• D Rolton, C Thakar, J Wilson-MacDonald, and C Nnadi.
• Department of Spinal Surgery, Oxford University Hospitals NHS Trust, Windmill Road, Headington, Oxford, UK. danrolton@hotmail.com.
• Eur Spine J. 2015 Sep 10.

PurposesMagnetically controlled growing rods (MCGR) allow controlled distraction of the immature spine for the treatment of early onset scoliosis. This study's primary aim was to determine the disparity between 'true' (TD) and 'intended' (ID) distraction. The secondary aim was to assess truncal growth and development during sequential lengthening.MethodsTwenty-one patients with a maximum follow up of 37 months were included in the study. Patients in the study underwent three monthly distractions. The amount of TD was determined by measuring the expansion gap on dedicated fluoroscopic images of the actuator. The total TD to date was compared to the ID measurement reported on the external adjustment device (EAD). Weight, sitting and standing heights were recorded at each distraction.ResultsThe average number of three monthly distractions was 8. The true to intended distraction ratio was calculated as 0.33. Patients who had undergone previous surgery gained less distraction with a ratio of 0.30 compared to patients undergoing MCGR as a primary procedure with a ratio of 0.35. Weight, sitting and standing heights increased in all patients by an average of 3.1 kg, 2.3 and 5.2 cm per year. The Cobb angle following surgical correction was maintained in 19 of 21 patients at the latest follow-up.ConclusionsThe TI ratio of 0.33 suggests that for every unit of distraction registered on the EAD approximately 33 % of true distraction occurs in vivo. Increases in sitting and standing heights were observed in all patients in the study.

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