General Session: Adult Spinal Deformity

Presented by: J.H. Tan - View Audio/Video Presentation (Members Only)

Author(s):

J.H. Tan(1), D. Hey Hwee Weng(1), G. Wong(1), H.-K. Wong(1), L.L. Lau(1)

(1) National University Hospital, Singapore, Department of Orthopaedic Surgery, Singapore, Singapore

Abstract

Introduction: Selective thoracic fusion offers deformity correction of Lenke I and II thoracic curves and maintain range of movement of lumbar curves. A small group of patients may develop post-operative lumbar adding-on. This study aimed to identify risk factors that predicts adding-on. Methodology: This was a retrospective cohort study, which included all patients ≤ 18 years old that underwent spinal instrumentation for Lenke I and II scoliotic curves in a single tertiary centre. Demographic, clinical, and radiographic data were included. Sagittal radiographic measurements including cervical, thoracic, thoracolumbar and lumbar angle were included. Coronal radiographic measurements included Cobb angle of proximal thoracic curve (PT), main thoracic curve (MT), and lumbar curve (L). The data was recorded pre-operatively, post-operatively, 6months, 1year, 2year, 5year, and 10year post-operatively. Lumbar adding-on was defined as progressive changes of more than 50 increase in Cobb angle at more than 2 consecutive instances.

Results: 161 patients were included (147 females and 14 males). The mean age was 14.0±2.1 years. 103 patients were Lenke I, and 58 patients were Lenke II curves. Lumbar modifier was as follows: (a) in 80 patients; (b) in 43 patients; and (c) in 37 patients. Neutral thoracic modifier was most common, with 119 patients. 22 patients were Risser 0, 26 Risser I, 18 Risser II, 28 Risser III, 27 Risser IV, and 40 Risser V. 97 patients underwent posterior approach surgery, while 64 via anterior approach. In the posterior approach group, 79 (81.4%) patients underwent selective fusion. All patients who underwent anterior approach had selective fusion. A mean of 9.9±2.2 levels was instrumented. Patients who underwent selective fusion had 2.3 levels preserved as compared to patients who underwent non-selective fusion. The mean follow-up period was 4.4±2.7 years (2.7-11 years).10 patients (6.2%) had lumbar curve adding-on. The mean age was 13.3±1.8 years, with 9 females and 1 male. There were 7 Lenke I and 3 Lenke II patients. All 10 patients were lumbar modifier (a), with 5 patients with neutral thoracic modifier, and 5 hypokyphotic patients. The flexibility index was 0.38 ± 0.2. The mean pre-operative PT angle was 27.50±15.80, MT angle 49.30±15.40, and L angle 21.30±13.10. 4 underwent surgery via the anterior approach, while the other 6 had posterior approach. Selective fusion was done in 9 patients (90%). Lumbar adding-on was seen most commonly between 6months to 1year post-operative period (5 patients). The average magnitude of adding-on was 10.70. 2 patients had adding-on because of incorrect distal fusion level, 6 were due to 1AR or 1AR-like curve, 1 due to the inadvertent fusion from the excessive long rod at the subjacent level. In 1 patient, no obvious cause can be identified. In multivariate analysis, hypokyphotic patients were at higher risk of lumbar adding-on (OR=9.2,95%CI:1.7-50.4, p=0.010). Patients with Risser classificaton 0, I, II, III were also at higher risk of lumbar adding-on (OR =6.1,95%CI:1.85-12.4,p=0.041) as compared to Risser IV and V.

Conclusion: The incidence of lumbar curve adding-on was 6.2% in this study. Patients who were hypokyphotic are 9 times more likely to have lumbar adding-on and patients who are skeletally immature were 6 times more likely to have lumbar adding-on.