 As clinical and radiographic performances of this ultra-short stem have been investigated only in a few studies and at short-term follow-ups, it remains to be elucidated whether an ultra-short stem shows a low incidence of implant loosening, stem misalignment, intraoperative fractures and revision rate. The purpose of this randomized controlled study to compare: 1 the clinical results, including Harris hip score, thigh pain, Western Ontario and McMaster Universities Osteoarthritis WOMAC Index score, and patients satisfaction; 2 radiographic results, including stress shielding, implant loosening, stem misalignment; and 3 intraoperative fractures and revision rates of cementless total hip arthroplasty using an ultra-short anatomic metaphyseal-fitting cementless femoral stem versus a conventional metaphyseal and diaphyseal fitting anatomi proximal porous-coated cementless stem in the same patients who underwent bilateral simultaneous sequential total hip arthroplasty under one anesthetic. 