الفهرس 
Introduction and aim of workOnly 14 pages are availabe for public view
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Abstract
function led to its use in younger and more active patients. The bearing surface is a key factor of performance of replaced joints. Over the last two decades, it has been clear that the major stumbling block to prolonged survival of the hip arthroplasty is the wear of the bearing surfaces. As a result, there is on going requirement for bearing surfaces with minimal friction and debris generation to improve survivorship of the total hip arthroplasty especially in younger and high demands patients. The commonly used bearing surface in total hip arthroplasty is a metallic femoral head against high molecular weight polyethylene acetabular component. Sir John Charnley had introduced this articulating combination in 1963 with good to excellent results and this was considered the standard against which all alternative bearings should be compared.(4) Unfortunately, traditional polyethylene cup liner used with metallic femoral head tends to wear out quickly leading to decrease the durability of the prosthesis especially with young and high active patients. As a result, there has been an interest in developing polyethylene with improved wear characteristic as well as a renewed interest in alternative bearing surfaces with less friction and wear rates. Alternative to metal on polyethylene, the following bearings are available: 1. Metal or ceramic on highly cross-linked polyethylene. 2. Ceramic on ceramic. 3. Metal on metal. Polyethylene durability has been improved through cross-linking, a process by which polyethylene molecules are bonded together to result in a stronger material with substantially improved wear resistance. Ceramic on ceramic bearing surfaces have been introduced since 1970 and show the lowest wear rates. The possibility of brittle fracture and the high cost of the ceramic components are factors that should be considered before their wide spread use. Modern ceramic on ceramic bearings with reduced risk of fracture are promising as the implant of choice in the near future for younger and active patients. The concept of metal on metal total hip replacements is not new and was first introduced in 1960 with designs such as McKee-Farrar, Ring, and Muller prostheses. Metal on metal bearings were reintroduced with improved alloys, design and manufacturing. This offers benefit of excellent wear and allow for large-sized head which gives better range of motion and a lower dislocation rate. The potential drawback of metal on metal articulation is the risk of elevated metal ions levels in the blood and other body tissues. This may develop kidney problems; can potentially cause cancers and allergic reaction to metal particles that may cause pain and osteolysis. Recently, metallic alloy with ceramic surface (Oxinium) has been introduced and provides wear resistance without brittleness. Oxinium material combines the best of both metals and ceramics.