• Qunfeng Guo, Bin Ni, Jian Yang, Kai Liu, Zhichao Sun, Fengjin Zhou, and Jianxin Zhang.
• Department of Orthopedics, Changzheng Hospital, The Second Military Medical University, 415 Fengyang Road, Huangpu District, Shanghai 200003, People's Republic of China.
• Arch Orthop Trauma Surg. 2011 Jun 1; 131 (6): 857-62.

ObjectiveTo reveal the relation between alignments of upper and subaxial cervical spine and deduce the optimal atlantoaxial fusion angle by a radiological study.Methods414 asymptomatic volunteers (213 males, 201 females) underwent cervical lateral radiographs in neutral position. The Oc-C2 angle, C1-C2 angle and C2-C7 angle were measured. Relations among these three angles and relations between angles and age were analyzed.ResultsThe mean Oc-C2 angle was 16.3° ± 7.0° in females, significantly larger than 14.9° ± 6.5° in males. The mean C1-C2 angles were 28.2° ± 4.0° in females and 26.4° ± 4.6° in males, and C2-C7 angles were 12.7° ± 6.6° and 16.3° ± 7.3°, correspondingly. The mean C1-C2 angle in females was significantly larger than that in males, while C2-C7 angle smaller than that in males. The C2-C7 angle correlated significantly not only with C1-C2 angle but also with Oc-C2 angle. And correlation between C1-C2 angle and C2-C7 angle was stronger than that between Oc-C2 angle and C2-C7 angle. There were also significant positive correlations between C1-C2 and Oc-C2 angles. Oc-C2 angle, C1-C2 angle, and C2-C7 angle correlated significantly with age in both sexes.ConclusionsThere were negative correlations between C1-C2 angle and C2-C7 angle as well as between Oc-C2 angle and C2-C7 angle, and the former correlation was stronger. C1-C2 fixation angle was the key to regulate postoperative subaxial alignment in atlantoaxial arthrodesis. The optimal atlantoaxial fusion angle may be between 25° and 30°.

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