Measurement of body segment parameters using dual energy X-ray absorptiometry and three-dimensional geometry: an application in gait analysis.

Body segment parameters (BSP) are essential input for the computations in kinetics of motion applied in the field of biomechanics. These data are usually obtained from population-specific predictive equations which present limitations in being representative of the population under study. More recently, medical imaging techniques have been adopted but are limited to two-dimensional (2-D) measurements or required extensive tomographic images for three-dimensional (3-D) reconstruction. We proposed an in vivo method to measure 3-D BSP using X-ray imaging and 3-D exterior geometry. Criterion values of the BSP were determined using magnetic resonance imaging (MRI) which has previously been validated. Errors for all BSP values were less than 2% when values derived from our method were compared to the criterion values. We found no significant difference between our method and four selected BSP models in both stance and swing phase. Significant phase effects were observed for our method and other BSP models between stance and swing phase. Significant differences (p<0.05) between root mean square error (RMSE) ranged from 0.0177 to 0.0234 and 0.0234 to 0.097 Nmkg(-1) for the knee and hip joints, respectively. However, these BSP variations brought about effects on moment output that were less than 0.09 Nmkg(-1). Our findings suggest joint kinetic computations during normal gait are relatively insensitive to BSP variations. However, the influence of BSP cannot be undermined in movements that generate higher acceleration at the limbs. Considering the accuracy of our method, it could be used as a novel in vivo method to obtain direct 3-D BSP measurements.