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Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_5 | Pages 34 - 34
1 Mar 2017
Mueller U Lee C Thomsen M Heisel C Kretzer J
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Introduction

This study was performed to investigate the failure mechanism of one specific hip arthroplasty cup design that has shown a high clinical failure rate. The aim of this study was to identify general design problems of this polyethylene inlay.

Material and Methods

55 consecutive retrievals of a cementless screw ring (Mecron) were collected. In any case a 32 mm ceramic head was used. All implants failed due to aseptic loosening. The follow-up of the implants was 3 to 16 years. We recorded backside wear, fatigue of the polyethylene at the flanges on the outer rim and at the cup opening (32 mm inner diameter). To assess the deformation of the inlay, the smallest and the median diameter of the cup opening were measured using a 3 dimensional coordinate measuring machine (Multisensor, Mahr, Germany).


Orthopaedic Proceedings
Vol. 95-B, Issue SUPP_34 | Pages 498 - 498
1 Dec 2013
Reinders J Von Stillfried F Sonntag R Heisel C Kretzer JP
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Background:

Total ankle replacements (TAR) are not as successful as total hip or total knee replacements. A three-time increased revision rate is reported in registry data [1]. Therefrom, wear associated revisions are frequent [2]. However, there is little knowledge about the wear behavior of TAR. This may be partly related to the fact, that currently no standard for wear testing of TAR exists.

The aim of this study is to define a biomechanical valid, force-controlled test specification for level walking of TAR.

Material and Methods:

Basic requirements for force-controlled testing of TAR is the definition joint flexion, as well as active forces and torques acting on the joint and the definition of the ligamental stabilization of the joint.

To specify flexion of the ankle, gait analysis was performed on patients treated with a TAR (HINTEGRA, Smith & Nephew) using skin mounted markers. Data about in-vivo forces is missing for TAR. Hence, determination of active forces and torques was based on mathematical models as described in the literature.

A new testing device (figure 1) has been developed to measure ligamental stabilization of the ankle joint. Measurements were performed on 10 paired cadaver feet (n = 20). Measurements were performed in different flexion angles when applying anterior-posterior forces (± 160N) and internal-external torques (± 2,5 Nm) between the talus and the tibia.


Orthopaedic Proceedings
Vol. 95-B, Issue SUPP_34 | Pages 499 - 499
1 Dec 2013
Reinders J Von Stillfried F Sonntag R Heisel C Kretzer JP
Full Access

Background:

There is little knowledge about wear performance of total ankle arthroplasties (TAR). However, revisions rates are high for TAR [1] and wear associated revisions are frequent [2].

Therefore, the aim of this study is

To test the wear behavior of a TAR using a biomechanically valid testing scenario.

To test the influence of an alternative ceramic tibial component.

To test the long term wear performance of TAR.

Material and Methods:

In the first part of this study the HINTEGRA (Smith & Nephew) TAR has been used for wear testing. Wear testing was performed on a modified AMTI knee simulator. Level walking according to a previous described testing standard [see abstract: Development of a force controlled testing scenario for total ankle replacements] has been used. Level walking was simulated in three clinical relevant situations, first simulating the reduced loading after implantation, secondly simulating an increasing range of motion and at last a loading pattern orientating at the loadings in the native/healthy joint. Every simulation was run for 3 million cycles, resulting in 9 million total cycles.

In the second part of this study the metal tibial plateau was replaced by a ceramic tibial component (Biolox® Delta, CeramTec). Simulation was run, as described above, for additional 9 million cycles. Termed as a long term test, in total 18 million cycles of testing are performed.


Orthopaedic Proceedings
Vol. 95-B, Issue SUPP_15 | Pages 276 - 276
1 Mar 2013
Nadorf J Jakubowitz E Heisel C Reinders J Sonntag R Kretzer JP
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Introduction

Concerning biomechanical research, human specimens are preferred to achieve conditions that are close to the clinical situation. On the other hand, synthetic femurs are used for biomechanical testing instead of fresh-frozen human femurs, to create standardized and comparable conditions. A new generation of synthetic femurs is currently available aiming to substitute the validated traditional one. Structural femoral properties of the new generation have already been validated, yet a biomechanical validation is missing.

The aim of our study was to analyse potential differences in the biomechanical behaviour of two different synthetic femoral designs by measuring the primary rotational stability of a cementless femoral hip stem.

Methods

The cementless SL-PLUS® standard stem (size 6, Smith&Nephew Orthopaedics AG, Rotkreuz, Swizerland) was implanted in two groups of synthetic femurs. Group A consists of three 2nd generation femurs and group B consists of three 4th generation femurs (both: size large, composite bone, Sawbones® Europe, Malmö, Sweden).

Using an established method to analyse the rotational stability, a cyclic axial torque of ±7.0 Nm along the longitudinal stem axis was applied. Micromotions were measured at defined levels of the bone and the implant. The calculation of relative micromotions at the bone-implant interface allowed classifying the rotational implant stability.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXV | Pages 118 - 118
1 Jun 2012
Kretzer JP Jakubowitz E Sonntag R Reinders J Heisel C
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Introduction

Osteolysis and aseptic loosening in total hip replacement (THR) is often associated with polyethylene (PE) wear. This caused interest in alternative bearing surfaces. Since the mid nineties, research focused on hard-hard bearings like metal-on-metal (MOM) or ceramic-on-ceramic (COC). However, concerns remain about biological reactions to metallic wear debris or failure of the ceramic components. A new approach to reduce wear with a minimized risk of failure may be the use of a metallic cup in combination with a ceramic head, the so called ceramic-on-metal bearing (COM). The aim of this study was to estimate the wear behaviour at an early stage of this COM bearing type in comparison to COC bearings using a hip simulator.

Material and Methods

Simulator studies were carried out on a single station hip simulator (MTS 858 Mini Bionix II, Eden Prairie, USA) in accordance to ISO 14242-1. Bovine serum was used as the test medium. Four COM and four COC bearings were used, both 36mm in diameter. The heads were made of a mixed-oxid ceramic (Biolox Delta(r)) paired with a high carbon wrought CoCrMo cup in the COM group whereas both components were made of Biolox Delta(r) in the COC group. Simulation was run to a total of 2.4×106 cycles. Wear measurements were performed in intervals of 0.2x106 cycles using a gravimetric method (Sartorius Genius ME235S, measuring solution: 15 μg, Sartorius, Göttingen, Germany).