Rotation movements of the spine with special reference to scoliosis.

In the latter half of the nineteenth and early part of the twentieth centuries surgeons and anatomists studied the movements of the spinal column, both in the living and in the cadaver (Weber and Weber 1836, Schulthess 1899, Lovett 1905, Virchow 1907, Fick 1910, Strasser 1913). These researches culminated in the work of Lovett (1905), who concluded that the spine is a tube of unequal flexibilities, that rotation and lateral bending are inevitably linked, that rotation does not occur in the lumbar region, and that side-bending does not occur in the thoracic region. Lovett stated : “ in forward flexion, lateral flexion is associated with rotation to the convex side. In extension, lateral flexion is associated with rotation to the concave side.” He did not state what happens in the neutral position. Lovett also implied that scoliosis is an exaggeration ofa normal movement and that the mechanism ofits production can be deduced from a study of models exaggerating one or other feature of unequal flexibilities. Frazer (1940) assumed that the axis of rotation is in the centre of the vertebral body. From this assumption he concluded that the shape of the articular facets prevents rotation in the lumbar region or side-bending in the thoracic region. It will be clear that observation of the movements of the vertebral bodies in the adult model is necessarily indirect. In the formalin-hardened cadaver the intervertebral disc loses its normal plasticity, and the post-mortem specimen does not necessarily reproduce exactly the movements of the living spine. Furthermore, the older investigators were influenced by a priori considerations and had not accepted the concept of an inconstant axis of movement in joints. With the development of radiology, spinal movements have been reinvestigated and, first, flexion, extension, and, more recently, side-bending movements have been studied (Bakke 1931, Brailsford 1934, Steindler 1929, Tanz 1950, Begg and Falconer 1949, Wiles 1935). There has, however, been comparatively little recent work on rotation movements, either in the living subject or in fresh, flexible, necropsy specimens. It seemed, therefore, worth re-examining 1) the normal movements of the spine, noting in particular whether the spine does, in fact, behave as a tube of unequal flexibilities and whether side-bending and rotation are inevitably linked ; and 2) the relationship between movements of the normal spine and the deformity of scoliosis.