title: Are Rib Versus Spine Anchors Protective Against Breakage of Growing Rods?
abstract: METHODS
  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.
  
  
  BACKGROUND
  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.
authors.affiliation: Department of Orthopaedic Surgery, University of California-Los Angeles, Los Angeles, CA, USA.
authors.forename: Kent T
authors.initials: KT
authors.lastname: Yamaguchi
authors.affiliation: Children's Orthopaedic Center, Children's Hospital Los Angeles, 4650 W Sunset Boulevard, Mailstop #69, Los Angeles, CA 90027, USA. Electronic address: dskaggs@chla.usc.edu.
authors.forename: David L
authors.initials: DL
authors.lastname: Skaggs
authors.affiliation: Children's Orthopaedic Center, Children's Hospital Los Angeles, 4650 W Sunset Boulevard, Mailstop #69, Los Angeles, CA 90027, USA.
authors.forename: Shaun
authors.initials: S
authors.lastname: Mansour
authors.affiliation: Children's Orthopaedic Center, Children's Hospital Los Angeles, 4650 W Sunset Boulevard, Mailstop #69, Los Angeles, CA 90027, USA.
authors.forename: Karen S
authors.initials: KS
authors.lastname: Myung
authors.affiliation: Department of Orthopaedic Surgery, Hacettepe University Faculty of Medicine, 06100 Sihhiye-Ankara/Turkey.
authors.forename: Muharram
authors.initials: M
authors.lastname: Yazici
authors.affiliation: Department of Orthopaedic Surgery, Texas Scottish Rite Hospital for Children, 2222 Welborn St, Dallas, TX 75219, USA.
authors.forename: Charles
authors.initials: C
authors.lastname: Johnston
authors.affiliation: Department of Orthopaedic Surgery, Rainbow Babies and Children's Hospital, Case Western Reserve University, 11100 Euclid Ave, Cleveland, OH 44106, USA.
authors.forename: George
authors.initials: G
authors.lastname: Thompson
authors.affiliation: Department of Orthopaedic Surgery, Johns Hopkins University, 601 North Caroline Street JHOC #5215, Baltimore, Maryland 21287-0882, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Sponseller
authors.affiliation: San Diego Center for Spinal Disorders, 4130 La Jolla Village Dr, La Jolla, CA 92037, USA.
authors.forename: Behrooz A
authors.initials: BA
authors.lastname: Akbarnia
authors.affiliation: Department of Orthopaedic Surgery, New YorkePresbyterian Morgan Stanley Children's Hospital, Columbia University Medical Center, 3959 Broadway, New York, NY 10032, USA.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Vitale
keywords: Anchors; Complications; Distraction-based growing rods; Rod breakage