Abstract
Study Design
Retrospective multicenter, case-control study.
Objective
To compare the risks of rod breakage and anchor complications between distraction-based growing rods with proximal spine versus rib anchors.
Summary of Background Data
Rod breakage is a known complication of distraction-based growing rod instrumentation.
Methods
A total of 176 patients met inclusion criteria: minimum 2-year follow-up, younger than age 9 years at index surgery, non—Vertical Expandable Prosthetic Titanium Rib distraction-based growing rods, and known anchor locations. Mean follow-up was 56 months (range, 24—152 months). Survival analyses using Cox proportional hazards model (accounting for varying lengths of follow-up) of rod breakage, anchor complications, preoperative Cobb angle, number of growing rods, age, and number of levels instrumented were performed using a significance level of p <.05.
Results
Thirty-four patients had rib-anchored growing rods and 142 had spine-anchored growing rods. This analysis found that proximal rib-anchored growing rods have a 23% risk of lifetime rod breakage compared with spine-anchored growing rods (6% vs. 29%) (p =.041) without a significant increase in risk of anchor complications (38% vs. 33%) (p =.117). The number of implanted rods (p =.839), age (p =.649), and number of instrumented levels (p =.447) were not statistically significant regarding rod breakage risk, although higher preoperative Cobb angles were significant (p =.014).
Conclusions
Preoperative Cobb angle appears to be the most influential factor in determining whether growing rods break (p =.014). Univariate analysis found that rib anchors were associated with less than one-fourth the risk of rod breakage than spine anchors (p =.04) but multivariate analysis found no significant association between anchors and rod breakage (p =.07). This trend suggests that rib-anchored growing rod systems may be associated with less rod breakage because the system is less rigid as a result of some “slop” at the hook—rib interface, as well as the normal motion of the costovertebral joint.
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Author disclosures: KTY (none); DLS (grants from POSNA, Scoliosis Research Society; personal fees from Biomet, Medtronic, Stryker, Wolters Kluwer Health—Lippincott Williams & Wilkins; non-financial support from Growing Spine Study Group, Scoliosis Research Society, Growing Spine Foundation Medtronic Strategic Advisory Board; personal fees from expert testimony; other from Medtronic, Stryker, Bio-met, Medtronic, outside the submitted work; patent issued by Medtronic); SM (none); KSM (none); MY (personal fees from DePuy Synthes, Stryker, outside the submitted work); CJ (other from Medtronic, outside the submitted work); GT (personal fees as Co-Editor, Journal of Pediatric Orthopaedics, Lippincott, Williams and Wilkins; personal fees from Medical Advisory Board, Shriner’s Hospital for Children; non-financial support as President/CEO SICOT Foundation; non-financial support from OrthoPediatrics; personal fees from Ortho-Pediatrics, non-financial support from SpineForm, outside the submitted work; son works for nuVasive Medical Technologies); PS (other from Journal of Bone and Joint Surgery, Oakstone Medical, Globus Medical, DePuy Synthes Spine, outside the submitted work); BA (personal fees from Kspine, K2M, Ellipse Technologies; grants and personal fees from Nuvasive, OREF, DePuy Spine, outside the submitted work); MV (non-financial support from AAP Section on Orthopaedics; personal fees, non-financial support and other from CSSG; personal fees from Stryker, Biomet; grants from AOSpine, CSSG, OREF, Scoliosis Research Society; grants and other from POSNA, grants and non-financial support from Medtronic, grants from OMeGA, other from Broadwater [Biomet, Synthes, Stryker, Medtronic, K2]; other from FoxPSDSG, outside the submitted work).
This work was supported by a research grant provided by the Growing Spine Foundation.
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Yamaguchi, K.T., Skaggs, D.L., Mansour, S. et al. Are Rib Versus Spine Anchors Protective Against Breakage of Growing Rods?. Spine Deform 2, 489–492 (2014). https://doi.org/10.1016/j.jspd.2014.08.007
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DOI: https://doi.org/10.1016/j.jspd.2014.08.007