| Objective:The morphological development and aging characteristics of the foramen magnum(FM)and occipital condyle(OC)were observed by three-dimensional reconstruction,which provided the basis for determining the gender of the unknown skeleton and anatomical parameters for the clinical approach to the far lateral skull base.Methods:Retrospectively analyzed 1074 normal head and neck CT images that taken by the Imaging Center of The Affiliated Hospital of Inner Mongolia Medical University,They were divided into <20 years old group and ≥20 years old group.The <20 years old group was divided into 6 subgroups: 0 ～years old group,4 ～ years old group,7 ～ years old group,10 ～ years old group,13 ～ years old group,16 ～ 19 years old group.The ≥20 years old group was divided into five subgroups: 20～ age group,0 ～ age group,40 ～ age group,50 ～ age group and ≥60 years old group.Mimics software was used to reconstruct the skull base,and the following loci were selected on the coordinate axis: 1.Anterior midpoint of foramen magnum.2.Midpoint of posterior margin of foramen magnum.3.Midpoint of lateral margin of foramen magnum.4.Lateral margin intersection of occipital condyle and foramen magnum.5.Midpoint of posterior wall of inner orifice of sublingual neural tube(HC).6.Anterior end of long axis of occipital condyle.7.Posterior end of long axis of occipital condyle.8.Midpoint of medial margin of occipital condyle.9.Midpoint of lateral margin of occipital condyle.Measurement indicators:Foramen magnum:1.Maximum length.2.Maximum width.3.Occipital condyle: 1.Length of occipital condyle.2.Occipital condyle width.3.Anterior condylar spacing.4.Posterior condylar spacing.5.Angle between occipital condyle long axis and median sagittal axis(∠O-S).6.Angle between the line connecting the midline point of the anterior and posterior margin of the foramen magnum and the line connecting the midpoint of the anterior edge of the foramen magnum to the intersection of the occipital condyle and the lateral edge of the foramen magnum(∠F-O).Angle between the line between the midpoint of the anterior and posterior edges of the foramen magnum and the midline point of the anterior margin of the foramen magnum and the midpoint of the posterior wall of the inner orifice of HC(∠F-H).Paired T test was used for gender and side,one-way an OVA was used for comparison of multiple text岁 means for the same index in different age groups,discriminant analysis was used to deduce the accuracy of gender inference for each index.Results:1.Foramen magnum(FM):In <20years old group and ≥20 years old group,FML,FMW and FMA were larger in male than in female(P <0.05),and FML was larger than FMW.2.Occipital condyle(OC):in both groups,OCL and AICD larger in male than in female(P<0.05),and∠ O-S was smaller in male than in female,and the ∠ F-O was larger in male than in female.3.Morphological parameters of FM and OC change with age:In <20 years old group:FML,FMW,FMA and FMI increased(the maximum value was in 10～12 years old group).OCW,AICD and PICD also increased(the maximum values were all in 16 ～ 19 years old group),while∠O-S and∠F-O were decreasing,and∠F-H was increasing.In ≥20 years old group:FMW,FMA,FMI,OCW,AICD,PICD,∠O-S,∠F-O and ∠F-H all showed a decreasing trend.4.Discriminant analysis accuracy of FM and OC morphological parameters: In <20 years old group:The highest single factor discriminant index of FM was FM area(67.2%,female),and the highest multiple factor discriminant index was FM area(67.2%,female).The highest single factor discriminant index of OC parameters was left occipital condyle length(66.4%,female),and the highest multiple factor was 67.2%(female).In ≥20 years old group:The single factor discriminant of FM parameter was highest in FM area(68.4%,female),and the multiple factor was highest in FM area(64.9%,female).The highest single factor of OC was left occipital condyle width(75.2%,female),while the highest multifactor was 68.8%,male).Conclusion:1.The parameters of foramen magnum were different between genders.The maximum length,width and area of the foramen magnum in the two age groups were larger in males than in females,which could be used for gender identification.2.The linear parameters of occipital condyle were different between males and females.The length,width and distance between occipital condyle were larger in males than in females.The length of occipital condyle,anterior condyle and posterior condyle in ≥20 years old group were larger in male than in female,which could be used for sex identification.3.The Angle parameters of occipital condyle were different between genders.∠O-S in the two age groups was smaller than that of female.∠F-O in the two age groups is larger than that of the female,so the gender difference should be considered in the distal lateral approach.4.The parameters of occipital condyle were different between in the two age groups.The length,width and ∠ O-S of occipital condyle were all larger on the left than on the right.∠F-O and Angle F-H in the two age groups were both smaller on the left than on the right,and the exposure range was relatively large and safe when the distal lateral approach entered through the right side.5.The highest accuracy of discriminant analysis was different between genders,and the parameters of foramen magnum were lower in males than in females in the two age groups.The parameters of occipital condyle in <20 years old group were lower in male than in female,but higher in ≥20 years old group.The highest accuracy of discriminant analysis of parameters of occipital condyle in ≥20 years old group was higher than that of foramen magnum,and the highest accuracy of discriminant analysis of width of left occipital condyle was 75.2%,which could be used for sex identification.6.The parameters of the foramen magnum and the occipital condyle differed with age in terms of development time,the former reached its peak at 13 years old,while the latter reached its peak at 19 years old. |
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