Utilizing the "Stable-to-be Vertebra" Saves Motion Segments in Growing Rods Treatment for Early-Onset Scoliosis

Background: There is no consensus on the selection of distal instrumentation levels in growing rod surgery. Many surgeons utilize the stable zone of Harrington, but there is not overwhelming evidence to support this preference. The aim of this study was to determine the value of bending/traction radiographs in selection of distal instrumentation levels of a growing rod construct in children with idiopathic or idiopathic-like early-onset scoliosis (EOS). Methods: Twenty-three consecutive patients with idiopathic or idiopathic-like EOS who underwent growing rod surgery at 2 separate institutions between 2006 and 2011 were included. Lengthening procedures were performed periodically at 6-month intervals. Analyses were performed retrospectively for age at index surgery, follow-up period, and radiographic measurements. Lower instrumented levels, neutral vertebra, stable vertebrae (SV), and stable-to-be vertebrae (StbV) were identified on the preoperative radiographs. Coronal Cobb angles, tilt of lower instrumented vertebra (LIV) and LIV+1, and disk wedging under the LIV and LIV+1 were measured on the early postoperative and latest follow-up radiographs. Results: Average age at index surgery was 83.6 months. Mean follow-up period was 68.1 months. Initial analysis showed that the relationship of LIV to the StbV was a better predictive of LIV+1 tilt than the SV at the final follow-up. Therefore, the patients were grouped according to the relationship of the LIV to the StbV. LIV was the StbV in 9 patients, proximal to the StbV in 8 patients, and distal to the StbV in 6 patients. At the latest follow-up, tilt of LIV+1 exceeded 10 degrees in 7 of the 8 patients where LIV was proximal to the StbV, whereas only in 1 of 9 patients where LIV was StbV, and in none of the 6 patients where LIV was distal to the StbV. The data indicate that selection of the StbV as the LIV could spare an average of 1.8 vertebral segments when compared with the SV, as StbV is never distal but almost always proximal to the SV. Conclusions: Choosing the StbV as the LIV saves motion segments and prevents distal adding on, while providing satisfactory deformity correction in idiopathic and idiopathic-like EOS.