Most hip and knee replacements heal without infection. But when a prosthetic joint infection does occur, recognizing it matters because the treatment is very different from the treatment for routine postoperative soreness, stiffness, tendon irritation, or implant loosening.
The challenge is that a joint replacement infection does not always look dramatic. Some infections cause fever, drainage, redness, and rapidly worsening pain. Others develop slowly and may present mainly as persistent pain, stiffness, recurrent swelling, or a joint that never seemed to recover as expected.
From my perspective as an orthopedic surgeon who evaluates primary and revision hip and knee replacements, the most important principle is simple: infection should be considered before a painful replacement is treated as a purely mechanical problem. No single blood test, X-ray, or aspiration result answers every case. Diagnosis usually comes from putting several pieces of evidence together.
The American Academy of Orthopaedic Surgeons has a dedicated clinical practice guideline for diagnosing and preventing periprosthetic joint infection, and current reviews continue to emphasize a combined clinical, laboratory, and synovial-fluid approach rather than relying on one test alone. Read the AAOS guideline overview and a 2024 JBJS review of serum and synovial diagnostic markers.
What is a prosthetic joint infection?
A prosthetic joint infection, often abbreviated PJI, is an infection involving the tissues around an artificial joint such as a total hip replacement or total knee replacement.
Bacteria can attach to implant surfaces and form a protective community called a biofilm. Biofilm makes implant-associated infection different from a simple skin infection. Once bacteria are established on an implant, antibiotics may have difficulty eradicating the infection without also addressing the infected tissue and, in some cases, the prosthetic components themselves.
The hero image above is an illustrative 3D rendering of biofilm on an orthopedic implant surface, not a photograph from a patient or an actual microscopic specimen.
What are the symptoms of a joint replacement infection?
Symptoms depend on how quickly the infection develops, the organism involved, how long the implant has been present, and the patient’s overall health.
Possible warning signs include:
- Increasing pain after a period of improvement
- Pain that never meaningfully improved after surgery
- Recurrent or progressively increasing swelling
- Persistent wound drainage
- A wound that opens after surgery
- Redness or increasing warmth around the joint
- Fever or chills
- New stiffness or loss of motion
- Increasing difficulty bearing weight
- A draining sinus or small opening near the surgical incision
- Unexplained fatigue or feeling generally ill
Importantly, the absence of fever does not rule out infection. Chronic or low-grade infections can be much less obvious.
When should symptoms be treated as urgent?
Contact your treating surgeon promptly or seek urgent medical care if you have a replaced joint and develop:
- Persistent or new wound drainage
- Rapidly increasing redness or swelling
- Fever or chills with worsening joint pain
- Severe pain with inability to bear weight
- A wound opening over the replaced joint
- Confusion, weakness, low blood pressure, or other signs of serious systemic illness
A patient who is systemically ill may need emergency evaluation and treatment. That situation is different from the more common outpatient workup of a stable patient with chronic pain or swelling.
Can a joint replacement become infected years later?
Yes. Prosthetic joint infection can occur soon after surgery, months later, or even years after a previously successful joint replacement.
Early infections may result from bacteria introduced around the time of surgery or from wound problems during healing. Later infections can occasionally occur when bacteria travel through the bloodstream from another infection elsewhere in the body.
That does not mean every illness, dental procedure, or skin infection will infect a joint replacement. The risk depends on the clinical situation. In fact, AAOS and the American Association of Hip and Knee Surgeons updated guidance in 2024 regarding dental procedures and joint replacement, reflecting that routine preventive antibiotics before dental work are not automatically appropriate for every patient with a prosthetic joint. AAOS lists the current dental-procedure PJI prevention guideline here.
How do doctors test for a possible joint replacement infection?
A good workup is usually stepwise. The goal is to gather enough evidence to determine whether infection is likely, unlikely, or still uncertain.
1. History and physical examination
The timing and pattern of symptoms matter.
Useful questions include:
- Did the joint ever feel good after the original replacement?
- When did the pain or swelling begin?
- Was there recent drainage or wound trouble?
- Were antibiotics taken recently?
- Was there a recent illness or infection elsewhere in the body?
- Has the joint already been aspirated?
- Has there been a previous revision operation?
The examination looks for swelling, warmth, drainage, wound problems, range of motion, instability, tenderness, and signs of infection outside the joint.
2. X-rays
X-rays are important, but an X-ray alone cannot reliably prove or exclude infection.
Radiographs may show:
- Implant loosening
- Bone loss
- Fracture
- Changes in implant position
- Progressive radiolucent lines
- Osteolysis
Some of these findings can occur with either infection or noninfectious implant failure. Serial films are often more useful than a single image because change over time can be informative.
3. Blood tests
Common screening tests include:
- C-reactive protein (CRP)
- Erythrocyte sedimentation rate (ESR)
These markers can support concern for infection, but neither is perfectly sensitive or specific. They can be elevated for other reasons, and some chronic infections may produce only modest abnormalities.
The AAOS diagnostic guideline supports using inflammatory markers as part of the evaluation rather than treating them as stand-alone answers. See the AAOS PJI guideline.
4. Joint aspiration
If infection remains a concern, aspiration of the replaced hip or knee may be one of the most important next steps.
Joint fluid may be tested for:
- Synovial white blood cell count
- Percentage of neutrophils
- Aerobic and anaerobic cultures
- Selected synovial biomarkers
- Other tests depending on the situation
No single synovial test is perfect. A 2024 Journal of Bone and Joint Surgery review emphasizes that clinicians generally combine serum tests, synovial markers, cultures, and clinical findings to reach a diagnosis. Read the review.
Should I take antibiotics before the joint is aspirated?
If a patient is medically stable and the purpose of the evaluation is to identify the organism causing a possible chronic prosthetic joint infection, antibiotics are often avoided until appropriate cultures have been obtained because antibiotics can reduce culture yield.
That is not a rule for a patient who is acutely ill or septic. Someone with signs of a serious systemic infection may need urgent antibiotics and hospital-level treatment. The sequence must be individualized to the clinical situation.
What if the aspiration is negative but infection is still suspected?
A negative culture does not automatically end the investigation.
Culture-negative prosthetic joint infection can occur, especially when antibiotics were taken before aspiration or surgery. The clinician may need to reconsider:
- Whether the aspiration produced enough fluid
- Whether the right cultures were obtained
- How long cultures were held
- Whether inflammatory markers support infection
- Whether repeat aspiration is useful
- Whether intraoperative tissue samples are needed
- Whether another diagnosis better explains the symptoms
This is why PJI is diagnosed using a pattern of evidence, not a single yes-or-no test.
How are prosthetic joint infections treated?
Treatment depends on the timing of infection, implant fixation, organism, soft-tissue condition, bone loss, patient health, and whether the infection is acute or chronic.
Debridement, antibiotics, and implant retention
For selected acute infections, surgeons may perform irrigation and debridement, exchange modular components when appropriate, retain well-fixed major components, and coordinate targeted antibiotic treatment.
This strategy is commonly called DAIR, meaning debridement, antibiotics, and implant retention.
DAIR is not appropriate for every infection. Chronic infections, loose implants, extensive biofilm, difficult organisms, major bone loss, or poor soft tissue may push treatment toward revision rather than implant retention.
One-stage revision
In a one-stage exchange, infected components are removed, the joint is thoroughly debrided, and new components are implanted during the same operation.
One-stage revision is increasingly discussed for carefully selected patients. Selection may depend on factors such as the organism, antibiotic options, bone and soft-tissue condition, implant reconstruction requirements, and the patient’s medical status.
A 2025 systematic review and meta-analysis of hip PJI found no clear difference in reinfection between one-stage and two-stage revision across the included observational studies, although patient selection differed between groups. Read the JAAOS meta-analysis.
Two-stage revision
Two-stage exchange has traditionally been used for many chronic hip and knee infections.
The general concept is:
- Remove the infected implant.
- Perform aggressive debridement of infected tissue.
- Place an antibiotic-loaded spacer when appropriate.
- Treat the infection with a coordinated antibiotic plan.
- Reassess the patient before later reconstruction with a new implant.
Two-stage revision is a major treatment course rather than one isolated operation. Patients need to understand the recovery, mobility limitations, medical risks, bone-loss considerations, and possibility that the second-stage reconstruction may need to change depending on what is found.
Long-term antibiotic suppression
In selected patients who are not candidates for major revision surgery, long-term suppressive antibiotics may sometimes be considered with infectious-disease input.
Suppressive treatment generally aims to control infection rather than remove infected biofilm from the implant. It is therefore a different strategy from curative revision surgery and should be discussed in the context of the patient’s goals, surgical risk, organism, and likelihood of durable infection control.
Does every painful replacement need aspiration?
No.
Pain after hip or knee replacement can come from many noninfectious causes, including:
- Implant loosening
- Instability
- Fracture
- Stiffness
- Tendon or soft-tissue problems
- Component position
- Nerve-related pain
- Hip or spine disease referring pain to the joint
The decision to aspirate should depend on the history, physical examination, inflammatory markers, imaging, timing, and overall suspicion for infection.
At the same time, aspiration should not be skipped merely because an X-ray looks acceptable if the clinical pattern raises legitimate concern for infection.
Why identifying infection before revision surgery matters
This is one of the most consequential decisions in revision joint replacement.
A revision operation planned for presumed aseptic loosening or instability is fundamentally different from a revision planned for confirmed or strongly suspected infection. Implant selection, surgical exposure, tissue sampling, antibiotic strategy, reconstruction planning, and the number of potential operations may all change.
For that reason, when infection is plausible, the diagnostic workup should be deliberate before proceeding with elective revision surgery.
What should I bring to an evaluation for possible joint replacement infection?
Bring as much of the prior treatment history as possible:
- Original operative report
- Implant records or implant card
- Prior revision operative reports
- X-rays from before and after surgery
- CT or MRI reports if available
- ESR and CRP results
- Aspiration cell counts and culture results
- Infectious-disease notes
- A list of antibiotics and the dates they were taken
- A timeline of wound drainage, swelling, fever, and pain
Even older records can matter because they help reconstruct what happened before the current symptoms developed.
What is Dr. Morton’s clinical perspective?
When evaluating a painful or failed hip or knee replacement, my approach is to define the failure mechanism before recommending revision.
If infection is possible, the goal is not simply to order more tests. It is to answer specific questions:
- How likely is infection?
- Is there enough evidence to aspirate the joint?
- Has prior antibiotic use affected culture reliability?
- Is the implant well fixed?
- Is the infection acute or chronic?
- Is there bone loss or soft-tissue compromise?
- Would implant retention, one-stage revision, two-stage revision, or another strategy best fit the individual situation?
That decision often benefits from coordination between orthopedic surgery, infectious disease, radiology, and the laboratory.
When should you schedule an orthopedic evaluation?
If a replaced hip or knee is becoming more painful, repeatedly swelling, losing motion, draining, or failing after a period of good function, an orthopedic evaluation can help determine whether infection belongs on the differential diagnosis and what testing is actually useful.
Pacific Bone & Joint evaluates bone and joint infections as well as painful and failed joint replacements in Hawaiʻi. Learn more about our bone and joint infection service and revision hip and knee replacement care.
If you are concerned that a hip or knee replacement may be infected, request an orthopedic evaluation so the cause can be identified before treatment decisions are made. Patients with fever, drainage, rapidly worsening redness or swelling, or signs of systemic illness should seek urgent medical care rather than wait for a routine appointment.
Sources and further reading
- American Academy of Orthopaedic Surgeons. Diagnosis and Prevention of Periprosthetic Joint Infections Clinical Practice Guideline. Published 2019. https://www.aaos.org/quality/quality-programs/diagnosis-and-prevention-of-periprosthetic-joint-infections/
- Tarabichi S, Goh GS, Fraval A, et al. “Serum and Synovial Markers in the Diagnosis of Periprosthetic Joint Infection of the Hip, Knee, and Shoulder: An Algorithmic Approach.” Journal of Bone and Joint Surgery American. 2024. https://pubmed.ncbi.nlm.nih.gov/38776388/
- Tabaja H, Abu Saleh OM, Osmon DR. “Periprosthetic Joint Infection: What’s New?” Infectious Disease Clinics of North America. 2024. https://pubmed.ncbi.nlm.nih.gov/39261141/
- Lamo-Espinosa JM, Mariscal G, Gómez-Álvarez J, et al. “One-Stage Versus Two-Stage Revision Surgery for Periprosthetic Hip Infection: An Updated Systematic Review and Meta-Analysis of Clinical Outcomes.” Journal of the American Academy of Orthopaedic Surgeons. 2025. https://pubmed.ncbi.nlm.nih.gov/39303283/
- Parvizi J, Tan TL, Goswami K, et al. “The 2018 Definition of Periprosthetic Hip and Knee Infection: An Evidence-Based and Validated Criteria.” Journal of Arthroplasty. 2018. https://pubmed.ncbi.nlm.nih.gov/29551303/
