A hemiarthroplasty of the hip is a surgical procedure that replaces only the ball (femoral head) of the hip joint while leaving the natural socket (acetabulum) intact. It is most commonly performed in older adults who break the top of their thighbone, specifically a displaced femoral neck fracture. Unlike a total hip replacement, which resurfaces both sides of the joint, a hemiarthroplasty addresses only the damaged femoral side.
How It Differs From Total Hip Replacement
The hip is a ball-and-socket joint. The ball is the rounded top of your thighbone, and the socket is a cup-shaped cavity in your pelvis lined with smooth cartilage. In a total hip replacement, both the ball and the socket get artificial components. In a hemiarthroplasty, the socket is left alone. The surgeon removes the broken ball, hollows out the upper portion of the thighbone, and inserts a metal stem topped with a new artificial ball that fits into your original socket.
This matters because it makes the surgery shorter and somewhat less invasive. There is no need to reshape and line the pelvic socket. That reduced complexity is a meaningful advantage for elderly patients or those with other health conditions, where longer time under anesthesia carries real risk. The tradeoff is that a total hip replacement tends to produce slightly better long-term function, which is why surgeons typically reserve hemiarthroplasty for patients with lower activity demands.
Who Gets a Hemiarthroplasty
The most common candidate is an older adult with a displaced femoral neck fracture, the type of broken hip where the bone fragments have shifted out of alignment. The American Academy of Orthopaedic Surgeons strongly recommends arthroplasty over trying to pin these fractures back together, based on high-quality evidence. For non-displaced fractures where the bone is still roughly in position, hemiarthroplasty is one of several options alongside internal fixation or even non-surgical care.
One critical requirement: the socket cartilage needs to be healthy. Because the new metal ball will articulate directly against your natural cartilage, any significant arthritis in the socket makes hemiarthroplasty a poor choice. In those cases, a total hip replacement that resurfaces the socket is the better option. Hemiarthroplasty is generally reserved for patients with minimal acetabular osteoarthritis, poor bone quality, and lower functional demands.
Unipolar vs. Bipolar Implants
There are two implant designs. A unipolar hemiarthroplasty uses a single solid metal ball attached to the stem. A bipolar design adds a second, outer shell that can move independently around the inner ball. The idea behind the bipolar design is that some of the joint’s movement happens between the two components rather than entirely between the metal ball and your cartilage, which should theoretically cause less wear on the socket over time.
In practice, the AAOS guidelines state that unipolar and bipolar hemiarthroplasty produce equally beneficial results, based on moderate-quality evidence. A pooled analysis of over 30,000 patients reached the same conclusion. So while the bipolar design sounds better in theory, the clinical outcomes are similar, and the choice often comes down to surgeon preference and cost.
What Happens During Surgery
Several surgical approaches exist, including anterior, lateral, and posterior routes into the hip. No single approach has proven superior, so the choice depends on surgeon experience and training. A posterior approach may carry a slightly higher risk of dislocation after surgery.
The basic sequence is straightforward. After accessing the hip joint, the surgeon removes the broken femoral head and measures it to select the correct size prosthesis. The upper canal of the thighbone is then carefully shaped using progressively larger tools called broaches, creating a precise channel for the metal stem. The stem is typically cemented into place. Current AAOS guidelines strongly recommend cemented stems for femoral neck fractures, as they provide immediate stability in bone that is often weakened by osteoporosis. Once the stem is secure, the appropriately sized ball component is attached, and the hip is put back into position.
Getting the alignment right is essential. The stem needs to sit at the correct angle and depth within the thighbone, matching the natural forward twist of the femoral neck (roughly 15 degrees). Poor alignment increases the risk of dislocation and uneven wear.
Recovery and Weight-Bearing
One of the main advantages of hemiarthroplasty, particularly with a cemented stem, is that most patients can bear weight on the operated leg almost immediately. This is critically important for elderly patients, since prolonged bed rest after a hip fracture dramatically increases the risk of blood clots, pneumonia, pressure sores, and muscle wasting. Physical therapy typically begins within a day of surgery, starting with assisted standing and short walks with a walker.
The early weeks focus on regaining the ability to walk safely and perform basic daily tasks like getting in and out of bed, sitting in a chair, and using the bathroom. Most people transition from a walker to a cane over the first several weeks, though the exact timeline varies with age, fitness level, and overall health.
Hip Precautions After Surgery
For the first 6 to 8 weeks, you will need to follow specific movement restrictions to prevent the new joint from dislocating while the surrounding tissues heal. These precautions apply regardless of which surgical approach was used, though the exact restrictions may vary slightly.
- Don’t bend your hip past 90 degrees. This means not leaning forward at the waist to pick things up or tying shoes the usual way.
- Don’t cross your legs at the knees.
- Don’t twist your foot sharply inward or outward when bending down.
- Don’t raise the knee on the surgical side above hip level while sitting or lying down.
Raised toilet seats, long-handled shoe horns, and grabber tools can make life much easier during this period. After 6 to 8 weeks, most patients can resume these movements without risking the implant.
Risks and Complications
Dislocation is the most talked-about complication. In one study of nearly 1,500 hemiarthroplasty patients, the dislocation rate was 1.2%. That number sounds small, but dislocation after hemiarthroplasty is a serious event. Patients who dislocate have dramatically worse outcomes: a 65% mortality rate within six months of the dislocation, rising to 75% if a second dislocation occurs. This is partly because dislocation tends to happen in the frailest patients, and the additional surgeries and immobility compound existing health problems.
Other potential complications include infection around the implant, loosening of the stem over time, and fracture of the bone around the prosthesis. Across all hip replacements, the most common reasons for eventual revision surgery are loosening of the implant, dislocation, fracture around the prosthesis, and infection.
How Long the Implant Lasts
For many hemiarthroplasty patients, the implant lasts the rest of their life. The procedure is typically performed in patients over 70 or 80, and the prosthesis generally outlasts the patient. Data from the National Joint Registry in England and Wales shows that roughly 4.3% of primary hip replacements are revised within 10 years, and cemented implants (the type recommended for hemiarthroplasty) have the lowest revision rates of any design, at 6.1% over 17 years.
When revision does become necessary, the most common reason is aseptic loosening, where the implant gradually loses its bond with the surrounding bone without any infection being present. Acetabular erosion is another concern specific to hemiarthroplasty: over years, the metal ball can wear down the natural cartilage lining the socket, causing increasing pain. If this happens, the hemiarthroplasty can be converted to a total hip replacement by adding a socket component. This is a more complex surgery than the original procedure, and about one in five revised hip replacements will need another revision within 15 years.
For younger, more active patients with femoral neck fractures, surgeons often lean toward total hip replacement from the start, precisely because it eliminates the socket erosion issue and tends to produce better functional outcomes over a longer lifespan. The AAOS notes that in properly selected patients, total hip replacement may offer a functional benefit over hemiarthroplasty, though it comes with a somewhat higher complication risk during the initial surgery.