Effect of Subject-Specific Vertebral Position and Head and Neck Size on Calculation of Spine Musculoskeletal Moments
Spine musculoskeletal models used to estimate loads and displacements require many simplifying assumptions. We examined how assumptions about subject size and vertebral positions can affect the model outcomes. Head and neck models were developed to represent 30 subjects (15 males and 15 females) in neutral posture and in forward head postures adopted while using tablet computers. We examined the effects of (1) subject size-specific parameters for head mass and muscle strength; and (2) vertebral positions obtained either directly from X-ray or estimated from photographs. The outcome metrics were maximum neck extensor muscle moment, gravitational moment of the head, and gravitational demand, the ratio between gravitational moment and maximum muscle moment. The estimates of maximum muscle moment, gravitational moment and gravitational demand were significantly different when models included subject-specific vertebral positions. Outcome metrics of models that included subject-specific head and neck size were not significantly different from generic models on average, but they had significant sex differences. This work suggests that developing models from X-rays rather than photographs has a large effect on model predictions. Moreover, size-specific model parameters may be important to evaluate sex differences in neck musculoskeletal disorders.
KeywordsMusculoskeletal modeling Cervical spine kinematics Anthropometry Neck loads
The authors thank Roseann Amundsen and Darin Porter of Pullman Regional Hospital Radiology for their assistance with radiographs, and Victor Small, Theodore Gross, Zane Duke and Chandler Shannon for data analysis. Funding was provided by the Office Ergonomics Research Committee and National Science Foundation (CBET #0748303).
Conflict of interest
The authors confirm that there have been no conflicts of interest interfering with the preparation of this manuscript.
- 8.Clauser, C. E., J. T. McConville, and J. M. Young. Weight volume and center of mass of segments of the human body. Yellow Springs: Wright-Patterson Air Force Base, 1979.Google Scholar
- 11.Desantis Klinich, K., S. M. Ebert, C. A. Van Ee, C. A. Flannagan, M. Prasad, M. P. Reed, and L. W. Schneider. Cervical spine geometry in the automotive seated posture: variations with age, stature, and gender. Stapp Car Crash J 48:301–330, 2004.Google Scholar
- 18.NASA. Anthropometric Source Book, vol. 1: Anthropometry for Designers [Reference Publication 1024]. Hanover, MD: National Aeronautics and Space Administration, Scientific and Technical Information Office, 1978.Google Scholar
- 27.Valero-Cuevas, F. J., M. E. Johanson, and J. D. Towles. Towards a realistic biomechanical model of the thumb: the choice of kinematic description may be more critical than the solution method or the variability/uncertainty of musculoskeletal parameters. J Biomech 36:1019–1030, 2003.CrossRefGoogle Scholar
- 33.Wu, G., S. Siegler, P. Allard, C. Kirtley, A. Leardini, D. Rosenbaum, M. Whittle, D. D. D’Lima, L. Cristofolini, H. Witte, O. Schmid, and I. Stokes. ISB recommendation on definitions of joint coordinate system of various joints for the reporting of human joint motion–part I: ankle, hip, and spine. Int Soc Biomech 35:543–548, 2002.CrossRefGoogle Scholar
- 34.Zajac, F. E. Muscle and tendon: properties, models, scaling, and application to biomechanics and motor control. Crit Rev Biomed Eng 17:359–411, 1989.Google Scholar