LARGE MAGNITUDE ADOLESCENT IDIOPATHIC SCOLIOSIS: ANTERIOR VS. POSTERIOR SURGICAL STABILIZATION

Jeffrey Wood MD,
Thomas Lowe MD,
Randal Betz MD,
David Clements MD,
Larry Lenke MD,
Peter Newton MD,
Andrew Merola MD,
Thomas Haher MD,
Dennis Wenger MD,
Jurgen Harms MD

PURPOSE:
This study was undertaken to evaluate the radiographic results of both anterior and posterior instrumentation in the treatment of AIS with primary curves >70°.

METHODS:
Patients with AIS and primary thoracic curves of >70° were selected from an AIS study group population compiled from 1995 – 1998. Preoperative, immediate postoperative, and 1 and 2 year follow–up radiographs were reviewed. Primary and secondary curves, flexibility, apical translation and rotation, end instrumented vertebral angulation, coronal and sagittal balance, and sagittal Cobb angles were measured.

RESULTS:
Twenty–one patients met criteria for this study with a mean age of 14.1 years. There were 17 females and 4 males with a minimum two–year follow–up. Nine procedures were performed from a posterior approach and 12 from an anterior approach. Three of the 9 posterior procedures also had an anterior release while only 2 of 12 anterior procedures had a concomitant posterior release. Flexibility of the curves in each group was not significantly different based on preoperative bending radiographs. The mean primary preop curve angle was 75° for the anterior group (70–96°) and 77° for the posterior group (70–97°) while immediate postoperative primary curves measured 32 and 24 degrees respectively (p=0.07). At 1 year, curve correction had been well maintained in both groups but at 2 years, the primary curves in the posterior group had a greater loss of correction and were equivalent to the anterior group (34° and 36° ; p=0.8). The average anterior instrumentation was 2.3 levels shorter for comparable curves than the posterior group. Apical translation showed a statistically significant improvement in the posterior group compared to the anterior group but this difference had been lost by the 2–year follow–up. There was a statistically significant improvement in the compensatory lumbar curve postoperatively within each group (p<0.001 anterior; p<0.001 posterior) which continued to improve throughout the follow–up period. However, there were no significant differences in the spontaneous lumbar curve correction between the two groups. Although end instrumented vertebral angulation (EIV–A) improved significantly in the postoperative follow–up period for both groups, there was a greater percentage change at each postoperative time point for the posterior group. Neither T1–rib angle nor global coronal balance showed any difference between the groups throughout the study. The preoperative sagittal profile demonstrated no significant differences between the two groups. The anterior group showed a postoperative trend toward increasing overall thoracic kyphosis from 37° to 46° (T2–TI2; p=0.3) and from 27° to 37° (T5–TI2; p=0.2).

CONCLUSIONS:
Final correction in both the coronal and sagittal planes were essentially equivalent. Although the construct was longer, correction of EIV–A is better accomplished through the posterior approach while the anterior procedure creates greater thoracic kyphosis. ASIF for large magnitude AIS curves is equally as effective as a PSIF with the advantage of saving motion segments.