The relationships of prolonged standing induced low back pain development with lumbopelvic posture and movement patterns

Over 80% of individuals will suffer from low back pain at least once in their lifetime. The cause within the population is not homogenous, leading to sub-classifications of non-specific low back pain. One such sub-classification is low back pain in response to prolonged standing. Over 50% of people who have never suffered a low back injury will develop transient low back pain when completing a prolonged standing occupational simulation where there is no option to sit. Many service and manufacturing tasks require prolonged standing and the introduction of sit-stand desks into the office workplace means that even more workers will be standing on the job. Many workplace health and safety societies recommend the use of standing aids to prevent the negative effects of prolonged standing; however, very few of these standing aids have been validated. Currently, it is difficult to provide advice for people who perform these jobs and get low back pain, as we still do not know enough about the origins of this pain. As a result, the purpose of this thesis was to investigate the relationships of prolonged standing induced low back pain development with lumbopelvic postures and movement patterns. The four specific questions asked were (1) Are movement patterns different between pain and non-pain developers (2) Do pain and non-pain developers have different lumbopelvic postures? (3) How do different foot positions alter lumbopelvic posture?, and (4) Can a standing aid that alters posture or movement patterns prevent low back pain development in standing? Study #1: Previous research points to the lack of movement during prolonged standing as a pre-disposing factor to low back pain. Such movements could be at the level of the lumbar spine or at the foot-ground interface. The primary purpose of this in vivo study was to determine if there were differences in magnitude, region, and frequency of movement patterns between pain and non-pain developers. Thirty-two participants reported their low back pain development using a visual analogue scale over 2-hrs of prolonged standing. Time-varying lumbar spine kinematics were used to assess the magnitude and frequency of lumbar spine fidgets and shifts. Ground reaction forces were used to assess the magnitude and frequency of whole body weight transfers and anterior-posterior center of pressure movements. Fourteen of 32 participants (43.75%) were categorized as pain developers. The first 15 minutes of standing distinguished the two pain groups, as non-pain developers performed a higher frequency of lumbar spine flexion/extension fidgets and large body weight transfers. Both of these differences may be pre-disposing factors for transient low back pain development, as they both occurred prior to pain developers reaching the 10 mm visual analog scale threshold for low back pain classification. Study #2: The purpose of this study was to investigate differences in lumbar posture between 17 participants categorized as a pain or non-pain developers during level ground standing. A secondary purpose was to evaluate the influence of two standing aids (an elevated surface to act as a foot rest and declined sloped surface) on lumbopelvic posture. Four sagittal plane radiographs were taken– a normal standing position on level ground, when using an elevated foot rest and declined sloped surface, and maximum lumbar spine extension to act as a reference posture. Lumbosacral lordosis, total lumbar lordosis, and individual intervertebral joint angles were measured on each radiograph. On level ground, pain developers stood closer to their maximum lumbosacral lordosis and L5/S1 intervertebral joint maximum extension angles. The elevated surface was most effective at causing lumbosacral lordosis flexion, while the declined surface was more effective at inducing L1/L2 intervertebral joint flexion. The differences between the posture and the influence of standing aids point to postural characteristics as a factor influencing pain development. Study #3: While it is common to assess postural characteristics that may predispose a person to low back pain, these measures do not capture valuable information on the intrinsic properties of the lumbar spine, such as stiffness. The purpose of this study was to assess the relationship between the in vivo lumbar spine lumped passive stiffness and the location of the neutral zone with the self-selected lumbar spine angle of pain and non-pain developers in four standing postures. Twenty-two participants with known pain group status stood in four postures for 5 minutes each: on level ground, while resting a foot on an elevated surface, with their feet staggered, and on a sloped decline. Median lumbar spine angle was calculated for each position. Participants were then placed in a near-frictionless jig and brought through passive lumbar spine extension and flexion to characterize their passive stiffness curve and location of their neutral zone. Overall, pain developers stood with a lumbar spine angle that was further beyond their passive lumbar spine neutral zone than non-pain developers. Not all aids thought to be successful at reducing low back pain worked in a similar manner, as only the elevated surface brought the lumbar spine into flexion and closer to the passive neutral zone. As a result, pain developers may be standing in a position that puts higher mechanical loads on the passive tissues of the lumbar spine. While flexion was induced by the elevated surface, the lack of changes caused by the sloped surface signal that there may be other postural changes other than just altered lumbar spine angle that are important for reducing low back pain. Study #4: While alternating standing position on a declined and inclined surface has proven successful at reducing low back pain during standing, the purpose of this study was to evaluate standing solely on a declining sloped surface to isolate the influence of the postural change alone. Seventeen participants performed two 75-minute prolonged standing occupational simulations in a random order – one on level ground and one a declining surface. Fifty-three percent of participants (9/17) were categorized as pain developers during the level ground standing condition; however, the average maximum pain scores of pain developers were 58% lower during sloped standing. All participants showed hip joint flexion, trunk-to-thigh angle flexion, and posterior translation of the trunk center of gravity towards the ankle joint when standing on the sloped surface compared to level ground. These postural changes could cause the muscles crossing the posterior aspect of the hip joint to increase their passive stiffness and assist with stabilizing the pelvis. This study stresses the importance of hip kinematics, not just lumbar spine posture alone, in reducing low back pain during prolonged standing. General Conclusions: The differences in posture of the lower lumbar arc between pain groups, the influence of standing aids on posture, and lower self-reported low back pain reports with a change in posture point to postural differences between the pain groups as being responsible for prolonged standing induced low back pain development. A working hypothesis for pain development is that when standing on level ground, pain developers stand with their lower lumbar arc closer to its end range of extension, placing additional mechanical load on the posterior elements of the lumbar spine resulting in transient pain. When mild flexion is induced, the mechanical load on these tissues would be decreased – a potential reason that low back pain is decreased as well. Future work should focus on lower lumbar arc and hip posture differences between the pain groups and alternative interventions that do not require a physical standing aid to reduce pain development. These include further assessment of the staggered standing position and the influence of an exercise intervention on posture and movement patterns