A quantitative and qualitative analysis of bone remodelling around custom uncemented femoral stems: a five-year DEXA follow-up

Background. After total hip replacement bone remodelling is determinant for the implant survival. This study asked whether the immediate postoperative amount and distribution of bone can predict the changes in bone amount and distribution after five years in the case of younger patients with custom uncemented implant. Methods. We investigated 17 hips with a mean follow-up of 5.1 years. The average patient age at follow-up was 48.5 years. We used immediate postoperative and five-year dual energy X-ray absorptiometry measurements of bone mineral content, density, and projected bone area in seven local zones forming a partition of the upper femur. A correlation was sought between the preoperative variables and the five-year variation. Qualitative bone remodelling was analysed considering each local zone in a density-area plane. Based on geometrical considerations, we introduced an index of structural remodelling, which expresses the preponderance of internal remodelling against external modelling. Findings. The bone mineral content at operation correlated significantly with its relative decrease locally laterally mid-proximally and medially (P < 0.01), distally, and globally for the femur (P < 0.05). For the bone mineral density, the correlation was significant distally, medially and globally (P < 0.05). The bone projected area shows only significant correlation laterally mid-proximally (P < 0.01). The index of structural remodelling was significantly positive (P < 0.01) in all local zones and was independent of the initial bone amount and structure (P > 0.1). Interpretation. High bone mineral content at operation correlates significantly with periprosthetic bone loss after five years in younger patients with cementless custom femoral implant. Independently of the net bone mineral content balance, external modelling is stronger than internal remodelling in all local zones.