• Gregory Cunningham, Dan Wright, and Colin Nnadi.
• Division of Spinal Surgery, Department of Orthopaedic and Spinal Surgery, University of Oxford Hospital NHS Foundation Trust, Oxford, England, UK. Greg@GregoryCunningham.com.
• Eur Spine J. 2020 Aug 1; 29 (8): 2025-2028.

PurposeThe purpose of this study is to report a novel smartphone app technique to localise a magnetically controlled growing rod (MCGR) actuator, along with determining this novel technique accuracy compared to current tactile localisation techniques through an experimental study.MethodsFive spinal surgery fellows recorded attempts localising the MCGR magnetic actuator using a novel smartphone app technique, MAGEC Wand and magnetic disc. Three attempts per technique were performed and repeated in both the average and overweight patient models.ResultsIn total, 90 separate localisation attempts were recorded. The smartphone app produced less localisation error than both the MAGEC Wand and magnetic disc. Mean difference was - 0.71 cm (95% CI - 1.24 to - 0.18 cm p = 0.06) and - 0.58 cm (95% CI - 1.11 to - 0.04 cm p = 0.031), respectively. Mean localisation error for the smartphone app, MAGEC Wand and magnetic disc, was 0.9 cm, 1.61 cm, 1.47 cm, respectively, for both average and overweight models combined.ConclusionsThis novel smartphone app localisation technique is accurate. Current MAGEC Wand and magnetic disc techniques produced more localisation error than the reported tolerance of the external remote control lengthening unit in this experiment.

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