Dual-energy x-ray absorptiometry analysis of implants in rat tibiae

Dual energy x-ray absorptiometry (DXA) was evaluated for its ability to measure changes in bone mineral density in isolated rat tibiae. This technique is available for in vivo use to potentially augment or replace some aspects of conventional histomorphometric techniques used for the evaluation of metallic implant-to-bone interfaces. Known quantities of hydroxyapatite powder, representing various bone densities, were measured using DXA in a series of 3 experiments: (1) the hydroxyapatite powder was placed within a plastic tube, (2) the hydroxyapatite was placed within an excised rat tibia, and (3) hydroxyapatite powder was placed within a rat tibia with soft tissue overlying it. Statistical analysis (analysis of variance) showed significant differences in bone mineral density among groups that varied by only 5% hydroxyapatite density within the plastic tubes. The system detected hydroxyapatite changes of 20% within the tibiae with and without overlying soft tissue (P < 0.05). These data were consistent and linear (R > 0.90). Although DXA analysis has been widely used in clinical and research applications for detection of osteoporosis, its use for documenting bone growth around implants has not been widely reported. The use of such a technique could have substantial benefits for both the clinical and research arenas. These data show that DXA analysis to identify bone density changes adjacent to implants has significant applications in small animal research models.