Key-Vertebral Screws Strategy for Main Thoracic Curve Correction in Patients With Adolescent Idiopathic Scoliosis
Authors: Li Jingfeng , Cheung Kenneth M.C. , Samartzis Dino , Ganal-Antonio Anne K.B. , Zhu Xiaodong , Li Ming , Luk Keith D.K. 
Published: July 2014

Study Design:
The following study was a prospective radiographic and retrospective clinical data assessment of adolescent idiopathic scoliosis (AIS) patients who had undergone a key-vertebral screws strategy (KVSS) at a single institution, with a minimum of 2 years’ follow-up.

Objectives:
The aim of the study was to introduce the KVSS for the operative treatment of AIS of the main thoracic curve, and to address the role of the fulcrum-bending radiograph (FBR) in predicting the outcome of surgical management by this method.

Summary of Background Data:
The application of multilevel pedicle screws for the main thoracic curve in AIS patients is popular in an effort to provide spinal stability, enhance fusion outcome, and provide optimal curve correction. However, with the application of pedicle screw also comes a potential risk for soft tissue and neural injury and increased health care costs. It remains unknown whether limited screw placement can provide proper curve correction without compromising patient outcome.

Methods:
A total of 17 consecutive patients with AIS extending to the main thoracic spine, who had undergone posterior fusion and fixation by the KVSS, a procedure in which screws are placed at important strategic points in the spine (ie, bilaterally at the upper and lower end segments of the fusion block, apical vertebra on the convex side, adjacent cephalad, and caudal screw placement on the concave side), at a single institution, with a minimum of 2 year’ follow-up, were included. The assessment of preoperative standing posteroanterior and sagittal, FBR, and postoperative standing posteroanterior and sagittal plain radiographs were assessed in all patients. The flexibility of the curve as well as the fulcrum-bending correction index (FBCI) were calculated for all patients. Postoperatively, radiographs were assessed at the immediate (ie, 1 wk) and last follow-up. Clinical assessment entailed evaluation of patient demographics and the presence of any intraoperative or postoperative complications.

Results:
The mean age at the time of surgery was 15.6 years. The mean follow-up was 39.8 months. The average FBR flexibility was 62.2%. The mean immediate curve correction was 71.2%, which did not differ in comparison with the last follow-up assessment (P>0.05). The mean immediate and last follow-up FBCIs were 119.3% and 112.5%, respectively (P=0.079). A significant negative correlation was found between immediate FBCI to that of the FBR curve flexibility (r=−0.706; P=0.002), which remained similar on the last follow-up (r=−0.681; P=0.003). Sagittal alignment did not significantly change from the immediate to last follow-up (P=0.163) Fusion was achieved in all patients. No instrumentation-related complications were noted.

Conclusions:
Key-vertebral screws strategy is a safe and cost-effective method for the surgical treatment of the main thoracic curve in AIS patients. Moreover, in the context of this strategy, the FBR may have some predictive utility in the correction of the main thoracic curve in AIS patients.