friction articulation, which is why it is preferred for more active patients or those with pre-existing arthritis affecting both the ball and socket.
Specific Circumstances for Choosing Partial Replacement
The decision to perform a partial hip replacement is driven by the nature of the injury and the patient’s overall health and activity level. The procedure is most commonly indicated for displaced femoral neck fractures, particularly in older patients with lower functional demands. A displaced fracture means the bone fragments have shifted, which can disrupt the blood supply to the femoral head, increasing the risk of bone death, or avascular necrosis.
Hemiarthroplasty is favored in this acute setting because it allows for rapid mobilization and has a shorter operative time, which is beneficial for elderly patients who may have other underlying medical conditions. The procedure is only considered when the acetabulum is confirmed to be healthy, without significant pre-existing arthritis or damage. If the patient is younger, more active, or has signs of joint disease in the socket, a total hip replacement may be chosen instead, even in the setting of an acute fracture, as it offers better long-term durability and function. For patients who are less active or have a shorter life expectancy, the reduced complexity and quicker recovery of the partial replacement outweigh the risk of future acetabular wear.
Immediate Post-Surgical Expectations
Immediate post-surgical care focuses on pain management and early movement. Hospital stays are typically short, often lasting only one to two days. Pain management is initiated immediately, often using a combination of intravenous and oral medications, which are transitioned to oral pain relievers before discharge.
Physical therapy begins very quickly, sometimes on the day of the operation, with the goal of getting the patient out of bed and walking short distances with assistance. Patients are often allowed immediate full weight-bearing on the operative leg, depending on the stem fixation method, which significantly aids in early rehabilitation. Therapists instruct patients on safe movement techniques, including using assistive devices like a walker or crutches, to prevent potential complications such as hip dislocation. Continued outpatient or home-based physical therapy is crucial for several weeks to months to regain strength and full range of motion.