Distraction failure in magnetically-controlled growing rods: prevalence and risk factors

Abstract

INTRODUCTION: Recently, the use of 'magnetically' controlled growing rods (MCGR) has advanced the surgical treatment of early onset scoliosis (EOS), providing non-invasive distractions. Occassionally the rod may fail to distract due to slippage of the internal mechanism. This study assessed the occurrence and potential determinants associated with slippage of the MCGR during distraction. METHODS: We prospectively assessed 4 EOS patients with implantation of dual MCGR. Each underwent monthly outpatient distractions. Rod slippage was noted if a 'clunking' noise occurred during distraction. Rradiographic parameters and demographics were analysed. RESULTS: The mean time period from operation to the first slippage was 11 months. Overall, in 168 distraction episodes, slippage was noted in 25%. Offset rod (35%) had more slippage compared to the standard rod (17%). Early slippage (within one year of surgery) occurred in 50% of the patients. Based on the sample size, demographics, number of vertebral levels involved, distance between magnets, and curve alignment/flexibility parameters were not distinctively involved in rod slippage. Despite this slippage, there was overall gain in the implant and the spine. Throughout follow-up, all patients had no pain, had good functional outcome, and were satisfied with the procedure. CONCLUSION: In MCGR patients, rod slippage can occur within the first year since implantation and may continue thereafter. This is the first study to identify this observation. Larger studies are needed to further validate our findings and determine if such an event is a potential complication or a naturally occurring, physiological fail-safe mechanism that benefits the patient.