Correction of flexible thoracic scoliosis below 65 degrees--a radiological comparison of anterior versus posterior segmental instrumentation applied to similar curves.

Unlabelled: Direct comparison of the correction of scoliosis achieved by different surgical methods is usually limited by the heterogeneity of the patients analyzed (their age, curve pattern, curve magnitude, etc.). The hypothesis is that an analysis of comparable scoliotic curves treated by different implant systems could detect subtle differences in outcome. The objective of this study was therefore: (1) to measure the 3D radiological parameters of scoliotic deformity and to quantify their postoperative changes, and (2) to compare the radiographic results achieved with one anterior and one posterior instrumentation methods applied to similar curves but representing different mechanisms of correction.

Material And Methods: The clinical notes and radiographs of 46 patients operated on for adolescent idiopathic scoliosis were reviewed. The inclusion criteria consisted of: a single thoracic curve, right convex, a frontal Cobb angle minimum of 45 degrees and a maximum of 65 degrees , flexibility on a lateral bending test of more than 30%, and a Risser test value of between 1 and 4. The operative procedures were: Cotrel-Dubousset instrumentation (CDI) for 25 patients (the CD group) and correction by anterior instrumentation (Pouliquen plate) for 21 patients (the ANT group). Preoperative and postoperative long cassette standing antero-posterior and lateral radiographs were examined. The frontal and sagittal thoracic Cobb angle, apical vertebra transposition (AVT), apical vertebra rotation (AVR), lowest instrumented vertebra (LIV) tilt, C7 vertebra shift and rib cage shift (RCS) were all compared. A computed reconstruction was produced with Rachis-91 software. Vertebral axial rotation angle was evaluated throughout the spine.

Results: Postoperative assessment revealed a mean correction of the frontal Cobb angle of 37.0 degrees for the CD group and 41.0 degrees for the ANT group. The AVT operative correction was 45.8 and 42.7 mm, respectively, and AVR correction was 1.8 and 12.6 degrees , respectively. The postoperative change of the sagittal Th4-Th12 Cobb angle was not significant for any method but it was significant (P=0.05) for the CD group if the curves were divided preoperatively into hypokyphotic and normokyphotic subgroups and then analyzed separately. Computed assessment demonstrated a correction of segmental axial rotation of more than 50% in the main thoracic curve in the ANT group, significantly more than that in the CD group (P<0.001).

Conclusions: Anterior instrumentation provided better correction of the vertebral axial rotation and of the rib hump. CD instrumentation was more powerful in translation and more specifically addressed the sagittal plane: the postoperative thoracic kyphosis angle increased in the hypokyphotic curves and slightly decreased in the normokyphotic curves.