Mechanism Failures in Externally Controlled Motorized Intramedullary Lengthening Nails

Background: Externally controlled intramedullary lengthening nails (IMNs) have reduced the soft-tissue morbidity associated with external fixation. However, these complex devices introduce specific risks related to their motorized and telescopic mechanisms. Existing literature often conflates structural fatigue fractures with internal mechanism dysfunction. This systematic review aims to analyze the incidence, etiology, and management of intrinsic mechanism failures in lengthening IMNs. Methods: A comprehensive search of PubMed, Embase, and Scopus was conducted from January 2000 to July 2025 in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines. The review included human studies reporting mechanism-related failures (e.g., jamming, backtracking, and motor failure) in externally controlled IMNs. Studies describing only structural fatigue fractures or nonexternally controlled devices were excluded (e.g., Intramedullary Skeletal Kinetic Distractor [ISKD]). Data were stratified by implant generation and material. Results: Twenty-nine studies encompassing 2,495 nails were included. The overall reported mechanism-related failure rate was 4.3% (n = 107/2,495). Distinct failure phenotypes emerged based on the implant material. Titanium-alloy nails (PRECICE P1/P2) demonstrated a 4.2% failure rate (n = 74/1,761), predominantly characterized by mechanical jamming or gear slippage due to load-induced yield. Stainless steel nails (STRYDE) exhibited a significantly higher failure rate of 12.9% (n = 12/93), primarily driven by tribocorrosion and biological reactions at the telescopic junction. The FITBONE system had a reported failure rate of 3.3% (n = 21/641). Management required surgical intervention in 97.2% of failure cases, with exchange nailing being the primary salvage strategy (94.4%). Despite the need for reoperation, the target limb length was reportedly achieved in the majority of studies where quantitative outcomes were specified. Conclusion: Mechanism failure in externally controlled lengthening IMNs is a clinically significant complication with a reported incidence of approximately 1 in 24 cases. A material trade-off is evident: Titanium implants are susceptible to mechanical gear yield, whereas stainless steel implants are prone to tribocorrosion-induced failure. While these failures necessitate revision surgery, they typically do not preclude successful limb reconstruction if managed with timely nail exchange. Level of Evidence: Level III . See Instructions for Authors for a complete description of levels of evidence.