Rib-Based Anchors are Associated with Proximal Translational Deformity in Early Onset Spinal Deformity Patients undergoing Growth-Friendly Surgical Treatment

Abstract

Objective/Background: No studies to date have evaluated the the effect of rib-based anchors on the translational relationship between the rib and spine. We hypothesized that there would be an increase in the translational distance between the rib anchor and anterior vertebral body in early onset spinal deformity patients managed with long-term rib-based anchors. Methods: All patients with EOSD from a single tertiary level institution treated with a growth-friendly technique surgery utilizing proximal rib-based anchors from 2006-2015 with a minimum of 2-year follow-up were included. Thoracic kyphosis and the translational distance from the rib anchor to the corresponding anterior vertebral body were measured. Results: Twenty-seven patients (13 female, 14 male) qualified for inclusion. Mean age at implantation of the index proximal rib-based construct was 5±1.9 years (range, 1-9). EOSD etiology was congenital: 3, neuromuscular: 17, syndromic: 3, and idiopathic: 4. Mean kyphosis improved from 31±33° preoperatively to 25±20° immediately post-operatively. No significant changes in kyphosis were noted over 1 and 2 year follow-up (p=0.3). Twenty-one (78%) patients demonstrated an increase in translational distance from the rib anchors to the adjacent anterior vertebral body. Immediately post-operatively, mean distance was 25±1 mm and increased at 1-year (26±1 mm) and significantly at 2-year (29±1 mm) follow-up (p=0.005). Conclusion: The use of long term rib-based anchors may lead to an increase in the distance between the rib utilized for proximal fixation and the associated vertebral body, generating what appears to be increased anterior translation of the spine. This translation, in conjunction with increased or increasing overall thoracic kyphosis, may be the source of unexpected obstacles at the time of future surgical procedures for revision or final fusion.