Hill Genevieve, Nagaraja Srinidhi, Akbarnia Behrooz A, Pawelek Jeff, Sponseller Paul, Sturm Peter, Emans John, Bonangelino Pablo, Cockrum Joshua, Kane William, Dreher Maureen
US Food and Drug Administration, 10903 New Hampshire Ave, Silver Spring, MD 20993, USA; Fischell Department of Bioengineering, University of Maryland, Room 2330, Jeong H. Kim Engineering Building, Bldg #225, College Park, MD 20742, USA.
US Food and Drug Administration, 10903 New Hampshire Ave, Silver Spring, MD 20993, USA; Fischell Department of Bioengineering, University of Maryland, Room 2330, Jeong H. Kim Engineering Building, Bldg #225, College Park, MD 20742, USA.
Spine J. 2017 Oct;17(10):1506-1518. doi: 10.1016/j.spinee.2017.04.020. Epub 2017 Apr 26.
Growing rod constructs are an important contribution for treating patients with early-onset scoliosis. These devices experience high failure rates, including rod fractures.
The objective of this study was to identify the failure mechanism of retrieved growing rods, and to identify differences between patients with failed and intact constructs.
STUDY DESIGN/SETTING: Growing rod patients who had implant removal and were previously enrolled in a multicenter registry were eligible for this study.
Forty dual-rod constructs were retrieved from 36 patients across four centers, and 34 of those constructs met the inclusion criteria. Eighteen constructs failed due to rod fracture. Sixteen intact constructs were removed due to final fusion (n=7), implant exchange (n=5), infection (n=2), or implant prominence (n=2).
Analyses of clinical registry data, radiographs, and retrievals were the outcome measures.
Retrievals were analyzed with microscopic imaging (optical and scanning electron microscopy) for areas of mechanical failure, damage, and corrosion. Failure analyses were conducted on the fracture surfaces to identify failure mechanism(s). Statistical analyses were performed to determine significant differences between the failed and intact groups.
The failed rods fractured due to bending fatigue under flexion motion. Construct configuration and loading dictate high bending stresses at three distinct locations along the construct: (1) mid-construct, (2) adjacent to the tandem connector, or (3) adjacent to the distal anchor foundation. In addition, high torques used to insert set screws may create an initiation point for fatigue. Syndromic scoliosis, prior rod fractures, increase in patient weight, and rigid constructs consisting of tandem connectors and multiple crosslinks were associated with failure.
This is the first study to examine retrieved, failed growing rod implants across multiple centers. Our analysis found that rod fractures are due to bending fatigue, and that stress concentrations play an important role in rod fractures. Recommendations are made on surgical techniques, such as the use of torque-limiting wrenches or not exceeding the prescribed torques. Additional recommendations include frequent rod replacement in select patients during scheduled surgeries.
生长棒装置是治疗早发性脊柱侧凸患者的一项重要贡献。这些装置的故障率很高，包括棒体骨折。
本研究的目的是确定取出的生长棒的失效机制，并确定植入物失败和未失败患者之间的差异。
研究设计/地点：曾参与多中心注册研究且已取出植入物的生长棒患者符合本研究条件。
从四个中心的36名患者中取出40个双棒装置，其中34个装置符合纳入标准。18个装置因棒体骨折而失效。16个未失效的装置因最终融合（n = 7）、植入物更换（n = 5）、感染（n = 2）或植入物突出（n = 2）而被取出。
临床注册数据、X线片和取出物分析为观察指标。
通过显微镜成像（光学显微镜和扫描电子显微镜）对取出物进行分析，以确定机械失效、损伤和腐蚀区域。对骨折表面进行失效分析，以确定失效机制。进行统计分析以确定失效组和未失效组之间的显著差异。
失效的棒体因屈曲运动下的弯曲疲劳而骨折。结构配置和负荷决定了沿结构三个不同位置的高弯曲应力：（1）结构中部，（2）串联连接器附近，或（3）远端锚固基础附近。此外，用于拧入固定螺钉的高扭矩可能会产生疲劳起始点。综合征性脊柱侧凸、先前的棒体骨折、患者体重增加以及由串联连接器和多个交联组成的刚性结构与失效有关。
这是第一项对多个中心取出的、失效的生长棒植入物进行研究的研究。我们的分析发现，棒体骨折是由于弯曲疲劳，并且应力集中在棒体骨折中起重要作用。对手术技术提出了建议，例如使用扭矩限制扳手或不超过规定扭矩。其他建议包括在计划手术期间对选定患者频繁更换棒体。
