Peri-prosthetic infection remains a leading cause of revision surgery. Recent publications from the American Musculoskeletal Infection Society have sought to establish a definition of peri-prosthetic infection based on clinical findings and laboratory investigations. The limitations of their approach are discussed and an alternative definition is proposed, which it is felt may better reflect the uncertainties encountered in clinical practice.

Introduction Infection is a disastrous complication of arthroplasty surgery, requiring multidisciplinary treatment and debilitating revision surgery. As between 80–90% of bacterial wound contaminants originate from colony forming units (CFU’s) present in operating room air tending to originate from bacteria shed by personnel present within the operating environment, any steps that can reduce this bacterial shedding should reduce the chances of wound contamination. These steps have included the use of unidirectional downward laminar airflow theatre systems, and the introduction of theatre attire modelled on this principle (e.g. total body exhaust suits). Our unit has introduced the use of the Stryker T4 Personal Protection System helmet in conjunction with laminar flow theatre systems. This study compares an enclosed helmet system used with standard gowns, with standard hood & mask attire.

Method 12 simulated hip arthroplasty operations were performed, six using disposable sterile impermeable gown, hood and mask, with a further 6 using the T4 helmet & hood. Each 20 minute operation consisted of a series of arm and head movements simulating movements performed during surgery. Air was sampled at wound level on a sterile draped operating table using a Casella slit sampler, sampling at 700l/minute. Samples were incubated on Blood agar for 48 hours at 37oc & the CFU’s grown were counted.

Results The mean number of CFU’s for the helmet was 9.33 with hood and mask attire yielding 49.16 CFU’s (S.Ds 6.34 & 26.17; p value 0.0126). In all cases, the organism isolated was a coagulase negative staphylococcus

Conclusion Although the sample size was small, we demonstrated a fivefold increase in the number of CFU’s shed when using hood and mask attire compared to personal helmet and sterile hood. We conclude that the helmet system is superior to non-sterile hood & mask at reducing bacterial shedding by theatre personnel.