A method to measure cervical spine motion over extended periods of time.

STUDY DESIGN: System validation study.

OBJECTIVE: To develop and validate a motion sensor system for measuring cervical spine motion over extended time periods.

SUMMARY OF BACKGROUND DATA: Many studies using different methodologies have tried to estimate cervical spine motion. These have mostly been carried out in a laboratory setting performing active/passive range of motion or activities of daily living. However, cervical spine performance over extended periods of time in natural environments remains unknown.

METHODS: A novel motion sensor system, Wisconsin Analysis of Spine Motion Performance (WASP), was validated using 2 benchmarks: a materials testing machine (MTS) and optical motion tracking laboratory. Parameters tested included drift, frequency response, accuracy, effect of sensor orientation, and coupled motions. Applied motions from the MTS and measured motions in subject volunteers under various conditions were compared with WASP using correlation coefficients. Intersubject and intrasubject variability analyses for WASP were also performed.

RESULTS: The average WASP slopes for accuracy (compared with MTS) in flexion-extension, lateral bending, and axial rotation were 0.89, 0.93, and 0.38, respectively. The correlation coefficient was 0.99 in all cases. Compared with optical motion tracking, the WASP regression slopes were 1.1, 1.02, and 0.4 and the correlation coefficients were 0.98, 0.92, and 0.93 in the 3 axes of motion. Coupled motion was noted during all subject motions. WASP peak detection algorithm had a 0% error discounting boundary conditions.

CONCLUSION: WASP was accurate in flexion-extension and lateral bending. In axial rotation, WASP was less accurate. However, the system was highly reliable with low intersubject and intrasubject variability. WASP can be used in estimating cervical spine motion with high reliability while keeping in mind the decreased accuracy in measuring axial rotation.