Rotational Assessment of Thoracolumbar/Lumbar Curves According to Lowest Instrumented Vertebra Level

It is not clearly defined in the literature how the lowest instrumented vertebra (LIV) selection effects the rotation of lumbar vertebrae at fused and unfused levels in thoracolumbar/lumbar (TL/L) curves. The aim of this study was to evaluate the rotational profile of structural TL/L curves, corrected with rod derotation manoeuvre, according to LIV level.

82 consecutive AIS patients with structural TL/L curves who were treated with long segment posterior instrumentation and fusion were retrospectively evaluated. Patients were divided into three groups according to LIV level: lower end vertebra (LEV) group (32 patients), LEV-1 group (23 patients) and LEV + 1 group (27 patients). Cobb angles of structural curves, coronal and sagittal balance were evaluated with direct roentgenograms. Rotation of upper end vertebra, apical vertebra, LIV-1, LIV and LIV + 1 was evaluated with computerised tomography. Clinical outcomes were assessed using SRS-22 questionnaire.

Mean follow-up time was 31 months (range 24-42 months). Preoperative LIV rotation was measured as 16.03°, 16.08° and 12.68° in LEV, LEV-1 and LEV + 1 groups, which changed postoperatively as 13.36°, 16.52° and 9.74° respectively. Postoperative LIV-1, LIV and LIV + 1 rotation values were significantly higher in LEV-1 group compared to LEV + 1 group. None of the patients developed coronal or sagittal imbalance. No significant differences were observed between the groups in terms of SRS-22 scores.

Axial rotation of LIV and vertebrae adjacent to LIV is higher when the fusion is stopped at LEV-1. However, higher rotation does not seem to cause poor radiologic and clinical outcomes in the last follow-up.