Abstract
Introduction
Several previous studies have reported spontaneous lumbar curve correction for both anterior and posterior selective fusion in patients with Lenke 1B or 1C; however, the mechanism for this phenomenon remains unclear. The objective of this study is to analyze the detailed response of compensatory lumbar curve to selective thoracic fusion in patients with adolescent idiopathic scoliosis (AIS) with Lenke 1B/1C curve.
Patients and Methods
This study included patients with AIS with Lenke type 1B or 1C curves treated with posterior selective thoracic fusion (LIV at L1) from 2006 to 2008 in our institution. They had a major right thoracic curve and a compensatory lumbar curve. They were followed for at least 24 months. Radiographic measurements including disc angle and vertebra tilt in the lumbar region were compared before surgery, after surgery, and at latest follow-up.
Results
A total of 20 patients (7 boys and 13 girls) with a mean age of 15 years were included in this study. The thoracic curve was corrected from 46 ± 7.2 degrees preoperatively to 8 ± 4.7 degrees postoperatively, and to 9 ± 5.1 degrees at the latest follow-up. The mean lumbar compensatory Cobb angle was 36 ± 6.9 degrees before surgery, spontaneously correcting to 12 ± 5.3 degrees at latest follow-up. The most significant change of vertebral tilt occurred at LIV and the L4 vertebra in the coronal plane. Change in disc angle was 6.4 ± 3.1 degrees at L1/L2, 3.2 ± 2.3 degrees at L2/L3, 1.0 ± 1.3degrees at L3/L4, −2.3 ± 1.9 degrees at L4/L5, and −0.7 ± 0.5degrees at L5/S1. L1/L2 disc ranks highest among all the discs in the contribution to correction of the lumbar curve.
Conclusion
LIV and the L4 vertebra have a trend to be horizontal after selective thoracic fusion. Spontaneous correction of the unfused lumbar curve relies on the compensatory changes of lumbar disc angle, which are mainly at the junctional disc right below LIV. This study suggests that the disc right below LIV assumes the greatest portion of correction force transmitting therefore is prone to degenerate earlier than normal.