The Journal of Bone and Joint Surgery, Vol 68, Issue 5 695-702, Copyright © 1986 by Journal of Bone and Joint Surgery, Inc
In vivo measurements of spinal column vibrations
MM Panjabi, GB Andersson, L Jorneus, E Hult and L Mattsson
Recent epidemiological studies have indicated high risk factors for persons
exposed to vibrations. We measured the in vivo responses of the lumbar
vertebrae and sacrum of five volunteers who were subjected to pure
sinusoidal vertical vibrations in the seated position. Two acceleration
amplitudes were used, one and three meters per second squared, with
frequencies ranging from two to fifteen hertz. Spinal vibration was
measured for two lumbar vertebrae using a transducer that was attached
directly to the spinous processes. Axial, horizontal, and rotatory
accelerations in the sagittal plane were determined for each vertebra.
Vertical acceleration at the sacrum was also measured. The amplitude ratios
of the accelerations at the vertebrae and sacrum with respect to the
acceleration of the seat were calculated. Our results show that the pure
vertical sinusoidal input vibration at the seat produced vibrations of the
lumbar vertebrae not only vertically but also horizontally, as well as a
rotational vibration. The resonance frequency of the lumbar vertebrae in
the vertical direction was an average of 4.4 hertz. Horizontal and rotatory
resonance frequencies could not be determined.
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