The Effect of Head Position on the Analysis of Cervical Motion

Abstract

The motion of the head and neck until injury, or the threshold of injury is normally limited by the tension of soft tissues along the cervical spine and by any obstruction. The relative range of motion (ROM) available during loading until injury is dependent partially upon the initial starting position and the combinations of motions. In this study, an electromagnetic six degree of freedom digitizer was used to quantitatively assess the effect of head position on cervical spine ROM measurements for a group of 25 subjects with no known cervical symptoms. Forward sagittal translation of the head with respect to the thorax (protrusion) diminished the amount of extension motion available by 4.6°/cm. Backward sagittal translation of the head (retraction) diminished the amount of flexion motion available by 6.1°/cm. In addition, when the head was axially rotated losses of approximately 50% were displayed for measurements of flexion, extension, and lateral bending. This paper illustrates the importance of a defined starting head position when measuring cervical motion and the effects of combined motions. Accurate cervical ROM measurements will be influential in the design of sports equipment and in determining mechanisms of injury.