Cervical circumduction in normal subjects: A study of maximal versus feigned effort

The feasibility of using the coefficient of variation in conjunction with m otion parameters derived from head circumduction to obtain a compact criter ion for differentiating maximal from feigned cervical motion was evaluated. Twenty-five healthy subjects were measured twice during a period of 3 week s using an ultrasonography-based motion analysis system. Subjects were aske d to produce maximal motion of the spine as well as to feign limitation. Ex tracted from the displayed traces of head circumduction. the angular values of the primary motions of flexion, extension, right and left lateral flexi on. as well as their additive score (AS) were determined, No test-retest di fferences were indicated. The average range of motion (ROM) was significant ly smaller and the coefficient of variation of the ROM was significantly la rger in the feigned compared with the maximal performance in both tests. Ho wever, tolerance interval analysis indicated that the coefficient of variat ion could not effectively separate between the effort levels, being particu larly deficient with respect to AS. In addition, a differential sensitivity in identifying false-negative cases as a function of the movement paradigm was revealed. This study indicates that in healthy subjects, the use of a complex cervical movement such as circumduction cannot serve for differenti ating between max imai and feigned performance using the coefficient of var iation. The results may also point out the existence of a mechanism for adj usting proportional reductions among the primary cervical motions that resu lt in excellent repeatability even in feigned efforts.