Whole-Epiphysis Trabecular Bone in Tamarin Limbs Suggests Effects of Leaping Distance Alongside Non-Biomechanical Factors

Abstract

Objectives

Beyond non-biomechanical factors, the trabecular architecture of long bone epiphyses variably underlies functional adaptations to locomotor behavior. A recent study, characterizing tamarin trabecular bone using traditional metrics derived from Volumes of Interest (VOIs), identified a preliminary relationship with leaping distance. We hypothesized that quantifying trabecular topological indices from whole epiphyses in the same system would enhance detection of locomotor signals.

Materials and Methods

We analyzed μCT scans of humeral and tibial whole-epiphyseal trabecular bone in four tamarin species representing short- and long-distance leapers. We quantified topological indices—node density (NodDen), trabecular tortuosity (TrabTort), trabecular length (TrabLen), and fractal dimension (FD)—alongside traditional metrics—degree of anisotropy (DA) and bone volume fraction (BV/TV). We tested relationships between trabecular traits and leaping distance and assessed the effects of non-functional factors (sex and captivity).

Results

Long-distance leapers exhibited significantly higher NodDen in humeral and tibial epiphyses and increased distal humeral TrabTort. Regions of elevated NodDen were concentrated beneath the humeroscapular joint (proximal humerus) and occurred variably across other epiphyses. In contrast, DA, BV/TV, TrabLen, and FD were more strongly associated with sex and captivity.

Discussion

Higher loading magnitudes associated with longer leaps may increase NodDen and, more tentatively, TrabTort in tamarin limb epiphyses. However, locomotion-related signals were weaker than those linked to sex and captivity, suggesting that leaping distance affects specific trabecular traits, whereas the overall trabecular organization is driven by non-functional factors. Whole-epiphysis analyses and topological indices provide a valuable complement to traditional VOI-based approaches and metrics.