Anatomical variability in determination of some dimensions of the foramen magnum

The aims of the present study were to determine some dimensions and their variability of the foramen magnum (FM). 25 adult dry occipital bones of unknown age and gender were selected for the study in the 1st part. Material was provided by the Anatomy Laboratory of the Department of Morphology of the Institute of Anatomy and Anthropology. In the 2nd part 25 adult occipital bones were studied on the virtual 3D dissection table “Anatomage”. Sagittal (FMSD) and transverse (FMTD) diameters of the FM were measured by one investigator. In dry occipital bones these sizes were taken using a sliding digital Vernier caliper to the nearest 0.01mm. In virtual images the sizes of FM were measured by digital ruler tool. FM index (FMI) was calculated using the formula: FMTDx100/FMSD. The area of the FM was calculated using Radinsky's formula; A=1/4x3.14xFMTDxFMSD. Collected data was analyzed using IBM SPSS Statistics 26.0. The shape of the FM was visually assessed and detected as round, oval, egg-shaped, tetragonal, pentagonal, hexagonal and irregular. In dry occipital bones FMSD and FMTD were respectively 36.15±3.37 mm and 30.44±2.62 mm while index of foramen and area were respectively 84.69±8.83 and 866.39±130.19 mm2. The FMSD diameter ranged from 30.15 to 42.44 mm, and FMTD ranged from 25.50 to 34.66 mm. Tetragonal and pentagonal shapes of FM were found to be the highest in occurrence. In digital occipital bones FMSD and FMTD were respectively 34.50±4.03 mm and 30.60±3.12 mm while index of foramen and area were respectively 89.33±9.17 and 834.35±159.04 mm2. FMSD diameter ranged from 25.01 to 40.79 mm, and FMTD ranged from 24.89 to 36.71 mm. FM were mainly hexagonal or irregular in shape (32.0% and 28.0%). This study illustrated the variability of some dimensions of the FM that are important in human anatomy, anthropometry, forensic medicine, radiology and neurology.