# Acute Calcium Pyrophosphate Crystal Arthritis Occurring Many Years After Total Knee Arthroplasty: A Case Report

## TL;DR

A 94-year-old woman developed knee pain years after a knee replacement, diagnosed with a rare form of arthritis caused by calcium crystals, not infection.

## Contribution

Reports a rare case of acute CPP crystal arthritis occurring many years after total knee arthroplasty.

## Key findings

- CPP dihydrate crystals were identified in synovial fluid, confirming acute CPP crystal arthritis.
- Clinical improvement was observed with celecoxib treatment.
- Residual synovial tissue post-TKA may produce CPPD crystals, leading to arthritis.

## Abstract

Acute calcium pyrophosphate (CPP) crystal arthritis, also known as pseudogout, is a form of crystal-induced arthritis. It is caused by acute inflammation triggered by CPP crystals deposited in articular cartilage and surrounding intra-articular tissues. A 94-year-old Japanese woman presented with left knee pain. She had undergone bilateral total knee arthroplasty (TKA) at 80 years of age. Septic arthritis of the prosthetic joint was initially suspected. Synovial fluid analysis showed negative Gram staining and no bacterial growth on culture. However, microscopic examination of the synovial fluid revealed CPP dihydrate (CPPD) crystals, leading to a diagnosis of acute CPP crystal arthritis. Celecoxib (200 mg/day) was initiated after admission, resulting in rapid clinical improvement. It has been suggested that residual synovial tissue after TKA may undergo chondrogenic differentiation and produce CPPD crystals, thereby inducing arthritis. Herein, we report a rare case of acute CPP crystal arthritis occurring many years after TKA. Prompt joint aspiration and synovial fluid evaluation are essential to differentiate this condition from septic arthritis of the prosthetic knee.