Association between Cervical Posterior Spondylolisthesis and Cervical Sagittal Alignment: The Role of T1 Slope in Pathophysiology.

Introduction: Degenerative cervical spondylolisthesis is associated with aging, neck pain, and myelopathy. While anterior spondylolisthesis (AS) has been extensively studied in relation to cervical sagittal parameters, posterior spondylolisthesis (PS) remains poorly understood despite its potential to cause myelopathy. This study investigates the association between PS and cervical sagittal parameters to elucidate its pathophysiology. Methods: This retrospective study included 169 patients who underwent cervical spine surgery to treat cervical myelopathy, classified into 3 groups: PS, AS, and a control group without spondylolisthesis. Variables assessed included age, sex, body mass index, smoking history, T1 slope, sagittal vertical axis C2-C7 (SVA C2-C7), C2-C7 angle, C2-C7 range of motion, C1-C2 angle, and cervical disk degeneration (summed Pfirrmann grades). Logistic regression analysis was conducted to identify factors significantly associated with PS, and comparisons were made between the PS and AS groups. Results: Of the 169 participants, 58 had PS, 22 had AS, and 89 formed the control group. A T1 slope ≥29° was significantly associated with PS (odds ratio: 1.090, p=0.005). PS was more common in younger men with mild disk degeneration, while AS was more frequent in older women with severe disk degeneration. Patients with PS exhibited larger C2-C7 angles and smaller SVA C2-C7 compared to those with AS. A high T1 slope appeared to induce a compensatory increase in the C2-C7 angle, generating posterior shear force that may have contributed to the development of PS. Conclusions: A T1 slope of ≥29° was associated with PS. Our findings suggest that a compensatory mechanism related to a high T1 slope may play a role in the pathophysiology of PS, providing new insights into its development in cervical spinal disorders.