Risk factors for C5 palsy: a systematic review and multivariate analysis

OBJECTIVE Postoperative C5 palsy (C5P) is a known complication in cervical spine surgery. However, its exact pathophysiology is unclear. The authors aimed to provide a review of the current understanding of C5P by performing a comprehensive, systematic review of the existing literature and conducting a critical appraisal of existing evidence to determine the risk factors of C5P. METHODS A systematic search of PubMed/MEDLINE (January 1, 2019, to July 2, 2021), EMBASE (inception to July 2, 2021), and Cochrane (inception to July 2, 2021) databases was conducted. Preestablished criteria were used to evaluate studies for inclusion. Studies that adjusted for one or more of the following factors were considered: preoperative foraminal diameter (FD) at C4/5, posterior spinal cord shift at C4/5, preoperative anterior-posterior diameter (APD) at C4/5, preoperative spinal cord rotation, and change in C2-7 Cobb angle. Studies were rated as good, fair, or poor based on the Quality in Prognosis Studies (QUIPS) tool. Random effects meta-analyses were done using methods outlined by Cochrane methodologists for pooling of prognostic studies. Overall quality (strength) of evidence was based on Grading of Recommendations Assessment, Development, and Evaluation (GRADE) methods for prognostic studies. The protocol for this review was published on the PROSPERO (CRD264358) website. RESULTS Of 303 potentially relevant citations of studies, 12 met the inclusion criteria set a priori. These works provide moderate-quality evidence that preoperative FD substantially increases the odds of C5P in patients undergoing posterior cervical surgery. Pooled estimates across 7 studies in which various surgical approaches were used indicate that the odds of C5P approximately triple for each millimeter decrease in preoperative FD (OR 3.05, 95% CI 2.07-4.49). Preoperative APD increases the odds of C5P, but the confidence is low. Across 3 studies, each using different surgical approaches, each millimeter decrease in preoperative APD was associated with a more than 2-fold increased odds of C5P (pooled OR 2.51, 95% CI 1.69-3.73). Confidence that there is an association with postoperative C5P and posterior spinal cord shift, change in sagittal Cobb angle, and preoperative spinal cord rotation is very low. CONCLUSIONS The exact pathophysiological process resulting in postoperative C5P remains an enigma but there is a clear association with foraminal stenosis, especially when performing posterior procedures. C5P is also related to decreased APD but the association is less clear. The overall quality (strength) of evidence provided by the current literature is low to very low for most factors.