Summary
In this prospective study we followed the bone mineral content (BMC) —changes over time at seven distinct well defined bone Zones (1–7), around the uncemented Zweymueller total hip arthroplasty (THA) components, using dual energy xray densitometry, and a roentgenographical analysis close to the tip of the Zweymueller stem, to measure any postoperative cortical thickness changes. A homogenous group of 36 female patients, average age of 55 years, with primary hip osteoarthritis was studied. The BMC — measurements were made preoperatively, 2 weeks, one year and four years postoperatively. The BMC-changes in this study were showen to be statistically significant at the Zones 1, 3, 4, 5, 6 and 7 (P-values 0.05–0.01), whereas at the Zone 2 they were not. The BMC- changes over time for all Zones of interest were not related to the age of the patients. We believe that the BMC-reduction, observed at the Zones 2 to 7, immediately after implantation of the Zweymueller THA, should be related to the intraoperatively removed bone. Conclusions :(1) the Zweymueller screw socket finds its definitive anchorage immediately postoperatively at the medial and distal thirds of the acetabulum and remains stable over time, without any further bone mineral content-changes; (2) the Zweymueller stem finds its main anchorage within the distal femoral cortex and remains stable up to 4-year-observation, without significant bone mineral content changes; and (3) the Zweymueller stem finds two additional points of fixation within the mass of the greater and lesser trochanter, where it induces a continuous bone turnover with bone trabeculae thickening, which probably extends more than 4 years.