Is MAGEC X better than earlier designs of magnetically controlled growing rod: an explant study.

Purpose: Determine the performance of MAGEC X rods through retrieval analysis and comparison with clinical data.

Methods: A multicentre explant database was searched to identify cases using MAGEC X device. Clinical and surgical data was gathered prospectively. Prior to rod disassembly, rods underwent testing with an external remote controller to measure the force output.

Results: Eleven cases from 6 centres were identified. Implantation occurred at mean age 6.9 years with mean duration of implantation 42 months. Dual rod constructs were used in all but one case, providing 21 MAGEC X rods for explant analysis. Tissue metallosis was identified at revision surgery in 8/11 cases (73%). Of the 21 rods, 13/21 (62%) produced no force while 8/21 (38%) produced the force stated by the manufacturer. Endcap separation was seen in 5/21 (24%) rods. Where full disassembly was possible, 13/14 (93%) rods had an intact locking pin. Average rod growth was 18 mm (range 2-45 mm), equivalent to 5.1 mm per year. Wear debris was found within 20/21 (95%) MAGEC X rods.

Conclusion: Despite the substantial design changes with MAGEC X tissue metallosis was seen in most cases; most explanted MAGEC X rods had lengthened only partially and produced no force output. While the previous issue of locking pin fracture appears to have been mitigated with MAGEC X, there are multiple other and new failure modes, such as endcap separation. Overall MAGEC X appears to give little improvement over earlier iterations of the rod.