Increased spinal kinematic variability in people with chronic low back pain revealed by alterations in helical axis parameters

Changes in spine kinematics are common in people with chronic low back pain (CLBP) and this includes changes in trunk angular displacement and angular velocity. The helical axis (HA) of motion is an approach to investigate three-dimensional variability of joint kinematics. In this study we investigate whether the variability of trunk movement is modified in people with CLBP by measuring the dispersion of HA parameters during repeated trunk movements performed at different movement speed. Nineteen people with CLBP and twenty asymptomatic volunteers performed repetitive continuous trunk movements at three different speeds. Two parameters of the HA were extracted to characterise movement variability at the lumbo-sacral and thoraco-lumbar regions: mean angle (MA) and mean distance (MD). Two-Way mixed ANOVA showed significantly higher MA and MD (p<0.001) especially at the thoraco-lumbar region for those with CLBP. Interestingly, this was not consistent across all directions or speed of movement; higher HA parameters for those with CLBP at the lumbo-sacral region was mainly observed during flexion/extension cycles. In addition, there was a speed and group interaction effect during rotational cycles (p=0.010) which showed higher thoraco-lumbar MA values for those with CLBP during the faster speed (p=0.029, mean dif.(95 % CI) = 2.28, (0.247;4.328)) and slower speed condition (p=0.003, mean dif.(95 % CI) = 2.78, (1.009;4.565)). This study shows that people with CLBP move their spine in a more variable way, a characteristic that could be influenced by speed and direction of trunk movement. This could reflect an adaptive behaviour to long-lasting pain.