The purposes of this study are to fully quantify the flexibility relationships for cervical motion segments, to examine the diagonal and nondiagonal components of the flexibility matrix, and to determine the extent to which multivariable relationships improve cervical spine motion prediction. To that end, using unembalmed human cervical spine motion segments, a full battery of flexibility tests were performed for a neutral orientation and also following an axial pretorque. Primary and coupled matrix components were described using linear and piecewise nonlinear incremental constants. An additional approach utilized multivariable incremental relationships to describe matrix terms. Measured motions were predicted using structural flexibility methods and were evaluated using root mean square (RMS) error of the difference between the predicted and measured responses. Results of the study provide a full set of flexibility relationships describing primary and coupled motions for C3-C4 and C5-C6 motion segment levels. Analysis of these data indicates that a flexibility matrix using incremental responses describing primary and coupled motions offers improved predictions over using linear methods. However, there is no significant improvement using more generalized nonlinear terms represented by the multivariable functional approach. Based on these findings, it is suggested that a multivariable approach for flexibility is more demanding experimentally and analytically while not offering improved motion prediction. (A)
Abstract