Abstract
Objective: To identify radiographic parameters which could predict postoperative spinal decompensation in the frontal plane in King type II adolescent idiopathic scoliosis after posterior thoracic correction and fusion with third generation instrumentation systems.
Design: Retrospective radiographic analysis.
Subjects: The radiographs of 36 patients with King type II adolescent idiopathic scoliosis (AIS) who had had posterior thoracic correction and fusion, either with the Cotrel-Dubousset instrumentation (CDI) or the Universal Spine System (USS), were evaluated in terms of frontal and sagittal plane balance, curve flexibility, and curve correction with a minimum follow up of two years. Postoperative spinal decompensation in the frontal plane was investigated with respect to preoperative radiolographic parameters on standing upright AP, thoracic and lumbar supine side-bending as well as lateral standing radiographs. Spinal decompensation in the frontal plane was defined as plumbline deviation of C7 of more than 2 cm with respect to the centre sacral line within two years postoperatively. Two groups of patients were analyzed.
Outcome measures: 26 patients (72%) showed satisfactory frontal plane alignement by means of C7 plumb line deviation (group A, 1.2 cm to the left), whereas 10 patients (28%) showed spinal decompensation (group B: 2.7 cm to the left). Group differences were significant (p=0003).
Results: The two groups were found statistically equivalent in terms of preoperative C7 plumbline deviation (p=0.112, group A: 0.8 cm, group B: 0.7 cm to the left), thoracic cobb angles (p=0.093, group A: 56°, group B: 62°), lumbar cobb angles (p=0.115, group A: 42°, group B: 47°), lumbar curve flexibility (p=0.153, group A: 78%, group B: 67%); thoracic kyphosis (p=0.153) and lumbar lordosis (p=0.534) and age at operation (p=0.195), Significant group differences, however could be revealed for thoracic curve flexibility (p=0.03, group A: 43%, groupB: 25%) and the percentage of derotation of lumbar apical vertebrae in lumbar supine side-bending films in comparison to AP upright standing radiographs (p=0.002, group A: 49%, group B: 27%). Average thoracic curve correction was 51% in group A and 41% in group B. Group differences were significant (p=0.05). Average lumbar curve correction was 34% in group A and 23% in group B (p=0.09). No group differences could be revealed for postoperative thoracic kyphosis and lumbar lordosis measurements. Logistic regression analysis with C7 plumbline deviation of more than 2 cm postoperatively as the dependent variable yielded the amount of lumbar apical vertebral derotation in lumbar supine side-bending films as the only risk-factor (p=0.007).
Conclusion: Fixed lumbar rotation, measured in terms of the percentage of derotation of lumbar apical vertebrae in lumbar supine side-bending films in comparison to AP upright standing radiographs, provided the radiographic prediction of spinal decompensation in the frontal plane after posterior thoracic correction and fusion of King II type curves.
The abstracts were prepared by Mr Peter Millner. Correspondence should be addressed to Peter Millner, Consultant Spinal Surgeon, Orthopaedic Surgery, Chancellor Wing, Ward 28 Office Suite, St James’ University Hospital, Beckett Street, Leeds LS9 7TF.
