MRI-derived moment-arms of the female and male spine loading muscles

Objective. Develop a comprehensive gender-specific database of trunk muscle moment-arms across multiple levels of the lower thoracic and lumbar spine, determine if gender differences exist across the different vertebral level s, and develop prediction equations for the moment-arms as a function of ex ternal anthropometric measures. Design. This study quantified trunk muscle moment-arms relative to the spin e from T-8 to S-1 of male and female spine loading muscles. Background: Knowledge of trunk muscle geometry is important for biomechanic al modeling of the low back and for understanding of spinal loading. Howeve r, there currently is a lack of comprehensive data regarding the moment-arm s of the female spine loading muscles. Additionally, little is known regard ing gender differences in moment-arms for the same muscles. Method. Magnetic resonance imaging scans through the vertebral bodies from T-8 through S-1 were performed on 20 females and 10 males. Moment-arms in t he coronal and sagittal plane between the muscle centroid and vertebral bod y centroid were recorded at each vertebral level. Linear regression techniq ues taking into account anthropometric measures were utilized to develop pr ediction equations for the moment-arms for each muscle, Results. Anthropometric measures were better predictors of coronal plane mo ment-arms than sagittal plane moment-arms for both genders. Measures consis ting of height and weight were consistent predictors of female moment-arms. Measures about the xyphoid process and combinations of height and weight w ere consistent predictors of coronal plane moment-arms for males at several lower lumbar levels. Males exhibited larger moment-arms than for females, for most muscles at most levels. Conclusions. Trunk muscle moment-arms of females and males are different, a nd should be considered in the development of biomechanical models of the t orso. Similar to other studies. external anthropometric measures were bette r predictors of coronal plane moment-arms than sagittal plane moment-arms.