MATERIALS AND METHODS

A prospective, randomized, blind study was conducted on 60 patients operated by THA at our Institution. Inclusion criteria were: primary hip arthritis, women, age between 55 and 70 years. Exclusion criteria were: other problems influencing walking ability (previous operations of the lower limbs, spine disorders, knee or controlateral hip arthritis). The same uncemented stem, same uncemented press-fit cup, same surgical technique and approach (posterolateral), same surgeons, same postoperative protocol and rehabilitation were employed. The only difference was the head diameter. The patients were randomized into three groups, of twenty patients each one (28mm Cer-on-XPE, 36mm Cer-on-XPE, >42mm Met-on-Met). The gait evaluation have been performed at three temporal steps: preoperatively, two months postoperatively and four months postoperatively. Kinematic parameters were acquired with Elite opto-electronic system (BTS, Milan, Italy) equipped with 6 cameras at 100 Hz frame rate. The system is integrated with a force platform (Kistler, CH) and a synchronic video system using two cameras (BTS, Milan, Italy). Data acquisition and processing were carried out using passive markers positioned according to Davis protocol. At least ten trials for each session were collected in order to assess the repeatability of the results. Gait analysis included kinematic parameters (temporal-spatial parameters and joint angular values) and kinetic parameters (ground interaction forces during walking). Articular moments and powers were computed on the basis of data obtained from dynamometric platform along with those given by kinematic analysis. All patients were compared to a control group. Wilcoxon signed rank test was employed for statistical evaluation.