Dynamic properties of the lumbar spine in people with non-specific low back pain

  • Marco Freddolini

Student thesis: Doctoral Thesis


Non-specific low back pain (LBP) has been associated with alterations in the biomechanical properties and muscle activities of the trunk, but it is unclear how these changes are related to the dynamic stability of the trunk. During sitting, the structures of the trunk stabilise the upper body counterbalancing external moments acting on the trunk. The aim of this research was to evaluate a range of biomechanical variables including the hip and lumbar spine joints range of motions, moments and powers the viscoelastic properties of the trunk, and the role of the muscles while a participant was performing a balancing task in sitting and to compare results between healthy and LBP subjects. A custom-made swinging chair was used to perform the balancing task. It was designed to challenge primarily the trunk and to minimise the effect of the lower limbs so that the role of the trunk could be examined in isolation. Twenty-four participants with LBP and thirty healthy participants were requested to sit on the custom-made swinging chair and to regain the balance after tilting the chair backward for 10° and 20º. Electromagnetic motion track system sensors were placed on the participants’ back, one at the sacrum level and one at the first lumbar vertebral level to measure hip and lumbar kinematics. One further sensor was placed on the chair to track its rotation, which was also the rotation of the lower limbs. Forces data were taken from a force-plate which was mounted at the bottom of the chair. Inverse dynamic equations were used to derive the muscle moment acting at the hip and lumbar spine joints using data from the force platform and the motion tracking system. Muscle power was then calculated by multiplying the muscle moment and the corresponding joint angular velocity. Trunk viscoelastic parameters were derived using a second order linear model combine trunk moment and motion. Chair motion and trial duration were used to evaluate dynamic stability and task performance, in particular, the angular displacement of the chair was fitted in an equation describing the underdamped second-order response to a step input to derive natural frequency and damping ratio and to evaluate possible differences between groups. Activities, reaction times and co-contraction of the trunk muscles were evaluated using surface electromyography (EMG). The surface electrodes were placed bilaterally on the erector spinae , rectus abdominus, external and internal oblique. Kinematic analysis showed that the hip range of motion increased whereas spine range of motion angle decreased in participants with LBP for both tilt angles (p. < 0.05). No significant differences were found in muscle moment and power between healthy and LBP subjects (p>0.05). The duration of contraction of various trunk muscles and co-contraction were significantly longer in the LBP subjects (p<0.05) when compared to healthy subjects, and the reaction times of the muscles were also significantly reduced in LBP subjects (p<0.05). Trunk stiffness was found increased for LBP subjects (p < .05) while no difference was found for damping coefficient. There were no significant differences between the 2 subject groups in the time required to regain balance, and in the dynamic stability parameters, the natural frequency and damping ratio. The present study showed LBP was associated with alterations in biomechanical variables; in particular stiffness, hip and lumbar spine joints kinematic and muscle responses were altered in subjects with LBP when compared with healthy group. However, these alterations did not affect dynamic stability and moment developed at joints level, suggesting that LBP subjects adopted a different strategy to maintain balance but with the same effectiveness as the healthy subjects without any worsening of the symptoms. This may suggest to clinicians to encourage patients to remain active rather than to avoid movements. On the other hand, compensatory strategies were achieved with increased co-contraction at the expenses of muscle efficiency. This may lead to muscle fatigue and increase in spinal stress. Future research should clarify if the observed biomechanical alterations in this study are consequences or causes of LBP; or if the biomechanical changes and pain operate in a vicious circle, reinforcing each other leading to chronic conditions. This would help achieve our ultimate goal of developing effective treatment strategies, and it is hoped that the work of this thesis has helped us take a significant forward towards this goal.
Date of Award2014
Original languageEnglish
Awarding Institution
  • University of Roehampton

Cite this