Compensatory mechanisms for kyphotic change in the cervical spine according to alignment analysis of the cases after anterior cervical corpectomy and fusion

Abstract Background Compensatory mechanisms for cervical kyphosis are unclear. Few alignment analyses targeted on ongoing cervical kyphosis and detailed each effect of compensatory alignment change. Methods We analyzed the radiographic alignment parameters of 31 patients (men=21, women=10) with postoperative kyphotic change after anterior cervical corpectomy and fusion (ACCF) (between 2006 and 2015). This analysis included lordotic angle of the fusion area, fusion-area length, cervical lordosis angle (CL), O-C7 angle (O-C7a), and cervical sagittal vertical axis (cSVA) as basic parameters and occipito-C2 angle (O-C2a), adjacent cranial angle, adjacent caudal angle, and T1 slope as compensatory parameters at two time points after surgery. Results Alignment analysis revealed that CL significantly decreased by 5.0±7.7° (p Conclusions If CL decreased after ACCF, ΔO-C2 immediately compensated the CL loss that could lead to failure of obtaining horizontal gaze. If cSVA increased, Δcaudal adjacent angle and ΔT1 slope (extension below the kyphosis) compensated the horizontal offset translation. The uncompensatory status (ΔcSVA and ΔT1 were positive) may demand further correction surgery in which the caudal fused level is beyond T1.