Reduction in Remote Site Bone Volume after Orthopedic Implant Surgery is Greater in Appendicular than Axial Skeleton

Abstract

PurposeThe purpose of this study was to investigate trabecular bone volume at remote sites after orthopedic implant surgery and to determine if particle challenge to induce peri‐implant osteolysis, a major cause of aseptic implant failure, was contributory.MethodsIn this IACUC‐approved study that followed FASEB guidelines, male Sprague‐Dawley rats (398 ± 11.5 g; n=8–9/group) were randomly allocated to 5 groups. In 4 groups, bilateral titanium femoral implants were placed in the medullary space by drilling through the intercondylar groove (n=33). These rats received weekly intra‐articular injections containing vehicle as a control or particle solutions (clean‐ or lipopolysaccharide‐doped‐polyethylene or cobalt chromium) to stimulate peri‐implant osteolysis. A 5th group remained intact (no implant surgery, no intra‐articular injections, n=8). Rats were weighed at the commencement and at the 6 week conclusion of the study. Trabecular bone of the proximal humerus and L2 vertebral body was assessed by micro‐computed tomography. Data were analyzed by one‐way analysis of variance (ANOVA) for between‐group effects with Bonferroni corrected post‐hoc comparisons.ResultsTrabecular bone volume fraction in the proximal humerus was reduced by ~30% in each implant group compared to the intact group (ANOVA p<0.001, p≤0.002 for post‐hoc comparisons of each implant group to the intact group). There were no differences among the 4 implant groups. Although the L2 trabecular bone volume fraction varied among the 5 groups (ANOVA p=0.013), the post‐hoc comparisons showed only marginal reductions for cobalt chromium‐challenged rats compared to both intact (~20% reduction; p=0.054) and clean‐polyethylene‐challenged rats (~15% reduction; p=0.055). Weight was not different between groups at the start of the study (ANOVA p=0.809); however, at 6 weeks after surgery there was a significant group effect (ANOVA p <0.001) with the cobalt chromium‐challenged animals having gained ~25 or 35 g less weight than the vehicle‐control (p=0.013) and intact (p<0.001) rats, respectively.DiscussionPreviously, we showed that remote bone remodeling did not differ between vehicle and particle challenged rats that had received an implant, but in that study there was no intact control group [Ross RD et al., J Orthop Res, 2014]. In the present study in which an intact control group was included, we now show that there was a reduction in bone volume fraction at two remote sites following orthopedic implant surgery. Consistent with our previous study, bone volume fraction of the proximal humerus was reduced in all groups that underwent implant surgery, but there was no particle challenge effect. There was only marginal evidence that implant placement or particle challenge affected axial bone volume. These results suggest that surgical placement of an orthopedic implant may lead to a systemic increase in bone remodeling that more strongly affects the appendicular than the axial skeleton, but that the additional particle challenge was not contributory.Support or Funding InformationNIH R01AR066562