Selection of Lowest Instrumented Vertebra in the Management of Thoracolumbar and Lumbar Adolescent Idiopathic Scoliosis using Pedicle Screw Instrumentation

Abstract

Introduction The aim of surgical treatment for adolescent idiopathic scoliosis (AIS) is correction of the three dimensional deformity, achievement of stability and preservation of as many distal motion segments as possible. In Thoracolumbar/ Lumbar adolescent idiopathic scoliosis (TL/L AIS) correction of C-shaped coronal curve into S-shaped saggital curve is a considerable challenge to a spine surgeon. In this regard, selection of Lowest Instrumented Vertebra (LIV) is of particular importance and remains controversial in literature. We conducted a retrospective study involving Lenke V patients to determine the exact distal fusion level (LIV) in the management of thoracolumbar/lumbar adolescent idiopathic scoliosis (TL/L AIS) using pedicle screw instrumentation. Material and Methods Analysis of radiographic parameters of 32 TL/L AIS was done. The patients were grouped according to the Lowest Instrumented Vertebra; Group I (fusion to L3, n = 25) and Group II (fusion to L4, n = 7). The Group I was subdivided into Group IA (L3 crosses the mid-sacral line with rotation of less than grade II on bending films, n = 14) and Group IB (L3 does not cross the mid-sacral line or rotation is grade II or more on bending films, n = 11). All of the patients in the Group II had the same location and rotation of L3 in bending films as that of patients in the Group IB. Patients with lowest instrumented vertebral tilt (LIVT) of more than 10° or coronal balance of more than 15 mm were considered to have unsatisfactory results. Results In these 3 groups, there was a significantly lesser correction in the TL/L curve and LIVT in the Group IB. Unsatisfactory results were obtained in 1 patients (7.1%) of the Group IA, in 7 patients (63.3%) of the Group IB, and in 1 patient (12.5%) of the Group II, which was found to be statistically significant. Conclusion In TL/L AIS patients undergoing treatment with pedicular screw instrumentation, the curve can be fused to L3 with good radiographic outcomes when L3 crosses the mid-sacral line with rotation of less than grade II on bending films. Otherwise, L4 should be selected as the Lowest Instrumented Vertebra.