3D reconstruction of shoulder muscles in hominoid primates: Correlating scapular attachment areas with muscle volume.

Digital muscle reconstructions have gained attraction in recent years, serving as powerful tools in both educational and research contexts. These reconstructions can be derived from various 2D and 3D data sources, enabling detailed anatomical analyses. In this study, we evaluate the efficacy of surface scans in accurately reconstructing the volumes of the rotator cuff and teres major muscles across a diverse sample of hominoids. Additionally, we investigate whether muscle origin area, as a dissection-based observation, can reliably predict muscle volume. Our findings reveal that surface scans provide sufficient coverage to accurately reproduce the in situ volumes of the rotator cuff muscles. However, the volume of the teres major was estimated less reliably, suggesting that muscles with less distinct skeletal boundaries may present challenges for accurate reconstruction. Future studies will explore whether such muscles can be reconstructed with greater precision. Furthermore, we identify a significant correlation between the origin area and muscle volume for the supraspinatus, infraspinatus, and subscapularis muscles. These results suggest that muscle origin area can serve as a reliable predictor of muscle volume, offering a skeletal indicator for estimating muscle size in both extant and extinct hominoids. These insights are particularly valuable for paleontological reconstructions, where direct soft tissue evidence is often lacking. By establishing a relationship between skeletal traits and muscle volume, our study provides a framework for evaluating the accuracy of soft tissue reconstructions in hominoid species. This approach not only enhances our understanding of hominoid anatomy but also offers new avenues for exploring the functional morphology of extinct taxa.