A novel device to measure acetabular inclination with patients in lateral decubitus

The ability to measure acetabular cup orientation accurately during total hip arthroplasty represents a significant challenge. The aim of this research was to develop and evaluate a novel low cost mechanical device for measuring operative acetabular inclination. Cup implantation was simulated in two trials using the novel device: firstly involving surgeons and engineers orientating acetabular cups with sawbone pelves at a range of inclination angles (20°-55° in 5° increments); secondly in a simulated intra-operative scenario with surgeons. Target angles were compared with achieved angles and deviations from desired angles were recorded. In addition, all participants orientated cups under the same conditions using two other techniques: freehand and with a propriatory Mechanical Alignment Guide. In the first trial, the mean errors (deviations) using freehand technique, the mechanical alignment guide and the new device were 5.2° +/- 4.3° (range 0.1-22.0), 3.6° +/- 3.9° (range 0.1°-33.6°) and 0.5° +/- 0.4° (range 0.0-1.9) respectively. In the second trial, the mean error for freehand technique, mechanical alignment guide and the new device were 6.2° +/- 4.2° (range 0.2-18.2), 3.8° +/- 3.3° (range 0.0-19.1) and 0.6° +/- 0.5° (range 0.0-1.8) respectively. The new device has the potential to allow the surgeon to choose and record operative inclination accurately during total hip arthroplasty in the lateral decubitus position.