RADIOLOGICAL CHANGES AROUND CEMENTED FEMORAL STEMS AT 12 YEARS

Abstract

Purpose: After cementing, various changes are observed in femoral bone resulting from various factors (ageing process, stress forces, granuloma…). The purpose of this work was to examine the radiological expression of these changes a mean 12 years after prosthesis implantation.

Material and methods: Charnley-Kerboull total hip arthroplasty was performed in 304 patients (338 hips) between January 1st, 1984 and December 31st, 1986. Mean age of the population was 65.5 years. Most of the patients had degenerative hip disease (81.4%). Among these 304 patients, 108 had died and 56 were lost to follow-up, giving 174 patients retained for analysis at a maximum follow-up of 16 years (mean 12 years). Noble and Nordin scores were recorded before surgery and during follow-up as were the cortical and cement thicknesses in the seven zones described by Gruen.

Results: The actuarial curve, calculated for the 338 hips showed 95.1% survival at 12 years (taking into account all revisions irrespective of the cause). Femoral stem survival was 97.1±2% taking certain or probable loosening as the endpoint. Several categories or radiological changes were observed: – femoral defects (18%) correlated with cup wear; – progressive widening of the medullary canal without loosening and a mean femoral score moving from 55.7 to 52.16 (p< 0.01) especially in thin women and for wide-mouthed femurs; – cortical thickening near the tip (57%) more frequently for greater distal filling; – stress shielding especially in women (p< 0.001) with a low initial score for the femur (p< 0.0006) and with greater distal filling.

Conclusion: Like Kerboull, we tried to achieve primary stem stability before cementing. Cementing results were good (97% at 12 years), but detailed radiographic analysis demonstrated that cortical thinning remained in zone 7, especially when the primary stability was achieved in the distal portion of the femur (high preoperative Noble index). Variations in the metaphyseal-diaphyseal ratio require adaptating the form of the stem to be cemented in order to achieve better filling and avoid primary stability mainly in the distal portion.