Digital 3D simulation study on posterior occipital condyle screw fixation

English Keywords:Ddigital  Occipital condyle  Occipital condyle screw  Occipitocervical fusion

English Abstract:

  【Abstract】 Objectives: To measure the best parameters for placing occipital condyle screw in posterior approach, and to discuss the safety of surgical procedure and the correlation among parameters by using digital 3D reconstruction technology. Methods: Fifty cases with occipital spiral CT data were randomly selected from the normal outpatients which meant no fracture, dislocation, infection, cancer, deformity or degeneration, including 25 males and 25 females with the age ranging from 25 to 60 years(average, 38.5±7.6 years). Then the obtained CT data were input into Mimics to reconstruct occipital bone and atlas. 3.5mm occipital condyle screw was simulated placing, the length, width and height of occipital condyle were measured, then the distances from the nailing point to the medial edge of occipital condyle and to the basis cranii were calculated. After that, the length, cranial angle, medial angle and tangent angle between nail and occipital tangent were measured by 3-matic. Results: A total of 100 occipital condyle screws were simulated to place, and there was no injury on hypoglossal canal, atlas joint surface, the medial or lateral wall of occipital condyle in 3D model. Left and right occipital condyle anatomical parameters, nailing point parameters and simulation nailing setting parameters were slightly different, but there was no statistical significance(P>0.05). The anatomical parameters of length, width and height of male occipital condyle, the horizontal distance from the nailing point to medial occipital condyle, and the vertical distance from the nailing point to the basis cranii of male were 22.00±1.67mm, 11.27±1.21mm, 10.72±1.13mm, 5.37±0.10mm and 2.95±0.47mm respectively, while those parameters of female were 21.07±1.43mm, 10.64±0.81mm, 9.62±0.95mm, 5.05±0.10mm, and 3.04±0.48mm respectively. The anatomical parameters of length, width and height of female occipital condyle, and the horizontal distance from the nailing point to medial occipital condyle of female were smaller than those of male obviously(P<0.05), but it showed no statistical significance in the parameter of vertical distance from nailing point to basis cranii between male and female(P>0.05). The cranial angulation, tangent angulation, medial angulation and nailing length measured after simulation nailing setting in male were 3.90°±2.01°, 12.45°±4.73°, 28.15°±4.53°, 22.47±1.48mm, which were 4.19°±2.01°, 11.25°±4.61°, 30.00°±4.70°, 21.59±1.62mm in female respectively, the nailing length of female was shorter than that of male(P<0.05), but there was no statistical significance in cranial angulation, tangent angulation or medial angulation between male and female(P>0.05). There was positive correlation between cranial angulation and tangent angulation(r=0.519, P<0.05), and there was no correlation of cranial angulation with the rest parameters of simulation nailing setting. Conclusions: The anatomical parameters of occipital condyle of female were smaller than those of male, screws can be safely placed in the occipital condyle under 3D reconstruction redardless of gender. Tangent angulation combine with nailing point and medial angulation can assist in safe placement of occipital condyle screws in theory.