Background The exclusion of infection at the site of a painful or failed prosthetic joint replacement is important for pre-operative planning and counselling. A variety of investigations can be used to assist in the diagnosis or exclusion of infection.

An ESR and CRP are widely used as the initial screening investigation to differentiate between aseptic and septic loosening of prosthetic joint replacements¹. Propionobacteria are organisms of low virulence, although they do cause deep peri-prosthetic infections². We believe that Propionobacteria do not always cause a significant rise in ESR and CRP.

Methods Between May 2001 and May 2004, we identified 78 patients with prosthetic joint replacements colonised with Propionobacteria. There were 48 hip joint replacements, 27 knee joint replacements, 2 endoprosthetic replacements of the femur and 1 shoulder joint replacement. There were 48 males and 30 females. The preoperative values of ESR and CRP were recorded. For the purposes of this study, an ESR rate of 30mm/hr or higher and a CRP level of 10mg/lt or higher were considered to be suggestive of infection and were deemed a positive result.

Results All of the 78 patients had both ESR and CRP measured preoperatively. In only 17 patients (22%) both ESR and CRP were higher than 30mm/hr and 10mg/l respectively. In 33 patients (42%) with prosthetic joint replacements colonised with Propionobacteria, the preoperative values of both ESR and CRP were normal.

Conclusion In our study we have shown that 33 out of 78 patients (42%) with prosthetic joint replacements colonised with Propionobacteria had normal preoperative of both ESR and CRP values. This is to suggest that normal preoperative values of ESR and CRP in suspected failed prosthetic joint replacements might not exclude infection, if the causative organism is of low virulence such as Propionobacteria.