Periprosthetic Joint Infection Detection and Monitoring

Diagnostic Performance and Monitoring

The American Academy of Orthopaedic Surgeons strongly recommends using ESR, CRP, and serum interleukin-6 together for optimal diagnostic accuracy in suspected periprosthetic joint infection (PJI) 1, 2
CRP demonstrates 73-91% sensitivity and 81-86% specificity for prosthetic knee infection using a cutoff of 13.5 mg/L 1, 2
When combining ESR (>27 mm/h), CRP (>0.93 mg/L), and fibrinogen (>432 mg/dL), achieving abnormality in at least 2 of 3 tests yields 93% sensitivity and 100% specificity for PJI 1, 2
CRP persistently elevated beyond 2 months postoperatively strongly suggests infection 1
Obtain baseline CRP and ESR, then recheck at 2-4 week intervals during active treatment 1, 3
Synovial fluid alpha-defensin achieves 97% sensitivity and 96% specificity for PJI diagnosis 3
When combined with synovial CRP, specificity increases to 100% for PJI diagnosis 3

ESR should be measured at baseline and repeated at 1-3 month intervals during active disease, then every 3-6 months once remission is achieved 1
ESR is incorporated into DAS28-ESR composite scores for rheumatoid arthritis disease activity assessment 1
Higher baseline ESR values indicate greater disease severity and identify patients requiring early DMARD therapy 1

CRP is preferred for acute infections and septic arthritis, as it rises within 12-24 hours and peaks at 48 hours 1
ESR is preferred for chronic inflammatory conditions, as fibrinogen has a longer half-life than CRP 1
ESR >40 mm/h has 93.2% sensitivity with negative likelihood ratio of 0.18 for giant cell arteritis screening 1

Never rely on normal ESR/CRP to exclude PJI, as up to 32% of culture-positive infections have normal inflammatory markers 2
Do not interpret isolated inflammatory marker elevations without clinical context, as pain characteristics matter 2
Avoid premature joint aspiration in patients on antibiotics, and wait at least 2 weeks off antibiotics when clinically feasible to maximize culture yield 2, 3

The American College of Radiology recommends using cutoffs of fibrinogen >432 mg/dL, ESR >27 mm/h, and CRP >0.93 mg/L, with abnormality in at least 2 of 3 tests yielding 93% sensitivity, 100% specificity, and 97% accuracy for PJI diagnosis 4, 5
Fibrinogen performs significantly better than traditional markers like peripheral WBC count, which remains normal in most PJI cases, with a sensitivity of 90% when used at a cutoff of 519 mg/dL 4

Night pain or pain at rest suggests infection, whereas pain only with weight-bearing suggests mechanical loosening, and fibrinogen elevation is expected in the former case 4
The American College of Radiology suggests that CRP typically returns to baseline within 2 months after uncomplicated arthroplasty, so persistent elevation of fibrinogen beyond this timeframe strongly suggests infection 4
Fibrinogen elevation is more specific to bacterial infection than ESR alone, which can be elevated in uninfected patients with mechanical complications 4