Association between early postoperative posterior displacement of the spinal cord and postoperative C5 nerve root dysfunction after anterior cervical decompression and fusion: a retrospective imaging cohort study using standardized measurements

C5 nerve root palsy is a challenging complication following anterior cervical decompression and fusion (ACDF) or anterior cervical corpectomy and fusion (ACCF) with a reported incidence of 1–5% (1). While posterior displacement of the spinal cord with resultant nerve root tethering is a leading hypothesis, high-quality evidence quantifying early postoperative cord migration and its association with C5 palsy risk, based on standardized imaging, remains scarce.

To investigate the association between early postoperative posterior displacement of the spinal cord, measured using a standardized magnetic resonance imaging (MRI) protocol, and the occurrence of symptomatic C5 palsy, and to explore its potential discriminative value with postoperative C5 palsy.

A retrospective cohort study was conducted. Patients who underwent single- or double-level ACDF/ACCF for cervical spondylotic myelopathy between January 2019 and December 2023 were included. An initial cohort was identified via surgical log review. Patients with eligible pre- and early postoperative (3 days to 6 weeks) MRI were enrolled. The distance from the anterior surface of the spinal cord to the posterior vertebral body line at the C4/5 and C5/6 levels was measured independently and in a blinded manner by two radiologists. The primary outcome was postoperative symptomatic C5 palsy. Multivariable logistic regression was used to identify independent risk factors, and receiver operating characteristic (ROC) curve analysis was performed to explore the discriminative ability.

One hundred patients were ultimately included, with a C5 palsy incidence of 10.0% (10/100). The C4/5 posterior migration distance was significantly greater in the C5 palsy group than in the non-palsy group (3.42 ± 0.47 mm vs. 2.04 ± 0.76 mm, P < 0.001). Multivariable analysis showed that, after adjusting for age and preoperative intramedullary high signal, C4/5 posterior migration was an independent risk factor for C5 palsy (adjusted odds ratio [aOR] = 2.89, 95% confidence interval [CI]: 1.35–6.20, P = 0.006). ROC analysis revealed that the C4/5 posterior migration distance predicted C5 palsy with an area under the curve (AUC) of 0.86. The optimal cut-off value was 2.85 mm (sensitivity 80.0%, specificity 84.4%).

This retrospective exploratory study suggests that greater early postoperative posterior displacement of the spinal cord at the C4/5 level may be associated with an increased risk of symptomatic C5 nerve root palsy following anterior cervical decompression and fusion. Although a migration distance of 2.85 mm demonstrated preliminary discriminative ability in this cohort, the small number of C5 palsy events and the retrospective single-center design substantially limit the robustness and external applicability of the findings. Therefore, the identified threshold should be considered hypothesis-generating and requires validation in larger prospective multicenter studies before clinical application.