A partial hip replacement, known in medical circles as hemiarthroplasty, is a surgical procedure that replaces only one side of the hip joint, specifically the ball (femoral head) at the top of the thighbone, while leaving the natural hip socket untouched. This makes it a less extensive operation than a total hip replacement, which swaps out both sides of the joint with artificial components. Partial hip replacements are most commonly performed after certain types of hip fractures in older adults, and the procedure carries a distinct set of trade-offs worth understanding.
How It Differs From a Total Hip Replacement
Your hip is a ball-and-socket joint. The ball is the rounded top of the femur, and the socket is a cup-shaped hollow in the pelvis called the acetabulum, lined with smooth cartilage. In a total hip replacement, the surgeon removes both the damaged ball and resurfaces the socket with an artificial cup. In a partial hip replacement, only the ball is removed and replaced with a metal prosthesis, and the natural socket cartilage stays in place.1PubMed Central. Surgical approaches for inserting hemiarthroplasty of the hip The metal ball then glides against your own cartilage rather than against a manufactured liner.
This distinction matters for a few reasons. Because the surgeon is not reconstructing the socket side, the operation tends to be shorter, involves less blood loss, and carries a lower risk of dislocation afterward. The trade-off is that the metal ball gradually wears against the natural cartilage of the socket over time, which can cause pain years down the road. That long-term wear issue is why partial replacements are typically chosen for patients who are less likely to outlive the implant’s functional life span.
Who Gets a Partial Hip Replacement
The most common reason for a partial 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, making it unlikely the bone will heal on its own with screws or pins. In older adults, these fractures are overwhelmingly caused by falls and represent a significant challenge because the goal is to get the patient up and walking again as quickly as possible.2PubMed Central. Hip replacement in femoral neck fractures: the role of cementation and its technical difficulties
Surgeons generally lean toward hemiarthroplasty for older, less active patients and for those with significant health problems that make a longer, more complex surgery risky. A total hip replacement takes more operating time, involves more tissue disruption, and demands more from the patient during recovery. For someone in their 80s who walks primarily around the house, the added durability of a total replacement often does not justify the added surgical stress. For younger, more active patients with the same fracture, surgeons are more likely to recommend the full replacement because the socket cartilage will wear out faster under greater demand.
Less commonly, a partial hip replacement may be considered for certain hip tumors or for advanced osteonecrosis, a condition where the bone of the femoral head dies from poor blood supply. However, results in osteonecrosis are less predictable because the natural socket cartilage tends to degrade over time, leading to pain and the need for conversion to a total replacement.3PubMed Central. Hip arthroplasty for treatment of advanced osteonecrosis: comprehensive review of implant options, outcomes and complications
Unipolar and Bipolar Implants
There are two main designs for the prosthetic ball used in a partial hip replacement. A unipolar prosthesis is a single solid metal head fixed onto a stem that fits into the hollow canal of the femur. A bipolar prosthesis adds a second, outer shell around the metal head, creating an extra joint-within-a-joint. The idea behind the bipolar design was that this extra layer of movement would distribute forces more evenly and reduce wear on the natural socket cartilage.
In practice, the advantage is modest at best. Research has shown that the motion between the inner and outer components of a bipolar prosthesis largely disappears within about three months, at which point the implant behaves much like a simpler unipolar device.4PubMed Central. Interprosthetic Joint Motion in Bipolar Partial Hip Arthroplasty After One-Year Follow-up Both designs remain in widespread use, though the theoretical benefit of the bipolar version has not translated into clearly better long-term outcomes in most comparative studies. Surgeons often choose based on personal experience and institutional preference.
Cemented Versus Uncemented Stems
Regardless of whether the ball is unipolar or bipolar, the metal stem that anchors the prosthesis inside the femur can be fixed in place in two ways. A cemented stem uses a fast-setting bone cement (polymethylmethacrylate) to bond the implant to the inside of the bone. An uncemented stem has a rough, textured surface designed so that the patient’s own bone grows into it over time, creating a biological bond.
A large randomized trial published in the New England Journal of Medicine compared the two approaches in over 1,200 patients with hip fractures. At four months, patients who received cemented stems reported modestly better quality of life. Cemented stems also carried a lower rate of periprosthetic fracture, meaning the bone around the implant was less likely to crack, at about 0.5% compared to roughly 2% for uncemented stems.5PubMed. Cemented or Uncemented Hemiarthroplasty for Intracapsular Hip Fracture By 12 months, the quality-of-life gap between the two groups had narrowed.
A separate randomized trial found largely similar functional scores between cemented and uncemented groups at two years, though the cemented group had longer operating times and more intraoperative blood loss. Prosthetic subsidence, where the stem sinks slightly within the bone, was more common in the uncemented group but did not reach a statistically meaningful difference.6PubMed Central. Cemented versus uncemented hemiarthroplasty for displaced femoral neck fractures: A randomized controlled trial with two years follow-up Another study comparing the two at six months found good functional results in roughly half of both groups, with no significant difference in hip scores.7International Journal of Research in Orthopaedics. Functional and radiological outcomes between cemented and uncemented partial hip replacement in the elderly
The general picture is that cemented fixation offers a slight early advantage and lower fracture risk, while uncemented fixation avoids the specific risks associated with bone cement. Both are considered acceptable, and the choice often depends on the patient’s bone quality and the surgeon’s assessment.
Bone Cement Implantation Syndrome
One risk unique to the cemented approach deserves its own mention because it can be life-threatening. Bone cement implantation syndrome, or BCIS, occurs when pressurizing cement into the bone canal forces fat, marrow particles, and air into the bloodstream. This can trigger a sudden drop in blood pressure, a fall in oxygen levels, and in severe cases, cardiac arrest. It happens around the time the cement is being applied, and the surgical team monitors for it closely.
A study categorizing BCIS severity found that mild episodes (grade 1) occurred in about one in five cemented hemiarthroplasties, and mortality in those cases was not dramatically different from patients with no reaction. But moderate episodes (grade 2, occurring in about 5% of cases) carried an early mortality rate of 35%, and the most severe grade (about 1.7% of cases) was fatal 88% of the time.8BJA: British Journal of Anaesthesia. Bone cement implantation syndrome in cemented hemiarthroplasty for femoral neck fracture: incidence, risk factors, and effect on outcome These severe reactions are uncommon, but they are the primary reason some surgeons prefer uncemented stems, particularly in patients who are already medically fragile.
A nationwide French survey of orthopedic surgeons found that cementing accidents in emergency hip fracture surgery were about six times more common than in planned elective operations, and mortality from those accidents was roughly ten times higher in the emergency setting.9PubMed. Bone cement implantation syndrome in hip arthroplasty: Frequency, severity and prevention Since most partial hip replacements are performed as urgent surgery after a fracture rather than as a scheduled procedure, this is a real consideration.
How a Partial Replacement Compares to a Total Replacement After Fracture
The question of whether to do a partial or total hip replacement after a hip fracture in a relatively fit older adult has been debated for decades. A major randomized trial of over 1,400 patients found that revision rates were nearly identical: about 8% for total hip replacement and 8% for hemiarthroplasty over the follow-up period. Function scores slightly favored total hip replacement on measures of pain, stiffness, and daily activities. But dislocation was roughly twice as common after total replacement compared to partial, and the rate of serious adverse events was somewhat higher as well. Mortality was similar between the two groups.10PubMed. Total Hip Arthroplasty or Hemiarthroplasty for Hip Fracture
So the trade-off is real: a total replacement offers somewhat better function and pain relief, but at the cost of a higher dislocation risk and a bigger operation. For active, cognitively sharp patients in their 60s or 70s who fracture their hip, a total replacement is often the better long-term investment. For less active or more medically complex patients, the simpler partial replacement gets the job done with less surgical risk.
Cost analyses have generally concluded that total hip replacement is cost-effective when compared to hemiarthroplasty, especially for healthier elderly patients, because it tends to lead to fewer revision surgeries over a 20-year horizon. One model estimated that a total replacement cost about $3,000 more upfront but gained an average of about 1.5 quality-adjusted life-years over two decades.11PubMed Central. A Cost-effectiveness Analysis of the Arthroplasty Options for Displaced Femoral Neck Fractures in the Active, Healthy, Elderly Population A separate systematic review reached a similar conclusion: total hip replacement appears more cost-effective over the long term, with higher initial costs but lower revision-related expenses down the line.12Health Technology Assessment. Hemiarthroplasty and total hip arthroplasty for treating primary intracapsular fracture of the hip: a systematic review and cost-effectiveness analysis
Acetabular Erosion and the Long Game
The main long-term concern specific to partial hip replacement is acetabular erosion, meaning the metal ball gradually wears away the natural cartilage lining of the socket. If enough cartilage is lost, the metal starts grinding against bare bone, causing deep groin pain. This is the complication that can eventually force a conversion to a total replacement.
The good news is that symptomatic erosion appears to be uncommon, at least within the first several years. A retrospective analysis of nearly 2,500 hemiarthroplasty cases found that only about 0.5% developed hip pain attributable to acetabular wear that was documented in clinical records. Among those who did develop it, half presented within the first six months, and the average time to symptom onset was about two years.13PubMed Central. Symptomatic Acetabular Erosion After Hip Hemiarthroplasty: Is It a Major Concern? A Retrospective Analysis of 2477 Hemiarthroplasty Cases The low rate likely reflects the fact that most hemiarthroplasty patients are elderly and many do not survive long enough for erosion to become a clinical problem. In younger, more active patients, the risk over a decade or more would be considerably higher.
When a Partial Replacement Needs to Be Converted
If a partial hip replacement fails, whether from acetabular erosion, loosening of the stem, infection, or persistent pain, the usual solution is to convert it to a total hip replacement. This is a bigger operation than a primary total replacement because the surgeon has to remove the old implant, deal with potential bone loss, and work within scar tissue from the first surgery.
A study of 44 patients who underwent this conversion found that groin pain was the most common complaint leading to the procedure. After conversion, Harris hip scores, a standard measure of hip function, improved substantially, from an average of 38 before surgery to 86 afterward. About half of the patients were able to walk without any support, and another 38% needed only a cane. Among those whose main problem was groin pain, 83% were completely pain-free after conversion, though 17% reported only partial relief.14PubMed Central. Conversion of failed hemiarthroplasty to total hip arthroplasty: a short to mid-term follow-up study
The caveat is that converting a hemiarthroplasty carries a higher dislocation risk than revising a failed total hip replacement. One study found a 22% dislocation rate after conversion from hemiarthroplasty compared to 10% after revision of a total replacement. Smaller femoral head components were particularly prone to dislocation in the conversion group.15Journal of Bone and Joint Surgery. Dislocation Rate After Conversion from Hip Hemiarthroplasty to Total Hip Arthroplasty This is one more reason why the initial decision between partial and total matters: if there is a reasonable chance you will need a total replacement eventually, getting it right the first time avoids a more difficult second surgery.
Recovery and Weight-Bearing
One of the advantages of a partial hip replacement is that most patients are allowed to put weight on the operated leg almost immediately. This is especially important for elderly patients, because prolonged bed rest after a hip fracture dramatically increases the risk of blood clots, pneumonia, and muscle wasting. The goal is to get you standing and taking a few steps with a walker within a day or two of surgery.
How much weight you are allowed to bear depends on the implant fixation. With a cemented stem, full weight-bearing is typically permitted right away because the cement provides immediate stability. With an uncemented stem, surgeons sometimes restrict weight-bearing for the first several weeks while bone grows into the implant surface, although many now allow weight as tolerated for modern press-fit designs.
A study of rehabilitation outcomes after hip fracture arthroplasty found that being allowed to bear weight as tolerated was a significant predictor of being discharged home rather than to a nursing facility. Restricted weight-bearing was cited by therapists as a barrier to effective rehabilitation in about 11% of cases.16PubMed. Outcomes and weight-bearing status during rehabilitation after arthroplasty for hip fractures For older patients, getting home after surgery is often as much about early mobility as it is about the surgery itself.
Most people who receive a partial hip replacement spend a few days in the hospital, followed by a period of physical therapy either at a rehabilitation facility or at home. The focus is on regaining strength in the hip muscles, improving balance, and building up walking endurance. By six weeks, many patients are walking with a cane. Full recovery to pre-fracture function, if it is achievable, typically takes three to six months.
Anesthesia Choices
Partial hip replacements can be performed under general anesthesia, where you are completely unconscious, or under spinal anesthesia, where you receive an injection in the lower back that numbs everything from the waist down while you remain awake or lightly sedated. Both approaches are widely used.
A large retrospective study of over 60,000 hip arthroplasty patients found no significant association between the type of anesthesia and early postoperative mortality, regardless of whether the surgery was partial or total.17medtigo Journal of Anesthesiology and Pain Medicine. A Comprehensive Review of Regional vs. General Anesthesia in Hip Surgery: Efficacy and Safety Outcomes However, a separate analysis of hip fracture surgery specifically found that general anesthesia was associated with a higher combined rate of stroke, heart attack, or death within 30 days compared to spinal anesthesia, along with modestly longer operating times.18PubMed. Improved outcomes for spinal versus general anesthesia for hip fracture surgery: a retrospective cohort study of the National Surgical Quality Improvement Program
The discrepancy likely reflects the fact that hip fracture patients tend to be older and sicker than people undergoing elective joint replacement, making them more vulnerable to the physiological stress of general anesthesia. Many anesthesiologists now favor spinal anesthesia for hip fracture surgery when it is feasible, though the choice depends on the patient’s spine anatomy, anticoagulation status, and overall health.
A Brief History of the Procedure
The concept of replacing just the ball of the hip dates back to the late 1930s, when Frederick Thompson in New York and Austin Moore in South Carolina independently began developing prostheses to replace the entire femoral head. Moore collaborated with Harold Bohlman to implant a custom-made metal femoral head prosthesis in a patient with a recurrent bone tumor in 1939. The prosthesis, made from vitallium, a cobalt-chromium alloy originally developed for dental work, functioned well and laid the groundwork for the long-stemmed designs that followed.19PubMed Central. Hip hemiarthroplasty: from Venable and Bohlman to Moore and Thompson
The Thompson and Moore prostheses, refined through the 1950s and 1960s, became the standard treatment for displaced femoral neck fractures and remained in use for decades. The development of bone cement in the 1960s and total hip replacement by surgeons like John Charnley eventually shifted much of hip surgery toward the full replacement approach. But hemiarthroplasty never disappeared. It remains the most commonly performed operation for elderly hip fracture patients worldwide, a role it has held for over 80 years.
Surgical Approach and Dislocation Risk
The surgeon can reach the hip joint through several different incisions and muscle-splitting pathways. The most common approaches are the posterior (from behind), the direct lateral (from the side), and the anterolateral (from the front-side). Each has advocates who argue for better visualization, less muscle damage, or lower dislocation rates.
A systematic review of 11 studies on hip arthroplasty found that dislocation rates across the three most common approaches were quite similar when the surgeon performed adequate soft tissue repair: about 0.7% for the anterolateral approach, 0.4% for the direct lateral approach, and 1.0% for the posterior approach with repair of the posterior capsule and external rotator muscles.20Clinical Orthopaedics and Related Research. Does Surgical Approach Affect Total Hip Arthroplasty Dislocation Rates? The takeaway for patients is that the surgeon’s skill and attention to soft tissue repair probably matter more than which direction they come at the hip from. If your surgeon has a preferred approach they are experienced with, that is usually the right one for you.