ABSTRACT
STUDY DESIGN: Retrospective cohort study. OBJECTIVES: We aimed to clarify the clinical relationship between the etiology of proximal-type cervical spondylotic amyotrophy (CSA) and cervical sagittal alignment and instability. SUMMARY OF BACKGROUND DATA: Although several researchers have discussed hypotheses regarding the etiology of CSA, the trigger and mechanism underlying the onset remain unclear. METHODS: We retrospectively analyzed 52 proximal-type CSA patients (CSA group) and 60 control patients (Control group). The following data were collected: age; sex; cervical lordosis (CL); T1 slope (TS); TS-CL; C2-7 sagittal vertical axis (SVA) on x-ray in the neutral position; flexion angle; extension angle and range of motion (ROM) of C3/4, C4/5 and C5/6; and C3/4, C4/5 and C5/6 instability (translation of >3 mm for adjacent segmental segments) on dynamic x-ray. RESULTS: Compared with the Control group, the CSA group was associated with an older age (mean age, 67.6 vs. 61.1 years' old, P= 0.029) and male sex (78.8% vs. 50.0%, P= 0.002). In the CSA group, the radiographic parameters showed smaller C4/5 and C5/6 extension angles and C5/6 ROM values and a greater C3/4 flexion angle than the Control group. Furthermore, compared with the Control group, the CSA group was associated with C3/4 instability (13.5% vs. 3.3%, P= 0.049) and C4/5 (21.2% vs. 3.3%, P = 0.003). A logistic regression analysis, with adjusting for the age and sex, showed that the C3/4 flexion angle (odds ratio [OR], 1.2; 95% confidence interval [CI], 1.08- 1.40, P =0.002), C3/4 instability (OR, 7.3; 95% CI 1.25-42.96, P =0.027) and C4/5 instability (OR, 8.1; 95% CI, 1.56-42.19, P = 0.012) were independent risk factors of CSA. CONCLUSION: This study suggested that a wide C3/4 flexion angle and high C3/4 or C4/5 spinal instability were closely associated with the etiology of proximal-type CSA.
