Long-term Retrospective of the Kaneda Anterior Scoliosis System in Thoracic Adolescent Idiopathic Scoliosis

Background: Currently, the Kaneda Anterior Scoliosis System (KASS) is reported to be acceptable for the treatment of adolescent idiopathic scoliosis (AIS), particularly thoracolumbar and lumbar deformities. Its use in thoracic AIS is not as established. Methods: Retrospective analysis of long-term results in patients treated with the KASS for thoracic AIS to determine specific factors associated with success or failure. We analyzed 16 consecutive patients who met the following criteria: thoracic AIS, anterior spinal fusion and KASS, and >= 24 months of follow-up or progression to failure, defined as the need for revision surgery or progression of the main thoracic curve (MTC) >= 50 degrees. Comparison of the MTC on the preoperative, postoperative, and final follow-up was the major evaluation criteria. On the basis of data analysis, patients were divided for comparison into 2 study groups: nonfailure group (n = 11) and failure group (n = 5). Statistical analysis was performed using paired and independent t tests. Results: All curves were classified as Lenke 1 (n = 14) and 2 (n = 2). Mean age at surgery and levels fused were 14.6 +/- 2.7 years and 5 +/- 1 vertebrae, respectively. Mean follow-up was 4.2 years (range, 1.0 to 6.2y). The failure group consisted of 5 patients that progressed to >= 50 degrees. In the nonfailure group, the mean MTC preoperative, postoperative, and at final follow-up were 52 +/- 8, 19 +/- 8, and 29 +/- 7 degrees, respectively. In the failure group, these measurements were 74 +/- 11, 35 +/- 8, and 56 +/- 12 degrees, respectively. Conclusions: This retrospective, long-term follow-up study found more KASS failures in thoracic AIS than previously reported. Even in the nonfailure group, 5 of the 11 patients progressed 10 degrees or more. Our results indicate an increased incidence of KASS failure with preoperative MTC curve >= 70 degrees. We consider an MTC >= 70 degrees a likely contraindication for KASS instrumentation for thoracic AIS. Four of the 5 failures were fused short of the end vertebrae either proximally, distally, or both. Although short apical fusions were popular during the time these cases were done, fusion to the end vertebrae is an important principle for anterior fusions. Reaching the upper end vertebrae may be more difficult in these larger curves. We also recommend continued follow-up past 2 years as progression can occur after this time. Level of Evidence: Retrospective comparative study, level III.