• Norimasa Ikeda, Seiichi Odate, and Jitsuhiko Shikata.
• Department of Orthopedic Surgery, Spine Center, Gakkentoshi Hospital, Seikadai, Sorakugun, Kyoto, Japan. Electronic address: i22525@yahoo.co.jp.
• World Neurosurg. 2020 Jan 1; 133: e233-e240.

BackgroundCompensatory mechanisms for cervical kyphosis are unclear. Few alignment analyses have targeted ongoing cervical kyphosis and detailed the effects of compensatory alignment changes.MethodsWe analyzed the radiographic alignment parameters of 31 patients (21 men and 10 women) with postoperative kyphotic changes 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 2 time points after surgery.ResultsAlignment analysis revealed that CL was significantly decreased by 5.0 ± 7.7° (P < 0.01) and O-C7a was changed by only -0.2 ± 6.8° (P = 0.75). An inverse correlation was found between ΔCL and ΔO-C2a (ρ = -0.40), with a nearly 1:1 relationship in the scatter diagram. ΔT1 slope had no direct compensatory correlation with ΔCL (P = 0.28) but was strongly correlated with ΔcSVA (ρ = 0.78). The scatter diagram of ΔcSVA and ΔT1 slope showed compensatory relevance and a shifted point to its collapse as the T1 slope lost control of cSVA; thereafter, both parameters incessantly increased, and ΔT1 and ΔcSVA became positive.ConclusionsWhen CL decreased after ACCF, ΔO-C2 immediately compensated for the CL loss that could lead to failure to obtain horizontal gaze. If cSVA increased, Δcaudal adjacent angle and ΔT1 slope (extension below the kyphosis) compensated for the horizontal offset translation. The noncompensatory status (ΔcSVA and ΔT1 positive) may necessitate further correction surgery in which the caudal fused level is beyond T1.Copyright © 2019 Elsevier Inc. All rights reserved.

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