The impact of the size of atlas pedicle medullary canal on C1 pedicle screw placement

English Keywords:Atlas  Pedicle  Medullary canal  Screw fixation  Anatomy

English Abstract:

  【Abstract】 Objectives: To investigate the impact of the size of atlas pedicle medullary canal on C1 pedicle screw placement. Methods: From patients who underwent posterior atlantoaxial fixation between January 2009 and June 2012, those with an age ≥20 year, and with the height of the C1 pedicle greater than 4mm were included in our study. 97 patients met the inclusion criterion. There were 41 males and 56 females, with an average age of 41.6 years(range, 20-79 years old). If the placement of atlas pedicle screws failed, then an alternative approach such as C1 lateral mass screws or lamina clamps were used. 145 pedicle screws were implanted successfully, but the other 49 atlas pedicle screw placements failed, subsequently other fixation methods were used. The height of the medullary canal of all patients′ pedicles were measured by using computed tomography(CT) multi-planar reconstruction technique. The pedicles of the atlas were classified into 3 types according to the size of the medullary canal. Type Ⅰ: the height of the medullary canal ≥2mm; type Ⅱ: the height of the medullary canal ＜2mm; type Ⅲ: no medullary canal in the pedicle. The percentage of atlas pedicle screw fixation in each type of pedicles was calculated, and the differences among the three types were compared. Results: In the pedicle screw fixation group, the number(percentage) of the pedicles of type Ⅰ, type Ⅱ, type Ⅲ was 104(71.7％), 39(26.9％), 2(1.4％)respectively; while in the non-pedicle screw fixation group, the number(percentage) of the pedicles of type Ⅰ, type Ⅱ, type Ⅲ was 2(4.1％), 28(57.1％), 19(38.8％) respectively. The percentage of atlas pedicle screw fixation in type Ⅰ, type Ⅱ, type Ⅲ pedicle was 98.1％(104/106), 58.2％(39/67), 9.5％(2/21), respectively. The percentage of C1 pedicle screw fixation in type Ⅰ pedicle was greater than type Ⅱ and type Ⅲ, and the percentage of C1 pedicle screw fixation in type Ⅱ pedicle was greater than type Ⅲ(P<0.001). Conclusions: The size of the medullary canal of the atlas pedicle is critical in atlas pedicle screw placement. When the size of the medullary canal of the atlas pedicle is ≥2mm, pedicle screw fixation is suggested; when it is ＜2mm, various fixation techniques can be considered based on the technology of the surgeon; pedicle screw fixation is not suggested when there is no medullary canal in the pedicle.