Idiopathic Thoracic Spinal Deformaties and Compensatory Mechanisms

Abstract

Idiopathic scoliotic and kyphotic deformities have been described since Hippocrates. During the early twentieth-century fusion techniques were introduced, but only during the last decades innovations in the operative techniques have improved the surgical outcome of idiopathic spinal deformities. Preoperative planning and surgical correction not only concerns the primary spinal deformity but is closely linked with compensatory mechanisms. The studies for this thesis were undertaken to assess the effect of selective fusion in adolescent thoracic idiopathic scoliosis and kyphosis and to analyse compensatory mechanisms in order to predict the surgical result. In scoliosis surgery correction will induce an en bloc postoperative rotation of the compensatory lumbar segments and affect the rib hump correction. The correcting forces applied by the instrumentation induce this en bloc rotation of the unfused lumbar segments. In detail: the unfused lumbar spine of a patient with a King type II curve will show a larger lumbar rotation shift and subsequent rib hump correction than that of a patient with a King type III curve. The rotational dynamics of the unfused compensatory lumbar spine seem to form an important component in the understanding and surgical management of scoliosis. For kyphosis the study results indicate that tight hamstring patients have a significant greater risk for postoperative imbalance. These patients have a fixed pelvis and can only compensate for imbalance by reducing their lumbar lordosis. Limitations in lumbar and pelvic ROM are predicted by hamstring tightness. Hamstring tightness should be considered as a predictor in the surgical management of thoracic Scheuermann's Disease. Tight hamstring patients can be classified as 'lumbar compensators' and as such are prone to overcorrection and imbalance. In conclusion: when planning surgery preoperative assessment of the compensatory mechanisms is essential