Biceps strength drop at diagnosis is associated with deltoid strength recovery in severe postoperative C5 palsy: a retrospective cohort study

Objective C5 nerve root palsy (C5P) following cervical decompression surgery remains a frustrating complication affecting patients' quality of life. C5P primarily affects the deltoid muscle, with the biceps brachii also involved in more severe cases. This study aimed to investigate the association between the degree of biceps brachii weakness and the recovery of deltoid muscle strength in patients with severe C5P. Methods A retrospective cohort study of 78 patients with new-onset severe C5P following unilateral open-door laminoplasty between 2010 and 2024 was analyzed. All patients were retrospectively enrolled and underwent standardized clinical follow-up assessments at 6 and 12 months postoperatively. Univariate and multivariate logistic regression analyses were performed at the 6-month and 12-month time points to investigate the predictive value of patient characteristics, radiological features, and biceps brachii muscle strength for recovery from severe C5P. Results A total of 78 patients developed severe C5P after surgery. Univariate logistic regression analysis revealed that biceps brachii strength deficit at diagnosis, high-intensity zone (HIZ) at C3/4 and C4/5, and cervical kyphosis were potential risk factors for lack of deltoid strength recovery at the 6-month follow-up. At the 12-month follow-up, biceps brachii strength deficit at diagnosis, HIZ at C4/5, and cervical kyphosis remained potential predictors of poor recovery of deltoid strength. Multivariate logistic regression identified the degree of biceps brachii strength deficit as an independent predictor of non-recovery at both 6 months (OR = 2.18, P < 0.001) and 12 months (Model 1: OR = 3.05, P < 0.001; Model 2: OR = 3.10, P < 0.001). Conclusion The degree of biceps brachii strength deficit is an independent predictor of intermediate- and long-term failure of deltoid muscle recovery following severe postoperative C5P. Identifying this risk factor may provide a critical time reference for timely consideration of nerve transfer surgery in affected patients.