Abstract
Background and Aim
Low back pain is highly prevalent, particularly in manual occupations. We previously showed that the lumbar spine has an intrinsic shape, identifiable in lying, sitting and standing postures, that affects the spine's response to load. Its effects on motion are unknown. Here we investigate whether intrinsic spinal shape is detectable throughout a greater range of postures and its effect on how healthy adults lift a weighted box.
Methods
The lumbar spine was imaged using a positional MRI with participants (n=30) in 6 postures ranging from extension to full flexion. Active shape modelling was used to identify and quantify ‘modes’ of variation in lumbar spine shape. 3D motion capture analysed participants' motion while lifting a box (6–15 kg, self-selected).
Results
Two modes accounted for 89.5% of variation in spinal shape, describing the overall curvature (mode 1) and distribution of curvature (mode 2). Within the first 9 modes, scores were significantly correlated between all six postures (r = 0.4−0.97, P<0.05), showing that intrinsic shape was partially maintained throughout. Individuals with straighter spines lifted with greater knee flexion (r = 0.4, P = 0.03) typical of squatting. Knee flexion negatively correlated with lumbar (r = −0.5 to −0.86, P<0.01) and pelvic flexion (r = −0.81, P<0.001). Those with curvier spines flexed significantly more at the back (r = −0.79, P=0.02) typical of stooping.
Conclusion
In summary, individuals with straight spines squatted to lift while those with curvy spines stooped, indicating that the way we move to pick up a load is associated with the shape of our spine.
