SRS119 - The impact of knee position on surgical skin preparation: a comparative study of flexion <i>versus</i> extension

Abstract Periprosthetic joint infection (PJI) is a serious complication after total knee arthroplasty (TKA). Effective preoperative skin antisepsis is essential for prevention, yet the influence of knee positioning during preparation remains poorly studied. This prospective, single-centre study evaluated whether maximal knee flexion improves antiseptic coverage and thoroughness compared with full extension. Ten healthy adult volunteers underwent standardised anterior knee preparation in both positions. Fluorescent dye (UV Germ lotion) was applied and removed using an alcohol-based chlorhexidine solution. Ultraviolet photography and ImageJ software quantified residual dye as a surrogate for antiseptic coverage. Two independent investigators performed all preparations, each repeating their image analyses to allow intra-observer reliability assessment. The primary outcome was percentage residual dye; intra- and inter-observer agreement were measured using intraclass correlation coefficients (ICC). Eighty preparations (40 flexion, 40 extension) were analysed. Pooled median residual dye was significantly lower in flexion (1.7%, interquartile range [IQR] 0.1–7.2%) than in extension (9.8%, IQR 2.6–19.0%; P &amp;lt; 0.0001). Investigator-specific medians showed the same pattern. Intrarater reliability was moderate to excellent (ICC 0.67–0.89), whereas interrater reliability was poor (ICC 0.07–0.35). No adverse events occurred. Maximal knee flexion during preparation significantly improves anterior surface antiseptic coverage compared with full extension, likely by exposing skin folds concealed in extension. As a simple, cost-neutral modification, flexion-based preparation has been adopted in our institution. Further studies should assess its impact on bacterial load and clinical infection rates in diverse TKA populations. Keywords: Total knee arthroplasty, periprosthetic joint infection, skin antisepsis, knee positioning, ultraviolet imaging