Brachial Plexus Birth Injury Causes Location-Dependent Detriments in Glenohumeral Trabecular Bone Microstructure

Brachial plexus birth injury (BPBI) is caused during a difficult childbirth when the head and neck are excessively stretched, and the brachial plexus nerve bundle is damaged. Injury causes lifelong arm impairment in 30-40% of those affected, but the extent to which bone microstructure is affected and how that relates to bone morphology alterations is unclear. Additionally, how injury location impacts trabecular bone, and the role limb disuse plays in these differential effects are unknown. Using two rat models of BPBI (postganglionic and preganglionic) and a disuse model (disarticulation), trabecular bone microstructure and glenohumeral morphology were characterized in the proximal humerus and distal scapula. For bone microstructure, the regions closest to the joint articulating surface incurred the greatest detriments with the least robust trabecular bone. These trabecular bone deficits in the humeral epiphysis and scapular neck were greater following preganglionic injury than postganglionic injury. The effects in the disarticulation group tended to align more with those in the postganglionic group, and greater detriments were observed in the scapula than in the humerus. Bone morphology metrics were explained mainly by quantity and architecture of trabecular bone but were not explained by the same metrics across all groups. Combining results with changes in bone morphology, data suggest differential effects with injury location and the effects of limb disuse to be most prominent in the postganglionic injury group and the distal scapula. In addition, the differences in results between postganglionic and preganglionic and macrostructural and microstructural deformity, suggest different drivers for postganglionic and preganglionic injuries and different factors causing macrostructural and microstructural alterations.