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The Joint EBJIS-MSIS 2026 Conference
17 - 19 September, 2026 | Porto, Portugal
EP395
Knee Infection is Associated with Lower Synovial Fluid pH Regardless of Prosthesis Joint Status or Antibiotic Exposure
Poster Presenter
Authors
James Hwang, Jonathan Thompson, Noreen J. Hickok, Thomas P. Schaer, Christopher M. Snyder, Antonia F. Chen
Affiliations
Department of Orthopaedic Surgery, University of Texas Southwestern Medical Center, Dallas, United States, Department of Orthopaedic Surgery, Thomas Jefferson University, Philadelphia, United States, Richard S. Reynolds, Jr. Comparative Orthopedic Research Laboratory, University of Pennsylvania School of Veterinary Medicine, Philadelphia, United States, Department of Microbiology & Immunology, Thomas Jefferson University, Philadelphia, United States, University Of Texas Southwestern Medical Center
Part of Topic
Prosthetic Joint Infections
Introduction & Aim
▪ Synovial fluid pH is a potential simple and rapid diagnostic parameter for periprosthetic joint infection (PJI) after total knee arthroplasty.
▪ Metal prosthesis dissolution and antibiotic administration could confound synovial fluid pH as a diagnostic signal.
▪ Aim: Evaluate whether infection, presence of a prosthetic joint, and antibiotic exposure affect synovial fluid pH.
Materials & Methods
▪ Synovial fluid collected from 112 patients (mean age 65.3±10.8 yrs; 50 M / 62 F) at a tertiary center, April 2025 to April 2026.
▪ Aspirated superolaterally through skin (outpatient; no antibiotics) or through the capsule after skin incision (operative; antibiotics).
▪ pH measured in triplicate per sample and averaged (mean ± standard deviation).
▪ Patients stratified into 6 cohorts by infection status (yes/no), joint type (native/prosthetic), and antibiotic exposure (yes/no).
Results: Synovial Fluid pH by Cohort
▪ All patients with knee infections received antibiotics prior to aspirate.
▪ Synovial fluid pH from infected native knees (6.77±0.19) was significantly lower than the pH of non-infected native knees with (7.57±0.18, p=0.016) or without (7.59±0.17, p=0.004) antibiotics.
▪ Synovial fluid pH from infected prosthetic knees (7.33±0.47) trended lower than non-infected prosthetic knees with (7.48±0.24, p=0.526) or without (7.45±0.11, p=0.606) antibiotics.
▪ Prosthesis presence and antibiotic exposure alone did not significantly alter synovial fluid pH (all p>0.05).
Conclusions
▪ Synovial fluid pH from human knees is slightly alkaline and above blood pH (7.4) in all cohorts except for infection.
▪ Infection is associated with decreased synovial fluid pH, albeit only infected native knees move into an acidic pH range (<7.0).
▪ This association persists in the presence of prosthesis and with prior antibiotic administration, neither of which appears to significantly influence synovial fluid pH.
▪ These findings support reevaluation of the predictive value of synovial fluid pH for PJI diagnosis and its potential role in guiding antibiotic treatment choice.