Variation in Three-Dimensional Shape of the Tibial Diaphysis and Relationships with Biological Sex

The tibial diaphysis is frequently viewed as a simple structure despite exhibiting complex morphological variation. While prior investigations have contextualized variation in tibial morphometry via cross-sectional and whole-bone approaches, variation present in the three-dimensional diaphysis alone is largely unknown. Moreover, specimen-specific geometry is often simplified and scaled in computational and biomechanical frameworks, limiting understanding of how diaphyseal morphology influences mechanical response. Therefore, the objective of this research is to characterize diaphyseal shape variation in human tibiae prior to experimental loading. Laser surface scans and computed tomography data were collected from 60 human tibiae obtained through an experimental trauma dataset. Diaphyseal shape was evaluated in both size-dependent (unscaled; UPC) and size-independent (scaled; SPC) analyses to distinguish size-associated from size-independent traits. In the unscaled analysis, variation was dominated by overall size, whereas size normalization redistributed variance across multiple dimensions of diaphyseal shape while preserving major morphological themes across analyses. Significant sex-associated differences were identified in overall length and diaphyseal circumference in the unscaled analysis and in anterior crest/lateral surface morphology and diaphyseal tapering after size normalization. These results define anatomically interpretable diaphyseal shape traits from pre-impact morphology within a sample with known experimental outcomes, providing an empirical basis for future work linking baseline morphology with biomechanical behavior and applied forensic contexts.