Spinal segments do not move together predictably during daily activities

Background: 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. Research question: 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). Methods: 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. Results: The upper/lower lumbar pairing showed weak correlations in the LBP group for all tasks and anatomical planes (R(xy)range: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. Significance: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.