Sensorimotor function of the cervical spine in healthy volunteers.

Background: Sensorimotor mechanisms are important for controlling head motion. However, relatively little is known about sensorimotor function in the cervical spine. This study investigated how age, gender and variations in the test conditions affect measures of position sense, movement sense and reflex activation in cervical muscles.

Methods: Forty healthy volunteers (19M/21F, aged 19-59 years) participated. Position sense was assessed by determining repositioning errors in upright and flexed neck postures during tests performed in 25%, 50% and 75% cervical flexion. Movement sense was assessed by detecting thresholds to passive flexion and extension at velocities between 1 and 25°s(-1). Reflexes were assessed by determining the latency and amplitude of reflex activation in trapezius and sternocleidomastoid muscles. Reliability was evaluated from intraclass correlation coefficients.

Findings: Mean repositioning errors ranged from 1.5° to 2.6°, were greater in flexed than upright postures (P=0.006) and in people aged over 25 years (P=0.05). Time to detect head motion decreased with increasing velocity (P<0.001) and was lower during flexion than extension movements (P=0.002). Reflexes demonstrated shorter latency (P<0.001) and greater amplitude (P=0.009) in trapezius compared to sternocleidomastoid, and became slower and weaker with age. None of the measures were influenced by gender. Reliability was good for movement sense measures, but was influenced by the test conditions when assessing position sense.

Interpretation: Increased repositioning errors and slower reflexes in older subjects suggest that sensorimotor function in the cervical spine becomes impaired with age. In position sense tests, reliability was influenced by the test conditions with mid-range flexion movements, performed in standing, providing the most reliable measurements.