Effect of perioperative multistrain probiotics on the CT callus volume fraction at 12 weeks after surgery for closed tibial shaft fracture: a single-center randomized controlled study.

Background: Conventional radiographs lack sensitivity for early healing, whereas computed tomography (CT)-derived bone volume fraction (BV/TV) allows quantitative assessment of callus mineralization. Perioperative antibiotics and surgical stress disrupt gut microbiota, potentially impairing fracture healing. Multistrain probiotics may enhance bone repair via immunomodulation and the gut-bone axis. Objective: To evaluate the effect of perioperative multistrain probiotics ( Methods: This single-center, randomized, double-blind, placebo-controlled trial enrolled 84 patients with closed tibial shaft fractures. The modified intention-to-treat population included participants who received at least one dose and completed follow-up. Probiotics or placebo were administered from the preoperative period through postoperative week 6. The primary outcome was BV/TV at 12 weeks, analyzed using ANCOVA adjusted for age, sex, AO/OTA fracture classification, smoking status, and postoperative interfragmentary gap. Secondary outcomes included time to uncomplicated full weight bearing (defined as ambulation without assistive devices and without pain in the affected limb; analyzed using Kaplan-Meier with the log-rank test), rest-pain visual analog scale (VAS) scores at postoperative weeks 2 and 6, and Radiographic Union Score for Tibial Fractures (RUST) at 12 weeks. CT segmentation reliability was assessed using intraclass correlation coefficients (ICC). Safety outcomes were analyzed using Fisher's exact test. Results: The probiotics group demonstrated significantly higher adjusted BV/TV at 12 weeks compared with placebo (Δ = 0.11; 95% CI 0.03-0.19; P = 0.012). In exploratory secondary analyses, for which nominal P values are reported without multiplicity adjustment, time to full weight bearing was shorter (P = 0.041). VAS pain scores were lower at postoperative week 2 (Δ = -0.55; P = 0.047), with no difference at week 6. RUST scores at 12 weeks were higher in the probiotics group (Δ = 0.68; P = 0.019). CT segmentation showed excellent reliability (ICC = 0.96). No significant differences were observed in adverse events and surgical site infection. Conclusions: Perioperative multistrain probiotics significantly enhanced CT-based bone mineralization at 12 weeks, while exploratory secondary findings suggested earlier functional recovery and improved radiographic healing. These findings warrant further evaluation of probiotics as a potential adjunct to standard fracture care.