Kinematics and movement sequencing during flexion of the lumbar spine

Objectives. This study investigated the sequence of intervertebral joint mo vements and range of motion during three tasks involving lumbar flexion. Design. Position sensors were used to measure position and rotation of lumb ar 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 ve rtebrae of 14 volunteers. Volunteers performed three flexion tasks; unconst rained 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 pos ition. Results. Four definitive movement sequences were identified for those subje cts with consistency between replicates; 'top down' motion (where the top o f 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 la st), 'all together' (where all segments commence movement together), and 'm iddle last' (where the middle segments of the lumbar spine are last to comm ence movement). Subjects not fitting one of these sequences were categorise d into a miscellaneous group. Only two subjects exhibited the same sequence for each of the three tasks, while other subjects exhibited two or three d ifferent 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 m ovement sequence exhibited by the sample population. Relevance Incorrect assumptions which are incorporated into mathematical mo dels have the potential to influence model output. Given that output from s pinal models is often used to assess ergonomic issues such as safe lifting loads, validation of the assumptions is essential. (C) 1999 Elsevier Scienc e Ltd. All rights reserved.