Three-dimensional kinematics of the human back.

This study examined the use of a new device, the 3space isotrak, to measure the kinematic behaviour of the backs of normal subjects and of patients from two orthopaedic practices. The device was shown to measure angles with a root mean square error of less than 0.2° and individuals showed a maximum standard deviation from the mean of movements repeated five times of less than 4°. Eighty normal subjects both male and female in four age ranges 20-29, 30-39, 40-49 and 50 years and over were measured. The three-dimensional kinematic patterns were similar for all groups, showing normals to have clearly identified patterns of movement. A general trend for decreasing mobility with age and some sex differences were also demonstrated. The clinical series showed widespread disruption to the primary and coupled movements of all the patients. When grouped together by clinical diagnosis the patient groups showed evidence of discrete and identifiable alterations from the normal kinematic patterns. However, further studies of homogeneous patient groups are required in order to demonstrate whether the measurements are of actual clinical use. The clinical studies also demonstrated that clinical subjective assessment of back mobility bore little relation to the true movements and therefore the clinical measurement of back movements should be reassessed. This study has shown the 3space isotrak to be an effective tool in the clinic for the three-dimensional kinematic measurement of low back mobility.