OBJECTIVES: Healing remains a clinical challenge in nonoperatively treated fragility fractures of the pelvis (FFPs). Modifying gut microbiota has been found to affect cytokine pathways involved in bone formation and resorption. This study examined the impact of probiotic treatment pre- and postunilateral pubic rami fracture on bone microstructure and load-to-failure of healing fractured and intact (unfractured) contralateral hemipelvises. METHODS: Twenty-one 6-month-old female Sprague Dawley rats were bilaterally ovariectomized and housed for 3 months to establish an osteoporotic phenotype. At 9 months old, stable unilateral fractures of the superior and inferior pubic rami of the left hemipelvis (type 1a FFP) were created. Before fracture creation, rats were randomly separated into control (phosphate-buffered saline administered for 12 weeks), prefracture treatment (probiotics administered for 12 weeks starting 6 weeks prefracture), and postfracture treatment (probiotics administered for 6 weeks postfracture) groups. At 6 weeks postfracture, rats were sacrificed, and their pelvises were harvested, microcomputed tomography imaged, and evaluated through microstructural analysis and biomechanical testing. RESULTS: On the intact hemipelvises, the prefracture treatment group (n = 5) had significantly higher bone volume (BV) ( P = 0.050), bone volume fraction (BV/TV) ( P = 0.019), bone mineral density ( P = 0.019), and tissue mineral density (TMD) ( P = 0.014) than those in the postfracture treatment group (n = 7). The intact hemipelvises of the prefracture treatment group also had significantly increased trabecular thickness (TbTh) ( P = 0.021) when compared with those in the control group (n = 6). On the fractured hemipelvises, the prefracture group had increased total volume (TV) ( P = 0.020), BV ( P = 0.011), and BV/TV ( P = 0.026) when compared with the control group (n = 4). Although load-to-failure was correlated with microstructural parameters (BV/TV (r = 0.42, P = 0.015), trabecular number (TbN) (r = 0.42, P = 0.014), bone mineral density (r = 0.55, P = 0.0008), TMD (r = 0.40, P = 0.019), and trabecular spacing (TbS) (r = −0.58, P = 0.0003), no significant differences in bone strength were found between groups. CONCLUSIONS: Probiotic treatment was shown to improve bone microstructure in osteoporotic rats; however, efficacy was related to treatment timing and duration. Administration of probiotics for 12 weeks beginning 6 weeks prefracture significantly enhanced bone quality in both the healing fractured and intact contralateral hemipelvises. This suggests a critical timing threshold exists for probiotic therapy to impact the gut microbiome, facilitating an alteration of the immune response postfracture and producing positive structural changes in osteoporotic pelvic bone.

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