Periprosthetic Joint Infection: Infected Knee Replacement Treatment in Birmingham
Periprosthetic joint infection (PJI) is one of the most serious complications after knee replacement, occurring when bacteria colonise the implant and form a protective biofilm that the immune system cannot easily clear. Mr Shakir Hussain, Consultant Orthopaedic Surgeon at the Royal Orthopaedic Hospital Birmingham, manages infected knee replacements with specialist two-stage revision surgery at a dedicated specialist orthopaedic centre.
What is periprosthetic joint infection (PJI)?
Periprosthetic joint infection is infection of the tissues and implant surrounding a knee replacement. Bacteria attach to the metal and plastic components and form a protective biofilm that the immune system cannot penetrate. Because artificial joints have no blood supply, the body cannot deliver the white cells and antibodies needed to clear the infection without surgical help.
Even with strict sterilisation protocols at the time of primary surgery, bacteria can occasionally reach the joint during the procedure or, later, via the bloodstream from another site of infection in the body (haematogenous spread). Once bacteria establish a biofilm on the implant surface, antibiotics alone cannot eradicate the infection. This is the fundamental reason PJI nearly always requires surgical treatment.
PJI is classified by timing. Early infection occurs within three months of surgery, typically caused by bacteria introduced at the time of the primary operation. Delayed infection occurs between three and 24 months, often with less virulent organisms and a more insidious presentation. Late infection occurs after 24 months and is usually haematogenous, seeded from a remote site such as a dental abscess, urinary tract infection, or skin wound.
Infection is widely recognised as one of the most common and complex reasons a patient may require a revision procedure. Specialist centre management, with access to dedicated infection teams and complex revision implant systems, is essential for the best outcomes.
What are the signs of an infected knee replacement?
Key warning signs include pain that has not improved as expected after surgery, swelling with warmth and redness around the joint, a wound that keeps leaking or develops a persistent sinus (a tract leading to the implant), and feeling systemically unwell with a fever. These features require urgent orthopaedic assessment.
Persistent or worsening pain
Pain that does not improve as expected after primary surgery, or that returns after a period of relative comfort, is the most consistent symptom of PJI across all timing categories.
Swelling, warmth, and redness
The knee feels hot to touch, looks swollen, and the skin may be red or discoloured around the joint. These inflammatory signs are more pronounced in acute and early infections.
Wound discharge or sinus tract
A wound that persistently leaks fluid, or a sinus that develops weeks or months after surgery tracking down toward the implant, is a strong indicator of deep infection and requires immediate assessment.
Fever and systemic illness
Acute haematogenous PJI can present abruptly with fever, chills, and general unwellness. Patients with systemic illness and a joint replacement must be assessed urgently to rule out septic arthritis of the prosthesis.
Stiffness that did not resolve
Persistent stiffness beyond the expected recovery period, particularly if accompanied by pain, may indicate a chronic low-grade infection that has been present since the primary surgery.
Elevated inflammatory blood markers
Raised CRP (C-reactive protein), ESR (erythrocyte sedimentation rate), and white cell count are important supporting findings, though they can also be elevated for other reasons in the post-operative period.
Who is at risk of periprosthetic knee infection?
PJI can affect any patient after knee replacement, but the risk is substantially higher in patients with diabetes, obesity, immunosuppression, or rheumatoid arthritis, and in those who had a prolonged primary operation or a remote site of infection at the time of surgery.
The risk of PJI after primary knee replacement at high-volume centres is approximately 1 to 2 per cent. However, for individual patients, certain factors significantly increase that risk:
- Obesity. Adipose tissue is relatively poorly vascularised, which reduces immune surveillance at the wound site and increases the risk of wound-healing complications that give bacteria access to the deep tissues.
- Diabetes mellitus. Both type 1 and type 2 diabetes impair neutrophil function, reduce skin and tissue healing capacity, and create a systemic environment that favours infection.
- Immunosuppression. Patients on corticosteroids, biologic disease-modifying agents (used in rheumatoid arthritis), or post-transplant immunosuppression have reduced ability to combat bacterial colonisation.
- Rheumatoid arthritis. The underlying disease and its treatment both increase infection risk. Many patients with RA are managed with biologic agents that require careful peri-operative management to balance infection risk against disease flare.
- Prior knee surgery. Each previous operation on the same knee leaves scar tissue, reduces skin quality, and may introduce organisms. The risk of PJI rises with each successive surgical episode.
- Prolonged surgical time. Extended operative time correlates with increased infection rates across all joint replacement surgeries, reflecting greater wound exposure and cumulative contamination risk.
- Remote site of infection. Having any active infection at the time of surgery, including a urinary tract infection, dental infection, or skin wound, substantially increases the risk of haematogenous seeding of the prosthesis. Surgery should be delayed until all remote infections are fully treated.
How is a periprosthetic knee infection diagnosed?
Diagnosis uses the MSIS (Musculoskeletal Infection Society) criteria, combining blood tests (CRP, ESR), synovial fluid aspiration with cell count and culture, and where needed, nuclear medicine imaging. The definitive bacteriological result comes from tissue cultures taken at revision surgery.
Diagnosing PJI requires a combination of clinical, laboratory, and imaging findings. No single test is sufficient. Mr Hussain follows the MSIS criteria, which define PJI as confirmed when one of the major criteria or three of five minor criteria are met:
- Blood tests: CRP, ESR, WCC. C-reactive protein above 10 mg/L (after the acute post-operative period) and ESR above 30 mm/hr are the most sensitive screening markers. A normal CRP makes PJI less likely.
- Joint aspiration. Synovial fluid is aspirated from the knee and sent for white cell count and differential (raised polymorphonuclear percentage supports infection), culture and sensitivity (identifies the organism and guides antibiotic choice), and alpha-defensin testing (highly specific biomarker for PJI).
- Nuclear medicine imaging. A labelled white cell scan (leukocyte scintigraphy) identifies areas of active white cell accumulation around the implant. Particularly useful in chronic or low-grade PJI where other markers may be borderline.
- Tissue cultures at surgery. Multiple samples of periprosthetic tissue taken at revision surgery and cultured for at least two weeks (to allow for slow-growing organisms such as Cutibacterium acnes) provide the definitive bacteriological diagnosis and guide targeted antibiotic therapy.
- Histology. Frozen section histology during surgery can confirm or exclude acute infection (more than five polymorphonuclear leukocytes per high-power field).
How is an infected knee replacement treated?
The treatment depends on the timing and type of infection. Early and acute haematogenous infections in a well-fixed implant may be treated with debridement, antibiotics, and implant retention (DAIR). Established delayed or late infections require two-stage revision: removal of all components, an antibiotic spacer, systemic antibiotics, and later re-implantation of a new replacement.
The choice of treatment is guided by the timing of infection, whether the implant is well-fixed or loose, the identity and antibiotic sensitivity of the organism, and the overall fitness of the patient.
DAIR (Debridement, Antibiotics, Implant Retention)
DAIR is appropriate when the implant is well-fixed, symptoms have been present for fewer than three to four weeks, and the organism is sensitive to antibiotics. The joint is washed out thoroughly, all infected tissue and the polyethylene insert are removed, a new insert is placed, and a prolonged course of antibiotics (including biofilm-active agents such as rifampicin for staphylococcal infection) is given.
- Implant components retained if well-fixed
- Thorough synovectomy and debridement
- Polyethylene spacer exchanged for a new one
- Prolonged antibiotic course (typically 3 to 6 months)
- Success rate approximately 50 to 70 per cent in carefully selected patients
Two-Stage Revision Knee Replacement
Stage 1: all implant components are removed, infected and devitalised tissue is debrided, and an antibiotic-loaded cement spacer is placed to fill the joint space, deliver high local antibiotic concentrations, and maintain soft-tissue length. Following a structured course of systemic antibiotics and confirmed infection eradication (via clinical assessment and inflammatory marker normalisation), Stage 2 implants a new definitive knee replacement, often using stemmed revision components for added fixation.
- All infected components removed at Stage 1
- Antibiotic-loaded cement spacer tailored to the causative organism
- 6 to 12 weeks of systemic antibiotic therapy between stages
- Infection eradication confirmed before Stage 2 reimplantation
- Success rate of 70 to 90 per cent in specialist centres
For elderly or medically frail patients who are not fit for two or more major operations, long-term suppressive antibiotic therapy may be offered to control symptoms without eradicating the infection. This is a palliative approach and does not cure the PJI. Resection arthroplasty (removal of implant without replacement) or arthrodesis (fusion) are salvage options in exceptional circumstances where reimplantation is not possible.
Mr Hussain performs complex revision knee surgery for PJI at the Royal Orthopaedic Hospital Birmingham, one of the largest specialist orthopaedic centres in Europe. See the dedicated revision knee surgery page for full details of the operative approach, recovery, and outcomes.
What are the outcomes of revision surgery for PJI?
Two-stage revision for PJI achieves infection eradication in 70 to 90 per cent of cases when performed at specialist centres with dedicated infection management pathways. Outcomes are best in patients with a single identified organism sensitive to antibiotics, a well-vascularised soft tissue envelope, and no significant bone loss at the time of revision.
The most important factors determining outcome are early diagnosis, appropriate antibiotic selection guided by sensitivity testing, complete surgical debridement at Stage 1, and the expertise of the revision surgical team. Reinfection after two-stage revision is more likely if bone loss is severe, if the organism is resistant to standard antibiotics, or if patient-related risk factors (obesity, diabetes, immunosuppression) are not optimised before Stage 2.
Specialist centre management matters. The Royal Orthopaedic Hospital Birmingham has dedicated orthopaedic infection services, microbiology support, and access to the full range of complex revision implant systems, including stems, augments, and constrained components. These are not universally available and make a substantial difference to outcomes in complex PJI cases.
Specialist expertise in infected knee replacement in Birmingham
Consultant at the Royal Orthopaedic Hospital
Mr Hussain practises at the Royal Orthopaedic Hospital Birmingham, one of the largest specialist orthopaedic hospitals in Europe, with dedicated orthopaedic infection pathways and microbiology support.
3,000+ arthroplasty cases from 5,000+ procedures
A high operative volume including complex primary and revision cases gives Mr Hussain the experience required for consistently excellent outcomes. Read more about Mr Hussain's training and background.
MAKO, ROSA, and CORI robotic certifications
Certified on all three major robotic platforms, enabling robotic-assisted implant positioning in revision cases where anatomy has been altered by prior surgery or infection.
Complex revision surgery expertise
Mr Hussain performs revision knee replacement for the full spectrum of failure modes, including PJI, loosening, and instability. See the revision surgery page for full details.
Doctify Outstanding Patient Experience 2024, 2025, and 2026
Awarded in three consecutive years, recognising consistently high patient-reported outcomes and communication throughout the surgical journey.
4.98 out of 5 from verified reviews on Doctify. Outstanding Patient Experience Award 2024, 2025, and 2026.
Frequently asked questions about knee replacement infection
For more questions about surgery, recovery, fees, and what to expect, see the full frequently asked questions page or read recent patient testimonials.