Annual frequency and magnitude of neck motion in healthy individuals.

STUDY DESIGN Descriptive, cross-sectional design of healthy young adults. Continuous motion monitoring of the cervical spine performed outside of a laboratory setting. OBJECTIVE The objective of this study was to quantify the daily frequency and magnitude of neck motion in healthy human subjects using continuous motion monitoring. SUMMARY AND BACKGROUND DATA Daily frequency and magnitudes of neck motion in healthy young adults may be useful for clinicians in appropriate treatment programs for individuals with cervical injury and pathology. In addition, the design of cervical disc prostheses requires such information to estimate annual wear. These data are not currently available and as a result current American Society for Testing and Materials (ASTM) testing standard F2423-05 may not be accurate. METHODS Ten healthy young adults were fitted with a portable device that measured neck kinematics about all 3 primary axes. Participants wore the unit continuously over a 5-day period. Data from each axis were processed to identify motion magnitude and the frequency of motion within 5 degrees increments. Results were extrapolated to yield daily and yearly values of total neck motion, and that attributed to the C5-C6 level for comparison to ASTM standard F2423-05. RESULTS Flexion-extension movements were twice as frequent as movements along the other 2 axes. The median motion magnitude was 13 degrees for both flexion-extension and axial rotation and 10 degrees for lateral bending. Estimates of yearly excursion indicate that the average healthy young adult will undergo 335.6 million degrees of flexion-extension, 109.3 million degrees of lateral bending, and 166.9 million degrees of axial rotation. Our findings indicate that while ASTM testing standard F2423-05 appears appropriate for lateral bending and axial rotation, it underestimates the motion experienced in flexion- extension. CONCLUSION Flexion-extension was the primary neck motion during normal daily living, with the majority ofmotions about all axes being less than 15 degrees . ASTM standard F2423-05 may need to be reviewed regarding flexion-extension.