Quantifying cortical bone in fragmentary archeological second metacarpals

Abstract

Objectives: Skeletal variation in cortical bone thickness is an indicator of bone quality and health in archeological populations. Second metacarpal radiogrammetry, which measures cortical thickness at the shaft midpoint, is traditionally used to evaluate bone loss in bioarcheological and some clinical contexts. However fragmentary elements are regularly omitted because the midpoint cannot be determined. This methodological limitation reduces sample sizes and biases them against individuals prone to fracture, such as older individuals with low bone mass. This study introduces a new technique for measuring cortical bone in second metacarpals, the "Region of Interest" (ROI) method, which quantifies bone in archeological remains with less-than-ideal preservation while accounting for cortical heterogeneity. Materials and methods: The ROI method was adapted from digital X-ray radiogrammetry (DXR), a clinical method used to estimate bone mineral density, and tested using second metacarpals from Middenbeemster, Netherlands, a 19th century known age and sex skeletal collection. The ROI method quantifies cortical bone area within a 1.9 cm-long, mid-diaphyseal region, standardized for body size differences using total area (CAI ROI). CAI ROI values were compared to traditional radiogrammetric cortical indices (CI) to assess the method's ability to identify age-related bone loss. Results: CAI ROI values have high intra-and interobserver replicability and are strongly and significantly correlated with CI values for both males (r[n = 39] = 0.906, p = 0.000) and females (r[n = 58] = 0.925, p = 0.000). Conclusion: The ROI method complements traditional radiogrammetry analyses and provides a reliable way to quantify cortical bone in incomplete second metacarpals, thereby maximizing sample sizes, allowing patterns in bone acquisition and loss to be more comprehensively depicted in archeological assemblages.

The changing shape of palaeopathology: The contribution of skeletal shape analyses to investigations of pathological conditions

“…Image (a) depicts traditional radiogrammetry involving measurement of the medullary and total bone diameters at the midshaft; image (b) shows the region of interest method that considers the area of bone within the narrowest 1.9 cm region of the diaphysis. Source: Adapted from Gilmour et al, 2021location (O'Neill & Ruff, 2004. Through the application of beam theory, researchers gain important insight into bone rigidity, facilitating an improved understanding of its resistance to bending and torsional strain (O'Neill & Ruff, 2004;Sparacello & Pearson, 2010).…”

“…In this approach, frequently used to address questions related to bone loss and osteoporosis, researchers typically use uniplanar X‐ray images to establish total cortical thickness based on measurements of total bone width relative to medullary width (Figure 1). Similar approaches have been proposed for fragmentary remains that rely on the calculation of cortical area within larger regions of interest instead of traditional linear measures (Figure 1; Gilmour et al, 2021). Radiogrammetry typically generates indices, however, in this case, their purpose is usually to represent thickness and even correct for the effect of size, rather than quantify bone geometry.…”

“…Image (a) depicts traditional radiogrammetry involving measurement of the medullary and total bone diameters at the midshaft; image (b) shows the region of interest method that considers the area of bone within the narrowest 1.9 cm region of the diaphysis. Source : Adapted from Gilmour et al, 2021 …”

Exploring radiogrammetry beyond the second metacarpal: Using the third, fourth, and fifth metacarpals to quantify cortical bone

“…Traditionally, the technique uses radiographs, usually of the second metacarpal, to calculate “cortical index” (CI), a size‐corrected measure based on the thickness of cortical bone at the midshaft metacarpal diaphysis. Recent variations in the approach have averaged multiple measurements on a single element, or across the metacarpal array, or quantified cortical bone within larger regions of interest (Gilmour et al, 2021; Nielsen, 2001; Wilczek et al, 2013), but the original technique remains simple, effective, and affordable. This has led to its adoption by biological anthropologists to investigate topics such as age‐ and sex‐related cortical bone loss and osteoporosis, as well as habitual activity and occupation in archeological skeletal remains (e.g., Curate et al, 2019; Glencross & Agarwal, 2011; Mays, 2001).…”

“…Fractures, along with other pathological conditions (e.g., arthropathy, infections, tumors), may obscure the second metacarpal measurement locations and prevent radiogrammetric measurements, leading to the exclusion of individuals from studies (e.g., Wilczek et al, 2013). Archeological samples are affected by these issues and also impacted by skeletal survivability and preservation (Gilmour et al, 2021). As these reasons lead to the exclusion of some second metacarpals from clinical and biological anthropological research, there is a need to develop approaches that help maximize sample sizes and ensure that accurate ranges of cortical bone mass are represented.…”