Brachial plexus nerve injury and repair in a rabbit model part II: Does middle trunk injury result in loss of biceps function while repair results in recovery of biceps function

Introduction: There is conflicting anatomic and innervation data regarding the rabbit brachial plexus injury model. This study aims to validate a rabbit brachial plexus injury model. We hypothesize the middle trunk (C6, C7) is the primary innervation of the biceps, and when cut and unrepaired, would demonstrate lack of recovery and when repaired would demonstrate evidence of recovery. Materials and Methods: Twenty two male New Zealand white rabbits (3–4 kg) underwent unilateral surgical division of the middle trunk. Five rabbits were randomly assigned to the “no-repair” group while the remaining 17 rabbits underwent direct coaptation (“repair” group). Rabbits were followed for 12 weeks, with ultrasound measurement of biceps cross-sectional area performed preoperatively, and at 4, 8, and 12 weeks postoperatively. At a euthanasia procedure, bilateral compound muscle action potential (CMAP) and isometric tetanic force (ITF) were measured. Bilateral biceps muscles were harvested and wet muscle weight was recorded. The operative side was expressed as a percentage of the non-operated side, and differences between the no repair and repair rabbits were statistically compared. Results: The repair group demonstrated significantly higher CMA (23.3 vs. 0%, p <.05), ITF (25.6 vs. 0%, p <.05), and wet muscle weight (65.8 vs. 52.0%, p <.05) as compared to the unrepaired group. At 4 weeks postoperatively, ultrasound-measured cross-sectional area of the biceps demonstrated atrophy in both groups. At 12 weeks, the repair group had a significantly larger cross-sectional area as compared to the no-repair group (89.1 vs. 59.3%, p <.05). Conclusions: This injury model demonstrated recovery with repair and lack of function without repair. Longer survival time is recommended for future investigations.