The geometry of the human paraspinal muscles with the aid of three-dimensional computed tomography scans and 3-Space Isotrak.

STUDY DESIGN Accurate determination of the three-dimensional coordinates of paraspinal muscles is presented. OBJECTIVES To determine the precise position and the size of the paraspinal muscles. SUMMARY OF BACKGROUND DATA The accurate measurements of the muscle moment arms are important in the evaluation of computer models for spinal movement. It has been reported that a change in the modelling of the erector spinae muscles can alter the compressive forces in the spinal column by 20% and can increase the offsetting shear forces. Classic studies used measurements from cross-sectional anatomic diagrams of human cadavers, scaled to the width and depth of the trunk of the subject, to calculate the moment that produces the joint torque. METHODS Computed tomography scans of two male cadavers provided data on the bony elements. Three-dimensional coordinates of the origins and insertions of the muscle-fascicles of the paraspinal muscles were obtained with the use of 3-Space Isotrak equipment. The bony and muscle coordinates were combined in the ANSYS (version 5.4; Swanson Analysis Systems, Canonsberg, PA) program. RESULTS Results of this combination and the three-dimensional coordinates of the paraspinal muscles as acquired by the 3-Space Isotrak are given. CONCLUSION The position and the moment arms of paraspinal muscles were accurately determined. This is important for further evaluation of mathematical models.