• Wei Ji, Minghui Zheng, Ganggang Kong, Dongbin Qu, Jianting Chen, and Qingan Zhu.
• Department of Spinal Surgery, Nanfang Hospital, Southern Medical University, Guangzhou, China.
• Spine. 2015 Sep 1.

Study DesignA CT-based study of pediatric atlas.ObjectivesTo identify morphometric patterns and dimensions of the pediatric C1 posterior arch to establish guidelines for the posterior arch crossing screw (PACS) fixation.Summary Of Background DateThe PACS fixation is an alternative or supplement to the C1 lateral mass screw or pedicle screw constructs. However, the anatomic feasibility of this technique has not been well documented in the pediatric population.MethodsA total of 123 pediatric patients were assigned into six groups based on age at an interval of three years. The C1 posterior arch unsuited to PACS fixation was classified as type 1 with synchondrosis, and type 2 without synchondrosis. Three subtypes of type 2 were included: the underdeveloped tubercle, the flat arch and the undersized tubercle (height<7 mm or width<3.5 mm), respectively. The C1 posterior tubercle height and arch width, the projected PACS length and angle were measured, respectively.ResultsThere were 19 patients of type 1 and 68 patients of type 2. Type 1 was mostly found in patients under age 3 years, whereas type 2 was largely observed in patients older than 4 years. The tubercle size was the most limiting variable for successful PACS placement. The PACS fixation was feasible for 42% patients over age 7 years and only 5% patients under age 6 years. The posterior tubercle height was increased with age, while the tubercle width, the PACS length and axial-plane angle were increased with age up to 12 years. The PACS length was between 16 and 18 mm with the angle between 18° and 23° for patients over age 7 years.ConclusionsThe PACS fixation was anatomically feasible in patients over age 7 years, but contraindicated in patients under age 6 years. Pediatric patients for the PACS fixation should be assessed before surgery.Level Of Evidence4.

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