As clinical and radiographic performance of an ultra-short anatomic cementless stem have been investigated only two randomized controlled studies, well-designed trials should aim for a thorough comparison of the outcomes of ultra-short and conventional cementless stems. The purpose of this study was to compare the outcomes of ultra-short and conventional stems in the same young patients who underwent simultaneous bilateral sequential total hip arthroplasties.

Conventional cementless femoral stems are known to provide a high rate of satisfactory clinical outcomes at long-term follow-ups. However, they may have potential clinical consequences related to stress shielding, thigh pain, periprosthetic fractures, proximal/distal dimensional mismatch, an easier access pathway for wear debries and removal during revision. In an effort to reduce the risk of stress shielding, thigh pain, periprosthetic fracture, proximal/distal stem mismatch, and to facilitate removal of well fixed stem, a new ultra-short anatomic metaphyseal-fitting cementless femoral stem was developed. It was designed to provide closely mimicking the original functioning hip. The absence of the diaphyseal anchorage attempt proximal load transfer to reduce stress shielding, thigh pain and proximal distal/mismatch. Furthermore, it attempts to preservation of the femoral canal and femoral elasticity and ease of revision. The question thus arises whether it is possible to obtain strong and long-lasting fixation of the femoral component without diaphyseal anchoring.

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.

Inclusion Criteria:

• End stage hip arthritis

Exclusion Criteria:

• Age above 50 years old
• Inflammatory arthritis
• Coexisting foot or ankle disorder limiting walking