Background. Sterile Surgical Helmet System (SSHS) are used routinely in hip and knee arthroplasty in order to decrease the risk of infection. It protects surgeon from splash and also prevents contamination of surgical field from reverse splash by virtue of its perceived sterility. A prospective study was conducted to confirm if SSHS remain sterile throughout the procedure in Hip (THA) and Knee (TKA) Arthroplasty. We also evaluated if type of theatre had any effect on degree of contamination. Material and Methods. Visor area of 40 SSHS was swabbed at half hourly interval until the end of the procedure. Two groups of 20 each were made on the basis of theatre used for performing surgery. Group 1 (Gp1) had surgery performed in laminar flow and Group 2 (Gp2) in non-laminar flow theatre. Swabs collected were processed to compare the time dependent contamination of the SSHS and identify the organisms responsible for contamination. Results. Overall 80% (70% laminar, 90% non-laminar) of masks were contaminated by end of the procedure. There was a statistically significant difference in degree of contamination after direct inoculation while there was no statistical difference after 24 hrs of incubation. Coagulase negative Staphylococcus was the most common bacteria grown in both the groups. Conclusion. SSHS lose their sterility peroperatively due to
