Estimating Sex from second and seventh cervical vertebras in Iranian adult population using Computed Tomography scan images

Objectives The study aimed to estimating the sex from several metric dimensions of second and seventh cervical vertebras using Computed Tomography (CT) scan images of a series of Iranian adult populations. In this study, sexual dimorphism of 15 indexes of second cervical vertebra and 10 indexes of the seventh cervical vertebra were investigated. Indexes were obtained from CT scan images of 70 patients who underwent CT scan imaging for other indications. Results Among measured dimensions of the second vertebra, 9 were associated with sex. Of these indexes, Maximum width of the superior Facet and Maximum height of axis were independent predictors of sex with correct sex classi�cation of 81.4% when used in combination. Four of 10 seventh vertebra’s indexes were associated with sex: Length of superior facets, Length of the inferior surface of the vertebral body, Width of the inferior surface of the vertebral body, and the Length of spinous process. Length of the inferior surface of the vertebral body and the Length of spinous process were independent sex predictors and together provided sex classi�cation accuracy of 78.6%. We found considerable accuracy in sex classi�cation by using metric dimensions of second and seventh cervical vertebras in the Iranian adult population.

The aim of the current study was focus on the level of sexual accuracy in the second and seventh cervical vertebrae to establish an accurate sex estimation method using measurement data obtained from the CT scan imaging of Iranian skeletal populations.

Study Design and Participants
This cross-sectional study was carried out on sexuality accuracy of several metric dimensions of second and seventh cervical vertebrae using CT scan imaging of a series of Iranian adult population.Seventy cases (35 females and 35 males) aged 18 and above, who have undergone imaging for other reasons in Hazrat-Rasool Hospital were selected.All cases were selected via multi-level cluster random sampling.

Inclusion and Exclusion Criteria
Patients who were ≥ 18-year old age and underwent CT imaging according to their physician's advice were included in this study.Cases under the age of and who had a history of the following disorders were excluded from the study:

History of neck trauma with any severity
Having structural or anatomical abnormalities in the neck area History of rheumatologic disorders with neck involvement History of any type of surgery, regenerative or therapeutic intervention in the neck area

Statistical Analysis
The collected data were analyzed using the SPSS version 21.To test the relationship between qualitative variables, Chi-squared test was used.Quantitative variables were compared between the two groups by Ttest.Pearson correlation test was used to examine the relationship between quantitative variables such as age and dimensions of vertebrae.Logistic Regression Model was applied to determine the independent predictor variables of gender and was selected as the reference in female gender regression.Statistically signi cant level was < 0.05.

Data Collection
The following indices of second and seventh cervical vertebrae were measured to determine sexual dimorphism using CT scan imaging of the cases.

Results
A total of 70 cases (35 females and 35 males) with the mean age of 40.91 ± 14.85 years (18-82) participated in this study.Data showed that there is no signi cant difference between male and female groups in this study (p-value = 0.8).The characteristics of the 10 and 15 indices of each cervical vertebra in the whole population are described in Tables 1.A total of 9 out of 15 indices measured in the second cervical vertebra were signi cantly different in males and females (p-value < 0.05).The AMA, LMA, DSD, DMFS, CMSF, LMFS, AMD, DSMC, and LMFI indices were signi cantly higher in males than in females Table 2. Four out of 10 indices measured in the seventh cervical vertebra were signi cantly different in males and females (p-value < 0.05).The LSF, LIVB, WIVB and LSP indices were signi cantly higher in men than in women Table 2. Regarding the relationship between a number of dimensions belong to each vertebra and gender, logistic regression was used to determine the independent predictive dimensions of sex in each vertebrate.The cases that were statistically signi cant with sex in Tables 2 were included in the logistic regression model.In order to predict the dependent variable of sex based on the dimensions of each vertebrate, the results of the Logistic regression are summarized in Tables 4. The reference point for logistic regression is the female sex.
The AMA and LMFS variables determined as the independent predictors of sex in the second cervical vertebra.The mentioned two variables, along with each other, had a diagnostic accuracy of 81.4% (82.9% for women and 80% for men) (Table 3).The LIVB and LSP variables considered as the independent predictors of sex in second cervical vertebra.The mentioned two variables, along with each other, had a diagnostic accuracy of 78.6% (80% for women and 77.1% for men) (Supplement).In order to evaluate the relationship between age and indices and due to the normal distribution of data, Pearson correlation test was used in the whole population and each sex (Supplement).

Discussion
Findings of the second cervical vertebra indices in males and females showed that in all cases, the dimensions of collected indices from the vertebrae of males are greater than that of females, but in 9 out of 15 indices, this difference was statistically signi cant.These 9 indices were including AMA, LMA, DSD, DMFS, CMFS, LMFS, AMD, DSMC, and LMFI.Among the 9 variables which had a signi cant correlation with sex, 2 variables of LMSF and AMA considered as the independent predictive of sex with an odds ratio of 2 and 1.47, respectively and they had diagnostic accuracy of 81.4%.This indicates the presence of sexual dimorphism in the measurements of the Iranian vertebrae.The most signi cant mean difference was found in the linear dimensions of the second vertebra of LMA and AMA between the two sexes.
In a study on the cervical vertebra of skeletal specimens, the 15 linear indices of cervical vertebra were examined, which were largely in accordance with the metric dimensions measured in our study [1].The size of the examined dimensions was slightly different from the dimensions of our study [1].In all cases, dimensions were higher in males, but the LMA and DSMC indices had the most difference between the two sexes [1].In their study, four indices including CMA, LMA, LMFSD, and DSMC were independent predictors of sex with a predictive accuracy of 87% between sexes [1].In another study by Marlow et al., 9 indices of cervical vertebra dimensions were measured, some of these dimensions are similar to those measured in our study.All of these dimensions in males were signi cantly larger than females [3].Of these dimensions, XSL, SFS, SFT, LVF, and XDH were sex-independent predictors that provided a total of 77% sex diagnostic accuracy [3].
In comparison of our study with the above-mentioned studies on second cervical vertebral indices, a few points were noted: First, in all of the mentioned cases, as well as our study, the upper fast was considered as an independent predictor of sex; Second, the diagnostic accuracy of sex determination in different dimensions was signi cant in all cases; Third, although all dimensions were larger in males than females, but the mean difference was low even in signi cant indices suggesting that it is essential to be more focused on practical points of these low rates of mean difference.
In terms of a seventh cervical vertebra of current study, the 10 linear indices were investigated.All dimensions in this vertebra were higher in males than in females, and statistically signi cant correlations with sex were observed in 4 indices including the LSF, LIVB, WIVB, and LSP.Of these four indices, only two variables LIVB and LSP were independent sex predictors.The two variables had a diagnostic accuracy of 78.6%.In con rmation of the ndings of the current study, assessment of the seventh cervical vertebra dimensions amongst the three groups of whites, blacks, and South Africa tribes showed that the anterior posterior's length, width and height of the vertebra were greater in males than females [26].
Studies have shown that the dimensions of the cervical vertebrae are correlated with skeletal dimensions and the larger dimensions of the skeletal vertebrae in males are attributed to the larger body size of them [27].However, in this study, both the dimensions of the vertebral bodies and their posterior pectorals were statistically signi cant with sex.In the present study, relationships between age and dimensions of the vertebrae were observed.Correlation between age and cervical vertebral dimensions was mostly positive and weak.Considering the age range of the population was under the 69 year, the possibility of degenerative changes in the vertebra should be considered, which affects the dimensions of the vertebra.
Other studies have shown the relationship between age and dimensions of cervical vertebra [4,28].
All dimensions measured for the second and seventh cervical vertebrae were higher in men than women in this study.The height of the second vertebra and the transverse diameter of the upper fast were independent sex predictors, with an accuracy of 81.4%.In the seventh vertebra, the anterior-posterior of the vertebral body and the posterior length of the vertebra were independent predictors of sex, which had an accuracy of 78.6% in sex determination.The results of this study showed a high accuracy of cervical vertebral dimensions in sex determination of skeletal remains in the Iranian population.

Limitation
It is better the study perform with a larger sample population.

The 15 indices of second cervical vertebra: 1 .
Max height of the axis (AMA): measured as sagittal view 2. Max length of the axis (CMA): measured as sagittal view 3. Odontoid process sagittal diameter (DSD): measured as axial view 4. Odontoid process transverse diameter (DTD): measured as axial view 5. Max distance between the superior facets (DMFS): measured as coronal view .Max length of the sup.Facet (CMFS): measured as sagittal view 7. Max width of sup.Facet (LMFS): measured as coronal view .Length of the vertebral foramen (CMFV): measured as axial view 9. Sagittal max body diameter (DSMC): measured as sagittal view 10.Max width of the vertebral foramen (LMFV): measured as axial view 11.Max height of the odontoid process (AMD): measured as coronal view 12. Max transvers diameter of the body (DTMC): measured as coronal view 13.Max width of the axis (LMA): measured as coronal view 14.Max length of the inf.Facet (CMFI): measured as sagittal view 15.Max width of the inf.Facet (LMFI): measured as coronal view The 10 indices of the seventh cervical vertebra: 1. Length of the sup.Facet (LSF): measured as sagittal view 2. Width of the sup.Facets (WSF): measured as coronal view 3. Length of the inf.Facets (LIF): measured as sagittal view 4. Width of the inf.Facets (WIF): measured as coronal view 5. Length of the vertebral foramen (LVF): measured as axial view .Width of the vertebral foramen (WVF): measured as axial view 7. Length of the inf.surface of the vertebral body (LVB): measured as sagittal view .Width of the inf.surface of the vertebral body (WVB): measured as coronal view 9. Length of spinous process (LSP): measured as axial view 10.Height of spinous process (HSP): measured as sagittal view AbbreviationsCT Computed Tomography; AMA:Max height of the axis; CMA:Max length of the axis; DSD:Odontoid process sagittal diameter; DTD:Odontoid process transverse diameter; DMFS:Max distance between the superior facets; CMFS:Max length of the sup.Facet; LMFS:Max width of sup.Facet; CMFV:Length of the vertebral foramen; DSMC:Sagittal max body diameter; LMFV:Max width of the vertebral foramen; AMD:Max height of the odontoid process; DTMC:Max transvers diameter of the body; LMA:Max width of the axis; CMFI:Max length of the inf.Facet; LMFI:Max width of the inf.Facet; LSF:Length of the sup.Facet; WSF:Width of the sup.Facets; LIF:Length of the inf.Facets; WVF:Width of the inf.Facets; LVF:Length of the vertebral foramen; WVF:Width of the vertebral foramen; LVB:Length of the inf.surface of the vertebral body; WVB:Width of the inf.surface of the vertebral body; LSP:Length of spinous process; HSP:Height of spinous process

Table 1
The characteristics of the 15 indices of the second cervical vertebra and 10 indices of the seventh cervical vertebra in the whole population

Table 2
Comparison of 15 indices related to second cervical vertebra and 10 indices related to seventh cervical vertebra between sex

Table 3 The
Logistic regression model to determine the predictive indices of sex in the second cervical vertebra DSMC, and CMFI indices of the second vertebra showed a slight correlation coe cient and positive signi cant correlation with age.There was no signi cant correlation between age and second vertebra indices in males.There was also a signi cant positive and moderate correlation between age in females and CMA, LMA, DTD, DMFS, CMFS indices.Only the LSF and LIVB indices of the seventh cervical vertebra had a slightly signi cant and positive correlation with age.Evaluation of correlation between age and the seventh vertebra indices showed that WIF had reverse and moderate correlation with age and HSP had a moderate and positive correlation with age.In the correlation analysis between the seventh indices with age in females, LIVB and WIVB showed a signi cant positive and moderate correlation.