Surgical management of kyphotic deformity in ankylosing spondylitis

Abstract

Ankylosing spondylitis typically affects the large girdle joints and the axial skeleton with bony ankyloses of the synovial joints resulting in stiffness and deformity. The commonest deformity is kyphosis affecting the thoracolumbosacral spine and less so at the cervical spine leading to sagittal balance and a low gaze angle. Stress fractures with or without dislocations can occur with minor injuries frequently complicated by nonunion and pseudoarthrosis formation. Fortunately with more effective medical treatment in the recent decades the incidence of severe deformity is obviously on the decline. There is still controversy on whether one should tackle the hips or spinal deformity first but most surgeons are in favor of the former which is a relatively simpler surgery with more reliable outcome. Spinal extension osteotomy with shortening of the posterior column is preferred to anterior column lengthening. Correction at the maximum kyphosis should give the best cosmetic effect. However an osteotomy at the lower lumbar segment can magnify the amount of sagittal translation and is safer neurologically. Multilevel Ponte type of osteotomy can produce a smoother contour of correction but each osteotomy can only provide <10 degrees of correction. A single level pedicular subtraction osteotomy with resection of the middle column can typically provide 30 degrees of extension correction. Vertebral column resection is seldom needed in AS. The location and number of the osteotomies depend on the morphology and severity of the deformity. A careful preoperative planning with simple xray templating or software programs should be done. One should be aware of the location of the ‘new apex’ of the kyphosis after correction and thus avoid ending the instrumentation at this site. Stress fractures at the junction can occur if not handled appropriately. Positioning of the patient intraoperatively can be a challenge to the anesthesiologist. Supporting frames may have to be tailor made for deformities of different severities. Electrophysiologic monitoring is mandatory especially when osteotomies are performed at the cord level. Successful correction of kyphotic deformity in ankylosing spondylitis is very rewarding not only physically but also on the self-esteem of the patient.