The phenomenon of twisted growth: humeral torsion in dominant arms of high performance tennis players

Abstract

This manuscript is driven by the need to understand the fundamental mechanisms that cause twisted bone growth and shoulder pain in high performance tennis players. Our ultimate goal is to predict bone mass density in the humerus through computational analysis. The underlying study spans a unique four level complete analysis consisting of a high-speed video analysis, a musculoskeletal analysis, a finite element based density growth analysis and an X-ray based bone mass density analysis. For high performance tennis players, critical loads are postulated to occur during the serve. From high-speed video analyses, the serve phases of maximum external shoulder rotation and ball impact are identified as most critical loading situations for the humerus. The corresponding posts from the video analysis are reproduced with a musculoskeletal analysis tool to determine muscle attachment points, muscle force vectors and overall forces of relevant muscle groups. Collective representative muscle forces of the deltoid, latissimus dorsi, pectoralis major and triceps are then applied as external loads in a fully 3D finite element analysis. A problem specific nonlinear finite element based density analysis tool is developed to predict functional adaptation over time. The density profiles in response to the identified critical muscle forces during serve are qualitatively compared to X-ray based bone mass density analyses.

Keywords:

• bone mass density changes
• functional adaptation
• musculoskeletal analysis
• finite element analysis
• sports medicine

Acknowledgements

The present research was initiated within the Stanford graduate class ME337 ‘Mechanics of Growth’. The computational tools are provided as open source software within SimTK at https://simtk.org as part of Simbios, the NIH Center for Biomedical Computation at Stanford the support of which, we gratefully acknowledge. In addition, we would like to thank Jeff A. Zeller for agreeing to provide his data as a case study.