The effect of marker placement deviations on spinal range of motion determined by video motion analysis

Physical Therapy, Spinal Treatment and Rehabilitation Program, Shands Hospital, University of Florida, Gainesville 32610.

BACKGROUND AND PURPOSE. Spinal range of motion (ROM) is an important indicator of spinal function and is used in the determination of disability and compensation. One technology that has been used to assess spinal ROM is video motion analysis. No studies, however, have been done to investigate the effects of marker placement on ROM. The purpose of this study was to investigate the effect of deviations in reflective marker placement on ROM measurements obtained via video motion analysis. METHODS. A model of the spine was constructed and used to obtain ROM measurements from three segments of the model to isolate error from marker placement without the confounding effects of subject error. A standard placement and six altered placements were used to determine the effect of moving reflective markers on ROM. RESULTS. Results indicated statistically significant effects of marker placement for a number of flexion/extension and lateral side-bending ROM measurements. When the mean differences were compared with data obtained in human test-retest studies with the same equipment, the differences from a 2.5-cm marker deviation did not appear to be clinically meaningful. CONCLUSION AND DISCUSSION. We conclude that small marker deviations (2.5 cm) are not likely to adversely affect clinical information obtained when using this type of apparatus.