# Sterile Inflammatory Synovitis as a Mimic for Prosthetic Joint Infection in Patients With Rheumatoid Arthritis Following Total Knee Arthroplasty: A Report of Two Cases

## TL;DR

This paper reports two cases where rheumatoid arthritis patients developed sterile synovitis after knee surgery, mimicking joint infection.

## Contribution

It highlights sterile inflammatory synovitis as a rare but important differential diagnosis in rheumatoid arthritis patients post-TKA.

## Key findings

- Two RA patients presented with symptoms resembling prosthetic joint infection after TKA but had sterile synovitis.
- Non-operative treatment resolved symptoms without antibiotics in both cases.
- Diagnostic tools like Synovasure and DNA sequencing can help distinguish sterile synovitis from infection.

## Abstract

Patients with rheumatoid arthritis (RA) present with unique challenges following total knee arthroplasty (TKA). Rarely, these patients may present with sterile inflammatory synovitis with a clinical picture that can mimic prosthetic joint infection (PJI).

We report on two patients with RA who underwent primary TKA performed by the senior author who presented with sterile inflammatory synovitis following TKA. Both patients presented several years after their index procedure with knee pain and effusion, concerning for PJI. Both patients underwent extensive evaluations for infection. Initial aspirations showed a synovial fluid white blood cell count of more than 3,000 WBC/uL but a differential of less than 80% and no growth on the final culture. Both patients were treated non-operatively without antibiotics with the resolution of their symptoms.

Sterile inflammatory synovitis is a rare post-operative complication that can present among patients with RA following TKA. While the initial presentation and evaluation may be concerning for PJI, a thorough laboratory evaluation must be performed to accurately diagnose these patients. The use of next-generation DNA sequencing, Synovasure alpha-defensin, and Synovasure microbial ID panel can aid in diagnoses. These patients may be treated without antibiotics or operative intervention. A thorough evaluation for PJI should be performed to ensure the correct diagnosis and appropriate management.