Mathematical evaluation of jumping distance in total hip arthroplasty

Abstract

Background and purpose The jumping distance (JD) is the degree of lateral translation of the femoral head center required before dislocation occurs. The smaller the distance, the higher the theoretical risk of dislocation. The aim of our study was to evaluate this jumping distance and its variation according to the characteristics of the implant, and also the theoretical gain in using large head diameters of above 38 mm. Methods The JD was calculated as a function of the cup ante-version and abduction angles, the head diameter, and the head offset (defined as the distance between the center of the femoral head and the cup opening plane). Head diameters of 28, 32, 36, 40, 44 and 48 mm were analyzed. The abduction angle was increased from 0° to 80° with a 10° increment. The anteversion angle was increased from 0° to 40° with a 5° increment. Results The jumping distance was found to decrease as the cup abduction angle increased (0.25 mm each 1° for 32-mm head diameter). It increased by 0.05 mm for a 1° incre...