, Volume 471, Issue 9, pp 2808-2814
Date: 23 Feb 2013

Implant Material and Design Alter Construct Stiffness in Distal Femur Locking Plate Fixation: A Pilot Study

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Abstract

Background

Construct stiffness affects healing of bones fixed with locking plates. However, variable construct stiffness reported in the literature may be attributable to differing test configurations and direct comparisons may clarify these differences.

Questions/purposes

We therefore asked whether different distal femur locking plate systems and constructs will lead to different (1) axial and rotational stiffness and (2) fatigue under cyclic loading.

Methods

We investigated four plate systems for distal femur fixation (AxSOS, LCP, PERI-LOC, POLYAX) of differing designs and materials using bone substitutes in a distal femur fracture model (OTA/AO 33-A3). We created six constructs of each of the four plating systems. Stiffness under static and cyclic loading and fatigue under cyclic loading were measured.

Results

Mean construct stiffness under axial loading was highest for AxSOS (100.8 N/mm) followed by PERI-LOC (80.8 N/mm) and LCP (62.6 N/mm). POLYAX construct stiffness testing showed the lowest stiffness (51.7 N/mm) with 50% stiffness of AxSOS construct testing. Mean construct stiffness under torsional loading was similar in the group of AxSOS and PERI-LOC (3.40 Nm/degree versus 3.15 Nm/degree) and in the group of LCP and POLYAX (2.63 Nm/degree versus 2.56 Nm/degree). The fourth load level of > 75,000 cycles was reached by three of six AxSOS, three of six POLYAX, and two of six PERI-LOC constructs. All others including all LCP constructs failed earlier.

Conclusions

Implant design and material of new-generation distal femur locking plate systems leads to a wide range of differences in construct stiffness.

Clinical Relevance

Assuming construct stiffness affects fracture healing, these data may influence surgical decision-making in choosing an implant system.

The institution of one of the authors (US) has received, during the study period, funding from the Association for Orthopaedic Research (AFOR) and from the Osteosynthesis and Trauma Care Foundation. The institution of one of the authors (PA) has received funding from Stryker Osteosynthesis (Stryker GmbH, Selzach, Switzerland), Smith & Nephew Inc (Memphis, TN, USA), Aesculap (Tuttlingen, Germany), Arthrex (Munich, Germany), and Synthes (Bettlach, Switzerland). One of the authors (SB) is an employee of Arthrex.
All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research editors and board members are on file with the publication and can be viewed on request.
Clinical Orthopaedics and Related Research neither advocates nor endorses the use of any treatment, drug, or device. Readers are encouraged to always seek additional information, including FDA-approval status, of any drug or device prior to clinical use.
This work was performed at the Institute of Biomechanics, Trauma Center Murnau, Murnau, Germany, and at the Department of Material Science, Regensburg University of Applied Sciences, Regensburg, Germany.