Unipolar hemiarthroplasty: Definition, Uses, and Clinical Overview

Posted on February 28, 2026 | by drhip

Unipolar hemiarthroplasty Introduction (What it is)

Unipolar hemiarthroplasty is a type of hip replacement surgery that replaces only the “ball” of the hip joint.
It uses a single-piece (unipolar) femoral head that moves directly against the patient’s natural hip socket.
It is most commonly used for certain hip fractures, especially fractures of the femoral neck.
It is considered a partial hip replacement rather than a total hip replacement.

Why Unipolar hemiarthroplasty used (Purpose / benefits)

The hip is a ball-and-socket joint: the femoral head (ball) sits inside the acetabulum (socket) of the pelvis. When the femoral head is badly damaged—most often from a displaced femoral neck fracture—repairing the bone with screws or plates may not reliably restore function. This is partly because the blood supply to the femoral head can be disrupted, increasing the risk that the bone will not heal well (nonunion) or will lose viability (avascular necrosis).

Unipolar hemiarthroplasty is used to address that problem by removing the damaged femoral head and replacing it with a prosthetic head attached to a femoral stem. The intent is to restore a stable, functional hip joint surface on the femoral side and allow earlier return to mobility compared with prolonged protection of a healing fracture.

Potential benefits clinicians may be aiming for include:

Pain relief by removing fractured or nonviable bone at the femoral head/neck.
Restoring hip stability and alignment after a displaced fracture.
Facilitating mobilization and basic function when internal fixation is less suitable.
A relatively streamlined operation compared with replacing both sides of the joint (varies by clinician and case).
Preserving the native acetabulum (socket) when it is healthy enough to articulate with the prosthetic head.

Indications (When orthopedic clinicians use it)

Common scenarios where orthopedic clinicians may consider Unipolar hemiarthroplasty include:

Displaced femoral neck fracture in older adults, particularly when bone quality or healing potential is a concern
Femoral head/neck injury where internal fixation is unlikely to succeed (varies by clinician and case)
Limited pre-injury mobility or lower functional demand where a partial replacement may meet goals (varies by clinician and case)
Situations where a shorter operative time or reduced surgical complexity is prioritized (varies by clinician and case)
Selected cases of femoral head pathology when the acetabulum is relatively preserved (less common; varies by clinician and case)

Contraindications / when it’s NOT ideal

Unipolar hemiarthroplasty may be less suitable when the socket side of the joint is significantly diseased or when a different reconstruction better matches expected activity and durability needs. Situations where it may not be ideal include:

Substantial acetabular cartilage damage or established inflammatory/degenerative arthritis of the hip socket, where a total hip replacement may better address pain drivers
Younger, highly active patients where long-term acetabular wear against a unipolar head is a concern (varies by clinician and case)
Certain complex fracture patterns involving the acetabulum or the proximal femur that require different fixation or reconstruction strategies
Active infection in or around the joint (a general contraindication to arthroplasty until addressed)
Severe neuromuscular conditions or high instability risk where implant choice, approach, and soft-tissue management may differ (varies by clinician and case)
Poor soft-tissue envelope or severe medical instability, where any major surgery may carry unacceptable risk (decision depends on overall clinical context)

How it works (Mechanism / physiology)

Unipolar hemiarthroplasty replaces the femoral head with a metal prosthetic head attached to a stem that sits inside the femur. The prosthetic head then articulates directly with the patient’s native acetabulum. In other words, only one side of the joint is replaced.

Key anatomy and structures involved include:

Femoral head and neck: removed as part of the reconstruction in typical fracture cases.
Acetabulum (hip socket): remains intact and becomes the bearing surface against the prosthetic head.
Articular cartilage and labrum: cartilage lines the acetabulum; the labrum is a fibrocartilaginous rim that contributes to stability. These structures influence how the new femoral head glides and how forces are distributed.
Capsule and surrounding muscles (especially abductors): soft tissues contribute substantially to postoperative stability and gait.

Biomechanically, the goals are to:

Recreate leg length and hip offset (the lateral distance that helps hip muscles function efficiently).
Provide a stable, congruent articulation so body weight can transfer through the pelvis and femur during standing and walking.
Reduce motion and stress at a fractured femoral neck by removing the fracture site as a load-bearing interface.

“Onset” and “duration” concepts apply differently to surgery than to medication. Pain relief and functional change typically occur as recovery progresses, not instantly in a single moment. The reconstruction is not reversible in the sense that native anatomy removed during arthroplasty is not restored, although conversion to another arthroplasty construct (such as total hip arthroplasty) can be considered in selected cases if problems arise (varies by clinician and case).

Unipolar hemiarthroplasty Procedure overview (How it’s applied)

Exact steps vary by surgeon, hospital protocols, implant system, and patient factors. At a high level, the workflow often looks like this:

Evaluation and diagnosis – Clinical assessment (pain, mobility, baseline function) and imaging such as X-ray to define fracture pattern or joint pathology. – Review of medical status, medications, and perioperative risks.
Preoperative planning and preparation – Selection of implant sizing strategy and fixation approach (cemented vs uncemented) based on bone quality and other factors (varies by clinician and case). – Anesthesia planning and perioperative risk management.
Surgical intervention – The surgeon accesses the hip through a chosen approach (posterior, lateral, or anterior variants are used in practice). – The femoral head is removed and the femoral canal is prepared for the stem. – Trial components are used to assess leg length, stability, and soft-tissue tension. – Final stem and unipolar head are implanted.
Immediate checks – Stability assessment through a range of motion (performed intraoperatively). – Postoperative imaging may be used to confirm component position (practice varies).
Follow-up and recovery – Hospital-based mobilization and transition planning. – Outpatient follow-up to monitor wound healing, function, and potential complications.

Types / variations

Although “unipolar” describes a specific bearing concept, several practical variations exist.

Cemented vs uncemented femoral stems
Cemented: bone cement anchors the stem inside the femur; often considered when bone quality is limited (varies by clinician and case).
Uncemented (press-fit): the stem achieves initial stability by fit and may allow bone to grow onto/into the implant surface depending on design (varies by material and manufacturer).
Monoblock vs modular designs
Monoblock: head and stem may be a single construct in some systems.
Modular: separate stem and head components allow sizing adjustments for leg length and offset (design varies by manufacturer).
Head size and neck options
Femoral head diameter and neck geometry are selected to match patient anatomy and optimize stability and soft-tissue tension (varies by system).
Materials
Femoral heads are commonly metal alloys (for example, cobalt-chromium in many systems). Stem materials and coatings vary by manufacturer and intended fixation strategy.
Surgical approach
Different approaches prioritize different exposure and soft-tissue handling. Choice can influence dislocation risk and early recovery patterns, but outcomes depend on many variables (varies by clinician and case).

Pros and cons

Pros:

Preserves the native acetabulum when it is healthy enough to serve as the socket surface
Can address pain and instability from a displaced femoral neck fracture by replacing the damaged femoral head
Often enables earlier functional mobilization compared with waiting for a fracture to heal (varies by clinician and case)
Avoids replacing the acetabular side of the joint, which may reduce surgical steps compared with total hip replacement (varies by clinician and case)
Implant selection and operative planning can be tailored (cemented vs uncemented, sizing options)
Can be an option when internal fixation is less likely to succeed due to blood supply or bone quality concerns

Cons:

The metal head moves against natural acetabular cartilage, which can contribute to acetabular wear over time (risk varies by clinician and case)
May provide less durable symptom control than total hip arthroplasty when the acetabulum is already arthritic (varies by clinician and case)
Dislocation, infection, blood clots, fracture around the implant, and leg-length/offset mismatch are recognized arthroplasty risks (rates vary)
Some patients later require conversion to total hip arthroplasty if pain or socket wear develops (varies by clinician and case)
Function may be limited by pre-existing weakness, balance issues, or other medical conditions even if the implant is stable
Outcomes can be influenced by rehabilitation access and comorbidities, not only the implant type

Aftercare & longevity

Recovery after Unipolar hemiarthroplasty is shaped by both the surgical reconstruction and the patient’s baseline health and mobility. Aftercare typically emphasizes safe return to movement, monitoring for complications, and progressive functional improvement.

Factors that commonly affect outcomes and longevity include:

The condition of the acetabulum: since the socket is not replaced, the health of its cartilage matters for longer-term comfort and wear patterns.
Implant fixation and bone quality: cemented vs uncemented stems behave differently early on, and osteoporosis can influence stability and fracture risk.
Soft-tissue function: hip abductor strength and overall balance can strongly influence gait and fall risk.
Weight-bearing status and activity progression: restrictions and timelines vary by clinician and case, and may depend on stability, bone quality, and intraoperative findings.
Rehabilitation and follow-up adherence: physical therapy, home safety planning, and scheduled check-ins can affect function and the ability to identify issues early.
Medical comorbidities: diabetes, vascular disease, cognitive impairment, or malnutrition can affect healing and complication risk (varies by clinician and case).
Implant design and materials: wear behavior and fixation surfaces vary by material and manufacturer.

Longevity is not a single number. Some patients do well for many years, while others may develop pain, instability, or acetabular wear that prompts further evaluation. Ongoing monitoring is individualized.

Alternatives / comparisons

Unipolar hemiarthroplasty is one option within a broader set of treatments for hip fractures and hip joint disease. Comparisons are best made based on diagnosis, bone quality, baseline function, and acetabular health.

Internal fixation (pins/screws or plates)
Often considered for certain femoral neck fractures, especially in younger patients or less displaced patterns.
Aims to preserve the native femoral head, but healing can be unpredictable when blood supply is compromised (varies by clinician and case).
Bipolar hemiarthroplasty
Replaces the femoral head with a component that has an additional internal articulation (a “head within a head” concept).
Intended to reduce motion and stress at the acetabular cartilage by allowing some movement inside the implant; real-world benefit varies by patient and implant design (varies by clinician and case).
Total hip arthroplasty (total hip replacement)
Replaces both the femoral head and the acetabulum.
Often considered when the acetabulum is arthritic or when higher functional demand is anticipated; it may involve different risks and operative considerations compared with hemiarthroplasty (varies by clinician and case).
Nonoperative management
May be considered in select cases where surgery is not feasible due to medical risk or goals of care, or for certain non-displaced injuries.
Typically involves pain control strategies and supportive care; functional outcomes vary widely and depend heavily on the underlying injury and patient health (varies by clinician and case).
Rehabilitation-focused care (physical therapy and assistive devices)
Essential after most hip injuries and surgeries, but it is not a substitute for mechanical reconstruction when the femoral head/neck is structurally compromised.
Often used alongside whichever surgical or nonsurgical path is selected.

Unipolar hemiarthroplasty Common questions (FAQ)

Q: Is Unipolar hemiarthroplasty the same as a total hip replacement?
No. Unipolar hemiarthroplasty replaces only the femoral head (the ball), while total hip arthroplasty replaces both the ball and the socket. The choice often depends on fracture type, acetabular condition, baseline function, and surgeon preference.

Q: Will it eliminate hip pain completely?
Many patients experience meaningful pain reduction when the fractured or damaged femoral head is replaced. However, pain levels vary and can be influenced by acetabular cartilage health, muscle weakness, back issues, or other medical conditions. Some discomfort during recovery is also expected after any major surgery.

Q: How long does the implant last?
There is no single lifespan that applies to everyone. Longevity depends on factors such as activity level, acetabular cartilage wear, implant fixation, bone quality, and overall health. Some people do well long-term, while others may need further evaluation or revision (varies by clinician and case).

Q: How does it compare with bipolar hemiarthroplasty?
Both are partial hip replacements that keep the native socket. Bipolar designs add an internal bearing surface intended to share motion between the implant and the socket, while unipolar designs articulate directly with the acetabulum. Which is preferred varies by clinician and case, and by implant design.

Q: Is the procedure considered safe?
All surgeries carry risks, and hip arthroplasty has known complications such as infection, dislocation, blood clots, and fracture around the implant. Overall safety depends on medical status, surgical technique, timing, and postoperative care. Your surgical team typically balances these factors when recommending an approach.

Q: What is recovery like, and how soon can someone walk?
Many patients begin assisted standing or walking during early recovery, often with a walker or other support, but the timeline varies. Weight-bearing and activity progression depend on the stability of the reconstruction, bone quality, and surgeon protocols. Functional recovery also depends on conditioning, balance, and rehabilitation access.

Q: When can someone drive or return to work after this surgery?
Timing varies based on pain control, mobility, reaction time, side of surgery, and type of work. Some jobs require more strength, endurance, or safe movement than others. Clearance is individualized and typically comes from the treating clinician based on functional readiness.

Q: Does Unipolar hemiarthroplasty limit certain movements?
After hip surgery, clinicians may recommend temporary movement precautions depending on surgical approach and stability concerns. These precautions are not identical for every patient or every approach. Longer-term motion is often guided by comfort, strength, and stability rather than a single universal rule (varies by clinician and case).

Q: Can it be converted to a total hip replacement later?
In some situations, yes. If acetabular wear, persistent pain, or other issues develop, conversion to total hip arthroplasty may be considered. Whether conversion is appropriate depends on bone quality, implant position, medical status, and the specific reason for revision (varies by clinician and case).

Q: What affects the overall cost?
Cost depends on many factors, including hospital setting, geographic region, insurance coverage, implant system, length of stay, and rehabilitation needs. Additional testing, medical optimization, and postoperative services can also change the total cost. For individualized estimates, patients typically need a facility-specific billing review.