Stiffness of a type II external skeletal fixator and locking compression plate in a fracture gap model.

Objective: To compare the stiffness of constructs fixed with a type II external skeletal fixator (ESF) or a 3.5-mm locking compression plate (LCP) in axial compression and bending with a fracture gap model.

Study Design: Quasi-static four-point bending and axial compression tests.

Sample Population: Ten LCP and 10 ESF immobilizing epoxy cylinders with a 40-mm fracture gap.

Methods: Five constructs of each type were tested in nondestructive mediolateral (ML) four-point bending and then rotated and tested in nondestructive craniocaudal (CC) four-point bending. Five additional constructs of each type were tested in nondestructive axial compression. Stiffness was compared between loading modes by construct type and between construct types by loading mode.

Results: Type II ESF were stiffer than LCP in ML bending (difference, 1474 N/mm, P < .0001) and in axial compression (difference, 458 N/mm, P = .008) but not in CC bending (P = .1673). Type II ESF were stiffer in ML bending than in CC bending (difference, 999 N/m, P < .0001), while LCP were stiffer in CC bending than in ML bending (difference, 634 N/mm, P < .0001).

Conclusion: Type II ESF generated stiffer constructs compared with LCP in ML bending and in axial compression without a difference in CC bending. External skeletal fixator and LCP bending stiffness varied by loading direction.

Clinical Significance: A type II ESF should be considered in a comminuted fracture requiring increased stability in ML and axial directions.