Surgical Outcomes Research

Comparison of Compensatory Curve Spontaneous Derotation After Selective Thoracic or Lumbar Fusions in Adolescent Idiopathic Scoliosis

Ritzman, Todd F. MD*; Upasani, Vidyadhar V. MD†; Bastrom, Tracey P. MA‡; Betz, Randal R. MD§; Lonner, Baron S. MD¶; Newton, Peter O. MD†‡

Study Design. Retrospective review of a multicenter prospectively collected series of adolescent idiopathic scoliosis (AIS) patients.

Objective. To compare uninstrumented compensatory curve spontaneous derotation of the rib hump and lumbar prominence after selective lumbar or thoracic fusions in AIS.

Summary of Background Data. Coronal correction of the unfused minor curve after selective fusions in AIS has been well-documented previously. However, little has been reported regarding spontaneous correction in the axial plane of the unfused minor curve after selective AIS surgery.

Methods. Patients with minimum 2-year follow-up after either a selective thoracic fusion (STF) (lowest instrumented vertebrae L2 or above), or a selective lumbar fusion (upper instrumented vertebrae T9 or below) for AIS, with an initial scoliometer value of ≥5° in the minor curve were analyzed. Prospectively acquired preoperative and 2-year postoperative radiographic and scoliometer measurements of both the fused and unfused curves were compared using repeated measures and univariate analysis of variance. The data were checked for normality and equal variances, and the level of significance was set at P ≤ 0.05.

Results. In patients that underwent a STF (n = 83), the mean thoracic rib hump improved significantly from a preoperative value of 15° ± 5° to 7° ± 4° at the 2-year follow-up (P ≤ 0.001). The mean lumbar prominence of the unfused curve also spontaneously improved significantly in this group of patients during the follow-up period from 9° ± 3° to 4° ± 3° (P ≤ 0.001). In patients who underwent a selective lumbar fusion (n = 27), the mean lumbar prominence corrected significantly from a preoperative value of 11° ± 5°, to a 2-year postoperative value of 3° ± 3° (P ≤ 0.001). The mean thoracic rib hump, however, only changed from 8° ± 3° before surgery to 6° ± 3° at the 2-year follow-up. This change was not found to be statistically significant (P = 0.14). The spontaneous lumbar prominence correction of 49% was significantly greater than the spontaneous thoracic rib hump correction of 26% (P = 0.04).

Conclusion. Axial plane rotational correction of the unfused minor curve in patients undergoing selective fusions does occur. Significant spontaneous correction of a thoracic rib hump after a selective lumbar fusion should not be anticipated, whereas an approximate 50% reduction in the lumbar prominence was the average after selective thoracic fusions.


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Spine: 15 November 2008 – Volume 33 – Issue 24 – pp 2643-2647