Evaluation of a Mobile Application for Multiplier Method Growth and Epiphysiodesis Timing Predictions

Wagner, Pablo MD; Standard, Shawn C. MD; Herzenberg, John E. MD, FRCSC

Journal of Pediatric Orthopaedics: April/May 2017 - Volume 37 - Issue 3 - p e188–e191
doi: 10.1097/BPO.0000000000000805
Lower Extremity

Background: The multiplier method (MM) is frequently used to predict limb-length discrepancy and timing of epiphysiodesis. The traditional MM uses complex formulae and requires a calculator. A mobile application was developed in an attempt to simplify and streamline these calculations. We compared the accuracy and speed of using the traditional pencil and paper technique with that using the Multiplier App (MA).

Methods: After attending a training lecture and a hands-on workshop on the MM and MA, 30 resident surgeons were asked to apply the traditional MM and the MA at different weeks of their rotations. They were randomized as to the method they applied first. Subjects performed calculations for 5 clinical exercises that involved congenital and developmental limb-length discrepancies and timing of epiphysiodesis. The amount of time required to complete the exercises and the accuracy of the answers were evaluated for each subject.

Results: The test subjects answered 60% of the questions correctly using the traditional MM and 80% of the questions correctly using the MA (P=0.001). The average amount of time to complete the 5 exercises with the MM and MA was 22 and 8 minutes, respectively (P<0.0001).

Conclusions: Several reports state that the traditional MM is quick and easy to use. Nevertheless, even in the most experienced hands, performing the calculations in clinical practice can be time-consuming. Errors may result from choosing the wrong formulae and from performing the calculations by hand. Our data show that the MA is simpler, more accurate, and faster than the traditional MM from a practical standpoint.

Level of Evidence: Level II.

*Department of Orthopaedic, Clínica Alemana de Santiago, Universidad del Desarrollo, Santiago, Chile

International Center for Limb Lengthening, Rubin Institute for Advanced Orthopedics, Sinai Hospital of Baltimore, Baltimore, MD

None of the authors received financial support for this study.

S.C.S. is a paid consultant for Ellipse Technologies, receives stock options from Ellipse Technologies, and receives royalties from Pega Medical and Ellipse Technologies. J.E.H. is a paid consultant for OrthoPediatrics and receives research support from Ellipse Technologies. The institution of S.C.S. and J.E.H. received support from the following companies to support its nonprofit organization: Stryker, Orthocare Solutions, and Metro Prosthetics. The following companies supported an annual course for orthopaedic surgeons that is held by the institution of J.E.H. and S.C.S.: Smith & Nephew, Ellipse Technologies, Stryker, Brainlab, Depuy Synthes, Orthofix, Biomet, KCI, OrthoPediatrics, OHK Medical Devices, and The MHE Coalition. P.W. declares no conflicts of interest.

Reprints: John E. Herzenberg, MD, FRCSC, International Center for Limb Lengthening, Rubin Institute for Advanced Orthopedics, Sinai Hospital of Baltimore, 2401 W. Belvedere Avenue, Baltimore, MD 21215. E-mail: jherzenberg@lifebridgehealth.org.

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