Send to

Choose Destination
HSS J. 2018 Jul;14(2):166-176. doi: 10.1007/s11420-017-9596-y. Epub 2018 Jan 5.

A Comparison of Femoral Lengthening Methods Favors the Magnetic Internal Lengthening Nail When Compared with Lengthening Over a Nail.

Author information

1Hospital for Special Surgery, Weill Medical College of Cornell University, 535 East 70th Street, New York, NY 10021 USA.
Maine Orthopedics, Portland, ME USA.
3Weill Cornell Medical College, New York, NY 10065 USA.



Bone lengthening with an internal lengthening nail (ILN) avoids the need for external fixation and requires one less surgical procedure than lengthening over a nail (LON). However, LON has been shown to be superior to femoral internal lengthening using a mechanical nail. The magnetic ILN, a remote-controlled and magnet-driven device, may have overcome the weaknesses of earlier internal lengthening technology and may be superior to LON.


(1) Is the magnetic ILN more accurate than LON for femoral lengthening? (2) Does the magnetic ILN demonstrate more precise distraction rate control than LON? (3) Does the magnetic ILN result in faster regenerate site healing, with more robust callus, than LON? (4) Does the magnetic ILN result in fewer complications, including impediments to knee motion, than LON?


We conducted a retrospective comparison of the records and radiographs of 21 consecutive patients with 22 femoral lengthenings using LONs and 35 consecutive patients with 40 femoral lengthenings using remote-controlled magnetic ILNs. Primary outcomes measured included accuracy, distraction rate precision, time to bony union, final knee range of motion, regenerate quality, and complications. The minimum follow-up times for the LON and ILN cohorts were 13 and 21 months, respectively.


Patients treated with ILN had a lower post-treatment residual limb-length discrepancy (0.3 mm) than those treated with LON (3.6 mm). The rate of distraction was closer to the goal of 1 mm/day and more tightly controlled for the ILN cohort (1 mm/day) than that for the LON group (0.8 mm/day; SD, 0.2). Regenerate quality was not significantly different between the cohorts. Bone healing index for ILN was not statistically significant. Time to union was shorter in the ILN group (3.3 months) than that in the LON group (4.5 months). A lower percentage of patients experienced a complication in the ILN group (18%) than in the LON group (45%). Knee flexion at the end of distraction was greater for ILN patients (105°) than that for LON patients (88.8°), but this difference was no longer observed after 1 year.


Femoral lengthening with magnetic ILN was more accurate than with LON. The magnetic ILN comports the additional advantage of greater precision with distraction rate control and fewer complications. Both techniques afford reliable healing and do not significantly affect knee motion at the final follow-up. The magnetic ILN method showed no superiority in regenerate quality and healing rate.


PRECICE; internal lengthening nail; lengthening over a nail; limb lengthening

Conflict of interest statement

Compliance with Ethical StandardsAnton M. Kurtz, MD, Jonathan R. Barclay, BS, and Joseph Nguyen, MPH, declare that they have no conflicts of interest. Austin T. Fragomen, MD, reports receiving personal fees from NuVasive, Smith and Nephew, and Synthes, outside the submitted work. S. Robert Rozbruch, MD, reports receiving personal fees from NuVasive, Smith and Nephew, and Stryker, outside the submitted work.All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2013.Informed consent was waived from all patients for being included in this study.Disclosure forms provided by the authors are available with the online version of this article.

Supplemental Content

Full text links

Icon for Springer Icon for PubMed Central
Loading ...
Support Center