Function of the Spine
Gracovetsky S.
Journal of Biomedical Engineering
8 : 217-233, 1986.
Abstract
In spite of the considerable effort which has been
invested in attempts to understand the mechanism of human
spines, substantial controversy remains, particularly in
connection with assumptions which have to be made by
those engaged in biological modelling. The hypothesis
presented here is that the living joint has stress
sensors driving a feedback mechanism, an arrangement
which could react to imposed loads by modifying muscular
action in such a way as to minimize stress at the joints
and therefore the risk of injury. A theory of this kind
gives an image of the spine not in terms of a spatial
picture, as would a CAT scan, but in terms of stresses,
forces and moments acting at the intervertebral joints.
Calculations show that the erectores spinae alone cannot
support more than about 50 kg; there must be some other
mechanism to explain man's ability substantially to
exceed that load. It is suggested that the interaction
between the erectores spinae and the abdominals are of
fundamental importance in the function of the spine; how
they are co-ordinated during the lifting of weights is
examined in detail. The theory resulting from this
hypothesis is used to relate spinal injury and an injured
subject's posture and behaviour. A mathematical
formulation permits an objective evaluation of the spine,
and a procedure for determining an automatic diagnosis of
lumbar spine disabilities is proposed.
