A Newer Way of Determining LIV in AIS Patients: Rotation of the Touched Vertebrae

A retrospective review.

The objective of this study was to determine whether fusing to touched vertebra (TV) on prone x-rays (XRs) with minimal rotation (Gd 0/1) allow for shorter fusion with optimal correction.

Previous studies have shown risk of "adding on" when TV is not selected as lowest instrumented vertebra (LIV). Fusion proximal to TV leads to suboptimal results but fusing to TV on standing XRs can result in longer fusions. On lying down XRs, TV moves proximally, and its rotation decreases by a grade.

TV patients with minimal rotation were selected on prone (TVP) or standing XRs (TVS). Patients fused to rotated (Gd 2+) TV on standing or prone XRs were considered touched vertebra rotated (TVR). In the non-TV (NTV) group, LIV was fused proximal to TV. Disk wedging ≥5° determined risk of "adding-on." To compare patients fused to minimally rotated TV, to those that were not, patients in group A (TVP + TVS) were compared with group B (TVR + NTV).In part II: TVP, TVS, TVR, and NTV patients were compared. Subanalysis compared levels saved as the difference between predicted and real LIV in TVP and TVS patients. Another subanalysis was carried out for Lenke 1+2 and Lenke 3, 4, 5.In part III: XRs of nonoperative adolescents idiopathic scoliosis patients with Cobb <30 and Risser 4/5 were analyzed to determine "acceptable" end vertebra tilt and disc wedging and served as controls.

There were a significantly greater number of patients in group B patients(TVR + NTV) with final disk wedging ≥5°, final LIV translation ≥1 and ≥2 cm ( P <0.001).Utilizing prone XRs in TVP saved average 1 level, and 1.2 levels in TVS patients. TVP patients also had similar LIV tilt, disk wedging and coronal balance( P >0.05) to controls.

Choosing minimally rotated (Gd 0/1) TV on prone XR saves levels without sacrificing radiographic outcomes.