Proximal Kyphosis After Posterior Spinal Fusion in Patients With Idiopathic Scoliosis

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Abstract

Study Design.

For this retrospective study, preoperative and postoperative radiographs of posterior spinal fusions for idiopathic scoliosis were reviewed.

Objectives.

To determine the prevalence and possible causes of proximal kyphosis after posterior spinal fusion for idiopathic scoliosis.

Summary of Background Data.

Proximal kyphosis has been anecdotally noted after the insertion of Harrington rods and after use of the new posterior multisegmented hook/rod systems. In this study no attempt was made to determine whether this condition is painful or an adverse outcome for the patient or just a radiographic abnormality; however, it is suspected that this may be a problem in the long term, and it may be worthwhile to try to avoid it if predictive values can be ascertained.

Methods.

Patients with adolescent idiopathic scoliosis who had undergone posterior 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 through 1994, 69 met the inclusion criteria. Abnormal kyphosis from T2 to the proximal level of the instrumented fusion was defined as kyphosis of more than 5° 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 patients with abnormal proximal kyphosis, the measurement from T2 to the fusion was 10.3° before surgery and 21.2° after surgery. The normal group had kyphosis measuring 2.7° from T2 to fusion before surgery and 5.3° after surgery (P < 0.00001). Junctional kyphosis in the kyphosis group measured 6.5° before surgery and 12.6° after surgery, compared with normal kyphosis of 1.7° and 2.6°, respectively (P < 0.00001). When analyzing who would develop proximal kyphosis, preoperative one-level junctional kyphosis of more than 5° above the proposed proximal instrumented vertebrae was shown to have the highest sensitivity (78%) and specificity (84%).

Conclusions.

In this study, 32 (46%) of 69 patients had abnormal proximal kyphosis after undergoing posterior spinal fusion. A preoperative junctional kyphosis of more than 5° above the proposed proximal instrumented vertebrae indicates that extending the fusion to a higher level in the thoracic spine would be beneficial in avoiding this problem.

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