Spine (Phila Pa 1976). 2010 Jun 30. [Epub ahead of print]
Prospective longitudinal study to evaluate the effect of bed rest on the lumbar musculature and soft-tissues. Earlier work has suggested that the risk of low back injury is higher after overnight bed rest or spaceflight. Changes in spinal morphology and atrophy in musculature important in stabilizing the spine could be responsible for this, but there are limited data on how the lumbar musculature and vertebral structures are affected during bed rest.
Nine male subjects underwent 60 days head down tilt bed rest as part of the second Berlin Bed Rest Study. Disc volume, intervertebral spinal length, intervertebral lordosis angle, and disc height were measured on sagittal plane magnetic resonance images. Axial magnetic resonance images were used to measure cross-sectional areas of the multifidus, erector spinae, quadratus lumborum, and psoas from L1 to L5. Subjects completed low back pain questionnaires for the first 7-days after bed-rest.
Increases in disc volume, spinal length (greatest at lower lumbar spine), loss of the lower lumbar lordosis, and move to a more lordotic position at the upper lumbar spine were seen. The cross-sectional areas of all muscles changed, with the rate of atrophy greatest at L4 and L5 in multifidus and at L1 and L2 in the erector spinae. Atrophy of the quadratus lumborum was consistent throughout the muscle, but cross-sectional areas of psoas muscle increased. Subjects who reported low back pain after bed rest showed, before reambulation, greater increases in posterior disc height, and greater losses of multifidus cross-sectional areas at L4 and L5 than subjects who did not report pain. These results provide evidence that changes in the lumbar discs during bed rest and selective atrophy of the multifidus muscle may be important factors in the occurrence of low back pain after prolonged bed rest.
