Periprosthetic Joint Infection After THA

Periprosthetic joint infection (PJI) is one of the most devastating complications following total hip arthroplasty. Despite advances in prevention, PJI remains a leading cause of early revision and has profound impact on patient outcomes.

Epidemiology:

• Primary THA: 1-2% infection rate
• Revision THA: 3-5% infection rate (higher risk)
• Increasing incidence despite improved prevention strategies (likely due to higher-risk patients)
• Costs: PJI treatment costs 3-4 times more than primary arthroplasty

Routes of infection:

1. Direct inoculation (most common for early PJI)

   • Intraoperative contamination
   • Postoperative wound complications
   • Accounts for majority of early infections

2. Hematogenous spread (late PJI)

   • Dental procedures
   • Urinary tract infections
   • Skin/soft tissue infections
   • GI sources (endoscopy, diverticulitis)

3. Contiguous spread (rare)

   • Adjacent osteomyelitis
   • Septic hip (pre-existing)

Biofilm development stages:

Organism-specific considerations:

Temporal classification (Tsukayama):

McPherson staging (host and extremity factors):

Clinical presentation varies by timing:

History taking:

• Timing of symptoms relative to surgery
• Previous function of the THA (was it ever pain-free?)
• Wound complications postoperatively
• Recent infections or procedures (dental, UTI)
• Risk factors: diabetes, immunosuppression, prior surgery
• Prior antibiotic use (affects culture yield)

Physical examination:

Examination findings:

• Wound erythema, warmth, swelling
• Sinus tract or wound drainage
• Pain with ROM (even passive)
• Reduced ROM (contracture from chronic inflammation)
• Previous surgical scars
• Systemic signs (fever, sepsis in severe cases)

Differential diagnosis of the painful THA:

MSIS/ICM 2018 Criteria for PJI:

Major criteria (ONE required for definite PJI):

1. Two positive cultures of the same organism from separate samples
2. Sinus tract communicating with the prosthesis

Minor criteria (FOUR required for definite PJI if no major criteria):

Diagnostic algorithm summary:

1. Clinical suspicion → Serum ESR/CRP
2. If elevated or high suspicion → Hip aspiration (off antibiotics if possible)
3. Aspiration: cell count, culture, alpha-defensin
4. Apply MSIS criteria for diagnosis
5. If diagnosis confirmed → Plan treatment based on timing and organism
6. Intraoperative cultures confirm and guide antibiotic therapy

Organism-specific antibiotic selection:

Key antibiotic principles:

The organism tables list fungi (Candida) as a cause "requiring antifungals, often two-stage or resection," but fungal PJI is never developed - it is rare, difficult, and examinable.

• When to suspect it. Fungal PJI (usually Candida, occasionally Aspergillus) is uncommon (around 1% of PJI) but should be considered in an immunocompromised or debilitated host, after prolonged broad-spectrum antibiotics, in culture-negative infection that fails to settle, or as part of a polymicrobial infection. It is typically indolent, and standard bacterial cultures may miss it - request fungal cultures with extended incubation, and consider sonication and molecular tests.
• Why it is hard. Candida forms a biofilm on the implant just as bacteria do, so eradication almost always needs implant removal and DAIR rarely works. Antifungal penetration is limited and treatment is prolonged.
• Treatment. Two-stage revision is the mainstay, with an antifungal-loaded spacer (amphotericin B is the agent usually added to cement, as azoles/echinocandins elute poorly) plus systemic antifungal therapy - an echinocandin or a lipid amphotericin formulation initially, stepping down to fluconazole for susceptible Candida - continued as a prolonged course (guided by infectious diseases). Outcomes are worse than for bacterial PJI, and resection arthroplasty (Girdlestone) or long-term suppression is a realistic endpoint in the frail or multiply-failed patient.

The Tsukayama classification includes Type IV - positive intraoperative cultures at a presumed-aseptic revision, and Scenario 2 asks what to do if cultures grow at reimplantation, but the significance and management of positive intraoperative cultures is never developed.

• The single-culture problem. At a revision done for presumed aseptic failure, one unexpected positive culture is usually a contaminant and does not by itself indicate infection; two or more cultures growing the same organism (Tsukayama Type IV) is the threshold that indicates a true, previously unrecognised low-grade infection. This is exactly why at least five separate deep tissue samples are taken and why a single positive result is interpreted with caution.
• What it means and what to do. A genuine Type IV infection (two or more concordant cultures) is treated with an organism-directed antibiotic course (commonly around 6 weeks, ID-guided) with the newly implanted components retained, and reported outcomes are relatively good because the biofilm burden is low. A single positive culture in a well-appearing patient is generally observed with vigilance rather than treated, unless it is a virulent organism (e.g. S. aureus) or other criteria are met.
• Positive cultures at second-stage reimplantation. Growth at stage 2 of a two-stage revision is more concerning - it suggests persistent infection. A single contaminant may again be observed, but two or more concordant cultures mean the infection was not cleared: continue or restart targeted antibiotics, reconsider whether reimplantation was premature, and be prepared for repeat resection or long-term suppression.

After DAIR:

Treatment-specific outcomes:

Long-term considerations:

• PJI survivors have increased mortality compared to matched controls
• Quality of life significantly impacted
• Economic burden substantial (lost work, caregiver needs)
• Psychological impact (depression, anxiety common)

System-level prevention (global):

• National surgical site infection surveillance programmes (e.g. NHSN in the US, the UK SSI surveillance service, ECDC HAI-Net) benchmark and drive down rates
• Standardised perioperative antibiotic prophylaxis protocols and WHO Surgical Safety Checklist
• Preoperative optimisation pathways (glycaemic control, MRSA decolonisation, nutrition, smoking cessation) in high-volume arthroplasty centres

Global epidemiology:

• Primary THA PJI incidence ~1-2%; revision THA 3-5%
• Infection is consistently among the top 3 indications for THA revision worldwide, alongside aseptic loosening and dislocation/instability
• Absolute case numbers are rising as arthroplasty volume and patient age/comorbidity increase, even where the percentage rate is stable

Registry evidence (cumulative revision for infection):

Side-by-side guideline comparison:

Resource-setting variation:

• High-resource: dedicated bone-infection MDTs (orthopaedics, ID, microbiology, plastics), sonication, molecular/next-generation sequencing, articulating spacers, and single-stage exchange programmes
• Limited-resource: reliance on serum markers and aspiration without alpha-defensin or sonication; two-stage and resection arthroplasty (Girdlestone) more frequently used where revision implants, prolonged IV antibiotics, or spacer fabrication are constrained

The evidence base in PJI is evolving, and several management questions remain genuinely contested - high-yield discussion points for vivas.