Intraoperative Radiographic Factors Related to Postoperative Distal Adding-On in Lenke Type 1A Adolescent Idiopathic...

Distal adding-on (DA) is a common radiographic complication following selective thoracic fusion for Lenke type 1A adolescent idiopathic scoliosis (AIS). This study aimed to investigate whether intraoperative radiographs can predict postoperative DA in Lenke type 1A AIS.

A total of 79 patients with AIS and Lenke type 1A (group A) who underwent posterior selective thoracic fusion were retrospectively evaluated. For comparison, another 79 patients with Lenke type 1B and 1C (group BC) were included. The occurrence and factors associated with DA at 2 years postoperatively were investigated using intraoperative radiographs.

Of 158 total cases, eight patients (10%) in group A and 13 (16%) in group BC developed DA at two years postoperatively. Intraoperative radiographs in group A showed that the mean angulation of the first disc below the lowest instrumented vertebra (LIV) was significantly greater in the DA group (-2.3±2.3°) compared to the non-DA group (-0.6±1.7°). Patients with angulation of the first disc below the LIV greater than 3° were significantly associated with DA (odds ratio, 18.0; p<0.01) in group A, as well as in group BC (odds ratio, 22.0; p<0.01). In group A, the mean intraoperative LIV tilt angle was greater in the DA group (4.8±7.0°) than in the non-DA group (1.2±3.7°), with greater tilt observed in 1A-L (L4 tilted left) compared to type 1A-R (L4 tilted right). Multivariate analysis revealed that intraoperative LIV tilt was significantly associated with DA in group A, but not in group BC.

Intraoperative radiographs showing angulation greater than 3° at the first disc below the LIV and larger LIV tilt angles were significantly associated with postoperative DA in Lenke type 1A. Surgeons should strive to achieve horizontalization of the LIV intraoperatively, especially in Lenke type 1A-L curves, to avoid postoperative DA.