Spinal segments do not move together predictably during daily activities

Considering the thoracic, lumbar spine or whole spine as rigid segments has been the norm until recent studies highlighted the importance of more detailed modelling. A better understanding of the requirement for spine multi-segmental analysis could guide planning of future studies and avoid missing clinically-relevant information.

This study aims to assess the correlation between adjacent spine segments movement thereby evaluating segmental redundancy in both healthy and participants with low back pain (LBP).

A 3D motion capture system tracked the movement of upper and lower thoracic and lumbar spine segments in twenty healthy and twenty participants with LBP. Tasks performed included walking, sit-to-stand and lifting, repeated 3 times. 3D angular kinematics were calculated for each spine segment. Segmental redundancy was evaluated through cross-correlation (R_xy) analysis of kinematics time series and correlation of range of motion (R_ROM) of adjacent spine segments.

The upper/lower lumbar pairing showed weak correlations in the LBP group for all tasks and anatomical planes (R_xyrange:0.02-0.36) but moderate and strong correlations during walking (R_xy _frontalplane:0.4) and lifting (R_xy _sagittalplane:0.64) in the healthy group. The lower thoracic/upper lumbar pairing had weak correlations for both groups during lifting and sit-to-stand in the frontal plane and for walking (R_xy:0.01) in the sagittal plane only. The upper/lower thoracic pairing had moderate correlations during sit-to-stand in sagittal and transverse plane in patients with LBP (R_xy _sagittalplane:0.41; R_xy _transverse plane:-0.42) but weak in healthy (R_xy _sagittalplane:0.23; R_xy _transverseplane:-0.34); the contrary was observed during lifting. The majority of R_ROM values (55/72) demonstrated weak correlations.

The results suggest that multi-segmental analysis of the spine is necessary if spine movement characteristics are to be fully understood. We cannot establish a priori where redundancy occurs based on healthy data, therefore extra consideration should be made when planning studies with pathological cohorts.