Authors Harry Hothi, Sean Bergiers, Martina Tognini, Johann Henckel, Anna Di Laura, John Skinner, Alister Hart, of the Royal National Orthopaedic Hospital look at The Stryde nail, CE-marked in February 2019 for use in patients
The process of limb lengthening using distraction osteogenesis is now an established procedure in orthopaedics. In the lower limb (tibia and femur), this is now more commonly being achieved using intramedullary techniques, with nails that are fully implantable in the patient. These are advantageous over traditionally used external fixators which have been linked to greater discomfort, long treatment times and the risk of pin site infections in the patient.
The Precice nail (NuVasive Specialised Orthopaedics (NSO)) is one such device that has been used in patients since 2011. Following implantation, the nail is lengthened using an external magnetic remote controller which interacts with magnets within the nail. This lengthening, typically by 1mm/day, can be carried out by the patient at home, in between regular outpatient clinic visits with the surgeon. The amount of lengthening possible is between 30 and 80mm, depending on the size of nail used, the size of the original bone, the wishes of the patient and the safe clinical amount determined by the surgeon.
These nails are intended to be removed from the patient after the planned lengthening has been achieved and after new bone has fully formed and strengthened. Precice nails, made of titanium alloy, are permitted for us in patients weighing up to 57-114 kg, depending on the size of the nail and limb being treated. These patients can only partially weight-bear on the treated limb until full lengthening and bone regeneration has been achieved; this can be up to 3 months post-implantation. Thousands of patients have successfully received limb lengthening treatment using this technology.
The Stryde nail (NSO), by the same manufacturer, was CE-marked in February 2019 for use in patients in the same way as Precice nails. The Stryde offered the advantage however of permitting weight-bearing, in patients weighing up to 69-114kg, during the initial lengthening stages post-implantation. This was achieved by making the Stryde out of a tougher, stainless-steel alloy (Biodur 108) and introducing several design modifications.
In January 2021 however, NSO issued a Field Safety Notice (FSN) declaring that they had voluntarily recalled and halted the UK supply of both the Precice and Stryde nails, as well as related Precice devices. This was due to the identification of the absence of several biological safety tests for these devices, as well as reports of adverse reactions in some patients implanted with Stryde nails. In March 2021, the CE certification of these devices was suspended by the manufacturers notified body. This suspension also applies to the MAGEC spine rods by the same manufacturer, which use a similar magnetic lengthening technology. The suspension of the CE mark was directly due to the absence of some biological safety data; the manufacturer is now working to address this.
As with the introduction of all new medical devices, effective post-market surveillance is essential in monitoring and ensuring patient safety. In the case of the Stryde, this was first achieved by surgeons at the RNOH through close monitoring of their patients and the reporting of their early clinical experiences [1]. They found that while all nails successfully lengthened the limb treated, there was evidence of adverse clinical and radiological findings in some patients. These findings were reported to the manufacturer and the UK regulator, the Medicines and Healthcare Products Regulatory Agency (MHRA).
The next stage of post-market surveillance involved forensic analysis of the nails following their removal from patients. This was performed at the RNOH Implant Science Centre, where it was shown that the adverse clinical and radiological changes were likely due to evidence of corrosion of the nails, Figure 1 [2]. These findings were consistent with those reported by other centres [3, 4]. Further retrieval analysis is now necessary with a greater number of nails in order to understand which surgeon, implant and patient factors are involved in the adverse outcomes observed. This is essential to informing future design modifications or changes to clinical practice which may be required to ensure the safe use of devices such as these.
The UK is now continuing to develop the UKCA system for approving medical devices, and the MDR is underway throughout the rest of Europe. Both models emphasise the role of post-market surveillance and it is clear that analysis of implants removed from patients must form part of this; this includes looking at implants that have performed as intended as well as those considered to be early failures.
Figure 1: X-ray (left) showing a patient with a Stryde nail in their femur, 2 days after implantation. X-ray (right) showing the same patient after 13 months. The nail has successful lengthened the femur as intended however there is evidence of cortical thickening around the junction of the nail (red arrow). Retrieval analysis found this junction to have corroded.
References
- Iliadis AD, Wright J, Stoddart MT, Goodier WD, Calder P. Early results from a single centre’s experience with the STRYDE nail : a cause for concern? Bone Joint J. 2021 Jun;103-B(6):1168-1172.
- Hothi H, Bergiers S, Henckel J, Iliadis AD, Goodier WD, Wright J, Skinner J, Calder P, Hart AJ. Analysis of retrieved STRYDE nails. Bone Jt Open. 2021 Aug;2(8):599-610.
- Frommer A, Roedl R, Gosheger G, Hasselmann J, Fuest C, Toporowski G, Laufer A, Tretow H, Schulze M, Vogt B. Focal osteolysis and corrosion at the junction of Precice Stryde intramedullary lengthening device : preliminary clinical, radiological, and metallurgic analysis of 57 lengthened segments. Bone Joint Res. 2021 Jul;10(7):425-436.
- Jellesen MS, Lomholt TN, Hansen RQ, Mathiesen T, Gundlach C, Kold S, Nygaard T, Mikuzis M, Olesen UK, Rölfing JD. The STRYDE limb lengthening nail is susceptible to mechanically assisted crevice corrosion: an analysis of 23 retrieved implants. Acta Orthop. 2021 Jun 8:1-7.
