Periprosthetic joint infection (PJI) is a devastating complication of joint arthroplasty surgery that is difficult to both diagnose and treat. Misdiagnosing a prosthetic infection has terrible consequences for both the patient and healthcare system. No currently used diagnostic test fulfills the requirements to be considered a gold standard. This shortcoming has been overcome through the implementation of multi-criteria diagnostic protocols elaborated by societies including the Infectious Diseases Society of America, International Consensus Meeting and European Bone and Joint Infection Society, using a combination of clinical, paraclinical and molecular findings in order to achieve the best accuracy in diagnosing PJI. This review aims to survey the current state of the techniques and technologies used for the diagnosis of PJI, investigating the accuracies of serum biomarkers (e.g., C-reactive protein, Interleukin-6, procalcitonin, D-dimers, Serum Intercellular Adhesion Molecule-1), synovial biomarkers (e.g., Antimicrobial peptides, lipocalin-2, leukocyte esterase, calprotectin), tissue biomarkers (e.g., Toll-like receptors, CD15) and advanced molecular techniques (e.g., Polymerase chain reaction, Metagenomic next-generation sequencing), as well as describing their ongoing limitations. In the search for an accurate, inexpensive and fast diagnostic test for PJI, we conclude that the accuracies of the currently studied biomarkers could be further enhanced through the development of novel detection technologies.

Knee osteoarthritis (KOA) is one of the most prevalent chronic joint disorders, with its incidence rising over the past decade due to an increase in risk factors, including age, obesity, metabolic conditions, sedentary behavior, and mechanical stress on the knee joints. We conducted a cross-sectional, two-group comparison including 70 knee-pain patients aged ≥ 44 years: 50 patients meeting clinical and radiological criteria for TKA and 20 patients undergoing knee arthroscopy as controls. All patients underwent clinical assessments, WOMAC scoring, radiography, and 3T knee MRI. Serum interleukin-6 (IL-6), cartilage oligomeric matrix protein (COMP), vitamin D3, calcium, and phosphorus were measured at admission. TKA patients were older and had higher WOMAC scores. WOMAC discriminated groups perfectly (AUC = 1.000), but age discriminated well (AUC = 0.911). IL-6 (AUC = 0.819) and COMP (AUC = 0.838) were significant discriminators, with IL-6 threshold ≥ 4.585 pg/mL achieving 66% sensitivity and 85% specificity and COMP cutoff ≥ 11.52 ng/mL achieving 84% sensitivity and 75% specificity. TKA group vitamin D3 levels were considerably lower but had limited discriminatory performance (AUC = 0.683). Although all patients had adequate mineral metabolism, TKA patients had lower serum calcium and higher serum phosphorus levels than controls.