Anatomical measurement of bicortical C1 anterior arch screw fixation

English Keywords:Anterior arch of atlas  Measurement  Bone spine reconstruction  Adjustable bicortical screw

English Abstract:

  【Abstract】 Objectives: To guide the insertion of the atlantoaxial bicortical screw by measuring the anatomical structure of the atlantoaxial anterior arch bicortical screw fixation, so as to provide reliable data for the design of bicortical adjustable screw that fits the atlas anatomy. Methods: 99 three-dimensional(3D) CT reconstructions of upper cervical spine of the patients in the outpatient service and the inpatient department from April 2017 to August 2018 were reviewed and analyzed. There were 54 males aged 31-81 years old(average 56.67±10.56 years old), height 159-180cm(average 172.24±4.95cm), weight 55-90kg(average 70.24±7.57kg), 45 females aged 46-77 years old(average 59.84±8.29 years old), height 154-171cm(average 163.11±5.24cm), weight 40-80kg(average 59.31±8.48kg). Through the three-dimensional measurement software, the distance between the midpoint of anterior nodule and the midpoint of posterior margin of the odontoid(DAP), the length of bilateral vertical titanium plate screw in the vertical direction(LVD), the length of bilateral vertical titanium plate screw in direction toward the midpoint of the odontoid posterior margin(DMOP), the tail extraversion angle of screw toward the midpoint of the odontoid posterior margin(TEA) was measured and the height of bilateral anterior arch in placing screw of the atlas(HAA) was measured. Patients were divided into groups according to gender. The quantitative data of different groups were compared by t test (homoscedasticity) or Satterthwaite t′ test (heteroscedasticity); the paired t test was used for the comparison of left and right sides. Simple linear regression was used to analyze the relationship between age and previous measurements. In addition, Pearson correlation coefficient and simple linear regression were used to analyze the relationship between height, weight and previous measurements. Results: The numerical differences of the symmetrical sides of LVD, DMOP, TEA and HAA were not statistically significant(P>0.05). The average measured data of DAP, LVD, DMOP, TEA, HAA in male group were 21.33±1.12mm, 8.92±1.48mm, 8.37±1.49mm, 13.20°±0.93° and 12.44±0.48mm respectively. The average measured data of DAP, LVD, DMOP, TEA, HAA in female group were 20.01±1.33mm, 8.18±1.56mm, 7.67±1.58mm, 13.88°±1.38° and 12.08±0.75mm respectively. Moreover, compared to female patients, male patients showed larger DAP, LVD, DMOP and HAA. In contrast, TEA of the female patients was larger than that of the male patients, which was statistically significant(P<0.05). However, there was no statistically significant correlation between height of patient and LVD as well as DMOP in both groups(P>0.05). Pearson correlation analysis showed that there was a significant negative correlation between the height and TEA in both groups(r=-0.123, P<0.05). There was no statistically significant correlation between age and other parameters(P>0.05). Conclusions: Compared to female patients, male patients show greater DAP, LVD, DMOP and HAA. In contrast, TEA of the female patients is larger than that of the male patients, which is statistically significant. According to the patient′s gender and related parameters, the surgeon can select the appropriate screw to improve the accuracy and safety of the screw placing into the anterior arch of atlas.