RESUMO
Background: Detection of neuraxial abnormality in neurologically asymptomatic adolescent idiopathic scoliosis (AIS) is crucial prior to surgery. It can only be detected on magnetic resonance imaging (MRI), which was not routinely done in this group of patient. On the other hand, whole spine radiographs for measurement of Cobb angle have been routinely included during clinic follow-up. This study aimed to determine the correlation between Cobb angle progression and neuraxial abnormality finding on MRI in asymptomatic AIS. Methods: A retrospective study was conducted in the Orthopaedic department of a tertiary hospital. Patients with asymptomatic AIS aged 10-20 years who attended scoliosis clinic from year 2007 to 2010 was reviewed. Patients who had whole spine MRI and two vertebral radiographs at least one year apart were further selected. Statistical analysis was done to see the association between Cobb angle progression and neuraxial abnormality on MRI. Results: The mean age at first presentation was 14.4 years old. Female (n=249) to male (n=50) ratio was 5:1. Only 19 patients fulfilled the selection criteria. There were 5 patients (26.3%) who had neuraxial abnormalities. The mean curve progression was 7.05° (range from -5° to 28°). Patients with and without neuroaxial abnormality showed mean curve progression of 0.6º and 9.36° respectively. There was no significant association between Cobb angle progression and neuroaxial abnormality (p=1.000). Conclusion: Cobb angle progression is not a reliable indicator for predicting neuroaxial abnormality in patients with asymptomatic AIS. However, this study stressed the need to perform MRI prior to operation to document any associated neuraxial abnormality in clinically asymptomatic AIS patients.
RESUMO
Posterior instrumentation is a common fixation method used to treat thoracolumbar burst fractures. However, the role of different cross-link configurations in improving fixation stability in these fractures has not been established. A 3D finite element model of T11-L3 was used to investigate the biomechanical behavior of short (2 level) and long (4 level) segmental spine pedicle screw fixation with various cross-links to treat a hypothetical L1 vertebra burst fracture. Three types of cross-link configurations with an applied moment of 7.5 Nm and 200 N axial force were evaluated. The long construct was stiffer than the short construct irrespective of whether the cross-links were used (p < 0.05). The short constructs showed no significant differences between the cross-link configurations. The XL cross-link provided the highest stiffness and was 14.9% stiffer than the one without a cross-link. The long construct resulted in reduced stress to the adjacent vertebral bodies and screw necks, with 66.7% reduction in bending stress on L2 when the XL cross-link was used. Thus, the stability for L1 burst fracture fixation was best achieved by using long segmental posterior instrumentation constructs and an XL cross-link configuration. Cross-links did not improved stability when a short structure was used.
