SP35. Effect of Brachial Plexus Birth Injury Model on Bone Growth

PURPOSE: Brachial plexus birth injuries (BPBI) occur in approximately 1 in 1,000 live births. Some will recover with minimal deficits, while others may require early microsurgical intervention to improve function. Despite this, ~30% will have residual deficits as they grow into adulthood, including limb size and length discrepancies and functional limitations. To understand the mechanistic relationship of neonatal nerve injury to skeletal growth, this study aimed to create a rat pup model of brachial plexus birth injury specifically to evaluate the resulting limb length inequality. METHODS: A brachial plexus birth injury was created in Sprague-Dawley rat pups aged 3-9 days. A dorsal approach was made to expose the entire brachial plexus under operative microscope magnification. A neurotomy was performed distal to the dorsal root ganglion by cauterizing the root to simulate a unilateral pan brachial plexus rupture. Pups had a survival period of 8 weeks. The bilateral humeri lengths were measured using microCT, and post-mortem dissection assessed the morphological changes of the humeri. RESULTS: Ten pan plexal injuries were successfully created in the rat pups. Two rat pups recovered full function, while the remaining continued with limb functional deficits. MicroCT measurements revealed a noticeable mean limb length inequality of 1.8mm in the operated humerus. (p = 0.0086, 95% CI: 0.76, 2.84) Post-mortem dissection of the humeri confirmed a significant difference between the operated and unoperated limb, with a mean limb length inequality of 2.25mm (p<0.001, 95% CI: 1.77, 2.73) and showed morphological differences compared to the unoperated humerus. CONCLUSION: A rat pup brachial plexus model was successfully developed, resulting in morphologic changes in the ipsilateral humeri. Limb length inequality was created through altered innervation of the proximal humeral physis. Further analysis of the physis will allow determination of the mechanism and relationship between nerve innervation and bone growth in the rat pup.