Antiphospholipid Syndrome-Associated Livedoid Vasculopathy Mimicking Recurrent Periprosthetic Joint Infection after Total Knee Arthroplasty: A Case Report.

INTRODUCTION

Periprosthetic joint infection (PJI) after total knee arthroplasty (TKA) is a serious complication whose diagnosis relies on a combination of serum and synovial biomarkers. Inflammatory non-infectious conditions can fulfill these same diagnostic criteria, creating a diagnostic and therapeutic challenge. We report the first case, to our knowledge, of antiphospholipid syndrome (APS)-associated Livedoid vasculopathy (LV) mimicking recurrent PJI.

CASE REPORT: A 74-year-old White male with a remote history of uncomplicated right TKA presented with two discrete episodes of presumed PJI (November 2025 and January 2026), each coinciding with a new right ankle lesion. Synovial fluid analysis on both occasions demonstrated markedly elevated white blood cell counts (WBC) (20,688 and 28,900 cells/µL; >93% neutrophils) and a positive synovasure α-defensin, yielding a 2018 International Consensus Meeting score of 10 on each presentation. Cultures and next-generation sequencing (NGS) were uniformly negative. The ankle lesions were ultimately biopsied and confirmed histologically as LV. Serology subsequently established a double-positive APS profile (positive lupus anticoagulant and anti-β2-glycoprotein I antibodies). All antimicrobials were discontinued; the patient declined two-stage revision arthroplasty. Repeat aspiration 3 weeks later showed completely normal synovial fluid (WBC 28 cells/µL, synovial C-reactive protein 0.01 mg/L). At 12 weeks off all therapy, the patient remains asymptomatic.

CONCLUSION

APS-associated LV can produce a thrombo-inflammatory sterile synovitis that satisfies established PJI diagnostic criteria, including a positive α-defensin. This case underscores the importance of evaluating concomitant dermatologic lesions, pursuing advanced microbiologic testing (NGS) before committing to surgical intervention, and considering hypercoagulable states in PJI workups with persistently negative cultures.