A partial hip replacement, medically called a hemiarthroplasty, is a surgery that replaces only the ball (femoral head) of the hip joint while leaving the socket intact. It differs from a total hip replacement, which replaces both the ball and the socket. Partial hip replacements are most commonly performed after a hip fracture in older adults, and they account for a significant share of all hip surgeries done each year.
What Gets Replaced and What Stays
Your hip is a ball-and-socket joint. The ball is the rounded top of your thighbone (femur), and the socket is a cup-shaped hollow in your pelvis called the acetabulum. In a partial hip replacement, the surgeon removes the damaged ball and replaces it with a metal or ceramic prosthetic head attached to a stem that fits down into the hollow center of your thighbone. The natural socket is left completely untouched.
This is the key distinction from a total hip replacement, where the surgeon also resurfaces or replaces the socket with an artificial cup. Because a partial replacement involves less work on the joint, the surgery is shorter, the risk of dislocation is lower, and recovery can be somewhat faster. The tradeoff is that the metal prosthetic head now moves against your natural cartilage-lined socket, which can wear down over time.
Two Implant Designs: Unipolar and Bipolar
Partial hip implants come in two main designs. A unipolar implant has a single large prosthetic head that moves directly against the natural socket. A bipolar implant adds a second layer of movement: a smaller metal head sits inside a larger outer shell lined with plastic, creating an extra point of rotation between the two components.
The idea behind the bipolar design is that some of the movement happens inside the implant itself, reducing friction against the natural socket. In practice, studies show the bipolar design does slow socket wear in the first year or two. At 12 months, about 20% of unipolar patients showed signs of socket erosion on imaging compared to 5% of bipolar patients. However, the inner bearing of a bipolar implant tends to stiffen over time, essentially turning it into a unipolar system. Quality-of-life scores favor bipolar implants beyond the two-year mark, but reoperation rates between the two designs are similar. Current guidelines from the American Academy of Orthopaedic Surgeons state that unipolar and bipolar implants can be equally beneficial.
Who Gets a Partial Hip Replacement
The most common reason for a partial hip replacement is a displaced femoral neck fracture, the type of broken hip where the ball of the thighbone snaps off and shifts out of position. This fracture is overwhelmingly a problem of aging: weakened bones break during a fall, and the blood supply to the femoral head is disrupted beyond repair. Rather than trying to pin the broken bone back together, surgeons replace the damaged ball entirely.
For these displaced fractures, guidelines strongly recommend replacement surgery over trying to fix the bone with screws or plates. The question then becomes whether a patient gets a partial or total replacement. Partial hip replacement is generally recommended for older, less active patients or those with significant health problems that make a longer surgery risky. The procedure is simpler, with a lower dislocation rate, which matters for patients who may have difficulty following movement precautions after surgery. Total hip replacement tends to be recommended for more active patients because it provides better long-term function, though it carries a slightly higher complication risk.
For stable, non-displaced hip fractures (where the bone cracks but stays in place), partial hip replacement is one of several options alongside pinning the bone or even non-surgical management, depending on the patient’s overall health.
What the Surgery and Hospital Stay Look Like
The surgery itself typically takes about an hour. The surgeon secures the metal stem inside the thighbone, usually with bone cement, which allows for immediate stability. Cemented stems are strongly recommended by current guidelines for hip fracture patients because they provide reliable fixation in bone that may already be weakened.
Many patients go home the same day or the next. If the medical team wants more time to monitor pain control, mobility, or other health concerns, a stay of one to two days is typical. You’ll begin working with a physical therapist before you leave the hospital, learning to move safely and use a walker or crutches.
Recovery Timeline
You’ll leave the hospital walking with a walker, crutches, or a cane, and you’ll likely need one of these mobility aids for several weeks. Physical therapy starts in the hospital and continues at home or at an outpatient facility. The more consistently you do your exercises, the faster you regain strength and range of motion.
For the first six weeks, you’ll need to sleep on your back with your legs slightly apart, or on your side with a pillow between your knees, to protect the new joint. Compression stockings are worn for four to six weeks to reduce the risk of blood clots. Mild pain and swelling around the hip can persist for three to four months, and ankle swelling on the affected side is common for about three months.
Most people return to work somewhere between four weeks and four months after surgery, depending on the physical demands of their job and their overall recovery. A desk job is realistic at the earlier end of that range, while work that involves standing, lifting, or walking may take longer.
Long-Term Durability and Socket Wear
The main long-term concern unique to partial hip replacement is wear on the natural socket. Because a metal prosthetic head is pressing and rotating against natural cartilage, the socket gradually erodes over months and years. This is the single biggest disadvantage compared to a total hip replacement, where both surfaces are artificial.
How much this matters in practice depends on the patient. A large study of nearly 2,500 partial hip replacements found that only 0.48% of patients developed chronic hip pain from socket wear. When pain did develop, it appeared on average about two years after surgery, though half of symptomatic cases showed up within the first six months. Of those who developed painful erosion, most were managed without further surgery, and only 0.2% of all patients in the study ultimately needed conversion to a total hip replacement.
Factors that increase the risk of socket erosion include younger biological age (meaning more years of use), higher activity levels, lower bone density, and a smaller prosthetic head size.
Implant Survival and Reasons for Revision
At the ten-year mark, about 90% of partial hip implants are still functioning without needing revision surgery. When revisions do happen, the most common reasons are infection (27% of revisions), dislocation (25%), loosening of the implant from the bone (19%), and persistent pain (13%). Fractures around the implant and socket erosion account for smaller shares.
These revision rates reflect the reality that partial hip replacements are most often placed in elderly patients with limited life expectancy. For a 75-year-old with moderate activity levels, a 90% ten-year survival rate means the implant will very likely last the rest of their life. For a younger, more active person, the combination of socket wear and a longer remaining lifespan makes a total hip replacement the better choice in most cases.