Ergonomic Risk in Total Hip Arthroplasty: Approach-Specific Postural Loads and Position-Swap Effects During Cup Preparation

Musculoskeletal disorders (MSDs) among orthopaedic surgeons are associated with sustained, constrained postures during demanding intraoperative tasks. Total hip arthroplasty (THA) comprises sequential steps that may impose different postural loads on both the surgeon and assistant, yet team-level ergonomic design interventions remain underexplored. This study compared ergonomic risk during primary THA performed through the direct lateral (modified Hardinge) and posterolateral (Moore) approaches and assessed a simple workflow redesign: swapping surgeon and assistant positions during acetabular cup preparation (bottom reaming, perimeter reaming, and cup impaction). In a controlled Sawbones-based simulation using standard THA instruments, eight standardised surgical steps were recorded with 360° photographs. Forty-two postural instances (22 for the surgeon, 20 for the assistant) were analysed. Joint angles were measured with Kinovea and converted to Rapid Entire Body Assessment (REBA) scores; intra- and inter-rater reliability (ICC) and minimum detectable change (MDC95) were calculated. Surgeon REBA scores were in the medium-risk range and slightly lower with the posterolateral approach (mean 5.5) than with the direct lateral approach (mean 5.88), whereas assistant scores were in the low-risk range (means 3.43 and 3.29, respectively). The position-swap intervention successfully lowered the surgeon’s REBA action level, most notably during cup impaction, where ergonomic risk dropped from 10 (high risk) to 4 (medium risk) in the posterolateral approach, and from 7 (medium risk) to 3 (low risk) in the direct lateral approach, without increasing assistant risk. These findings provide controlled simulation-based evidence that this simple, zero-cost positional change can reduce the surgeon’s ergonomic action level during THA, although confirmation under real operative conditions is needed before broad generalization.