Lumbar coupling during lateral translations of the thoracic cage relative to a fixed pelvis

Objective. To determine lumbar coupling during lateral postural translation s (lumbosacral list) of the thoracic cage relative to a fixed pelvis. Design. Digitized measurements from anteroposterior lumbar radiographs of 1 7 volunteers were obtained in neutral, maximal left lateral translation and maximal right lateral translation posture of the thoracic cage compared to a fixed pelvis. Subjects were constrained with two sets of clamps at the l ateral borders of the pelvis and lower ribs. Background Data. Clinically, lumbosacral list is a common posture. Range of motion and spinal coupling results have not been reported for the lumbosac ral list movement. Methods. Four vertebral body corners, mid narrow-waisted body margins, supe rior and inferior pedicle margins, and spinous-lamina junction of T12-L5 we re digitized on 51 anterior-posterior lumbar radiographs. Using the orthogo nal axes of positive.udirection to the left, vertical as positive y, and an terior as positive z, digitized points were used to measure projected segme ntal z-axis rotation, y-axis rotation, and segmental lateral translations o f each vertebra. Results. Using the displacement of T12, subjects could translate 35-70 mm l eft or right along the x-axis with an average of 53.2 mm to the left and 52 .1 mm to the right. Using superior endplates to superior sacral base, later al flexion was largest at L1 and decreased from L1 to L5, but the segmental rotation angles for lateral flexion were largest at L2-L3 (3.9 degrees), L 3-L4 (6.2 degrees) and L4-L5 (5.7 degrees) and were in the same direction a s the main motion translation. The relative z-axis rotation of T12 was oppo site to the direction of L1-L5. The coupled y-axis rotations were less than 1 degrees and coupled segmental lateral translations were averaging less t han 1 mm. Conclusions. Thoracic cage x-axis translations compared to a fixed pelvis a re significant, between 35 and 70 mm. The z-axis lumbar coupled rotation wa s largest at L2-L3, L3-L4 and L4-L5 and to the same side of the main motion translation in L1-L5, but opposite the main motion direction for T12. AU o ther movements were small, averaging less than 1 degrees or 1 mm. (C) 1999 Elsevier Science Ltd. All rights reserved.