Eur Spine J (1996) 5 : 332-337 9 Springer-Verlag 1996 M. Szpalski F. Michel J.-P. Hayez Determination of trunk motion patterns associated with permanent or transient stenosis of the lumbar spine Received: 17 January 1996 Revised: 1 April 1996 Accepted: 4 May 1996 M. Szpalski (N~) 9 F. Michel 9 J.-P. Hayez Department of Orthopedics, Centre Hospitalier Molibre Longchamp, 142 rue Marconi, B-1180 Brussels, Belgium Tel. +32-2-348 51 11; Fax +32-2-348 51 45 Abstract Dynamometric devices used to assess back function are be- coming increasingly used in research as well as in clinical practice. These devices provide values for a variety of movement variables such as torque, displacement, and velocity, but they also enable the study of movement patterns. The purpose of this study was to determine the movement pat- terns of patients presenting with spe- cific spinal pathologies. Thirteen pa- tients with spinal stenosis and 14 pa- tients with degenerative changes and a borderline spinal canal diameter, as well as a control group of 30 symp- tom-free subjects, were studied. An isoinertial trunk-testing dynamomet- ric device was used. Sagittal velocity and position were measured against a resistance set to 50% of the subject's maximum isometric torque. A phase plane analysis (velocity against posi- tion) was performed for each subject. An ensemble averaging technique was used to average the repetitions of every subject and a normalization technique was employed to draw an average graph for each group. This graph showed distinct patterns of movement for the three groups. The differences appeared mostly during the extension phase of movement, as confirmed by statistical analysis. The spinal stenosis group showed lower velocities than the controls during the entire extension phase (P < 0.05), while the borderline spinal canal group demonstrated a significant de- crease in velocity at the end of the extension phase (P < 0.01). These findings can be related to the increase in disk bulge and decrease in the di- ameter of the spinal canal during ex- tension. This study shows the rela- tion between some spinal pathologies and movement patterns. This type of functional assessment may be a valu- able tool for assessing the relation between anatomical lesions and function and for determining the re- sponsibility of findings such as bulging disk and/or facet syndrome in causing a patient's complaints. Key words Trunk function 9 Motion patterns - Spinal stenosis 9 Isoinertial 9 Lumbar spine Introduction Low back pain is certainly one of the most frequent and most disabling health problems affecting our society, and its incidence appears to be increasing. This complaint will affect 80% of the population in the United States and Great Britain at some point during their lifetime [2, 3, 27]. Approximately 2.4 million US Americans are disabled because of low back disorders, the major cause of disabil- ity under the age of 45 [ 11]. In Belgium, the average level of industrial compensation for back pain is twice the aver- age of other compensation cases [8]. In the same country, a recent population study showed that 22% of adults re- port daily low back pain [27].