Biomechanical properties of five different currently used implants for open-wedge high tibial osteotomy

Diffo Kaze et al. Journal of Experimental Orthopaedics (2015) 2:14 DOI 10.1186/s40634-015-0030-4 RESEARCH Open Access Biomechanical properties of five different currently used implants for open-wedge high tibial osteotomy Arnaud Diffo Kaze1*, Stefan Maas1, Danièle Waldmann1, Andreas Zilian1, Klaus Dueck and Dietrich Pape Abstract Background: As several new tibial osteotomy plates recently appeared on the market, the aim of the present study was to compare mechanical static and fatigue strength of three newly designed plates with gold standard plates for the treatment of medial knee joint osteoarthritis. Methods: Sixteen fourth-generation tibial bone composites underwent a medial open-wedge high tibial osteotomy (HTO) according to standard techniques, using five TomoFix standard plates, five PEEKPower plates and six iBalance implants. Static compression load to failure and load-controlled cyclic fatigue failure tests were performed. Forces, horizontal and vertical displacements were measured; rotational permanent plastic deformations, maximal displacement ranges in the hysteresis loops of the cyclic loading responses and dynamic stiffness were determined. Results: Static compression load to failure tests revealed that all plates showed sufficient stability up to 2400 N without any signs of opposite cortex fracture, which occurred above this load in all constructs at different load levels. During the fatigue failure tests, screw breakage in the iBalance group and opposite cortex fractures in all constructs occurred only under physiological loading conditions (<2400 N). The highest fatigue strength in terms of maximal load and number of cycles performed prior to failure was observed for the ContourLock group followed by the iBalance implants, the TomoFix standard (std) and small stature (sm) plates. The PEEKPower group showed the lowest fatigue strength. Conclusions: All plates showed sufficient stability under static loading. Compared to the TomoFix and the PEEKPower plates, the ContourLock plate and iBalance implant showed a higher mechanical fatigue strength during cyclic fatigue testing. These data suggest that both mechanical static and fatigue strength increase with a wider proximal T-shaped plate design together with diverging proximal screws as used in the ContourLock plate or a closed-wedge construction as in the iBalance design. Mechanical strength of the bone-implant constructs decreases with a narrow T-shaped proximal end design and converging proximal screws (TomoFix) or a short vertical plate design (PEEKPower Plate). Whenever high mechanical strength is required, a ContourLock or iBalance plate should be selected. Keywords: High tibial osteotomy (HTO); Osteoarthritis; Biomechanics; Mechanical test; Cyclic and static loading; TomoFix; ContourLock; PEEKPower; iBalance; Stiffness; Valgus malrotation * Correspondence: 1 Faculty of Science, Technology and Communication, University of Luxembourg, 6, rue R. Coudenhove-Kalergi, L-1359 Luxembourg, Luxembourg Full list of author information is available at the end of the article © 2015 Diffo Kaze et al. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. Diffo Kaze et al. Journal of Experimental Orthopaedics (2015) 2:14 Background High tibial osteotomy (HTO) is a well-established method for the treatment of unicompartmental varus gonarthrosis. Both lateral closing and medial opening techniques exist to produce a valgus alignment (Staubli 2008; Staubli and Jacob 2010). The latter is becoming increasingly popular when performed in a biplanar fashion. Since the introduction of long and rigid-angle stable plates, the frequency of non-unions after an open-wedge HTO has declined significantly (Staubli and Jacob 2010). Apart from a good vascularization of the bone, solid plate fixation is mandatory for rapid bone healing (Staubli 2008; Staubli and Jacob 2010). Although clinical results after HTO often are encouraging some factors associated with a poor long-term outcome such as imprecise osteotomy or loss of the primary correction angle due to poor primary fixation stability of the implant (Spahn et al. 2006; Pornrattanamaneewong et al. 2012). There are many different implants from different manufacturers available. Biomechanical (Luo et al. 2013; Spahn and Wittig 2002; Stoffel et al. 2004; Zhim et al. 2005; Agneskirchner et al. 2006; Maas et al. 2013; Watanabe et al. 2014) and clinical (Pape et al. 2011; Saeed and Rae 2009; Valkering et al. 2009; Cotic et al. 2014; Woon-Hwa et al. 2013) comparative studies are often performed to help surgeons choose the most appropriate fixation device for the osteotomy. TomoFix, the long and rigid T-shaped titanium internal fixator with uniaxial locking system (Synthes GmbH, Oberdorf, Switzerland), is currently the gold standard. It combines biomechanical properties that are held accountable for fast bone healing: (1) high primary fixation stability; (2) a compliant bone-implant construct which allows residual micromotion within the osteotomy gap to promote a “callus massage”. TomoFix plates exist in two versions, such as the small stature (sm) version designed for lighter patients and the standard (std) version without weight restriction. Both plates have a narrow proximal design which allows for a biplanar osteotomy, thus enlarging the surface for rapid contact healing (Pape et al. 2010, 2011). PEEKPower (carbon-fiber reinforced polyetheretherketone (PEEK)) and iBalance (non-absorbable polyetheretherketone)–two implants also indicated for a biplanar osteotomy–were recently designed by Arthrex, a company based in Munich (Germany). The PEEKPower plate is T-shaped, shorter than the TomoFix but coming with a multidirectional locking system. The iBalance implant, a PEEK spacer, is inserted into the osteotomy gap in a uniplanar and closed-wedge-like technique with immediate close contact between the PEEK material and the proximal and distal cortical and spongious bone surface (Pape et al. 2012). In our previously performed comparative biomechanical study (Maas et al. 2013) comparing the TomoFix sm Page 2 of 17 plate and the Contour Lock plate (Arthrex, Munich, Germany) (Fig. 1) Static and fatigue strength for both plates were investigated. The same materials and methods were used in this study to perform static and cyclic tests on bone-implant constructs with the TomoFix std, the PEEK Power and the iBalance fixators (Fig. 2). The results obtained were then compared to those of our previous study, thus allowing a comparison between (1) the TomoFix sm plate, (2) the Contour Lock plate, (3) the iBalance implant, (4) the PEEK Power plate and (5) the TomoFix std plate. The hypothesis of the present study was that implants well attached with a wide proximal end to th (...truncated)