A method for the 3D quantification of enthesis rugosity

Introduction Many methods for evaluating enthesis rugosity are qualitative or fail to capture the entire entheseal surface. Here we present a new 3D method quantifying rugosity across the entire entheseal surface and test it by measuring and comparing the rugosity of the opponens pollicis enthesis to a non-enthesis region on the same bone in a sample of great apes.Methods To quantify rugosity, the enthesis area is isolated on high-resolution 3D models and deviations are measured between a best-fit surface and the 3D point cloud representing the enthesis.Results We demonstrate that this method quantifies entheseal rugosity and is resilient to interobserver differences in defining entheseal boundaries. It is also sufficiently sensitive to detect intergeneri differences. In Gorilla, Homo, and Pan the magnitude of entheseal rugosity is significantly greater than non-entheseal rugosity. In Pongo, there are no significant differences between the two regions or between the entheseal region of Pongo and the non-entheseal regions of the other genera, indicating a unique pollical metacarpal morphology among great apes.Discussion The results support the validity and repeatability of the method for measuring rugosity. The observed pattern of enthesis rugosity reaffirms a complex relationship among entheses, muscle anatomy, and behaviour.