Local probiotic treatment attenuates suprascapular nerve injury–associated inflammatory and histological changes in a rat rotator cuff repair model

Abstract Background Suprascapular nerve dysfunction may impair rotator cuff healing by exacerbating local inflammation, particularly tumor necrosis factor-alpha (TNF-α) expression, and inducing denervation-related changes. This study aimed to determine whether local probiotic administration could counteract these detrimental effects in a rat rotator cuff repair model. Methods Thirty-six male Sprague-Dawley rats were randomly allocated into four groups ( n = 9 per group): nerve injury (NI) with local probiotic treatment, no NI with local probiotic treatment, NI without probiotic treatment, and no NI without probiotic treatment. All animals underwent supraspinatus tendon transection and modified Mason-Allen repair. In the NI groups, the suprascapular nerve was sharply transected at the suprascapular notch. Local probiotic treatment was applied directly to the repair site in the designated groups. At 21 days postoperatively, tendon healing was evaluated histologically using Bonar and Movin scores and immunohistochemically using TNF-α H-scores. Biomechanical properties, including failure load, energy to failure, and axial stiffness, were also assessed. Results The untreated NI group exhibited the poorest histological healing, with the highest Bonar score (8.33 ± 0.82) and Movin score (11.00 ± 1.41). Local probiotic treatment in the presence of NI was associated with lower Bonar (5.50 ± 1.87) and Movin (7.50 ± 1.22) scores. Bonar and Movin scores differed significantly among groups ( p = 0.001 and p < 0.001, respectively), and the untreated NI group had significantly higher scores than all other groups. TNF-α H-scores also differed significantly among groups ( p < 0.001), with the highest expression in the untreated NI group (52.73 ± 4.36) and lower expression in the NI with probiotic treatment group (43.92 ± 3.82). The lowest TNF-α expression was observed in the nerve-intact probiotic-treated group (26.47 ± 3.91). Biomechanical findings were consistent with the histological and immunohistochemical results; the untreated NI group showed the lowest failure load (15.48 ± 2.21 N) and energy to failure (29.66 ± 21.63 N·mm), whereas the NI with probiotic treatment group showed higher values (27.31 ± 4.15 N and 118.11 ± 26.72 N·mm, respectively). Axial stiffness did not differ significantly among groups. Given the limited biomechanical sample size ( n = 3 per group), these findings should be interpreted as exploratory. Conclusion Local probiotic treatment attenuated nerve injury-associated inflammatory and histological deterioration in a rat rotator cuff repair model. These findings suggest that local probiotic administration may represent a promising biological strategy to improve the repair-site environment under adverse denervation conditions.