Fixation of the cemented acetabular component in hip arthroplasty

Abstract: In total hip arthroplasty cemented fixation of the acetabular component is a generally successful concept, but the rate of aseptic loosening and consequent revision surgery is still too high. One of the crucial factors for longterm implant survival is the initial fixation and stability. This thesis comprises experimental and clinical studies, including radiostereometry (RSA) with up to 5 years follow-up, all investigating the requirements for improved cement fixation of the acetabular component. The results and conclusions of the studies are: Higher cementation pressure than normally can be achieved is needed for desirable cement penetration, especially as there is obstructing blood circulation in the recipient bone bed. There is no difference between cancellous bone from the acetabulum and from load-bearing areas of the femoral head regarding permeability and structural parameters. Results from studies made on bone from the more obtainable femoral heads can thus be extrapolated to the acetabulum. Sequential pressurization of individual anchorage holes before filling the rest of acetabulum with cement is one method of reaching higher pressure and better cement penetration than is achievable with fingerpacking or conventional pressurization. This technique does not impair the cement strength, provided it is performed within 4 minutes of cement mixing and the cement area is kept free from blood or washed with saline. Pressure applied during the early phase of cementation has the greatest effect on cement penetration. However, the highest pressure is attained later during cup insertion, but does not further increase the penetration. Improved cement penetration in the anchorage holes has a stabilizing effect on cup inclination over time. Early radiolucency, even as a thin demarcation line, is a strong predictor of later cup migration as measured by RSA. Preparation of the acetabular bone bed is an important factor for cup fixation. Contrary to earlier theories, removal of the subchondral bone plate, where possible, appears advantageous. It results in a radiographically superior cement-bone interface, and RSA indicates similar or even better cup stability as compared to retention of the subchondral bone plate. Correct preparation of the bone bed in combination with adequate cement pressurization and cup insertion according to the principles delineated in this thesis should result in better long-term survival in hip arthroplasty.