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.

Level of Evidence: 

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

中文翻译：

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磁性髓内加长钉的机械故障

背景： 

近年来，磁性髓内延长钉 (MILN) 在治疗肢体延长差异方面受到欢迎。我们试图在大型单一机构系列中对机械故障及其预防和管理进行分类。我们专门评估了机械故障率、观察到的故障类型和管理策略。

方法： 

我们回顾性地回顾了 377 名患者（420 条肢体），这些患者接受了早期 (P1) 或晚期 (P2) MILN 迭代的肢体延长术，随访时间≥12 个月。机械故障被定义为仪器或钉的机械破损和/或内部延长机构的故障。失败评估按延长阶段安排，并根据并发症分类系统进行分类。所有延长和对准参数均通过射线照相评估。

结果： 

在 40 个钉子 (9.5%) 中观察到机械故障，其中大部分 (63%) 通过额外的外科手术进行了矫正。P1 钉的机械故障率为 11.3%，P2 钉的机械故障率为 9%。2 根髓内钉未通过术中牵引测试，1 根髓内钉在置入阶段发现垫圈破损。十六根钉子在延长阶段出现机械故障。一些指甲（16 个中的 8 个）需要进行指甲置换手术。13 个钉子在巩固阶段失败；其中 7 例通过使用功能性 MILN 或传统髓内钉进行置换治疗。在拔牙阶段发生了 8 次失败，并在术中进行了处理。

结论： 

在这个大型系列中观察到 MILN 的总体机械故障率为 9.5%。在大多数情况下，通过额外的手术可以解决问题。在延长和巩固阶段应密切监测指甲牵引和负重依从性。取钉可能很困难，需要仔细研究 X 光片以了解锁定螺钉骨过度生长和备用移除设备。

证据等级： 

治疗等级IV。有关证据等级的完整描述，请参阅作者须知。