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Magnetic Expansion Control System Achieves Cost Savings Compared to Traditional Growth Rods

An Economic Analysis Model

Su, Alvin W. MD, PhD*,†; Milbrandt, Todd A. MD, MS*; Larson, A. Noelle MD*

doi: 10.1097/BRS.0000000000001077

Study Design. Medical economic model with multi-way sensitivity analysis.

Objective. To compare the direct costs of growing rod (GR) versus Magnetic Expansion Control System (MG) from a payer's perspective. We hypothesized that over time the MG will become more cost-effective.

Summary of Background Data. Traditional GRs provide effective treatment, but require periodic lengthening surgery. MG allows rod lengthening in clinic, but the implant is expensive. The cumulative cost savings are not well understood.

Methods. Index surgery, implant cost, lengthening procedure, and revision surgery due to implant failure or infection were identified as major parameters contributing to the cumulative cost. The “base,” “low,” and “high” values for the cost and the incidence of each parameter were determined by literature reports, health care database search, or expert consultation. The cumulative cost was compared annually during 5 years of follow-up. Marginal cost was defined as the cost of (GR−MG) for each cumulative year. Final cumulative cost and extreme case scenario at year 5 were assessed by deterministic sensitivity analysis.

Results. MG resulted in higher cumulative cost at years 1 and 2, and became lower cost at years 3 through 5. The marginal cost at year 1 was a negative value of $16K, and trended toward positive values of $12K at year 3 and $40K by year 5. Sensitivity analysis revealed that in extreme case, MG could cost more, shown by a marginal cost of $26K by implementing the extreme values of the 3 parameters carrying highest variance: MG-infection management, GR-revision surgery, and GR-lengthening procedure.

Conclusion. MG achieved cost neutrality to GR at 3 years after index surgery. This is the first medical economic study in the United States comparing the cost of GR versus MG and demonstrates potential cost-effectiveness of MG from payer's perspective if in place for more than 3 years.

Level of Evidence: 2

*Department of Orthopaedic Surgery, Mayo Clinic, Rochester, MN

School of Medicine, National Yang-Ming University, Taipei, Taiwan.

Address correspondence and reprint requests to A. Noelle Larson, MD, Department of Orthopedic Surgery, Mayo Clinic, 200 1st St SW, Rochester, MN 55905; E-mail:

Received 29 January, 2015

Revised 23 April, 2015

Accepted 19 June, 2015

The device(s)/drug(s) is/are FDA-approved or approved by corresponding national agency for this indication.

No funds were received in support of this work.

Relevant financial activities outside the submitted work: grants.

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