Re-use of Motorised Intramedullary Limb Lengthening Nails

INTRODUCTION

Lengthening of long bone segments was first described by Ilizarov by his method of distraction osteogenesis utilising external fixators.^1,2 Limb lengthening techniques have undergone a transition from external fixation-based techniques to largely all-internal implants primarily with motorised intramedullary lengthening nails. Motorised intramedullary limb lengthening (MILL) has been reported for the surgical lengthening of femoral, tibial, and humeral segments.^3–5

Some patients require separate episodes of lengthening to achieve limb length equalisation either because of the magnitude of discrepancy or the need to temporally separate lengthening treatments. In these cases, a MILL device can be re-used. To accomplish this, the distal interlocking screws are removed, the telescoping portion of the nail is reversed, the nail is relocked, and the nail is redeployed for further lengthening.

This procedure may be performed in two situations: to continue an ongoing treatment for cases in which the nail is maximally deployed but further lengthening is desired, or to use a “sleeping nail” technique.⁶ In this technique, the index lengthening site is allowed to consolidate. When further lengthening is desired at a later time, the nail is retracted and re-locked, then a corticotomy is performed at separate site from the previous lengthening site. A new lengthening then begins with the same device.

Studies reporting the outcomes of nail reutilisation remain sparse. If successful, this strategy could avoid the additional trauma of implant exchange and can save the cost of an additional lengthening device. We review our experience with re-use of motorised intramedullary lengthening nails for limb lengthening in children. In this report, the terms re-use and redeployment are used interchangeably to denote a nail that was retracted and then distracted by any timeline. The term “reactivation” is used to denote a specific subset of nails that were dormant for a period and then re-used or re-deployed for a second, later lengthening treatment.

MATERIALS AND METHODS

This study was Institutional Review Board (IRB) approved and a waiver of consent obtained. Patients were eligible if they had undergone reversal of a previously deployed MILL nail (PRECICE®, Nuvasive, San Diego, CA, USA) between 2015 and 2022 by a single surgeon with the intention to re-deploy the implanted intramedullary device for lengthening. Variables of interest included length of time the nail was inactive, magnitude of previous lengthenings, specific implant considerations (diameter, length, and “stroke”), timing of nail interlocking screw removal and retraction, complications associated with re-deployment of the nail, and the amount of lengthening achieved with the second use of the nail. Complications specific to the nail re-use were categorised according to the modified Clavien-Dindo classification for orthopaedic surgery.⁷

RESULTS

Ten patients (with 12 lengthening episodes) were included over an 8-year period (2015–2022). Five tibial segments, five femoral segments, and two humeral segments were included. The mean age at surgery was 14.0 years old (9.3–19.6 years old). The aetiology of the limb length discrepancy included congenital short femur (n = 2), post-infectious growth arrest (n = 2), post-traumatic growth arrest (n = 2), fibular hemimelia (n = 1), ischaemic growth arrest (n = 1), Ollier disease (n = 1), and congenital pseudarthrosis of the tibia (CPT, n = 1).

Seven of 12 nails (58%) were successfully re-used. This was attempted at a mean of 29.6 months from index placement of the MILL nail (1.4–84.0 months). Successful second use of the nail occurred at a mean of 17.6 months after insertion compared with 46.4 months for nails that failed re-use. In four cases, the nails underwent the distal interlocking screw removal in a prior, temporally separate procedure (mean 22.6 months, range 13.1–43.0 months), and three of these nails were successfully re-deployed (75%). Three nails (two humeral and one femoral) underwent attempted re-use to extend the same lengthening treatment, two successfully.

Eleven nails were 8.5 mm in diameter and one nail was 10.7 mm in diameter. Overall implant lengths ranged from 150 to 305 mm. All nails were P2 generation (a technical detail meaning the nails were composed of a single male and female component with a crown moulding at the telescopic junction, in distinction to the first generation of nails, P1, which were assembled from multiple parts without crown moulding). The average first lengthening was 3.6 cm (–0.5–7.6 cm) and two of the three nails reaching their maximum deployment were successfully re-used. The mean lengthening prior to attempted redeployment was 2.8 cm among nails that were successful, compared with 4.5 cm among nails not successfully re-deployed. The mean second lengthening was 3.4 cm (1.2–5 cm).

One nail was first placed in compression mode (viz., partially deployed) to achieve compression and healing of a refractured congenital tibial pseudarthrosis prior to successful reactivation for lengthening. No complications directly referable to re-used nails were identified intraoperatively or in the subsequent lengthening treatment.

DISCUSSION

In this series, 58% of magnetically controlled intramedullary lengthening nails were successfully re-used. Statistical conclusions associated with failure were not possible due to the small number of patients, heterogeneity of implant sizes, absolute and relative lengthening magnitudes, time until re-use attempts, and differences in timing of interlocking screw removal.

Eltayeby et al. performed a study of MILL nails in which explanted devices were retracted and re-deployed ex vivo.⁶ Their results suggested that 84% performed successfully according to a standardised protocol and concluded that full deployment to the maximum nail stroke could damage the internal mechanism and decrease the likelihood of successful re-use. In another study of patients with achondroplasia undergoing lower extremity lengthening, Alonso-Hernandez et al. utilised a planned two-stage lengthening strategy in which magnetically controlled intramedullary lengthening nails were unlocked after the first stage of lengthening, reversed and locked again followed by a second lengthening as part of one continuous treatment.⁴ In that series, 92% of nail successfully retracted. Three case reports (two in femoral lengthening and one in tibial lengthening) re-deployed the MILL nail in the same lengthening episode.^8–10 When a rest period is desired between lengthenings, it is possible to await consolidation of a first lengthening, and follow with a later osteotomy and continue nail deployment without retraction if sufficient stroke is still available.¹¹

In our series, a majority of nails (58%) were successfully re-used. A similar majority (55%) of the subset of “sleeping nails” were successfully “re-activated” after prolonged quiescence. Postulated reasons for failure of reactivation are multiple. It seemed that the successfully re-used nails had been implanted for a shorter duration and had smaller lengthenings, well below the maximum stroke, although two of three nails which had reached maximum deployment were still successfully re-used.

Bony ingrowth into interlocking screw holes may have given resistance to an otherwise functioning nail, preventing the nail from retracting or re-deploying. For example, in one procedure a tibial nail had had distal interlocking bolts removed as a separate procedure 43 months prior (Case ID 6). At the time of attempted re-use, the nail did not retract, in vivo and a nail exchange was performed. However, intraoperative examination of the extracted device revealed that the nail functioned properly both retracting and re-deploying (Fig. 3). It is likely that the nail failed to retract in vivo because bone had filled the vacant distal interlocking holes. The authors suggest that if MILL nail re-use is planned, all interlocks could be filled at index lengthening and maintained until future surgery, to mitigate the likelihood of bony ingrowth, particularly if the dormant period will be long. Not all nails were systematically tested ex vivo, so the authors cannot comment about other nails that failed attempted re-use.

In principle, re-use of a functioning medical device can save the burden of tissue dissection, minimise operating room and anaesthetic time, and decrease cost of care. No complications directly related to nail re-use were recognised in this study; therefore, an attempt at nail reactivation prior to exchanging to another lengthening nail may be beneficial. Other authors caution against reactivation of early generation PRECICE nails (P1) due to corrosion in the nails and concern for mechanical failure.¹¹ However, macroscopic analysis of retrieved P2 nails in the above study demonstrated no corrosion.

This study is limited by is retrospective nature and small numbers. Owing to these factors, statistically significant predictors for successful re-use could not be determined. In addition, this is an off-label use of the PRECICE nail as it was not specifically designed for such re-deployment. Consequently, specific discussions are performed with each patient who is a candidate for reactivation of a motorised internal lengthening nail.

CONCLUSION

This study demonstrates that retraction and re-deployment of magnetically controlled intramedullary lengthening nails is successful in 58% of cases. Goal lengthening was successfully achieved among all re-used nails.

REFERENCES

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