Measurement of head relocation accuracy in the sagittal plane using static photogrammetry and inertial measurement unit

The high densities and complex arrays of joint mechanoreceptors and muscle spindles of the cervical spine suggest that disturbances of such structures may change the proprioceptive information to the neuromuscular system and thus, may play a key role in neck presentation. Errors in head positioning may arise in response to such proprioceptive disturbances and are considered to be a clinical sign of somatosensory impairment. The objective of this study is to compare the performance of a commercial 3D inertial measurement unit (IMU) with static photogrammetry in the head relocation accuracy test in the sagittal plane. Fourteen asymptomatic subjects were enrolled in the investigation. A paired observations experimental design was conducted and three error parameters (absolute, constant and variable) were calculated for each method. Results showed no significant difference between error parameter means obtained by both measurement methods. Bland and Altman plots were used to assess agreement levels between error estimates and showed good agreement levels among absolute and constant errors. The study concludes that the IMU is a valid method for head error position assessment in the sagittal plane, and future studies should focus on potential clinical applications involving different subgroups of neck pain patients.