Kinematics and movement sequencing during flexion of the lumbar spine

Objectives. This study investigated the sequence of intervertebral joint movements and range of motion during three tasks involving lumbar flexion. Design. Position sensors were used to measure position and rotation of lumbar vertebrae during unconstrained flexion. Background. In the development of mathematical models, numerous assumptions need to be made. Few studies have attempted to assess the validity of the assumptions regarding kinematics in models of the lumbar spine. Methods. Position sensors were attached to the skin overlying the lumbar vertebrae of 14 volunteers. Volunteers performed three flexion tasks; unconstrained flexion from upright standing, with and without a mass of 5 kg held close to the body, and the transition from upright standing to a seated position. Results. Four definitive movement sequences were identified for those subjects with consistency between replicates; 'top down' motion (where the top of the lumbar spine starts to move first and the bottom moves last), 'bottom up' (where the bottom of the lumbar spine moves first and the top moves last), 'all together' (where all segments commence movement together), and 'middle last' (where the middle segments of the lumbar spine are last to commence movement). Subjects not fitting one of these sequences were categorised into a miscellaneous group. Only two subjects exhibited the same sequence for each of the three tasks, while other subjects exhibited two or three different sequences for the three tasks, or showed a lack of consistency for one of the tasks. Conclusions. The results from this study indicate that there is no single movement sequence exhibited by the sample population. Relevance Incorrect assumptions which are incorporated into mathematical models have the potential to influence model output. Given that output from spinal models is often used to assess ergonomic issues such as safe lifting loads, validation of the assumptions is essential. (C) 1999 Elsevier Science Ltd. All rights reserved.