Actuator pin fracture in magnetically controlled growing rods: two cases.

Abstract

Magnetically controlled growing rods (MCGRs) are used in the management of early-onset scoliosis (EOS). Each MCGR contains a telescopic actuator that serves as the distraction element when stimulated by an external remote controller (ERC), permitting non-invasive lengthening in the outpatient clinic. This report highlights a subtle cause of MCGR failure. We present the first two reported cases of lengthening pin fracture in patients with dual-MCGR constructs. We present two cases of patients with EOS treated with dual-construct MAGEC (MAGnetic Expansion Control, Ellipse Technologies Inc, Aliso Viejo, CA, USA) MCGRs. A 12-year-old boy presented describing a "popping" sensation in his thoracic spine and resultant grating 36 months following MCGR insertion. A plain radiograph revealed a subtle fracture of the lengthening pin within the actuator of the right MCGR. Following identification of this case of implant failure, we reviewed the most recent radiographs of all nine of our patients treated with this MCGR in our institution, resulting in the discovery of bilateral MCGR lengthening pin fractures in an otherwise asymptomatic 11-year-old girl. Clinicians should have a high index of suspicion of structural implant failure when presented with histories similar to those reported in our first case, or following unsuccessful distraction of MCGRs. In such cases new radiographs should be taken, and all previous images should be reviewed for evidence of this phenomenon. Centers that document MCGR lengthening with ultrasound should obtain plain radiographs every 6 months to evaluate the structural integrity of the implant.