Proximal kyphosis after posterior spinal fusion in patients with idiopathic scoliosis

Study Design. For this retrospective study, preoperative and postoperative radiographs of posterior spinal fusions for idiopathic scoliosis were revie wed. Objectives. To determine the prevalence and possible causes of proximal kyp hosis after posterior spinal fusion for idiopathic scoliosis. Summary of Background Data. Proximal kyphosis has been anecdotally noted af ter the insertion of Harrington rods and after use of the new posterior mul tisegmented hook/rod systems. In this study no attempt was made to determin e whether this condition is painful or an adverse outcome for the patient o r just a radiographic abnormality; however, it is suspected that this may b e a problem in the long term, and it may be worthwhile to try to avoid it i f predictive values can be ascertained. Methods. Patients with adolescent idiopathic scoliosis who had undergone po sterior spinal fusion not extending above T3 with good-quality radiographs of the proximal thoracic spine and a minimum 2-year follow-up were studied. Of the 106 patients who underwent posterior spinal fusion from 1990 throug h 1994, 69 met the inclusion criteria. Abnormal kyphosis from T2 to the pro ximal level of the instrumented fusion was defined as kyphosis of more than 5 degrees above the summed normal angular segments. Results. Of 69 patients, 37 (54%) had normal proximal kyphosis, and 32 (46% ) of the 69 were defined as having abnormal proximal kyphosis. In the 32 pa tients with abnormal proximal kyphosis, the measurement from T2 to the fusi on was 10.3 degrees before surgery and 21.2 degrees after surgery. The norm al group had kyphosis measuring 2.7 degrees from T2 to fusion before surger y and 5.3 degrees after surgery (P < 0.00001). Junctional kyphosis in the k yphosis group measured 6.5 degrees before surgery and 12.6 degrees after su rgery, compared with normal kyphosis of 1.7 degrees and 2.6 degrees, respec tively (P < 0.00001). When analyzing who would develop proximal kyphosis, p reoperative one-level junctional kyphosis of more than 5 degrees above the proposed proximal instrumented vertebrae was shown to have the highest sens itivity (78%) and specificity (84%). Conclusions. In this study, 32 (46%) of 69 patients had abnormal proximal k yphosis after undergoing posterior spinal fusion. A preoperative junctional kyphosis of more than 5 degrees above the proposed proximal instrumented v ertebrae indicates that extending the fusion to a higher level in the thora cic spine would be beneficial in avoiding this problem.