Incidence of Secondary Osteoarthritis after Primary Shoulder and Knee Empyema and Its Risk Factors.

Empyema of the joint is an orthopedic emergency that is associated with a prolonged healing process despite adequate surgical and medical therapy. The risk of developing postinfectious osteoarthritis (OA) after successfully treated joint empyema is unknown. Both incidence and risk factors are important for prognostication and would therefore be clinically relevant for the selection of an adequate infectious therapy as well as for the individual follow-up of patients. The aim of this retrospective clinical study was to describe the risk of secondary OA after empyema based on knee and shoulder joint infections after successful primary infection treatment and its risk factors. Thirty-two patients were examined clinically and radiographically after completion of treatment for primary empyema of the knee or shoulder joint. Patients with previous surgery or injections in the affected joint were excluded from the study. The cumulative incidence of new-onset radiographic OA was 28.6%, representing a 5.5-fold increased risk of developing OA compared to the normal population. A figure of 25% of patients underwent total knee arthroplasty after knee empyema. Identified risk factors for primary empyema were obesity, hyperuricemia, and rheumatoid arthritis. Only about 60% of the patients tested positive for bacteria. Staphylococcus aureus, the most common pathogen causing joint empyema, was present in approximately 40% of cases. Secondary osteoarthritis, as a possible secondary disease after joint empyema, could be demonstrated and several risk factors for the primary empyema were identified.