Pain and reduced function are the most common symptoms of coxarthritis. Pain relief and normal range of motion (ROM) restoration are the objectives of a Total Hip Arthroplasty (THA) procedure. It is recognized that increased head-neck ratio results in increased ROM due to the fact that prosthetic impingement between neck and acetabular liner occurs with wider arcs of motion. This head-neck ratio has been investigated extensively only in vitro (on cadavers or sawbones) or using mathematical modeling in computer simulations. These studies are limited by the lack of soft tissues and muscle activations in the models. This study will clinically assess the effect of prosthetic head diameter on patient capability of performing movements which require extreme arcs of motion of the hip joint. Therefore, the research questions are: