Spinal Lengthening With Magnetically Controlled Growing Rods

Abstract

Study Design. Laboratory analysis of explanted MAGnetic Expansion Control (MAGEC) rods. Objective. The aim of this study was to identify the in vivo lengthening of MAGEC rods. Summary of Background Data. Little data is available regarding the lengthening achieved by MAGEC rods. Methods. Cases were identified from the largest series of independently analyzed explanted MAGEC rods. The in vivo growth of rods was determined by the distance between the first “growth mark” and the actuator. The instrumented spinal lengthening was calculated for each construct. Constructs were considered functional if all rods could lengthen with external remote controller activation and no rods were “telescoping”. Results. Fifty-five MAGEC constructs (99 rods) from 53 patients treated at 10 centers were included. The mean age at insertion was 8.5 years with rods implanted a mean of 35 months. Sixty rods were suitable for analysis with mean lengthening 21.7 mm, 8.9 mm/year. Of these 60 rods, three were maximally distracted. Mean instrumented spinal lengthening for 38 suitable cases was 22.1 mm, 8.4 mm/year. This was positively correlated with the duration of implantation (r = 0.34, P = 0.04) but negatively with patient age at insertion (r = −0.35, P = 0.03). The rate of instrumented spinal lengthening was negatively correlated with duration of implantation (r = −0.47, P = 0.004). Of 55 constructs, 34 were nonfunctional at time of removal with nine functional and 12 indeterminate. Functional constructs had been implanted significantly less time (20.0 vs. 39.7 months, P < 0.001) and lengthened less than those nonfunctional (12.3 mm vs. 23.3 mm, P = 0.04). Conclusion. This multicenter explant study represents the largest cohort managed with MAGEC rods reported. Rods are very rarely removed having fully lengthened with mean instrumented spinal growth of 22 mm over the implant's life. This may be explained by a high rate of lengthening mechanism failure in received rods after around 3 years in vivo. Our findings question the effectiveness of the MAGEC system and mandate urgent comparative clinical studies. Level of Evidence: 4

Spring distraction system for dynamic growth guidance of early onset scoliosis: two-year prospective follow-up of 24 patients

“…This is in contrast to MCGR, where failure to distract is common due to component failure of the driving mechanism. [15][16][17]34,40] Strengths of the current study include the relatively large patient cohort that was prospectively followed for at least 2 years. In addition, the diverse patient group represents a varied EOS population, as observed by the considerable variation in baseline EOSQ-24 domain scores.…”

“…Recent studies have shown that less than 1 in 5 retrieved MCGRs still function as intended. [15][16][17] It is also an expensive device, precluding its use in large parts of the world. To address these drawbacks, we developed the Spring Distraction System (SDS), which employs the continuous distraction force of a compressed helical coil spring that is positioned around a standard rod that is allowed to slide at the proximal-or distal foundation ( Figure 1).…”

<p>Magnetic Controlled Growth Rods in the Treatment of Scoliosis: Safety, Efficacy and Patient Selection</p>

“…Further detailed analysis of the mechanism of failure of MAGEC rods and associated metallosis has been reported in studies by Joyce et al 23 and Rushton et al 49,50 as part of a UK retrieval analysis project. In a first report of 34 explanted MAGEC rods, abrasive marks on the extending bar and internal titanium wear debris were identified in all explants.…”

“…In a further study, Rushton et al 50 assessed the capacity of explanted MAGEC rods to still generate force compared to their intended pre-implantation standard. A bespoke force gauge provided by the MAGEC manufacturer was used to test 45 explants from 25 patients; the majority of these were Modification 2 MAGEC rods.…”

“…[39][40][41] Explant studies indicate that the in vivo lengthening achieved by MAGEC would be exceeded by treatment with TGR after 2-3 lengthenings, which might occur by 12-18 months following implantation of TGRs. 50 Both TGR and MCGR constructs are associated with release of titanium and possibly aluminium, though MCGR constructs may release a higher concentration of metal ions with long-term unknown consequences. 53 Generation of extensive titanium wear debris and adjacent soft tissue metallosis are specific complications of MAGEC implants related to offset loading.…”