The study aimed to develop and assess a new classification system for Segmentation Defects of the Vertebrae (SDV), a frequent cause of congenital scoliosis. Existing nomenclature for the wide range of SDV phenotypes is inadequate and confusing eg ‘Jarcho-Levin syndrome’. A multidisciplinary group of the International Consortium for Vertebral Anomalies and Scoliosis (ICVAS) met to formulate a new classification system, based primarily on radiology. SDV are identified by number affected, contiguity, and spinal region(s). The size, shape and symmetry of the thoracic cage, and rib number, symmetry and fusion are included, and familiar vertebral morphology terms retained, together with accepted syndrome names. The terms spondylocostal and spondylothoracic dysostosis apply only to phenotypes typified by the monogenic disorders due to mutated DLL3, MESP2, LNFG and HES7 genes. Five ICVAS members (Group 1) then independently assessed 10 new cases, inter-observer reliability assessed using kappa. Seven independent radiologists (Group 2) then assessed the same cases before and after introduction to the new system. Inter-observer reliability for Group 1 yielded a kappa value of 0.21 (95% confidence intervals (CI) 0.052, 0.366, p=0.0046). For Group 2, before introduction to the new system, 1/70 responses (1.4%) agreed with the Group 1 consensus,12 different diagnoses were offered, and 38/70 (54.3%) responses were ‘Unknown’. After introduction to the new system 47/70 responses (67.1%; 95% CI 55.5, 77.0) agreed with Group 1 consensus, a 65.7% improvement (95% CI 52.5, 75.6, p<
0.00005). The system was well received by 6/7 radiologists. The new system was found to be reliable and acceptable.
