105 patients undergoing instrumented spinal surgery were randomized to have implants covered by sterile surgical towels following the opening of the surgical implant tray or not. The purpose was to determine if coverage of instruments would lower the risk of implant contamination. Microbiologic assessment of sterile swabs obtained from implants indicated a significantly lower rate of contamination in those that were covered compared to those that were not. The duration the surgical tray was opened, the type of implant, the number of implants, and number of scrubbed personnel were not found to influence contamination rate.