Axial plane lumbar responses after anterior selective thoracic fusion for main thoracic adolescent idiopathic scoliosis

Abstract

Study design: A retrospective radiographic study.

Purpose: To evaluate the axial plane lumbar responses after anterior selective thoracic fusion (STF) in patients with main thoracic adolescent idiopathic scoliosis (MT-AIS).

Overview of literature: Anterior scoliosis surgery induces more MT derotation through disc preparation than posterior surgery.

Methods: Twenty-eight MT-AIS patients treated with STF were evaluated after a minimum follow-up (FU) of 2 years. The MT and lumbar coronal angles, as well as the MT and lumbar rotational angles at the most rotated vertebrae were measured.

Results: At the last FU, the MT coronal correction and derotation rates were 65% and 41%, respectively. The lumbar coronal correction rate was 61% but there was minimal lumbar derotation (2%). Nine cases were decompensated (coronal balance >10 mm). After surgery, the compensated and decompensated groups showed similar MT coronal and axial correction rates. During the FU, the MT and lumbar apecies rotated in the same direction (r=0.443). In addition, significant MT derotation occurred in the decompensated group with increasing lumbar rotational correction loss. At the last FU, while the MT coronal correction was similar between the two groups, there was more MT derotation in the decompensated group. Furthermore, the MT rotational change was strongly associated with the coronal C7 plumb line position (r=0.728).

Conclusions: After anterior STF in patients with MT-AIS, the final MT derotation is strongly associated with the coronal C7 plumb line position. During the FU, the excessive MT derotation in the decompensated group was attributed to excessive lumbar rotational correction loss.

Keywords: Adolescent idiopathic scoliosis; Anterior spinal fusion; Decompensation; Derotation; Selective thoracic fusion.

Fig. 1

Sagittal plane change in the proximal lumbar area (lowest instrumented vertebra - apical vertebra) was moderately correlated with the rotational angle change in the lumbar apex immediately after surgery (A), and during follow-up (B).

Fig. 2

Axial block motion. Main thoracic apex and lumbar apex tend to rotate to the same side. Axial block motion immediately after surgery (A), and during the follow-up (B).

Fig. 3

Self-regulation in the axial plane. The follow-up motion tends to be in the opposite direction to the surgical motion, which suggests that surgical motion is regulated during the follow-up. Self-regulation of the MT apical rotational angle (A), and of lumbar apical one (B).

Fig. 4

The distance of the C7 plumb line from center sacral vertical line at the last follow-up is associated with the main thoracic (MT) apical derotation rate at the last follow-up (A). At last follow-up, the final C7 PL lies more on the left side with increasing correction of MT rotation (B). CSVL: center sacral vertical line, PL: plumb line.