Growth Modulation Techniques: Titanium Clip-Screw Implant System (HemiBridge)

Abstract

Spinal growth modification using a thoracoscopically implanted clip-screw construct has been under investigation since 1997. Preclinical to clinical studies are described, including design objectives, theoretical advantages, mechanical function, clinical safety, surgical technique, and early radiographic and quality of life results. Most recently, a titanium construct and custom surgical instruments have been tested prospectively from first human use in a US FDA-approved clinical trial under an Investigational Device Exemption (IDE) (IRB approved) for treatment of late juvenile and early adolescent idiopathic thoracic scoliosis. Eligibility criteria were designed to include only those subjects at very high risk of curve progression to >50° by published criteria. The first six children who met the eligibility criteria assented, with parental consent. In the longest follow-up of the cohort to date, mean curvatures at 18 months had not increased from preoperative values. Individual longitudinal results were variable and included one subject who required instrumentation and fusion. Proof of concept in humans, however, was demonstrated in a child whose curvature was corrected by 71 % at 1 year. The corrected thoracic curve, coupled with a simultaneously developing compensatory lumbar curve, started to decrease coronal alignment. By 21 months, both lumbar curvature and coronal plane alignment improved. This time course suggests that the method may not only arrest thoracic curve progression, but may also alter the progression of compensatory curvatures. Implant design factors relative to anatomical dimensions and physiologic loading may be critical to consistent curve arrest. Longer-term results and a larger cohort are essential to determine the device performance. If successful, this minimally invasive thoracoscopic surgical approach and clip-screw construct may become a standard of care for late juvenile and early adolescent idiopathic scoliosis. The device is approved for use in the European Union (CE Mark) for the labeled indications. The pivotal-phase IDE clinical trial is approved by the US FDA.