Abstract
Background: The study evaluates the inter-relationships between Cobb angle (CA), apical vertebral rotation (AVR), apical vertebral translation (AVT) and maximal angle of trunk inclination (max ATI). The effects of sex, curve laterality, curve type and apical levels will be studied
Methods: This is a study of consecutive pre-operative AIS patients. There are 122 pre-operative AIS patients (106 thoracic, 16 thoracolumbar), with a mean age of 15.6 years. From the pre-operative AP radiograph, CA, AVR (Perdriolle) and AVT are measured. The max ATI is measured using the Scoliometer with the patient in a standing forward bending position. Ratios between the measurements are calculated to allow comparison between different curve types and curves at different apical levels.
Results: For a given Cobb angle, each of AVR, AVT and max ATI are largest in King type IV curves, less in King type III curves and smallest in King type II curves (p=0.001 to 0.015). For curves without a significant compensatory curve, for a given AVR, the max ATI reduces significantly as the curve apex passes caudally (p=0.002 to 0.019). Sex and curve laterality are not significant factors.
Conclusion: It is suggested that as a curve develops, the interaction between the measurements in different planes may be responsible for determining the curve type (presence or absence of a compensatory curve). The smaller surface hump as the curve apex passes caudally is probably due to the transition from fixed ribs to floating ribs to no ribs. These finding also have implications for surgery. In King type IV and III curves, the emphasis should be on correcting translation and derotation perhaps with a primary costoplasty whilst in King type II curves, the emphasis should be on the correct selection of fusion levels and achieving a balanced spine.
The abstracts were prepared by Mr Colin E. Bruce. Correspondence should be addressed to Colin E. Bruce, Consultant Orthopaedic Surgeon, Alder Hey Children’s Hospital, Eaton Road, Liverpool, L12 2AP.
