Bipolar Hip Prosthesis – Definition, Use & Risks
A bipolar hip prosthesis is a dual-head hip implant used primarily for femoral neck fractures. It replaces the femoral head while preserving the natural acetabulum, enabling rapid patient mobilization.
Things worth knowing about "Bipolar Hip Prosthesis"
A bipolar hip prosthesis is a dual-head hip implant used primarily for femoral neck fractures. It replaces the femoral head while preserving the natural acetabulum, enabling rapid patient mobilization.
What is a Bipolar Hip Prosthesis?
A bipolar hip prosthesis (also called a bipolar hemiarthroplasty) is a specialized type of hip implant. It consists of a femoral stem inserted into the thigh bone and a double-layered articulating head. This bipolar head contains an inner metal ball and an outer polyethylene cup, both of which can move independently of each other. The outer shell articulates directly with the natural hip socket (acetabulum), which does not need to be surgically replaced.
Indications: When is a Bipolar Hip Prosthesis Used?
A bipolar hip prosthesis is typically indicated in the following situations:
- Medial femoral neck fracture: A break in the femoral neck close to the femoral head, commonly occurring in elderly patients after a fall
- Patients with limited physical activity and reduced life expectancy, where a total hip replacement is not considered necessary
- Osteoporosis-related fractures where internal fixation (e.g., screws or nails) would not provide sufficient stability
Unlike a total hip arthroplasty (THA), where both the femoral head and the acetabulum are replaced, the bipolar prosthesis preserves the natural acetabular socket. This shortens the operating time and reduces surgical trauma.
Design and Mechanism of Action
The distinctive bipolar design allows movement at two levels:
- Inner articulation: The metal femoral head rotates inside the polyethylene cup, reducing friction and protecting the natural acetabulum.
- Outer articulation: The entire bipolar head moves within the natural hip socket.
This dual-motion mechanism distributes joint loads more evenly and helps protect the native acetabular cartilage over time.
Fixation Methods
The femoral stem can be anchored in two ways:
- Cemented: Fixed with bone cement (polymethylmethacrylate) – preferred in elderly patients with poor bone quality
- Cementless: Relies on bone ingrowth into a porous surface coating – more suitable for younger patients with good bone density
Advantages of the Bipolar Hip Prosthesis
- Shorter operating time compared to total hip replacement
- Less surgical trauma due to preservation of the natural acetabulum
- Allows early postoperative mobilization
- Well-suited for elderly and medically complex patients
Possible Risks and Complications
As with any surgical procedure and implant, complications can occur:
- Implant loosening: Over time, the stem may become loose within the bone
- Hip dislocation: The femoral head may dislocate from the socket
- Acetabular protrusion: The outer head may gradually migrate into the acetabulum, particularly in younger or more active patients
- Infection: Periprosthetic infection is a serious potential complication
- Deep vein thrombosis and pulmonary embolism: Associated with perioperative immobility
Rehabilitation After Surgery
Rehabilitation typically begins on the first day after surgery with physiotherapy exercises. The primary goal is rapid restoration of walking ability. Gait training, muscle strengthening, and instruction on protective postures are key components of postoperative care. Full weight-bearing on the operated leg is often permitted shortly after the procedure.
Comparison with Total Hip Arthroplasty
In younger, more active patients or in those with pre-existing hip osteoarthritis, a total hip arthroplasty is generally preferred, as it also replaces the acetabular socket and offers a longer expected implant lifespan. The bipolar hip prosthesis is primarily designed for older, less active patients in whom a short and minimally invasive procedure is the priority.
References
- Bonnaire F, Lein T, Bula P. Femoral neck fractures in adults: classification, biomechanics and therapeutic options. Unfallchirurg. 2011;114(6):491-500.
- German Society for Trauma Surgery (DGU). S2e Guideline: Femoral Neck Fracture in Adults. AWMF Registration No. 012-001. Berlin: AWMF; 2015.
- Breusch SJ, Malchau H (eds.). The Well-Cemented Total Hip Arthroplasty. Heidelberg: Springer; 2005.
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