Mechanical Failures in Magnetic Intramedullary Lengthening Nails

Abstract

Background: Magnetic intramedullary lengthening nails (MILNs) have gained popularity in recent years for the treatment of limb-lengthening discrepancies. We sought to catalog mechanical failures and their prevention and management in a large, single-institution series. We specifically assessed the rate of mechanical failures, the types of failures observed, and management strategies.Methods: We retrospectively reviewed 377 patients (420 limbs) who underwent limb lengthening with early (P1) or later (P2) MILN iterations with ‡12-month follow-up. Mechanical failure was defined as mechanical breakage of the instrumentation or nail and/or failure of the internal lengthening mechanism. Failure assessment was arranged by lengthening phases and was sorted with a complication classification system. All lengthening and alignment parameters were assessed radiographically.Results: Mechanical failure was observed in 40 nails (9.5%), most of which (63%) were corrected with an additional surgical procedure. The mechanical failure rate was 11.3% in P1 nails and 9% in P2 nails. Two nails failed the intraoperative distraction test, and 1 nail was found to have a broken washer during the insertion phase. Sixteen nails had mechanical failures in the lengthening phase. Some nails (8 of 16) required nail replacement surgery. Thirteen nails failed during the consolidation phase; 7 of these cases were managed by replacement with either a functional MILN or a conventional intramedullary nail. Eight failures happened during the extraction phase and were managed intraoperatively.Conclusions: A 9.5% overall rate of mechanical failure of MILNs was observed in this large series. Resolution was achieved with an additional surgery in most cases. Nail distraction and weight-bearing compliance should be closely monitored during the lengthening and consolidation phases. Nail removal can be difficult and requires a careful study of radiographs for locking-screw bone overgrowth and backup removal equipment.

Breakage of a re-activated PRECICE® nail: A case report

“…Standard nail removal instruments may not be sufficient to extract broken PRECICE® nails. Hlukha et al reported an intra-operative disintegration of PRECICE® nail upon extraction which required collecting pieces with pituitary forceps [3] . In this case report, the motor unit elements disintegrated outside of the medullary canal and subsequently easily removed.…”

“…The remaining length capacity can be determined based on knowledge of the consumed length. It is not recommended to reactivate nails which have reached their maximum length due to probability of distraction mechanism jamming [3] . Re-activation of lengthening nails for more than once should be extremely avoided.…”

“…Progressive soft tissue resistance, adjacent joint contracture, subluxation, dislocation, neurovascular stretch injury, infection, poor regenerate formation, and premature consolidation are examples of such obstacles. Furthermore, reversal of lengthening is occasionally required to manage these emerging conditions [3] . For these reasons, it is not uncommon to achieve certain length target in multiple stages rather than a single smooth go.…”

“…The surgeons understand that and tend to be minimalist as possible. In that context, concept of re-activation of sleeper lengthening nail was advocated aiming for reducing extra operative time, surgical trauma, and subsequent cost required for exchange with a new lengthening nail [3] , [4] . Re-activation of sleeper lengthening nails entails re-osteotomy and re-employment of the retained lengthening nail for an additional lengthening round.…”

What’s New in Pediatric Orthopaedics

“…In the first 2 generations of magnetic intramedullary lengthening nails used at a single institution, 40 (9.5%) of 420 failed and 63% of those required an additional surgical procedure. Many of these failures happened during the lengthening process, leading the authors to suggest close monitoring of nail distraction and weight-bearing 22 . In the second study, limb lengthening was performed with a novel motorized expandable plate for 7 children who were 2.7 to 9.7 years of age.…”