Selective Anterior or Posterior Thoracic Fusions in Lenke 1 Adolescent Idiopathic Scoliosis with Lumbar Curves Greater than Forty Degrees

·(a – DePuy Acromed – Implants)

Introduction: Adolescent idiopathic scoliosis (AIS) has been effectively treated with either anterior or posterior instrumentation. Selective anterior thoracic instrumentation demonstrates greater thoracic and lumbar curve correction. Selective thoracic fusions have not been fully evaluated in type 1 Lenke curve patterns with high magnitude lumbar secondary curves.

Purpose: To evaluate the outcome of selective anterior or posterior thoracic fusion in type 1 Lenke curves with secondary lumbar curves > 40 degrees in AIS.

Materials and Methods: Thirty-eight patients average age 14+7 with Lenke 1 curve patterns having a lumber curve > 40 degrees were treated with selective thoracic instrumentation with either an anterior (n=31) or posterior (n=7) approach. Anterior instrumentation consisted of either a 4.0 or 5.0 solid rod/screw construct. Posterior instrumentation consisted of dual rod hook and screw constructs. Radiographs were evaluated pre-op and post-op at one and two years. Measurements included: Cobb levels of thoracic and lumbar curves, percent flexibility and magnitude, end instrumented vertebral angulation (EIVA), end instrumented vertebral disc angulation (EVA), coronal balance, instrumented levels, and Lenke lumbar modifiers.

Results: In the ASF group (n=31), the mean thoracic curve was 58 degrees (range 46-72 degrees) and the secondary lumbar curve was 44 degrees (range 40-58 degrees). In the PSF group (n=7), the mean thoracic curve was 66 degrees (range 53-83 degrees) and the lumbar curve was 45 degrees (range 40-55 degrees). Pre-op, there was no statistical differences between curve magnitude, curve flexibility, Lenke lumbar modifiers, coronal balance, and EIVA between the groups. Also pre-op, the Lenke lumbar modifier in 2/7 PSF patients and 9/31 ASF patients was grade C. Post-op, there was no statistical difference between the % thoracic and lumbar curve correction, EIVA, and EVA between the groups. The posterior group had a mean of 0.9 more levels fused distally. There was a statistical difference in the post-op C7-S1 coronal balance with the PSF group having mean of 2.5 cm greater imbalance than the ASF group (p=0.026). The mean spontaneous correction of the lumbar curve in the posterior group was 49% (range 16-65%)and in the anterior group 46% (range 33- 73%). In the posterior group, the Lenke lumbar modifier remained the same in 3/5, improved in 2/7, and worsened in 2/7 patients. In the anterior group, 19/31 remained the same, 10/31 improved, and 2/31 worsened.

Discussion: Previous reports comparing selective anterior versus posterior instrumentation for Lenke 1 curve patterns suggest better instrumented and un-instrumented curve correction with selective anterior thoracic instrumentation and fusion. This study suggests that high magnitude (>40 degrees) lumbar curves respond differently than smaller curves to selective anterior thoracic instrumentation with results being very similar between the two groups except for a higher incidence of coronal postoperative imbalance in the PSF group. The number of patients with large magnitude secondary lumbar curves undergoing selective thoracic instrumentation and fusion alone is small, however, PSF and ASF have similar results but maintain a flexible lumbar spine.

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