This will be a prospective comparative randomized double-blind Study (both patient and the clinical engineer performing the gait analysis will be blind with respect to the prosthetic head diameter implanted). Patient recruitment will last 12 months and the Study will have a follow-up period of 12 months. A total number of 45 patients will be recruited. Patients will be randomly allocated into three groups: the first group will undergo THA with a 28mm diameter head (Pinnacle Acetabular System, with a ceramic on ceramic - CoC - bearing), in the second group THA will be performed using a 36 mm diameter head (DeltaMotion), finally patients in the third group will undergo THA with a 40 mm diameter head (DeltaMotion). Patients will be operated by three surgeons of the same hospital according to the same surgical procedure and using the same direct lateral approach. All patients will receive a Corail stem and will follow the same rehabilitation program.