 Hip replacement implants are a ball in cup design, and consist of two articulating components: a femoral head replacement which can consist of a ball attached to a stem that is inserted into the proximal femur, and an acetabular component, which can be made of different materials that are inserted into a liner of metal that is inserted into the pelvis. These components can be attached to the patients bone using either polymethylmethacrylate - a polymer more commonly referred to as bone cement - or by roughening the surface of the implant to allow bone ingrowth. Hip replacements can therefore be broadly classified by the fixation technique used: cemented, uncemented, or hybrid, consisting of a cemented femoral component and an uncemented acetabular component. The uncemented design is very commonly used in younger patients because the quality of bone is better in the patient, the implants have demonstrated long term survival, and the cementing step is no longer necessary for achieving long term fixation. 