Magnetically-activated Limb Lengthening Nails: Mechanical Failure Rate And Types Of Failures Observed in 245 Limb Segments

Introduction: Mechanical failure rate of magnetically-activated limb lengthening nails has not yet been determined. The aim is to present the mechanical failure rate and types of failures observed for magnetically-activated limb lengthening nails.

Methods: Retrospective medical record review was conducted of 180 patients (245 segments) who underwent limb lengthening using magnetically-activated nails. Mechanical failure was recognized as (1) instrumentation/nail mechanical breakage or (2) internal mechanism failure that resulted in backwinding or that stopped the nail from lengthening.

Results: Mechanical failure was observed in 23 nails (22 patients, 23 limb segments). Mechanical failure rate was 9.3% (23 of 247 nails). Only 4.9% (12 of 245 segments) required an additional, unplanned surgery as a result of mechanical failure. Mechanical failure rates of the original nail and a redesigned nail were 11.3% (11/97 nails) and 8.0% (12/150 nails), respectively. During insertion, 2 nails failed intraoperative distraction test and were replaced with functional nails during the same procedure. Mechanical failures during the lengthening stage were observed in 8 nails (3 nonfunctioning mechanisms, 2 proximal fixation failure, 1 lead screw failure, 1 backwinding, and 1 crown fragmentation). Mechanical failures were observed in 8 nails during the consolidation period (2 nail fractures, 2 nail plastic deformations, 2 combined plastic deformations and crown fragmentations, 1 isolated crown fragmentation, and 1 backwinding). Extraction-related mechanical failures were reported in 6 nails (2 crown fragmentation, 1 backwinding, 1 set-screw fracture, 1 extractor assembly breakage, 1 mechanism disassembly).

Discussion: In 247 nails, a 9.3% mechanical failure rate was observed. However, only 4.9% (12 of 245 segments) required an unplanned surgery due to mechanical failure. Mechanical failure rate decreased for the newer device model. Nail function should be closely monitored throughout the lengthening phase. We recommend that efforts continue to be made to improve the nail strength and reliability.