Background: 

Cervical alignment is vital for maintaining horizontal gaze and sagittal balance. The aims of this study were to summarize previously published descriptions of normative cervical alignment and to analyze a cohort of asymptomatic volunteers in order to identify natural clusters of normal radiographic parameters.

Methods: 

We performed a systematic review of the literature on radiographic measurements of asymptomatic volunteers through a search of MEDLINE and ScienceDirect databases. We then performed an analysis of demographic and radiographic parameters of volunteers without back or neck complaints. Only subjects with a chin-brow vertical angle (CBVA) within previously published normal limits were retained for analysis. A 2-step cluster analysis was used to find natural groups of cervical alignment. Differences among groups were investigated with a post hoc analysis of variance (ANOVA).

Results: 

We included 37 articles in our analysis. There was a broad spectrum of both C2-C7 lordosis-kyphosis and T1 slope across ages and sexes. Of the 119 asymptomatic volunteers who were available for analysis, 84 (with a mean age [and standard deviation] of 49.0 ± 17.1 years) had a CBVA ranging from −4.7° to 17.7°. The cluster analysis identified 3 alignment groups based on cervical lordosis-kyphosis and T1 slope (silhouette measure of cohesion, >0.6). Twenty-seven volunteers (32.1%) were identified as the “kyphotic curve cohort” (KCC) (mean C2-C7 Cobb angle, −8.6° ± 7.3°; mean T1 slope, 17.4° ± 6.6°), 43 volunteers (51.2%) were identified as the “medium lordosis cohort” (MLC) (mean C2-C7 Cobb angle, 8.7° ± 7.2°; mean T1 slope, 26.6° ± 4.0°), and 14 volunteers (16.7%) were identified as the “large lordosis cohort” (LLC) (mean C2-C7 Cobb angle, 21.2° ± 7.2°, mean T1 slope, 39.5° ± 6.4°) (p < 0.001 for both). Moving from KCC to LLC, there was a significant decrease in C0-C2 lordosis (p = 0.016). Examination of the cervical vertebral orientation demonstrated that C4 had a constant orientation relative to the horizontal (p = 0.665). Correlation analysis between C2-C7 and vertebral orientations again demonstrated that C4 orientation was independent of C2-C7 alignment.

Conclusions: 

We have identified 3 morphotypes of the cervical spine based on C2-C7 alignment and T1 slope. These findings demonstrate the broad definition of normal cervical alignment and the range of cervical lordosis-kyphosis that is acceptable.

中文翻译：

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定义正常颈椎的 3 种矢状形态：文献的系统回顾和无症状志愿者的分析。

 背景：

颈椎对齐对于维持水平凝视和矢状平衡至关重要。本研究的目的是总结之前发表的规范颈椎排列的描述，并分析一组无症状志愿者，以确定正常放射学参数的自然集群。

 方法：

我们通过检索 MEDLINE 和 ScienceDirect 数据库，对无症状志愿者的放射学测量文献进行了系统回顾。然后，我们对没有背部或颈部不适的志愿者进行了人口统计和放射学参数分析。仅保留下巴-眉毛垂直角 (CBVA) 在先前公布的正常范围内的受试者进行分析。使用两步聚类分析来寻找颈椎排列的自然组。通过事后方差分析（ANOVA）研究组间差异。

 结果：

我们的分析中纳入了 37 篇文章。 C2-C7 脊柱前凸-后凸和 T1 斜率在不同年龄和性别中均存在广泛的谱系。在可供分析的 119 名无症状志愿者中，84 名（平均年龄[和标准差]为 49.0 ± 17.1 岁）的 CBVA 范围为 -4.7° 至 17.7°。聚类分析根据颈椎前凸-后凸和 T1 斜率（内聚力轮廓测量值，>0.6）确定了 3 个排列组。 27 名志愿者 (32.1%) 被确定为“后凸曲线队列”(KCC)（平均 C2-C7 Cobb 角，-8.6° ± 7.3°；平均 T1 斜率，17.4° ± 6.6°），43 名志愿者（51.2 %）被确定为“中等前凸队列”（MLC）（平均 C2-C7 Cobb 角，8.7° ± 7.2°；平均 T1 斜率，26.6° ± 4.0°），14 名志愿者（16.7%）被确定为“大脊柱前凸队列”(LLC)（平均 C2-C7 Cobb 角，21.2° ± 7.2°，平均 T1 斜率，39.5° ± 6.4°）（两者均 p < 0.001）。从 KCC 转移到 LLC，C0-C2 脊柱前凸显着下降 (p = 0.016)。颈椎方向的检查表明 C4 相对于水平面具有恒定的方向 (p = 0.665)。 C2-C7 和椎骨方向之间的相关性分析再次证明 C4 方向与 C2-C7 对齐无关。

 结论：

我们根据 C2-C7 排列和 T1 斜率确定了颈椎的 3 种形态类型。这些发现证明了正常颈椎排列的广泛定义以及可接受的颈椎前凸-后凸范围。