2015 ISAKOS Biennial Congress ePoster #127

A New Mini External Fixator for Severe Hallux Valgus Treatment; A Biomechanical Study

Mehmet Erdil, MD, Ass.Prof., Istanbul TURKEY
Hasan Huseyin Ceylan, MD, Istanbul TURKEY
Deniz Kara, MD, Istanbul TURKEY
Gokhan Polat, Istanbul TURKEY
Ergün Bozdag, PhD, Istanbul TURKEY
Emin Sunbuloglu, PhD, Istanbul TURKEY

Bezmialem Vakif University, Istanbul, TURKEY

The FDA has not cleared the following pharmaceuticals and/or medical device for the use described in this presentation. The following pharmaceuticals and/or medical device are being discussed for an off-label use: tasarimmed, mini external fixator

Summary: biomechanical testing of a new device for hallux valgus surgery

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Abstract:

Introduction

More than a hundred surgical techniques had defined for the treatment of symptomatic hallux valgus. In cases of moderate and severe hallux valgus that intermetatarsal angle (IMA) is above 15 degrees, proximal osteotomy had advised for an effective correction. But proximal and shaft osteotomies are biomechanically more unstable in comparison to distal osteotomies. A rigid fixation is needed in proximal metatarsal osteotomy in order to provide union of osteotomy. Conventional screw fixation in proximal osteotomy is not sufficient for early weight bearing due to biomechanical insufficiency. The purpose of this study is to compare the stability of conventional screw fixation and our new design mini external fixator.

Material And Methods

18 metatarsal sawbones had prepared for biomechanical study. First all specimens osteotomized proximally with a saw blade and divided into two groups. 9 of these metatarsals fixed with a Headless Compression Screw (Acutrac, Acumed, Beaverton, OR) and remaining metatarsals had fixed with our new mini external fixator. All the specimens tested with an “MTS 858 Mini Bionix 2” universal dynamic test system and axial compression, distraction, torsion and bending tests had applied. The measurements of these tests recorded and controlled by a “MTS Multipurpose Testware” software. Displacement of the osteotomy site was measured by a ‘’static optical camera and 3D correlation system’’. Dynamic, axial and torsional loading capacity of the system was 100Hz, 25kN and 200Nm, respectively. Construct stiffness and the amount of interfragment angulation were calculated on the 1st, 10th, 50th, 100th, 200th, 300th… and 1000th load cycles.

Results

Of the 9 metatarsals tested in the screw constructs failed (that exceeded 10 degrees of angulations) before completion of 1000 load cycles. The most stable one was failed at 823th cycle. But only 2 of the 9 external fixator constructs failed before 1000 cycles. Both failed between the 600th and 700th load cycles, and demonstrated a similar mechanism of failure. Statistically significant difference was found between 2 groups in the stability of fixation (p<0.001).

Discussion

This study demonstrated that mini external fixator provided superior osteotomy stability in comparison to the conventional screw fixation. To our knowledge this is the first technical report that compares the external fixator and screw fixation in the treatment of hallux valgus. The stability of osteotomy site is crucial for the union of a proximal metatarsal osteotomy. Ideal proximal osteotomy should provide rigid stability, prevent dorsal malunion and allow early weight bearing. Clinical studies had demonstrated that the dorsal malunion and transfer metatarsagia rate was nearly 28% after proximal osteotomy. Dorsal angulation, malunion and metatarsal shortening may trigger dorsal bunion and transfer metatarsalgia. First metatarsus is the main structure that transfers load in weight bearing. Our new mini external fixator has superior stability in comparison to conventional screw fixation and provides early weight bearing in proximal metatarsal osteotomy.