Lowest instrumented vertebra (LIV) selection is critical to preventing complications following posterior spinal arthrodesis (PSA) for thoracolumbar/lumbar adolescent idiopathic scoliosis (TL/L AIS), but evidence guiding LIV selection is limited. This study aimed to investigate the efficacy of PSA using novel unilateral convex segmental pedicle screw instrumentation (UCS) in correcting TL/L AIS, to identify radiographic parameters correlating with distal extension of PSA, and to develop a predictive equation for distal fusion extension using these parameters. We reviewed data (demographic, clinical, radiographic, and SRS-22 questionnaires) preoperatively to 2-years' follow-up for TL/L AIS patients treated by PSA using UCS between 2006 to 2011. 53 patients were included and divided into 2 groups: Group-1 (n=36) patients had PSA between Cobb-to-Cobb levels; Group-2 (n=17) patients required distal fusion extension. A mean curve correction of 80% was achieved. Mean postoperative LIV angle, TL/L apical vertebra translation (AVT), and trunk shift were lower than previous studies. Six preoperative radiographic parameters significantly differed between groups and correlated with distal fusion extension: thoracic curve size, thoracolumbar curve size, LIVA, AVT, lumbar flexibility index, and Cobb angle on lumbar convex bending. Regression analysis optimised an equation (incorporating the first five parameters) which is 81% accurate in predicting Cobb-to-Cobb fusion or distal extension. SRS-22 scores were similar between groups. We conclude that TL/L AIS is effectively treated by PSA using UCS, six radiographic parameters correlate with distal fusion extension, and a predictive equation incorporating these parameters reliably informs LIV selection and the need for fusion extension beyond the caudal Cobb level

Introduction. To introduce a new classification method and analyze related risk factor about lateral wall perforation associated with lower cervical pedicle screw and free-hand insertion technique. Methods. A Retrospective study was made to analyze 214 patients (1024 screws) with various cervical spine disorders, involved in pedicle screw instrumentation at C3-7 from July 2004 to July 2009. Researchers assessed the position of the screws in the pedicle by carefully probing intraoperatively and studying postoperative thin-slice computed tomography scan. Perforation of lateral wall was classified into two phases. Phase I refers to the burst of the pedicle by screw, which means that the length of screw threads penetrating the external cortex of pedicles on CT scan is 2 mm, whereas in Phase, the length is >2 mm. The Penetrated screws and related factors were analyzed though Backward Stepwise (Wald) Logistic regression. Results. During the follow-up, 2 screws were reported to be broken and 1 screw loosened. Of the screws inserted, total of 129 screws 12.60% have shown violated of lateral pedicle walls, included 101 screws (9.86%) causative of Phase I and 28 screws (2.73%) of Phase II. Two variance were deduced in the regression analysis, which concerned to ratio variance between inner and lateral walls, PRC 0.695, OR value = 2.003and angle difference variance between screws implanted and measurements preoperativePRC −1.542, OR value = 0.214). Conclusions. Free-hand lower cervical pedicle screw insertion in this series was comparatively safety. Phase I Penetration was believed to be safe of vertebral artery and Phase II faced to higher risk of artery damage. The main risk factor of lateral wall perforation was the ratio variance between inner and lateral wall, while the main protection factor was the angle difference variance between screws implanted and CT measurements