Compartmentalization Index: Description and Applications in Anthropological Studies

Abstract

Objectives: The cross-sectional area occupied by mineralized tissues is so high in non-adult individuals that linear methods provide limited information about its variation along their bones. This issue can be addressed using the compartmentalization index, a non-linear index that amplifies differences in cross sections with more than 90% of the mineralized area.

Materials and methods: We selected five femur diaphyseal cross sections of 35 non-adult Homo sapiens individuals from perinatal to 5 years old. Then we measured the percentage of mineralized area of each section and calculated the corresponding compartmentalization index. Subsequently, the distribution of both measurements was graphically tested.

Results and discussion: As expected, variations of femur diaphyseal mineralized areas are visually magnified using the compartmentalization index for values exceeding 90%, but the significance of statistical comparisons between groups is not affected. This makes the index particularly useful for exploring subtle variations in the early stages of growth and development. In addition, we found that using either the compartmentalization index or direct percentage measurements is equally effective for cross sections with lower mineralized area, as the data distributions are comparable. This also allows applying the compartmentalization index in research focused exclusively on adult individuals.

Keywords: compartmentalization index; cross section; femur; mineralized area; ontogeny.

FIGURE 1

(A) Graphical representation of the compartmentalization index's domain, (B) values of mineralized area contemplated in the selected sample, (C) values where the magnification effects of the compartmentalization index are most pronounced.

FIGURE 2

From 1 to 5, numbered cross sections selected along the diaphysis of the left femur belonging to individual ID 110562 (4 years old). The percentage (%) of bone length where each section was obtained is also indicated at the right part of the plane, emulating Gosman et al. (2013). In addition, an example of sections belonging to a random premature and five‐year‐old individual is included to visually appreciate the magnitude of their differences.

FIGURE 3

Line plots with standard deviation bars representing the percentage of mineralized tissues (A1) and compartmentalization index (B1) of the studied femur diaphyseal cross sections. A2 and B2 are enlarged sections of the A1 and B1 plots.