Long-term results of a soft interface- (Proplast-) coated femoral stem (original) (raw)

the polyethylene used in acetabular components are known to affect the rate of wear 11. Since air sterilisation of Ultra High Molecular Weight Polyethylene acetabular liners is associated with substantial oxidation and radical formation causing early degradation of the material, sterilisation in a low oxygen environment (inert gas) became the method of choice in the late 1990s 12,13. 2. Stress shielding Another problem in uncemented total hip arthroplasty is stress shielding, which is the term used for diffuse loss of bone mass of the periprosthetic bone. This is caused by the fact that the mechanical load is partly taken over by the implant 14. Stress shielding is a predominant cause of bone loss in patient treated with stiff (high modulus), press-fit acetabular and femoral components 15,16. In contrast, cemented components show a significantly lower bone mineral density loss than uncemented components, due to the fundamental difference in load transfer 17. Retrieval and animal studies have indicated that bone remodeling is related to the ratio of the stem stiffness to femoral stiffnes: The stiffer the stem in relation to the femur is, the less stress is carried by the femur, and the greater the subsequent bone loss 18. In the early 1970s, a soft-interface coating of a composite of polytetrafluoroethylene (PTFE) reinforced with carbon fibre or aluminium oxide was introduced as Proplast. Proplast was considered to exhibit extraordinary chemical and thermal resistance, permitting fusion to metallic implants 19. As the elasticity of Proplast matches that of the surrounding cancellous bone, it was expected to have the advantage of a more natural tranfer of stress, causing less stress shielding and aseptic loosening 20. Despite the possible theoretical benefits, mid-term clinical results on uncemented femoral components with a Proplast coating were not favorable 20-23. Because of these reports, the low modulus system was considered to be a failure and was abandoned in the mid-1990s. 3. Early Component Fixation Inferior primary fixation of the components in total hip arthroplasty can lead to a higher probability of aseptic loosening on the long term 24. As the interface between the component and the surrounding bone becomes a continuous compartment filled with synovial fluid (the "virtual joint space"), micromotion of the component can result in high fluid pressures and the distal migration of wear particles 25. In the late 1980s, hydroxyapatite was applied on the implant surface in uncemented total hip arthroplasty in an effort to enhance prosthesis to bone fixation, and thus seal this virtual joint space. Hydroxyapatite is highly biocompatible and has an osteoconductive potential enhancing early fixation and stability 26. Hydroxyapatite is the 14 Questions addressed in this thesis are: 1. What is the clinical and radiological outcome of proximally hydroxyapatite coated uncemented femoral stems after a short to mid-term follow-up? 2. Is there a clinical and radiological benefit of hydroxyapatite coating on porous coated stems in uncemented primary total hip arthroplasty? 3. What is the long-term clinical and radiological outcome of low modulus Proplast coated uncemented femoral stems and when is revision indicated? 4. What is the clinical and radiological outcome of porous coated cobalt chrome high modulus femoral stems, used both as an uncemented and a cemented stem in hemiarthroplasty after a short follow-up? 5. What is the way to diagnose and, if observed, how to treat and monitor silent osteolysis associated with an uncemented acetabular component? 6. Is there an association with implantation time and position of the component and the rate of wear in metal backed uncemented acetabular components? 7. Are argon-sterilised polyethylene liners less susceptible to wear than air-sterilised liners in vivo during a mid-term follow-up? 8. Do patients have an improved clinical outcome, when treated with a posterolateral or anterolateral mini incision, compared with both the classical incisions during a short-term follow-up?