Mri-derived Moment Arms of Neck Muscles during Sagittal Plane Motion

INTRODUCTION In musculoskeletal models of the cervical spine, the most common method for modeling muscles is straight paths from origin to insertion [1]. However, muscle paths in the neck are constrained by bone and other soft tissues, and some studies have found that applying curvature to muscle paths improves anatomical accuracy [2; 3] and affects muscle parameters such as moment arm [3] and moment [4]. Currently, data available in the literature for neck muscle moment arms (MA) is sparse. In this study we estimated in-vivo MAs of MRI-derived neck muscle paths modeled with curvature and those modeled as straight paths for head rotation in the sagittal plane. We hypothesize that MA estimates for curved paths will be significantly different from estimates for straight paths. METHODS Subject-specific cervical spine musculoskeletal models of two approximate 50 percentile males were created from 5 static magnetic resonance image (MRI) postures to develop kinematically functional models from approximately 30° head flexion to 30° extension. Fifteen muscle pairs were modeled using the centroid (anatomic) path derived from consecutive cross-sectional areas on MRIs (Fig. 1A). Both straight and curved paths were modeled for each muscle. Straight paths were modeled using a straight line connecting the first and last centroid points (Fig. 1B).