Shimizu T, et al. - In this investigation, researchers examined the normative value of the distance between the spinous processes (inter-spinous process distance, ISPD), correlations between the demographics of patients and ISPD, and determined cutoff values of ISPD, which lead to segmental lordosis in posterior cervical-thoracic arthrodesis with instrumentation. For this investigation, patients with visible lower cervical and cervicothoracic spinous processes (C5-T2) on dynamic X-rays were reviewed. The following cutoff values of ISPD provided 100% positive predictive value for segmental lordosis on the basis of the receiver operating characteristics (ROC) curves: < 10 mm at C5-6; < 15 mm at each level from C6 to T2. Findings suggested that ISPD is a simple and useful parameter corresponding to the segmental Cobb angle. Surgeons can intraoperatively anticipate adequate segmental lordosis by utilizing the vertebral level specific cutoff values of ISPD during posterior cervical deformity surgery.