The Unappreciated Morbidity of Brachial Plexus Injuries Following Low Energy Shoulder Trauma: Understanding Risk Factors and Natural History

BACKGROUND: Brachial plexus injury (BPI) following shoulder trauma is an uncommon but potentially disabling complication that is often underrecognized, leading to delayed diagnosis. This study aimed to define the institutional incidence, nerve distribution, and recovery patterns of BPI after shoulder trauma and to identify factors associated with injury severity and recovery. METHODS: We performed a retrospective review of adult patients diagnosed with BPI following isolated shoulder trauma at a single academic center from January 2016 to July 2023. Patients with BPI were compared with a randomized cohort of shoulder trauma patients without BPI. Variables included demographics, mechanism of injury, injury pattern, nerve involvement, severity grading, management, and ≥1-year outcomes. BPI severity was categorized using a standardized clinical grading system. Logistic regression was used to evaluate factors associated with severity and predictors of recovery. RESULTS: Among 6,195 patients with shoulder trauma, 111 (1.8%) were diagnosed with BPI. Patients with BPI were younger than controls (51.5 vs. 58.8 years, p=0.004), and fracture-dislocations were more common (p<0.001). The axillary nerve was most frequently affected (67.1%), followed by radial (41.5%), median (36.6%), ulnar (32.9%), and musculocutaneous nerves (22.0%). Most patients (74.4%) achieved complete recovery within one year, and 85.4% were managed nonoperatively. Musculocutaneous nerve injury was associated with reduced odds of recovery (OR 0.17, p=0.002), whereas dislocation (OR 5.43, p=0.017) and fracture-dislocation (OR 5.60, p=0.020) were associated with improved recovery compared with isolated fracture. CONCLUSION: BPI occurred in 1.8% of shoulder trauma cases and was most associated with fracture-dislocations. Musculocutaneous nerve injury and female sex were independently associated with lower likelihood of recovery, whereas dislocation and fracture-dislocation patterns were associated with improved recovery compared with isolated fractures. These findings underscore the importance of early, nerve-specific evaluation and more refined prognostic stratification following shoulder trauma.