Periprosthetic mineralization changes around femoral stems: a prospective 12-month study with DEXA

OBJECTIVE: The objective was to evaluate bone mineral density (BMD) changes around the proximal femur after implantation of two different anatomical stems. MATERIALS AND METHODS: Thirty-six patients (19 women and 17 men) who underwent total hip replacement were recruited. A Bihapro stem was implanted in 23 patients (with a mean age of 60.9 years) and a Citation stem in 13 patients (with a mean age of 59.7 years). All patients underwent serial radiography of the affected hip (follow-up time: 12 months). Baseline periprosthetic and overall BMD were measured with dual-energy X-ray absorptiometry (DEXA) 1 week and 12 months after hip replacement. Regions of interest (ROIs) were defined according to Gruen's system (ROIs 1-7). RESULTS: All stems were classified as radiographically stable. Bone ongrowth (spot welds) was present in zones 1 and 2 in all patients with the Bihapro stem. The distribution of baseline densities was very similar in the two groups of patients. In Bihapro implants a significant increment of mineralisation was present in ROI 1 after 1 year; ROIs 2 to 7 showed no density variation. The following observations were made regarding the Citation implants: no increment in density was shown in ROI 1; the differences in densities among the ROIs were significant after 1 year in the global evaluation (p = 0.004); the comparison between the single ROIs showed decalcification in ROIs 2 and 7 and a density increment in ROI 5. CONCLUSIONS: Bihapro stems appear to achieve adequate proximal fixation, avoiding the "stress shielding" phenomenon.