Batta, Vineet; (2019) The Use of Hydroxyapatite-coated Collars Enhances Osteointegrated Extra-cortical Bone Formation and Improves Long Term Survival of Distal Femoral Endoprostheses. Doctoral thesis (M.D(Res)), UCL (University College London).

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Abstract

The fixation of massive segmental prostheses is more problematic than standard joint replacements. The aims of this study are: 1) To evaluate the long-term survival of cemented and uncemented distal femoral bone tumour endoprostheses in adults and skeletally immature patients. 2) To investigate the relationship between the degree of osteointegration onto the hydroxyapatite (HA) coated collar located at the boneimplant junction and relate this to aseptic loosening (ASL) of these endoprostheses. The hypothesis is that a hydroxyapatite collar at the shoulder of bone and implant junction enhances osteointegration and extra-cortical bone formation, reducing aseptic loosening of the endoprostheses. Three separate studies to evaluate the long-term survival of distal femoral endoprosthetic replacements (DFR) implanted at our institute since 1992 were carried out. The first included 61 adult patients with cemented DFR, the second study involved 69 uncemented DFR in adults and the third comprised 24 cemented, non-invasive and expandable DFR in skeletally immature patients. For the first time, the degree of osteointegration at the bone-implant junction was evaluated and the amount of extracortical bone formation was evaluated. Finally the effect of osteointegration of the HA collar on the rate of aseptic loosening (ASL) and on implant survival was investigated. Uncemented, custom made distal femoral endoprostheses have a higher rate of aseptic loosening compared to cemented fixation but this was associated with early loosening and implants that survived for greater than two years, were well fixed for the duration of follow-up. Initial fixation of uncemented DFR is crucial as most cases of loosening occur early. The use of grooved HA coated collar located at the shoulder of distal femoral massive prostheses resulted in increased formation and attachment of the extra-cortical bone and showed a reduced rate of revision due to aseptic loosening. However in cases where osteointegration could not be identified on radiographs, the loosening was higher than in those cases which were well osteointegrated. Survivorship at 10 and 15 years was 98% for those patients with well osteoinetgrated implants but only 75% for those without osteointegration. In paediatric cases, the use of a HA collar reduces the progression of radiolucent lines and results indicate that implants with osteointegrated HA collars, inserted into adolescent patients remain more firmly attached to the skeleton than nonosteoinegrated HA collars. This suggests that HA collars can enhance the survival of the prosthesis inserted when these patients achieve skeletally maturity. These results suggest that HA collars are beneficial when they are osteointegrated as they allow load distribution onto the adjacent cortical bone in a more physiological manner resulting in a reduced load on the intramedullary stem leading to a reduction of aseptic loosening.

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