Biomechanical Analysis of Unilateral-Ring Hybrid External Fixation

Choi, In Ho; Choi, Kui Won; Lee, Ki Seok; Chung, Chin Youb; Cho, Tae Joon; Lee, Duk Yong

Abstract

The mechanical stiffness of Unilateral-Ring Hybrid External Fixation(URHEF) was analyzed and compared with conventional Ilizarov circular external fixation system and unilateral fixation with DynaExtor(R). Our URHEF is basically a unilateral external fixation system which affords easier incorporation and removal of the Ilizarov rings(200mm in diameter) coupled with connecting clamps at anytime, if needed. It allows controlled axial micromotion in due time. For mechanical test, URHEF system was constructed using a DynaExtor(R) fixed with two or three half pins(6 mm in diameter) attached with two proximal and distal Ilizarov rings fixed with an olive pin and a half pin on each ring. Unilateral fixation system was constructed with a DynaExtor(R) fixed with 2 or 3 half pins. Ring fixation system was constructed with four Ilizarov rings(140mm in diameter). Ilizarov system were assembled into 90degrees-90degrees and 45degrees-13 5degrees configurations with 2 olive pins, respectively. The distance between the center of pylon and the pin-clamp interface was equalized, being 70mm, in all the systems. Stiffness in axial compression, anteroposterior and lateral bending was measured. On axial compression and lateral bending tests, URHEF was stiffer than DynaExtor(R) and Ilizarov systems. On anteroposterior bending test, URHEF was less stiff than 90degrees-50degrees configuration of the Ilizarov system but stiffer than 45degrees-135degrees configuration. Considering the fact that instead of 90degrees-90degrees transfixing pin fixatin system, 45degrees-135degrees configuration system is generally used in clinical practice, URHEF appears to be significantly stiffer than unilateral(DynaExtor(R)) and circular (Ilizarov)fixation systems. This mechanical study implicates that URHEF can be beneficially applied in the clinical use with assurance of mechanical stability.