A hemi hip replacement, formally called a hemiarthroplasty, is a surgery that replaces only one half of the hip joint. Specifically, the surgeon removes the damaged ball (the femoral head) at the top of the thighbone and replaces it with a metal implant, while leaving the natural hip socket completely untouched. This makes it a smaller operation than a total hip replacement, which swaps out both the ball and the socket. Hemiarthroplasty is most commonly performed after a broken hip in older adults.
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 piece of your pelvis called the acetabulum. In a hemi hip replacement, the surgeon removes the damaged femoral head and inserts a metal stem down into the hollow center of the thighbone, topped with a smooth metal ball that sits inside your original socket. Because the socket isn’t touched, the surgery is faster and involves less bone work than a total replacement.
The tradeoff is that the metal ball now moves against natural cartilage in the socket instead of against a manufactured plastic or ceramic liner. Over time, this can cause gradual wearing of the socket cartilage, a process called acetabular erosion. For younger, more active patients, this wear becomes a real concern. For older patients with lower activity levels and shorter life expectancy, it rarely becomes a problem before other health issues take priority.
Why Surgeons Choose It
The most common reason for a hemi hip replacement is a displaced fracture of the femoral neck, the narrow section of bone just below the ball of the hip. This type of break disrupts the blood supply to the femoral head, meaning the bone often can’t heal on its own. In surveys of orthopedic surgeons, 94 to 96% preferred an arthroplasty for patients aged 80 or older with a displaced femoral neck fracture rather than attempting to pin the bone back together.
Total hip replacement produces better long-term functional scores for fracture patients, based on multiple randomized trials. But hemiarthroplasty is a shorter, less invasive operation with a quicker recovery. For elderly patients who are less physically active or who have significant health conditions that make longer surgeries riskier, a hemi replacement strikes a practical balance between restoring mobility and minimizing surgical stress. The general thinking: if someone has lower functional demands and a shorter life expectancy, hemiarthroplasty is usually sufficient.
Unipolar vs. Bipolar Implants
There are two implant designs used in hemiarthroplasty. A unipolar implant has a single solid metal head that moves directly against the natural socket. A bipolar implant adds a second bearing surface: a smaller metal ball sits inside a larger outer shell with a plastic lining between them. The idea is that some of the movement happens between the two parts of the implant itself, reducing friction against the socket cartilage.
In practice, the difference is modest. Studies show bipolar implants do cause less socket erosion in the first year, but by two to four years out, complication rates, functional outcomes, and erosion rates are similar between the two designs. Bipolar implants cost more, and they carry a small risk of the inner and outer components separating. In international surveys, about 60% of surgeons chose unipolar and 32 to 33% chose bipolar for elderly fracture patients. Some patients with very small hip sockets can’t receive a bipolar implant because the inner plastic lining would be too thin to function safely.
What Happens During Surgery
The procedure typically takes less than an hour. Surgeons reach the hip through one of two main approaches. The posterior approach goes through the back of the hip, dividing small rotator muscles behind the joint. The direct lateral approach goes through the side, splitting part of the muscles that control hip stability during walking.
Research from large registries shows patients report less pain, better satisfaction, and better quality of life with the posterior approach compared to the lateral approach. Walking ability was also significantly better at both 4 and 12 months after surgery in the posterior group. UK national guidelines, however, have historically recommended the lateral approach because it carries a lower dislocation risk: about 3.3% compared to 9% with the posterior approach in one study of over 3,000 cases. Many surgeons now use the posterior approach with added soft tissue repair to reduce that dislocation gap.
The metal stem can be fixed inside the thighbone with or without bone cement. Cemented stems take slightly longer to implant but have lower rates of complications afterward, particularly fewer fractures around the implant and less thigh pain. Most guidelines now favor cemented fixation for elderly patients.
Recovery Timeline
Most patients are encouraged to put full weight on the operated leg immediately after surgery. The goal in the first three days is to get out of bed independently, manage transfers in and out of a chair, and walk at least 100 feet with a walker or cane. Hospital stays are typically short, often just a few days.
During weeks one through three at home, the focus shifts to improving your walking pattern. Most patients are encouraged to wean off their walker or cane between weeks two and three. By weeks three through six, rehabilitation progresses to sidestepping, walking backward, and navigating uneven surfaces. A common milestone for clearing this phase is walking 800 feet without an assistive device and without limping.
Your surgeon will give you specific movement restrictions to protect against dislocation in the early weeks. The standard precautions include not bending your hip past 90 degrees (no deep squatting or leaning far forward while seated), keeping your leg facing forward rather than rotating it inward, and using a raised toilet seat or high chair to avoid deep bending. These restrictions typically ease as the tissues heal and the muscles around the joint regain strength.
Risks and Complications
Dislocation is the most talked-about complication, with reported rates ranging from 1 to 15% depending on the surgical approach, implant type, and patient factors. Wound infection is the other common early concern. In a large study of hip fracture patients, the overall 30-day mortality rate was 6%, reflecting that this surgery is most often performed on frail, elderly patients with serious underlying health conditions rather than a reflection of the surgery being unusually dangerous. Delayed surgery, male sex, and older age all increased mortality risk.
Over the longer term, the main concern is erosion of the natural hip socket from the metal ball grinding against cartilage. If this causes significant pain, the hemiarthroplasty can be converted to a total hip replacement, though this revision surgery is more complex than a primary total replacement would have been. For most elderly patients, the implant outlasts them. In a large Canadian population study, only 18% of hip fracture arthroplasty patients were still alive at 10 years after surgery, underscoring that implant longevity is rarely the limiting factor in this age group.
Hemi vs. Total Hip Replacement
The key differences come down to what’s replaced and who benefits most. A total hip replacement resurfaces both the ball and the socket, eliminating any concern about socket cartilage wearing down. Multiple trials confirm it delivers better functional results for fracture patients. But it’s a longer operation with more blood loss and a slightly higher dislocation risk in some studies.
For active patients in their 60s or early 70s with a hip fracture and otherwise good health, many surgeons now lean toward total replacement because the functional benefits outweigh the added surgical time. For patients in their 80s and beyond, particularly those with dementia, limited mobility before the fracture, or multiple medical problems, hemiarthroplasty remains the standard choice. It gets patients mobile again quickly with a procedure their body can handle.