Sr‐loaded deproteinized bovine bone improves bone repair in ovarectomized rats

Background Strontium (Sr) is known to enhance osteoblastic activity and suppress osteoclastic activity. Recently, deproteinized bovine bone (DBB) loaded with Sr appeared to improve bone regeneration in critical-size calvaria defects (CSD) in systemically healthy rats. However, the effect of Sr-loaded DBB grafting in critical-size defects under conditions showing delayed bone formation due to systemic problems, needs to be investigated. Aim/Hypothesis To evaluate bone healing after grafting CSD in ovariectomized rats with Sr-loaded deproteinized bovine bone. Material and Methods One circular CSD (Ø 5 mm) was prepared on each parietal bone of 42 female rats that have been ovariectomized (Ovx) 30 days before the surgical procedure. One of the CSD, randomly chosen, was grafted with: (a) DBB, (b) DBB loaded with 140 μM/g of Sr (DBB/Sr1), or (c) DBB loaded with 700 μM/g of Sr (DBB/Sr 2). The other CSD was left empty as negative control. Groups of 7 animals from each of the 3 grafting groups were euthanized 15 and 60 days post-op. Bone regeneration was assessed by micro-CT into a circular region of interest (ROI) 5 mm in diameter and encompassing the entire defect thickness. The following parameters were evaluated: (1) residual radiographic defect length (R-RDL): average of the distance (in mm) between the new bone margins measured at the center of the original defect, in the sagittal and coronal plane, using only the first dural section within the ROI, and (2) radiographic mineralized tissue fill (R-MTF): new bone formation and DBB volume expressed as % of the ROI. Results Empty CSDs (4.44–4.71 mm) presented always lower R-RDL compared with the grafted ones (4.71–5.03 mm) (P < 0.05). Regarding the grafted CSDs, those grafted with DBB/Sr1 (4.71 ± 0.07 mm) and DBB/Sr2 (5.03 ± 0.11 mm) presented higher average R-RDL than those grafted with DBB (4.43 ± 0.11 mm) at 15 days post-op (P < 0.05). Further, grafted CSDs showed larger (48.53 to 53.10%) R-MTF than the empty CSDs (5.16–14.72%) (P < 0.05), and defects grafted with DBB/Sr1 (51.84 ± 2.78%) or DBB/Sr2 (51.59 ± 2.21%) presented larger R-MTF compared with the DBB group (48.53 ± 1.41%) at 15 days (P < 0.05). There were no significant differences at 60 days among the groups neither for R-RDL nor for R-MTF. Conclusions and Clinical Implications Grafting of CSD in ovariectomized rats with Sr-loaded DBB enhances slightly bone formation when compared with non-Sr-loaded DBB grafting, albeit at a moderate extent with the d