The selection of lowest instrumented vertebra for Lenke 1A/2A adolescent idiopathic scoliosis / 中华骨科杂志

ABSTRACT

Objective:The purpose of the study is to investigate how to select lowest instrumented vertebra (LIV) in posterior spinal corrective surgery for Lenke 1A/2A adolescent idiopathic scoliosis (AIS) patients,and to further identify the risk factor for postoperative distal adding-on.Methods:FromJanuary 2008 to January 2014, a total of 85 Lenke 1A/2A AIS patients with one level proximal to last substantially touching vertebra (LSTV-1) selected as LIV were enrolled in the study. There were 45 Lenke 1A and 40 Lenke 2A, and 70 females and 15 males. The average age of surgery was 14.4±2.2 years (10-18 years). They were followed up over 2 years. The upright posteroanterior and lateral radiographs were performed preoperatively, immediately after surgery and at the final follow-up. Several radiographic parameters were measured such as Cobb angle, thoracic curve length, apex location, LIV rotation, deviated distance of LIV from central sacral vertical line, coronal balance and sagittal balance, etc. Distal adding-on was defined as a progressive increase in the number of vertebrae in the distal curve at the last follow-up. Patients were classified into adding-on and non adding-on group. The risk factors associated with the incidence of adding-on were analyzed. Subgroup analysis were further performed according to the curve type.Results:The mean duration of follow-up was 37.8±16.3 months (24-95 months). The average Cobb angle of main thoracic curve was 51.9°±6.8° (42°-85°). At the last follow-up, 36 patients (42.4%) had ideal outcome without distal adding-on. For Lenke 1A patients, the risk factor for adding-on included low Risser ( t=2.730, P=0.005), long thoracic curve ( t=1.930, P=0.030) with low apex ( t=1.734, P=0.045), preoperative large rotation and deviation of the LSTV-1 ( t=2.319, P=0.013; t=3.288, P=0.001), and preoperative coronal imbalance ( t=1.729, P=0.046). For Lenke 2A patients, the risk factor for adding-on included low Risser ( t=2.246, P=0.015), preoperative large rotation and deviation of the LSTV-1 ( t=2.534, P=0.008; t=1.972, P=0.028), and preoperative coronal imbalance ( t=1.702, P=0.048). Conclusion:When choosing LSTV-1 as LIV, skeletal immaturity, large rotation and deviation of LSTV-1 and preoperative coronal imbalance are risk factors for distal adding-on in Lenke 1A/2A curves; Also, long thoracic curve with low apex is associated with distal adding-on in Lenke 1A curves. Therefore, for skeletal immature patients with large rotation and deviation of LSTV-1, preoperative coronal imbalance and long thoracic curve with low apex,the 'LSTV’ rule should be followed to decrease the incidence of distal adding-on. While in other case, it could safely distally stop at LSTV-1.