Morphology and Progression of Congenital Scoliosis: An Analysis of Unilateral Unsegmented Bar and Abnormal Rib Alignment

PURPOSE: Although the Winter’s classification is widely used to predict progression of congenital scoliosis, a reliable indicator has not yet established. The purpose of this study is to clarify the association between curve progression and unilateral unsegmented bar (BAR) or abnormal rib alignment (ARA).

METHODS: Firstly, we examined X-rays of 20 idiopathic scoliosis (IS) patients (all female, age: 14±4 yo with a range of 7^ÿ23 yo) with thoracic curve of 23.5±9.1° on average to determine the rib alignment of IS. We found rib interval of concave side is narrowest at the one or two level cranial to the apex and the interval demonstrated successive change in all cases. Thus we defined ARA as follows: “the narrowest rib interval exists other than one or two level cranial to the apex” or “the change of the interval is not continuous”. 32 patients of congenital scoliosis (M/F=15/17, age=7.1+5.0 y.o.) were followed for 6 years and 4 months on average. The curve was classified into four groups by the simplified Winter’s classification. I: failure of segmentation (BAR), II: failure of vertebral segmentation, III: failure of formation, IV: combination of I-III. We also investigated the relationship between curve progression and ARA. Progression rate was calculated as increased Cobb angle divided by follow-up period (deg/year). Progression rate was compared regarding to the Winter’s classification, BAR and ARA.

RESULTS: Progression rates were I: 6.1+7.6 (n=4), II: 13.6+7.7 (n=5), III: 3.7+3.4 (n=8), and IV: 4.2+4.9 (n=15). Progression rate of group II was significantly higher than group III or IV (p<0.05). There was no significant difference in curve progression between the patients with BAR (n=4) and the patients without BAR (n=28). On the other hand, the patients with ARA (n=19) demonstrated significantly higher progression rate than the cases without ARA (n=13) (8.6+6.7 v.s. 1.8+1.8, p<0.01).

CONCLUSIONS: BAR in this series was not related to progression of the curve probably due to difficulty in determination of the anomaly in immature patients. Whereas, it was easier to identify ARA. The patients with ARA demonstrated greater progression in Cobb angle than the patients without ARA. If failure of segmentation occurred in vertebra, adjacent rib head can be involved. This suggests that ARA that can be an indicator of curve progression in congenital scoliosis.