Effect of pelvic-femoral position on vertebral separation produced by lumbar traction

The purpose of this study was to determine the relationship between hip position and the amount of vertebral separation produced by intermittent lumbar traction. Ten subjects received intermittent lumbar traction at a force of 31.8 kg (70 lb) for 15 minutes in each of three positions of hip flexion (supine): 0 degrees, 45 degrees, and 90 degrees. Vertebral separation was measured on lateral roentgenograms by outlining and marking the vertebral bodies and measuring interspaces with fine-point calipers. Except for the T12-L1 interspace, traction produced greater posterior interspace separation as the angle of hip flexion increased from 0 to 90 degrees. These differences were statistically significant at interspaces L4-5 and L5-S1. We found no systematic changes in anterior interspace distance. To produce maximal posterior vertebral interspace separation, pelvic traction should be applied with the hip flexed 90 degrees.