Ultrasound lumbar canal measurement in hospital employees with back pain

The oblique parasagittal diameter of the lumbar spinal canal at the L5-S I level was measured in 49 employees of the Wm Jennings Bryan Dorn Veterans' Hospital using real time ultrasound in a case-control study. Individuals with a canal diameter of less than 14 mm represented the lowest 10th percentile in this population and being in the narrowest 10th percentile constituted a risk factor for time missed from work because oflow back pain (odds ratio 10-7). Whereas numbers in this pilot study are small, results are consistent with earlier ultrasound studies done in the United Kingdom and with other research showing increased morbidity from low back pain in individuals with small lumbar canals. Ultrasound has advantages over other modalities for measuring the size of the lumbar canal and may be useful as a preplacement screening examination in industry. Low back pain (LBP) is a common condition that costs industry billions of dollars annually in workers' compensation claims alone.'2 A few claims result in a disproportionate amount of cost.23 In a study of Boeing Company employees 10% ofclaims accounted for 79% of the total costs from LBP.4 If workers at increased risk for developing high cost back injuries could be identified before injury occurs special training or job placement, or both, might lower their risk of serious low back disability, which would reduce both employee suffering and employer costs. An anatomically narrow lumbar spinal canal is associated with increased morbidity arising from at least three major conditions: intervertebral disc disease, neurogenic claudication (spinal stenosis syndrome), and root entrapment syndromes. The clinical importance of a stenotic lumbar canal has been increasingly understood in recent decades."2' The usefulness of this knowledge, however, has been severely limited by the difficulty in obtaining in vivo canal measurements without undue cost, exposure to radiation, or discomfort.22 In 1978 Porter et al first showed that midsagittal lumbar spinal canal diameters could be measured by ultrasound.23 They determined that lumbar canals were smaller in patients with disc symptoms than in controls, and that the greater the morbidity the smaller the canal size.2 13 Macdonald et al, using ultrasound, Accepted 24 August 1987 looked at 204 British coalminers and also found a strong tie between narrow lumbar canals and increased morbidity from LBP.'6 Since ultrasound examinations do not expose individuals to ionising radiation, and since the procedure is non-invasive, painless, and may be performed quickly and relatively inexpensively, it has decided advantages over other methods that may be used to measure canal diameters. This case-control study was undertaken as a pilot project. Its purpose was twofold: to confirm the observations of Porter et al that ultrasound may, in fact, be used to measure lumbar spinal canal diameters accurately'2 '3 and to determine if an association between narrow lumbar canal diameters and time lost from work because oflow back pain could be found in hospital workers (hospital workers do have a higher than usual incidence of low back injuries).' It is hoped that a long term prospective cohort study ofemployees at a veterans' hospital will follow. Materials and methods SUBJECTS Volunteers for the study were recruited from current employees of a VA hospital. Sixteen employees who had missed time from work in the past two years because of low back pain constituted the "back" group. The "control" group consisted of23 employees who denied ever having had low back pain of consequence. Those with previous low back surgery (which distorts ultrasound images) were excluded. All 552 group.bmj.com on May 29, 2017 Published by http://oem.bmj.com/ Downloaded from