to provide enhanced component accuracy. Several commercial CAS and robotic systems are available for use worldwide. Improved patient outcomes and reduced complications have not been demonstrated when these systems are used when compared to standard techniques. Implants The prosthetic implant used in hip replacement consists of three parts: the acetabular cup, the femoral component, and the articular interface. Options exist for different people and indications. The evidence for a number of newer devices is not very good, including: ceramic-on-ceramic bearings, modular femoral necks, and uncemented monoblock cups. Correct selection of the prosthesis is important. Acetabular cup The acetabular cup is the component which is placed into the acetabulum (hip socket). Cartilage and bone are removed from the acetabulum and the acetabular cup is attached using friction or cement. Some acetabular cups are one piece, while others are modular. One-piece (monobloc) shells are either ultra-high-molecular-weight polyethylene (UHMWPE) or metal, they have their articular surface machined on the inside surface of the cup and do not rely on a locking mechanism to hold a liner in place. A monobloc polyethylene cup is cemented in place while a metal cup is held in place by a metal coating on the outside of the cup. Modular cups consist of two pieces, a shell and liner. The shell is made of metal; the outside has a porous coating while the inside contains a locking mechanism designed to accept a liner. Two types of porous coating used to form a friction fit are sintered beads and a foam metal design to mimic the trabeculae of cancellous bone and initial stability is influenced by under-reaming and insertion force. Permanent fixation is achieved as bone grows onto or into the porous coating. Screws can be used to lag the shell to the bone providing even more fixation. Polyethylene liners are placed into the shell and connected by a rim locking mechanism; ceramic and metal liners are attached with a Morse taper. Femoral component The femoral component is the component that fits in the femur (thigh bone). Bone is removed and the femur is shaped to accept the femoral stem with attached prosthetic femoral head (ball). There are two types of fixation: cemented and uncemented. Cemented stems use acrylic bone cement to form a mantle between the stem and to the bone. Uncemented stems use friction, shape and surface coatings to stimulate bone to remodel and bond to the