Effect of intracorporeal-extracorporeal instrument length ratio on endoscopic task performance and surgeon movements.

HYPOTHESIS Better endoscopic task performance and more ergonomic movements of a surgeon's dominant upper limb can be achieved within a certain range of intracorporeal-extracorporeal instrument length ratio. DESIGN Investigating the effect of 3 intracorporeal-extracorporeal instrument length ratios (240:120 mm, level 1; 180:180 mm, level 2; and 120:240 mm, level 3) on efficiency and quality of a standardized endoscopic task (intracorporeal surgeon's knot). Ten surgeons tied 360 knots inside a trainer in a random sequence. Task efficiency was measured by the execution time, which was recorded for each knot. Task quality was measured by the knot quality score, derived from the force-extension curves obtained by distraction of each knot in a tensiometer. Motion analysis parameters were obtained at the elbow and shoulder joints using a 3-dimensional motion analysis system (Kinemetrix Model 5.0-3D/3MBM; Medical Research Ltd, Leeds, England). The Kruskal-Wallis and Mann-Whitney tests were used for analysis. RESULTS The level 3 ratio had the lowest knot quality score (P = .07) and longest execution time (P<.05). The range of movement at the elbow was significantly greater with the level 3 ratio than with the level 1 ratio (P<.05). The level 3 ratio also resulted in the widest range of movement at the shoulder (P<.05 for level 2 vs 3; P = .06 for level 1 vs 3). The median angular velocity was 329.5 degrees/s, 360 degrees/s, and 530 degrees/s for levels 1, 2, and 3, respectively (P = .10). CONCLUSIONS Intracorporeal-extracorporeal instrument length ratio below 1.0 degrades task performance and is associated with a wider range of movement at the elbow and shoulder and a higher angular velocity at the shoulder.