Internal lengthening nails

An internal lengthening nail is a device implanted inside a long bone that can be lengthened gradually after the operation. The orthopaedic literature calls it an intramedullary nail, meaning it sits within the bone. AAOS patient information describes the surgeon cutting the bone and implanting an expandable metal rod; as the rod lengthens, the bone segments are gradually pulled apart and new bone grows in the space created.

This is the same principle of gradual lengthening, distraction osteogenesis, that external frames rely on. A published review of limb lengthening describes the methods as having evolved from external fixators to lengthening intramedullary nails while still resting on the same biological principles. What differs is where the device sits and how the lengthening is driven.

An external fixator is a frame outside the limb, connected to the bone with wires or pins that pass through the skin. An internal nail sits inside the body: Cleveland Clinic patient information describes it as a device the surgeon places inside the bone that is not visible outside the body, and a 2026 systematic review describes these devices as eliminating the need for external hardware.

The same review notes that these devices introduce specific risks of their own, related to their motorized and telescopic mechanisms. This guide describes the structural difference only. It does not state that either approach is safer, less painful, faster or more effective — those are clinical questions for a treating surgeon.

Earlier internal nails lengthened through mechanical mechanisms; the published review describes one early design that required rotation of the limb to lengthen, and describes current motorized nails as not requiring rotation. A 2021 systematic review describes FITBONE as a motorized nail and PRECICE as a magnetically driven nail — named here as technical examples from the literature, not as a recommendation of any product.

Patient information from Cleveland Clinic describes using a remote control that rotates the rod inside the bone, and Hospital for Special Surgery describes an external magnet that connects to a magnet within the rod. How much lengthening takes place, and on what schedule, is set by the treating team for the individual patient and is not described here.

An internal device does not remove the need for monitoring or rehabilitation. AAOS patient information describes both internal and external lengthening as requiring regular follow-up visits and extensive rehabilitation, including physical therapy and home exercise. Cleveland Clinic describes the care team using X-rays to check new bone growth and adjusting treatment if it is progressing too quickly or too slowly.

How rehabilitation is organised — on-site, through a partner or remotely — differs between providers and is covered in the guide Understanding rehabilitation.

Internal nails have complications of their own. A 2021 systematic review of complications with two motorized nail systems, covering 983 lengthened bone segments, found that device and bone complications were the types most often reported. Its authors caution that, because no standardised method of reporting complications exists, the true rate might be different. A 2026 systematic review focused specifically on failures of the lengthening mechanism, such as jamming, and reported that these were usually managed with further surgery. This guide does not quote complication rates, because figures pooled across different patients, devices and study designs do not describe any individual's risk.

Cleveland Clinic patient information describes the lengthening device being removed in a further surgical procedure after the new bone has hardened, and the 2021 review classifies complications by whether they occurred before or after implant removal. Whether and when removal is planned is a question for the treating team.

This guide does not claim that internal nails are safer, faster, less painful or more effective than external fixation or hybrid methods, and it makes no claims about typical timelines, costs or complication rates. It does not describe who is a suitable candidate: individual suitability for any method depends on clinical factors that only a qualified orthopaedic surgeon can assess for a specific patient.

If a provider lists internal nail lengthening among its treatment methods, the questions below can help make its answers comparable with other providers'. They are prompts for your own research, not a checklist of correct answers.