Muscle forces in the posterior thoracic spine.

Using a three-dimensional model, the theoretical maximal forces that can be generated by electrical stimulation of several posterior thoracic muscles have been analyzed to investigate the kinesiology of scoliosis. None provides a pure lateral bending moment, and most exaggerate lordosis. None satisfactorily generates a rotary force for correction of scoliotic deformity. Although maximum muscle contraction can ideally produce lateral bending moments of the same magnitude as the Milwaukee brace, current techniques do not cause continuous, complete muscle contraction. The best muscle studied for electrospinal intrumentation is the lateral erector spinae. Multiple sites of stimulating electrodes are probably necessary. None of the individual muscles studied is ideal. Further investigation should be directed to the stimulation of anterior thoracic muscles.