Biomechanical Evaluation of Disposable Digital External Fixators (DDEFs) :A Comparative Study with New Design.

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Ekamol Thumroj
Surut Jianmongkol
Weerachai Kowsuwon

Abstract

Background : There are many conditions of phalangeal fractures require digital external fixators  both  commercial  and disposable. The biomechanical comparative studies of these fixators have not been reported especially for disposable digital external fixators(DDEFs). The new design,  adjustable length digital external fixator (ALDiEs) was innovated

Purpose : To compare the biomechanical properties of various DDEFs.

Materials and Methods : Synbone ; Swiss made, Model 4060 900285 were used to be the phalangeal model for the biomechanical testing. Three types of DDEs and their applications were tested. Ten samples of each type were fixed into phalangeal models. Biomechanical analyses were performed by material testing machine, Loyed Instrument interfaced with Windap data analysis software. The structural stiffness (SS), Yield stress (YS) and ultimate stress (US) both in compression and distraction forces were recorded. Statistical analysis was performed using ANOVA and a post hoc LSD .

Study  design :  Experimental  study

Setting :  Orthopedics  department,  Faculty  of Medicine,  Khon  Kaen  University

Results : The SS of one frame Poorman DDEFs, Godwin DDEFs and ALDiEs were 14.54, 14.83 and 12.43 N/mm. in orderly. The Godwin DDEFs had the highest SS (P<0.05). No statistical different in YS and US between the various one frame DDEFs. The SS of the two-frame group, the  Poorman DDEFs, Godwin DDEFs and ALDiEs are 25.03, 35.23 and 35.29 N/mm in orderly. Godwin DDEFs had the highest SS (P<0.05). The two-frame of the ALDiEs have the highest YS and US (P<0.05). All ALDiEs were failed by deformation. All the Poorman DDEFs were failed by cemented fractures. The Godwin DDEFs were failed by pin-rod displacement.

Discussion and conclusions : According to the previous study4. All one frame DDEFs can resist only physiologic load but can’t resist the load during pinching or light grip. From this study, we found that only two-frame of the ALDiEs and Godwin DDEFs could resist to loading force during pinching and light grip but couldn’t resist to the force grip. Because of the low stiffness, one- frame of the Poorman DDEFs may not be appropriate fixation method for proximal phalangeal fractures.

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