Localized corticosteroid injection is used to treat a number of musculoskeletal disorders of the knee and shoulder. Some have estimated the risk of post-injection infection to be 4.6 per 100, 000 injections. As ultrasound (US) is commonly used to assist with these injections, this study was designed to determine whether the use of nonsterile gel increases the risk of contamination.

Subjects were 26, healthy volunteers whose skin was prepared in a manner simulating therapeutic intra-articular shoulder injections under US guidance. Skin swabs were taken at the injection site before skin preparation, after skin preparation, after sterile gel application, and after nonsterile gel application. In addition, swabs were taken of the US transducer, and 10 sample swabs of nonsterile US transmission gel for determination of bacterial contamination.

Increased skin contamination was found with sterile US gel use, but not with nonsterile gel use. Of those with positive cultures after the first swab, no contamination was noted after alcohol preparation. Of the cultures from the nonsterile gel, none were positive. None of the cultures from the US probe were positive for bacteria.

This study found that the use of US probes and transmission gel may result in greater contamination of the site. The authors suggest sterile preparation of the entire field, including the area of US use.