OBJECTIVETo investigate the feasibility of posterior fixation with 3.5-mm pedicle screws in the atlantoaxial vertebrae of children.

METHODSIn this study, atlantoaxial vertebrae specimens were obtained from 10 cadavers of children aged 6-8 years. We measured the height and width of the C(1) pedicle and the midportion of C(1) lateral mass; the width of C(1) posterior arch under the vertebral artery groove and the height of the external and internal one-third of this part; the external, internal height and the superior, middle, inferior width of the C(2) pedicle (transverse foramen). Furthermore, computed tomography (CT) axial scan was performed on 20 age-matched volunteers to obtain relative data of their atlantoaxial vertebrae. We measured the length and width of the C(1) and C(2) pedicles in the atlantoaxial cross-sectional plane. On CT workstation, we also measured the angles between the longitudinal axes of the atlantoaxial pedicles and the midsagittal plane.

RESULTSFor the cadaveric specimen group, the height and width of the C1 pedicle were (5.26+/-0.44) mm and (6.26+/-0.75) mm respectively. The height of the medial one-third of the C1 posterior arch under the vertebral artery groove was (4.07+/-0.24) mm. The external, internal height and superior, middle, inferior width of the C2 pedicle was (6.86+/-0.48) mm, (6.67+/-0.49) mm, (6.63+/-0.61) mm, (5.41+/-0.39) mm and (3.71+/-0.30) mm, respectively. For the volunteer group measured by CT scan, the height and width of the C(1) pedicle were (5.47+/-0.34) mm and (6.63+/-0.54) mm respectively, while (6.59+/-0.51) mm and (5.13+/-0.42) mm of the C2 pedicle. The angles between the atlas, axis pedicles and the midsagittal plane were (9.60+/-1.32) degree and (27.80+/-2.22) degree respectively.

CONCLUSIONIt is feasible to place a 3.5-mm pedicle screw in the C(1) and C(2) pedicles of children aged 6-8 years old.