Mechanism Failures in Externally Controlled Motorized Intramedullary Lengthening Nails: A Systematic Review.

Area of Science:

• Orthopedic surgery
• Biomaterials engineering
• Medical device technology

Background:

• Externally controlled intramedullary lengthening nails (IMNs) offer reduced soft-tissue morbidity compared to external fixation.
• These devices have complex motorized and telescopic mechanisms, introducing unique failure risks.
• Distinguishing structural fractures from intrinsic mechanism failures is crucial for accurate analysis.

Purpose of the Study:

• To systematically review the incidence, etiology, and management of intrinsic mechanism failures in externally controlled lengthening IMNs.
• To analyze failure patterns based on implant material and generation.
• To provide insights into the clinical significance and outcomes of IMN mechanism failures.

Main Methods:

• A systematic literature search was performed across PubMed, Embase, and Scopus (January 2000 - July 2025).
• Studies included human cases of externally controlled IMNs with mechanism-related failures (jamming, motor failure, backtracking).
• Exclusion criteria: structural fatigue fractures, non-externally controlled devices, and case reports.

Main Results:

• Overall mechanism-related failure rate was 4.3% (107/2,495 nails) across 29 studies.
• Titanium nails (PRECICE P1/P2) had a 4.2% failure rate (jamming/gear slippage).
• Stainless steel nails (STRYDE) showed a higher 12.9% failure rate (tribocorrosion/biological reactions).
• FITBONE system had a 3.3% failure rate.
• 97.2% of failures required surgical intervention, with nail exchange being the primary strategy (94.4%).

Conclusions:

• Mechanism failure in lengthening IMNs is a significant complication, occurring in approximately 4.3% of cases.
• Titanium implants risk mechanical yield failure, while stainless steel implants are prone to tribocorrosion.
• Despite requiring revision surgery, successful limb reconstruction is achievable with timely nail exchange.