A Standardized, Three-Dimensional Cropping Protocol for Analyzing the Medial Epicondyle of the Humerus

The medial epicondyle of the humerus has been considered particularly relevant for investigating past activity-related skeletal changes. Yet, the characterization of these skeletal changes on the humerus has been challenging. This study introduces a semi-automated cropping protocol to standardize the analysis of this anatomical region and its entheseal surfaces.

A landmark-based cropping protocol was established in 3DSlicer to capture the region of interest, identified based on anatomical literature. Before applying this protocol, mesh resolution and orientation were standardized. Repeatability and reproducibility were assessed in 20 humeri through landmark placement precision and cropped model surface area.

The final cropped surface effectively encompassed the entire entheseal region. Mean landmark distances were mostly below 1 mm for intra-observer comparisons and more variable (between < 1 and 4 mm) for inter-observer comparisons. Distance-based Intraclass Correlation Coefficients (dICC) were all above 0.99. Mean percentage errors between surface areas were predominantly below 5%, with the highest value at 10.39%. Intraclass Correlation Coefficient and Lin's Correlation Coefficient values all exceeded 0.94.

The proposed protocol offers a holistic approach to studying entheseal changes at the medial epicondyle while accommodating morphological variation. Despite some subjectivity in landmark placement, the statistical results for both landmark placement and surface area found the method's observer error to be among the lowest in comparable studies. This method provides a valuable tool for examining entheseal surface changes and morphology, with the potential, pending experimental validation, to support research on reconstructing physical activity, pathological conditions, and human evolutionary adaptation.