Are rib versus spine anchors protective against breakage of growing rods?

esults 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.

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.