Using the clinical and radiological parameters , we formulated a combined model with five risk factors : gender , mouth opening , atlanto-occipital gap , the angle from the second to sixth cervical vertebraes in the neutral position , and the angle difference of d ( the angle between the laryngeal axis and the epiglottic axis ) from the neutral position to extension ( OR : 0.107 , 0.355 , 0.846 , 1.057 , and 0.952 , respectively ) .