Mechanical evaluation of additively manufactured polymer rings for circular external fixators

Purpose: The aim of this study was to assess the feasibility of using additively manufactured polymer rings as structural components of circular external fixators for limb lengthening in pediatric patients. The analysis focused on whether such rings can provide sufficient mechanical performance while simultaneously reducing device mass and improving radiographic transparency compared with conventional metallic solutions.

Methods: Two design variants of circular rings with different cross-sectional geometries were developed and manufactured using fused filament fabrication from a thermoplastic polymer. Their mechanical behavior was assessed through numerical finite element simulations and experimental testing. Radial and axial loading conditions corresponding to clinical use were analyzed at the ring level. Subsequently, complete external fixator assemblies incorporating the printed rings were constructed and subjected to quasi static axial compression tests. Comparative radiographic imaging was also conducted to evaluate the influence of polymer-based rings on image quality relative to conventional aluminum rings.

Results: The polymer rings exhibited lower radial stiffness than aluminum reference rings; however, the resulting deformations were elastic, repeatable and associated with stress levels below the material yield limit. External fixators equipped with printed rings demonstrated axial stiffness values within the range reported for conventional circular fixators used in clinical practice. In addition, the polymer-based configurations showed a notable reduction in mass and significantly improved radiographic transparency compared to metallic systems.

Conclusions: Additively manufactured polymer rings with appropriately optimized geometry can provide mechanically acceptable performance for use in circular external fixators, while offering advantages in weight reduction and radiographic assessment.