Changes of Bone Mineral Density in Total Hip Arthroplasty - A Prospective Comparison of Isoelastic and Metal-backed Cup Designs

The study was performed as a prospective, single center study at the Department of Orthopedics, Sacred Heart of Jesus Hospital Vienna, Austria.

Inclusion criteria were as follows: any patient aged from 18 years onwards undergoing primary cementless THA for degenerative joint disease, including osteoarthritis, post-traumatic arthritis, congenital hip dysplasia and avascular necrosis. Excluded were all patients with malignant diseases and pregnant women, additionally, patients were excluded if severe complications such as fracture or revision surgery occurred during the study period.

Patients were enrolled from January 2016 to May 2017, a total of 117 patients were included. All patients underwent uncemented THA, patients either received a monoblock cup (RM Pressfit vitamys®; Mathys Ltd. Bettlach, Switzerland), or a titanium shell (ANA.NOVA® Implantec, Mödling, Austria). DEXA measurements according to the DeLee and Charnley Zones were performed postoperatively, 3, 6, 12 and 24 months after primary hip arthroplasty. Bone mineral density (BMD) was measured by using the bone densiometer (Lunar, Prodigy, GE Medical Sytsems). A special legholder was used to fix the leg to ensure the same rotation and avoid measurement errors. DEXA measurements were performed and analyzed by two trained authors. Statistical analysis focused on differences in BMD between monoblock cup and modular cup after 3, 6, 12 and 24 months as well as changes in BMD in relation to cup inclination. In order to gain valid results, the nonparametric Wilcoxon rank-sum test was used. We used t-Test to evaluate differences to the baseline. A probability value of p ≤0.05 was considered as statistically significant. Data was analyzed using Microsoft Excel® and SPSS® (version 26.0, SPSS Inc., Chicago, IL, USA) representing standard statistical software. We hypothesized that the more elastic monoblock cup performs better than the more rigid modular cup with regard to changes in BMD.