The clinical biomechanics of scoliosis

Abstract

Removal of the posterior elements will allow increased correction of axial deformity, in scoliosis. The clinician may take advantage of the creep and relaxation characteristic of the tissues to improve efficiency of correction. Axial loading has been shown theoretically to be more efficient for the more severe curves, (greater than 53 degrees) and transverse loading more efficient for the less severe curves (less than 53 degrees). Combined loading is always more efficient than either type alone. The Milwaukee brace can be just as effective as a cast in resisting deforming forces in scoliosis. Removal of axillary supports or thoracic pads or not wearing the brace when recumbent reduces the effectiveness of the Milwaukee brace. The strength of the thoracid lamina is a limiting factor in the amount of forces that may be applied to correct the deformity; 30 kilopond (65.8 lb) is the upper limit of this force. Coughing or buckling can apply dangerously high forces with the Harrington rod. Greater surgace contact of the hook to the lamina and small increments between notches on the rod may increase the tolerance limits of the system. Compression rods on the convex side probably add little or no correctional value. The Dwyer technique is biomechanically sound and effective and has the additional advantage of applying asymmetrical loads to the epiphyseal plates.