Anatomical basis of screw fixation through lateral arch of C2 vertebra

    HOU Liª²Sheng, JIA Lianª²Shun, TAN Jun, RUAN Diª²Ke, YE Xiaoª²Jian, WANG Renª²Peng3, HE Qing

    1Department of Orthopaedics, Navy General Hospital, Beijing 100037, China, 2Department of Orthopaedics, Changzheng Hospital, Second Military Medical University, Shanghai 200003, China, 3Department of Architecture Engineering, Tongji University, Shanghai 200093, China

    ¡¾Abstract¡¿ AIM: To provide the anatomical basis for lateral arch screw fixation in C2 vertebra of Chinese. METHODS: Fiftyª²seven dry C2 vertebra of Chinese were measured. RESULTS: The parameters obtained of anterior portion of lateral arch were (including Left/Right): Medial inclination from superior view [ ¦Ás = (38¡À8)¡ã/(40¡À8)¡ã], superior inclination [¦Ã = (63¡À9)¡ã/(62¡À8)¡ã], and the superior, middle and inferior width [bs = (7.4¡À1.7) mm/(6.9¡À1.7) mm, bm = 5.2¡À1.4 mm/5.2¡À1.4 mm. bi = (4.2¡À1.1) mm/(4.2¡À1.0) mm], height of superior articular process [dsa = (2.1¡À0.9) mm/(2.0¡À0.9) mm], superior and inferior height [hup=(5.1¡À1.4) mm/(5.0¡À1.4) mm, hip=(6.1¡À1.5) mm/(5.8¡À1.2) mm]. Other parameters were (including Left/Right ): Horizontal distance from standard screw entrance point (O) to lateral edge of inferior articular process [lla= (4.2¡À1.2) mm/(3.9¡À1.1) mm], posterior edge of superior articular process [los= (6.4¡À1.5) mm/(5.0¡À1.5) mm] and midª²position of isthmus on superior aspect [loi = (4.4¡À1.3) mm /(2.6¡À1.3) mm], and vertical distance from O to inferior edge of inferior articular process [hia=(9.4¡À1.6) mm/(9.4¡À1.8) mm]. bm in 26 (45.61%)left and 27(47.37%)right sides was less than 5.00 mm. If set ¦Ás as medial inclination of lateral screw insertion, 36 left screws and 40 right ones would penetrate into the corresponding side of anterior structure of C2 vertebra, and if set ¦Ã as superior angle, all screws would violate the superior facet of axis. CONCLUSION: Neither ¦Ás nor ¦Ã can guarantee safe and applicable screw insertion of lateral arch. If set 5.0 mm width of middle part of anterior portion of lateral arch as the technical difficult limit, almost one half of C2 vertebra will not be suitable for 3.5 mm screw insertion. ......