Anatomy of the extrinsic spinal muscles related to the deformities of scoliosis.

The spatial displacement of vertebrae in idiopathic scoliosis is not explicable by forces created by the muscles which act upon the spine only (intrinsic muscles). The trapezius and latissimus muscles are attached to the spinous processes and the upper limb. In keeping with Newton's third law, these muscles act on the spine as well as upon the upper extremity. The peculiarity of the vertebral anatomy, together with the direction of pull of these muscles, permits an explanation of the biomechanics of the development of 'idiopathic' scoliosis.