Analysis of functional outcomes and risk factors for facet joint distraction during anterior cervical discectomy and fusion for cervical spondylotic myelopathy

This study aimed to clarify functional outcomes of facet joint distraction (FJD) and identify specific risk factors for excessive FJD during single-level anterior cervical discectomy and fusion (ACDF) for cervical spondylotic myelopathy (CSM). This study retrospectively analyzed 100 patients who underwent single-level ACDF for CSM from January 2016 to May 2020. Anteroposterior and lateral radiographs were obtained before surgery and 12 months after surgery. Radiographic parameters including anterior intervertebral height (AIH), posterior intervertebral height, facet joint gap, cage posterior depth (CPD), upper vertebral length, cervical segmental Cobb angle (CSCA), C2–C7 Cobb angle, and C2–C7 sagittal vertical axis were analyzed. Functional outcomes were evaluated using the modified Japanese Orthopedic Association Score , visual analog scale (VAS), and Neck Disability Index (NDI). Comparison between the appropriate FJD and excessive FJD groups showed statistically significant differences in the NDI, VAS, CPD, and ΔAIH ( P < 0.05). Multivariate logistic regression analysis showed that independent factors associated with excessive FJD were as follows: a ΔAIH > 2.28 mm (odds ratio [OR] = 6.792, 95% confidence interval [CI] = 1.885–24.470, P = 0.003), CPD > 12.45 mm (OR = 5.876, 95% CI = 1.828–18.895, P = 0.003), and post-CSCA < 0° (OR = 6.251, 95% CI = 1.275–30.633, P = 0.024). Furthermore, receiver operating characteristic curve analysis for the multilevel logistic regression model produced an area under the curve of 0.783 ( P < 0.001). Patients with an FJD of >0.905 mm had worse NDI and VAS pain scores, but not a poorer modified Japanese Orthopedic Association Score recovery rate. Our findings suggested that a ΔAIH > 2.28 mm, CPD > 12.45 mm, and post-CSCA < 0° were independent risk factors for excessive FJD after single-level ACDF for CSM.