Biomechanical Analysis of Unilateral External Skeletal Fixators Combined with IM-Pin and Without IM-Pin Using Finite-Element Method.
OBJECTIVE
To determine if a unilateral external skeletal fixator (ESF) with a carbon fiber connecting rod (IMEX SK) without an intramedullary (IM)-pin is mechanically comparable with a unilateral ESF with a stainless-steel connecting rod (IMEX KE) with an IM-pin.


METHODS
Finite-element method (FEM)-computer simulation.


METHODS
FEM models were validated by comparison against data from mechanical testing. Three-dimensional FEM models of a femur with a mid-diaphyseal fracture with a 20 mm gap were developed with 4 unilateral external skeletal fixator devices (6-pin KE, 6-pin KE IM-pin, 6-pin SK, and 6-pin SK IM-pin). A 300 N load was applied to the femur at the proximal end in a direction of theta = 10 degrees distally and phi = 10 degrees laterally cranially. Relative displacements in x-, y- and z-directions at the gap were obtained and the overall stiffness was calculated as 300 N/total displacement. Load transfer at the pin-bone interface (PBI) was assessed by determining the von Mises stress maxima at the PBI-related nodes.


RESULTS
The 6-pin SK had superior mechanical performance compared with the 6-pin KE by exhibiting smaller displacements in all directions and higher stiffness. Compared with the 6-pin KE IM-pin, the 6-pin SK (without IM-pin) was superior in craniocaudal and lateromedial displacements, but inferior in axial displacements, overall stiffness and von Mises stress maxima. The 6-pin SK IM-pin was superior to the 6-pin KE IM-pin based on smaller displacements and higher stiffness.


CONCLUSIONS
Although the SK device had superior mechanical performance compared with a KE device in a unilateral configuration, the addition of an IM-pin continues to be a powerful method of enhancing mechanical performance of either IMEX SK or IMEX KE unilateral constructs in clinical cases.


CONCLUSIONS
Based on the results of this FEM study we recommend the use of the "tied-in" IM-pin with the ESF clinically when striving for high rigidity. In less challenging situations, a unilateral SK ESF without IM-pin might provide sufficient rigidity for a successful fracture repair.
Radke
Heidi
H
Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, Athens, GA, USA. heidi.radke@kkh.unibe.ch
Aron
Dennis N
DN
Applewhite
Aric
A
Zhang
Guigen
G
D000818:Animals; D001696:Biomechanical Phenomena; D001858:Bone Nails / Q000662:veterinary*; D003198:Computer Simulation; D004867:Equipment Design / Q000295:instrumentation / Q000379:methods / Q000662:veterinary*; D016267:External Fixators / Q000662:veterinary*; D020342:Finite Element Analysis; D005592:Fracture Fixation / Q000295:instrumentation / Q000379:methods / Q000662:veterinary*; D050723:Fractures, Bone / Q000601:surgery / Q000662:veterinary*; D008422:Materials Testing; D008954:Models, Biological; D013193:Stainless Steel; D013314:Stress, Mechanical
D013193:Stainless Steel