Bone Remodelling in the Proximal Femur after Uncemented Total Hip Arthroplasty in Patients with Osteoporosis

The aim of the study was to investigate the involvement of osteoporosis during remodelling of the proximal femur after uncemented total hip arthroplasty (THA) and the effect of bisphospohonate treatment on these changes.Sixty evaluated patients with non-cemented THA were divided into three groups on the basis of pre-operative densitometric examinations. Group 1 (15 patients with osteoporosis) received a single dose of 5 mg zoledronic acid in infusion during the second post-operative week. Group 2 (15 patients with osteoporosis) were not treated by bisphospohonate. The patients of both groups took oral calcium and vitamin D medication. Group 3 (control) comprised 30 patients with normal bone density who did not take any osteoactive drugs. By measurement of bone mineral density (BMD) at 12 months after surgery, changes in periprosthetic bone of the proximal femur in 7 Gruen zones were recorded by densitometry. In addition, radiological findings on native X-ray images were assessed and the patients' clinical health status was rated by the Harris hip score.No significant differences in either the average age or the body mass index were found between the groups at the time of THA surgery. The mean BMD value in all assessed Gruen zones measured at the first post-operative week was higher in patients with normal bone density than in those with osteoporosis. The mean BMD value measured at 12 months decreased in all Gruen zones in comparison with the initial value, and this was found in all three groups. The lowest values were recorded in the untreated patients (group 2); in comparison with the patients who had normal bone density, the difference was statistically significant in Gruen zones 1, 2, 6 and 7. Although the patients with treated osteoporosis also showed lower BMD values, these were not statistically significant compared to group 3. The worst post-operative outcome in clinical health status was recorded in the patients with untreated osteoporosis. X-ray examination revealed stable fibrous ingrowth in one patient with untreated osteoporosis and in one with normal bone density. All remaining patients had stable bone ingrowth fixation.In THA the majority of compressive loads are transferred through the stem to the femoral bone below the apex of the stem. This results in reduction of bone density in the calcar and greater trochanter regions. Osteoporosis is the most important factor related to changes in periprosthetic bone mass. Therefore, it can be anticipated that an excess loss of bone mass in the proximal femur may, in a long term, interfere with THA stability and may increase the risk of periprosthetic fractures and aseptic loosening.The results of our study showed that the patients with untreated osteoporosis, who underwent uncemented THA, experienced a considerable decrease in the periprosthetic bone density of the proximal femur and were in worse clinical health. A bisphospohonate therapy was effective in eliminating this negative outcome. Both the clinical and densitometric findings in patients with treated osteoporosis were similar to those in patients with no osteoporosis.