Unwin, Paul Simon; (1998) Investigation of improved fixation in massive endo-prosthetic replacements of the lower limb. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This retrospective study of 1149 of cemented intra-medullary stemmed Stanmore bone tumour lower limb massive endo-prostheses, identified that aseptic loosening was the most common form of implant related failure. Revision for aseptic loosening occurred in 14.5% of the 1149 cases. The probability of surviving aseptic loosening for 10 year for proximal femoral, distal femoral and proximal tibial replacements was 87.9%, 65.1% and 51.5% respectively. Patients at greatest risk of loosening were young patients with a distal femoral or proximal tibial replacement, or patients with extensive resections of the distal femur or proximal tibia. Those patients with short proximal femoral resections were at greater risk than those with extensive resections. Clinical and radiographic evaluations of patients were poor predictors of loosening. However, there was a correlation between pain and radiographic radiolucent lines. This study provided impetus to develop three new method of improving implant fixation. These were - 1. enhanced fixation of cemented intra-medullary stemmed replacements using porous beaded collars or hydroxyapatite coated collars. Bony bridging did not occur with porous collared replacements but did with 81.8% of hydroxyapatite coated replacements. 2. uncemented intra-medullary fixation using press-fit, hydroxyapatite coated custom-made stems. After laboratory and cadaveric studies, a clinical trial of 20 patients was undertaken. Early radiographic results of target groups were encouraging. 3. extra-cortical fixation using hydroxyapatite coated extra-cortical plates. Inspired by the first Stanmore replacements, extra-cortical plated fixation was investigated using a goat model. Histological results of mid-shaft tibial replacements identified osseointegrated encompassed plates. The success of the animal model, led to the insertion of an extra-cortical plated distal femoral endo-prosthesis. All three methods of improving the fixation showed encouraging results. The acceptance and increasing use of enhanced methods of fixation has reinforced the value of this work.

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