ZUMWALT, A.C.; Johns Hopkins University, Baltimore, MD: A new method to quantify the 3D morphology of bone surfaces, with application to muscle enthesis rugosity

There is a long tradition in paleontology of reconstructing the size and in vivo activity of a muscle from the location and appearance of its skeletal attachment site. In general, larger and more obvious attachment sites on a bone or fossil are thought to denote more active muscles during life. In the past, studies of attachment site morphology have relied upon linear measurements of size and semi-quantitative assessments of rugosity. Unfortunately, these methods are unable to assess variations in the complex 3D morphology of attachment sites in a repeatable, objective way. The quantification of complex 3D surfaces is an ongoing challenge for morphologists. Only recently has the technology for capturing a three-dimensional surface at a resolution adequate for the analysis of bone surfaces become relatively widely available. This paper presents a new method to quantify the 3D morphology of muscle and tendon attachment sites. This technique is demonstrated in a study of seven muscle attachment sites in exercised and sedentary sheep. The attachment sites were scanned with the LaserDesign RPS-120 high-resolution laser scanner. Following methods that have been previously applied to the quantification of tooth wear, the volume, slope, aspect and 3D/2D surface area ratios of these scans were calculated using ArcView GIS 3.3 (ESRI). Additionally, a method was developed to specifically quantify attachment site rugosity, a feature that is often thought to reflect in vivo muscle use. Rugosity was quantified via fractal analysis of profiles extracted from the laser scans at regular intervals along the primary anatomical axes of the attachment sites. These methods are useful in that they are objective and repeatable, and provide a new way to assess functionally significant aspects of skeletal morphology in ancient populations.