本研究由回顾性队列研究、系统综述和荟萃分析组成，各自进行。本研究旨在调查Atlas弓缺损的患病率，生成基于证据的综合分析，并提出前弓和合并弓缺损的通用分类系统。Atlas弓缺损指的是Atlas前弓或后弓部位有良性结晶突缺损。当两者同时存在时，称之为合并弓缺损。了解这些缺损对于避免上脊柱手术并发症至关重要。我们通过包含606例咽喉癌患者头颈部计算机断层扫描的公开数据库OPC-Radiomics (Radiomic Biomarkers in Oropharyngeal Carcinoma) 进行弓缺损患病率的调查。通过系统综述和荟萃分析，得出前弓和合并弓缺损的患病率估计，并提出一个分类系统。我们发现，在所研究的606例患者中，20例患者（3.3%）表现为后弓缺损。前弓缺损在任何患者中均未观察到，而合并弓缺损在1例患者中观察到（0.2%）。纳入了本研究的14项研究共计13,539名参与者的荟萃分析结果显示，后弓缺损的总体患病率为2.07%（95%可信区间[CI]，1.22%-2.92%）。前弓和合并弓缺损的患病率分别为0.00%（95% CI，0.00%-0.10%）和0.14%（95% CI，0.04%-0.25%）。根据形态学和频率，我们将前弓和合并弓缺损分为五个亚型。本研究表明，大约在2%左右的普通人群中存在Atlas弓缺损。未来的研究应该使用更大的样本量来研究弓缺损，以避免小样本效应，并准确预测患病率。

This study consists of a retrospective cohort study, a systematic review, and a meta-analysis which were separately conducted. This study aimed to investigate the prevalence of atlas arch defects, generate an evidence-based synthesis, and propose a common classification system for the anterior and combined atlas arch defects. Atlas arch defects are well-corticated gaps in the anterior or posterior arch of the atlas. When both arches are involved, it is known as a combined arch defect. Awareness of these defects is essential for avoiding complications during surgical procedures on the upper spine. The prevalence of arch defects was investigated in an open-access OPC-Radiomics (Radiomic Biomarkers in Oropharyngeal Carcinoma) dataset comprising 606 head and neck computed tomography scans from oropharyngeal cancer patients. A systematic review and meta-analysis were performed to generate prevalence estimates of atlas arch defects and propose a classification system for the anterior and combined atlas arch defects. The posterior arch defect was found in 20 patients (3.3%) out of the 606 patients investigated. The anterior arch defect was not observed in any patient, while a combined arch defect was observed in one patient (0.2%). A meta-analysis of 13,539 participants from 14 studies, including the present study, yielded a pooled-posterior arch defect prevalence of 2.07% (95% confidence interval [CI], 1.22%-2.92%). The prevalences of anterior and combined arch defects were 0.00% (95% CI, 0.00%-0.10%) and 0.14% (95% CI, 0.04%-0.25%), respectively. The anterior and combined arch defects were classified into five subtypes based on their morphology and frequency. The present study showed that atlas arch defects were present in approximately 2% of the general population. For future studies, larger sample sizes should be used for studying arch defects to avoid the small-study effect and to predict the prevalence accurately.