A bipolar hemiarthroplasty is a specific surgical procedure used to replace the head of the thigh bone, or femur, which forms the ball part of the hip’s ball-and-socket joint. This surgery is a type of partial hip replacement, known as a hemiarthroplasty, because it replaces only the femoral head while leaving the natural hip socket, the acetabulum, intact. The procedure is typically chosen to treat acute fractures in the hip, especially those common in older adults, allowing for pain relief and the restoration of joint function.
Defining the Procedure
A hemiarthroplasty is a surgical approach that replaces one half of the hip joint with a prosthetic implant, specifically addressing the femoral head. The term “bipolar” describes the unique mechanical design of the implant used in this partial replacement.
The bipolar mechanism involves a nested system that creates two separate points of articulation, or movement. An inner, smaller prosthetic head is fixed to the femoral stem and rotates within a larger, surrounding metal or polyethylene shell. This outer shell then articulates with the patient’s natural acetabulum.
This dual-articulation design is what distinguishes a bipolar hemiarthroplasty from a simpler “unipolar” hemiarthroplasty, which features only one point of movement between a single prosthetic head and the natural hip socket. The inner head rotating within the outer shell is intended to absorb most of the motion. This results in less friction where the outer shell meets the patient’s cartilage-lined hip socket, theoretically reducing wear and tear on the natural acetabulum over time. While a total hip replacement (THR) substitutes both the femoral head and the acetabulum, the bipolar hemiarthroplasty preserves the natural socket, making it a less extensive procedure.
Why This Procedure is Necessary
The most frequent reason for choosing a bipolar hemiarthroplasty is the treatment of a displaced femoral neck fracture, particularly in older patients. A fracture in the femoral neck can disrupt the blood supply to the femoral head, leading to avascular necrosis where the bone tissue dies. Replacing the damaged part is required to restore function since the dead bone cannot heal properly.
This procedure is often favored for elderly individuals who have lower physical demands or who are not active enough to warrant a total hip replacement. It is generally quicker to perform than a total hip replacement and can allow for earlier weight-bearing. The decision also considers the patient’s overall health and ability to follow post-surgical instructions.
While acute trauma is the primary indication, bipolar hemiarthroplasty can also be used in select cases of avascular necrosis of the femoral head where the acetabulum remains healthy. It may also be considered for certain types of failed internal fixation surgeries or for patients with underlying neurological conditions. The goal is to provide a stable, mobile, and relatively quick solution to alleviate severe pain and restore the ability to walk.
The Implant Components
The bipolar hemiarthroplasty implant consists of three primary parts that work together to create the dual-articulation system. The foundation of the implant is the femoral stem, a long metal component inserted down the hollowed-out center of the femur. This stem can be fixed into the bone using specialized bone cement (cemented) or through a press-fit design that encourages bone growth (uncemented).
Attached to the top of the femoral stem is the smaller, inner femoral head, which is typically made of metal. This inner head acts as the first ball in the double-ball system and articulates within a plastic liner contained inside the larger, outer shell component.
The outer shell, often called the bipolar head, is made of a smooth, polished metal. This outer shell then rests and moves against the patient’s natural cartilage in the acetabulum. The design allows the inner head to rotate within the outer shell, and the entire outer shell to rotate against the hip socket.
Post-Surgical Expectations
Recovery begins immediately after the procedure, with the patient typically moved to a recovery area for close monitoring of vital signs and pain levels. Pain management is a priority, and a combination of medications is used to control discomfort and facilitate early movement. Most patients are encouraged to begin physical therapy and light movement as soon as the same day or the day following surgery.
The initial hospital stay usually lasts a few days. During this time, physical therapists guide the patient through exercises for sitting, standing, and walking short distances with the aid of a walker or crutches. Early mobilization is strongly emphasized to prevent complications like blood clots and promote a faster return to function. Blood thinners are commonly administered, starting before surgery and continuing after discharge, to minimize the risk of deep vein thrombosis.
Upon discharge, consistent physical therapy remains a central part of the recovery process. Patients work to strengthen the muscles surrounding the hip and restore their range of motion and balance. Movement precautions, such as avoiding bending the hip past 90 degrees or crossing the legs, are strictly followed for several weeks to reduce the risk of implant dislocation.
Most individuals can expect to transition from a walker to a cane and gradually resume normal daily activities over about six weeks. Full recovery and the maximum return of strength may take between three to six months, depending on the individual’s age and adherence to the rehabilitation plan. Regular follow-up appointments with the orthopedic surgeon are necessary to monitor the healing process and ensure the implant is functioning correctly.