The potential of the angle of the first rib, head to tubercle, in sexing adult individuals in forensic contexts

Abstract

Accurately assessing the sex of an adult human skeleton is fundamental in forming the biological profile used in forensic anthropology (Patil and Mody, 2005). The first rib was chosen due to its distinct shape, compact size and increased sustainability to the taphonomic processes encountered in forensic and bioarchaeological situations. The first rib has been examined in previous studies; however, these studies have focused mainly on the sternal end of the rib. This study looks at the angle created between the tubercle and head and its potential use as an indication of the sex of an individual. This angle, created by the tubercle and head, is present when the rib is viewed in its non-anatomical orientation, or with the head pointing upward. When a rib is sided in anatomical position, the head will point downward and the subclavian grooves will be located on the superior surface. This study was conducted using 137 males and 149 females, including black and white individuals, from the William M. Bass and Hamann-Todd Skeletal Collections. The left and right first ribs of 286 individuals were measured using sliding calipers; all measurements were recorded in millimeters. The four measurements included: total exterior length (ASHL), interior length from sternal end to head (PSMH), height of the head off of a surface and length from the tubercle to the head. The angle was determined by calculating the inverse sine. The calculated angles were then compared using logistic regression analysis, to determine the odds that a given angle was male. Of the 572 measured samples, 555 were calculated; 266 angles were male and 289 female. Logistic regression showed that angle alone is 60.2 percent concordant, while angle and total length combine to yield a 70.5 percent concordance. The data suggest that the angle can be used to predict the sex of an individual. This research concludes that the angle of the first rib is able to determine the sex of an individual. These data could be combined with previously studied age methods to assess both age and sex of an unknown individual. Few skeletal elements are able to both sex and age individuals.