Introduction

Long-term cup fixation and stability in total hip arthroplasty (THA) is directly related to the bone ingrowths between the porous cup and the acetabulum. To achieve the initial cup setting, 1 mm of under reaming is becoming the gold standard for cementless cup and what is at stake is usually the actual contact between cup and acetabulum wall. During impact and cup placement, friction forces are generated from the “not permanent” deformations of the acetabular wall that are translated into a gap between the reamed bone and the cup. Clinically the surgeon objective is to have the gap extended to a limited portion of the cup in order to improve bone ingrowth. Hence, the need arises from examining this cup bone stability interface by examining the selected “under reaming” conditions, the surface of contact between the acetabular cup and the bone and its relation to the impact force resulting from the hammering of the cup.