Technical considerations and early results of magnetic compressive intramedullary nailing for tibial and femoral shaft non-unions: a case series

Introduction

Fractures of the tibial and femoral shaft can be reliably treated with intramedullary nails (IMNs). However, given the sheer volume of these fractures, with reported incidences of 16.9 and 10–21 per 100,000 per year (1-3), respectively, a significant number may still progress to non-union. Despite effective fixation in many cases, a significant proportion of these fractures progress to non-union, presenting major clinical challenges. Understanding the epidemiology and treatment outcomes for these non-unions is essential for guiding therapeutic decisions.

Tibial and femoral non-unions including hypertrophic, atrophic, and defect non-unions as classified by Weber and Cech (4), represent a substantial challenge as compared to acute fractures, but when considering their management, the fundamental principles of bone healing still apply. This includes preserving or restoring biologic healing potential, providing adequate compression and stability for osteogenesis (5-9). While conventional techniques, such as intramedullary nailing and plating, provide some degree of compression across a fracture at the time of surgery, there has previously been no way to maintain or increase compression afterwards, aside from dynamization, which has more recently come under scrutiny (10). However, the creation of magnetic intramedullary nails (mIMNs), originally employed in limb lengthening, has made this possible (11-14).

As opposed to conventional intramedullary implants, magnetic nails provide the theoretical benefit of sustained and sequential compression. Additionally, mIMNs overcome many of the limitations noted with other techniques, such as circular external fixators, which include high complication rates, cosmetic dissatisfaction, and intensive treatment courses.

Although the use of mIMNs for non-unions is still relatively novel, there have been several early reports exploring their use (15-17), including a preliminary analysis by Fragomen et al. (18) who helped design the implant. While these authors’ results show early promise, with overall good union rates (13 of 14 cases), the variety in terms of fracture selection is still relatively limited.

With the complexity and varied treatment for tibial and femoral shaft non-unions, research to study the outcomes of compressive mIMNs at different centers with different fracture patterns is needed. Therefore, the purpose of the current study was to analyze the results of compressive mIMNs to treat these non-unions and to emphasize technical considerations in their application. We present this article in accordance with the AME Case Series reporting checklist (available at https://aoj.amegroups.com/article/view/10.21037/aoj-25-33/rc).

Case presentation

All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Publication of this case series and accompanying images was waived from patient consent according to the UT Health San Antonio institutional review board. A retrospective review was performed on all patients who underwent magnetic intramedullary nailing (PRECICE and PRECICE STRYDE Nails; Nuvasive Specialized Orthopedics, San Diego, CA, USA) (Figure 1) of tibial or femoral shaft non-union by two trauma fellowship trained surgeons from 2017–2022. Non-unions were defined as fractures that remained unhealed both clinically and radiographically six months after surgery, in line with common practice despite variability in classification. Patients treated for leg length discrepancy were excluded. Collected variables included patient demographics, comorbid medical conditions, mechanism of injury, fracture characteristics (open versus closed, anatomical location, segmental, comminuted patterns), history of prior surgeries and complications, duration of follow-up, and use of biologic adjuncts. Time to radiographic union was recorded, with radiographic union defined as bridging callus formation across at least three of four cortices on orthogonal anteroposterior and lateral radiographs, accompanied by the absence of fracture line visibility or hardware loosening, consistent with established orthopedic criteria. Presence of osteolysis was also documented.

Figure 1 Radiograph demonstrating magnetic intramedullary nail internal components.

Our institutional protocol for compression during the study period commenced at the 2-week postoperative visit with 2 mm of compression. This was followed by a 2–2.5-mm interval of compression at each visit, every 2 weeks, typically for a total of 5 visits or approximately 1 cm of compression. Evidence of compression was indicated by visible bolt deflection (bending) on X-rays. In cases where no deflection was apparent, additional compression was applied. However, more recently we have started moving towards at home protocols, with periodic check-ins. One patient in the current study was trained how to properly use the external remote controller (ERC) at the first postoperative visit, followed by self-guided adjustments at home with 0.3 mm shortening per day for 14 days.

Thirteen consecutive patients underwent mIMN of the tibia or femur from 2017–2022 (Figure 2). Eight patients with non-unions (five femurs, three tibias) were included in the final analysis, whereas five others were excluded as they were treated with mIMNs for leg length discrepancy. The mean age at surgery was 38±16 years and the mean follow-up duration was 16.1±8.7 months. All fractures were classified as non-unions, being more than 6 months out from their initial fixation. Each patient had at least one prior surgery before magnetic intramedullary nailing and five patients (62.5%) had open fractures initially. Further demographics can be found in Table 1.

Figure 2 Flow diagram showing patient inclusion and exclusion for the study cohort. mIMN, magnetic intramedullary nail.

Six of eight patients went onto union (Figures 3,4), with a mean time to union of 6.1±4 months (range, 3–12 months) and a median time to union of 4.6 months. However, it’s essential to note that two patients did not achieve union for distinct reasons. One patient underwent an above-knee amputation due to a severe infection, while the other experienced a persistent non-union at the distal docking site following bone transport with the mIMN. Nail recharge, a mechanical complication involving unintended retraction of the nail resulting in loss of lengthening, was noted. Although iliac crest bone grafting was recommended to address the non-union, the patient declined the planned secondary surgery (Figure 5). Other complications included one patient with chronic pain despite fracture union. Three patients underwent mIMN with the stainless steel PRECICE Stryde IMN with no osteolysis noted radiographically. Further details can be found in Table 2.

Figure 3 Radiographs of proximal tibia non-union treated with magnetic intramedullary nail. Images include preoperative and serial follow-up radiographs from multiple cases demonstrating progressive healing and consolidation over the course of treatment.

Figure 4 Radiographs of femoral shaft non-unions treated with magnetic intramedullary nail. Composite images from multiple cases illustrating progression from preoperative non-union through serial postoperative follow-up, showing successful union and bone remodeling.

Figure 5 Radiographs demonstrating bone transport utilizing magnetic intramedullary nail.

Discussion

Femoral and tibial non-unions represent considerable challenges for treating surgeons, with techniques like circular external fixators and exchange nailing, with and without compressive plating, having several notable drawbacks. In the context of non-unions, where prolonged healing times are almost inevitable, the demand for technologies which enhance or expedite healing becomes paramount. Thus, this study presents promising early results and technical considerations for treating femoral and tibial non-unions with acceptable union rates overall. Additionally, this study further demonstrates the power of a mIMN to overcome segmental bone loss by means of bone transport.

Similar to our study, Fragomen et al. (18) accomplished union in 13 out of 14 patients treated. However, while our results align, they also demonstrate the generalizability of this technology remote to a high-volume limb lengthening center where the authors helped design the very implant being utilized. Nevertheless, in the absence of comparative studies that evaluate union rates and time to union against that of standard exchange nailing or external fixators, it is a daunting task to discern the comparative advantages. However, a key limitation of this study is the small sample size of only eight patients, which restricts the generalizability of our conclusions and warrants cautious interpretation. Although this initial case series provides important preliminary insights, larger and more robust studies are necessary to validate the clinical applicability of mIMNs for non-union treatment. Moreover, the considerable clinical heterogeneity of the cohort—including variations in anatomical site (femur versus tibia), patient age, and infection status—reflects real-world complexity but complicates cohesive analysis. These limitations underscore the need for larger, more homogeneous case series or prospective trials to rigorously evaluate the efficacy and safety of mIMN across diverse patient populations.

Though mIMNs have revolutionized limb lengthening, their advantages for non-unions are still in the process of clinical validation. However, recent concerns about osteolysis in an updated iteration of one of the implants temporarily halted their use altogether. Initially composed of titanium, the original PRECICE nail requires restricted weight bearing during the healing process. The PRECICE STRYDE nail, composed of stainless steel, eliminated these restrictions. Unfortunately, reports emerged over the past few years indicating osteolysis and pain associated with the implants and thus all PRECICE nails were temporally pulled from market (19-21). Subsequently, PRECICE titanium nails have been reinstated, but the PRECICE STRYDE Nail, or at least its next iteration has yet to return. Although none of the STRYDE implants utilized in this study demonstrated osteolysis, close surveillance and removal of these previously placed implants when able is advisable.

Within our study, one patient underwent bone transport with a mIMN for segmental bone loss. Bone transport was initially introduced by Iliziarov in the 1950s, and relied on circular external fixation (22). However, in recent years, bone transport using a mIMN has gained popularity and has shown satisfactory results when treating complex traumatic bone loss (23-25). Compared to traditional exchange nailing and Ilizarov/circular external fixation techniques, mIMN reduces the duration of external fixation and improves patient comfort by allowing internalized distraction and stabilization. However, there are several important treatment considerations with this technique. First, although compression can continue to be applied through the nail after cortical contact has occurred, there remains a risk of non-union or fragmentation at the docking site. Typically, a docking site delayed union or non-union can be managed with a secondary surgery wherein interposed soft tissue is removed and bone graft is added. However, if stability is a concern, particularly in a metaphyseal segment, some have advocated plating, while others have advocated removal of the magnetic nail in favor of a conventional IMN with further blocking screws given the manufacturers recommendation for removal eventually.

Compared to exchange nailing and Illizarov methods, the risk of docking site non-union remains a significant challenge, with non-union rates ranging from 10–17% reported in the literature (26-28). Complications such as infection and mechanical failure have been reported across all methods, highlighting the complexity of treating segmental bone defects. Bone transport with mIMN offers the advantage of reduced external fixation time and improved patient comfort but necessitates meticulous surgical planning and postoperative surveillance to address potential complications such as nail recharge and delayed union. The uncertainty surrounding these late-stage treatments highlight the need for further research on bone transport magnetic intramedullary nailing.

Regarding infection risk and patient selection, careful preoperative planning is essential to minimizing complications. While two patients in this study had infected non-unions, the patient who ultimately required an above-knee amputation (AKA) did not have a documented infection before undergoing compressive intramedullary nailing. This patient had multiple prior procedures, including hardware removal, bone grafting, and debridement, but no confirmed infection at the time of mIMN placement. These findings highlight the need for thorough patient evaluation, as septic non-unions may be more appropriately managed with external fixation or a staged approach rather than immediate compressive nailing.

Moreover, patient selection remains a critical factor in optimizing outcomes with mIMN. Ideal candidates typically include skeletally mature patients without active infection and with deformities that are amenable to correction. Evaluations should also carefully consider comorbidities, prior surgeries, bone quality, and overall health status to mitigate the risk of complications. As growing clinical experience and new evidence accumulate, patient selection criteria will likely continue to evolve to better stratify risk and improve outcomes. A multidisciplinary preoperative approach involving orthopedic surgeons, infectious disease specialists, and rehabilitation teams is essential to identify patients most likely to benefit from this technology while minimizing potential treatment failures. Future studies should focus on refining selection algorithms and identifying predictive factors for successful treatment with mIMN in diverse patient populations.

While mIMNs offer compelling technical and patient-centered advantages, it is important to consider their cost-effectiveness compared to traditional methods. Although mIMN devices incur higher up-front costs relative to exchange nailing or external fixation, emerging evidence suggests these may be offset by reduced external fixation time, lower complication and reoperation rates, and shorter hospital stays, ultimately benefiting both patients and healthcare systems (25,29,30).

Conclusions

In summary, although non-unions have been conventionally treated with exchange nailing and/or external fixators, these modalities may not be ideal for certain scenarios and may result in prolonged treatment. mIMNs, through the ability to deliver sustained compression internally, demonstrate promising early results in the treatment of both femoral and tibial non-unions. These nails may be particularly preferred in skeletally mature patients with diaphyseal or distal metaphyseal non-unions without active infection and who can comply with close clinical monitoring. Practical limitations include higher upfront costs, the need for frequent follow-up to monitor compression and device function, patient compliance, and planned implant removal according to manufacturer guidelines. To fully establish the clinical utility of mIMN, further investigation with larger prospective cohorts comparing union rates, time to union, cost-effectiveness, and patient-centered outcomes against conventional modalities is warranted.

Acknowledgments

This work was previously presented as a video presentation at the Orthopaedic Trauma Association 2023 Annual Meeting (Seattle, WA, October 2023).

Footnote

Reporting Checklist: The authors have completed the AME Case Series reporting checklist. Available at https://aoj.amegroups.com/article/view/10.21037/aoj-25-33/rc

Peer Review File: Available at https://aoj.amegroups.com/article/view/10.21037/aoj-25-33/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://aoj.amegroups.com/article/view/10.21037/aoj-25-33/coif). R.A.K. reports he has received consultant fees for Smith & Nephew Inc., Zimmer Biomet, and Acelity; speaker fees from Zimmer Biomet; and research grants from Smith & Nephew Inc. None of these activities are related to the content of this article. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Publication of this case series and accompanying images was waived from patient consent according to the UT Health San Antonio institutional review board.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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