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Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_6 | Pages 13 - 13
1 Mar 2017
Sonntag R Al-Salehi L Braun S Mueller U Reinders J Kretzer J
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Introduction

Wear plays a key role in the clinical outcome of total hip replacements (THR). In addition, increased frictional moment can stress the implant interfaces which may lead to high torsional loadings in the intermodular taper junction (fretting) and cup loosening and to the development of noise (squeaking). Against the background of larger head diameters (increased range of motion and decreased risk of dislocation), the friction induced by the joint articulation is of particular interest. As of now, the investigation of friction with the use of relevant joint kinematics and loadings are limited to numerical studies. Experimental approaches use simplified models which do not take into consideration complex activities. Thus, with the aim of this study is the identification of articular frictional moments that consider critical in vivo loading conditions and kinematics as well as the clinical cup inclination, head size and clearance of ceramic-on-ceramic hip bearings.

Materials and Methods

A standard hip simulator (Minibionix 852 with 4 DOF Hip setup, MTS, Eden Prairie, USA) was modified in order to allow for high-precision friction measurements during head-insert articulation in all 6 DOF (MC2.5D-500, AMTI, Boston, USA). Disturbing systemic effects have been minimized by using quasi frictionless aerostatic lateral force compensation (Eitzenberger, Wessobrunn, Germany) and cross talk compensation. Beside the standard protocoll for in vitro wear assessment (ISO 14242-1), more complex profiles from in vivo patient data (Heidelberg Motion Lab and Orthoload database) have been used: normal walking with different walking speeds and patient's weights, stairs up/down and start-stop conditions. All-ceramic bearings (Biolox delta, Ceramtec, Plochingen, Germany) have been orientated in clinically relevant cup inclinations (30, 45, 60 and 75 deg). For each head diameter (28, 36 and 48 mm) n=8 specimens have been devided in two groups: small and large clearance according to the manufacturer's specification. All tests were run at 37°C in diluted bovine serum (20 g/l protein content).


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_5 | Pages 33 - 33
1 Mar 2017
Mueller U Kretzer J
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Introduction

In total hip arthroplasty the femoral head is connected to the stem based on a taper connection (Fig. 1). Implant manufacturers proclaim that the modular tapers are not standardized and can vary from manufacturer to manufacturer. The combination of different implant components from different manufacturers (Mix & Match) is not permitted. However, in case of revision surgery, where the stem is still well fixed, the surgeon may decide to use a femoral head of a different manufacturer (Mix & Match). This decision may be related to a limited availability of a manufacturer-identical head or the manufacturer can't be identified. In this study, different taper combinations were experimentally investigated to assess the effect of Mix & Match on taper strength.

Methods

Hip stems and metal heads (n=3) of four different implant manufacturers (Biomet, DePuy, Smith&Nephew, Zimmer) were used. Firstly, torque-off tests similar to the ISO draft (ISO/DIS 7206-13) were performed without mixing the components. Subsequently, the stems were combined with metal heads from other manufacturers. All taper connections were impacted with 3 kN and then an increasing torque was applied until the head disconnected using a material testing machine (MTS Mini Bionix), (Fig. 2). The maximal torque off value was used as a measure for the taper strength.


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_5 | Pages 36 - 36
1 Mar 2017
Mueller U Kretzer J
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Introduction

Taper corrosion and fretting has been identified to be a major problem in total hip replacement during the past years. Taper design and manufacturing are not been standardised, and therefore it can be assumed that the tapers vary among different implant manufacturers. This can lead to variable contact situations and stresses in the taper junction depending on the combination. It can be assumed that the taper strength will influence the occurrence and magnitude of micromotions which are known to influence corrosion. Therefore, the aim of this study was to assess the influence of the taper angle clearance on the taper connection strength.

Material & Methods

For the investigation stem dummys with different taper angles were used that were manufactured from titanium alloy. The stem dummys were combined with ceramic heads with identically taper angles. Out of this, there were seven groups ranging from distal contact through full contact up to proximal contact. Three samples were used in each group and five repetitive measurements per samples were performed.

All taper connections were impacted with different forces (1 kN, 3 kN, 6 kN and 10 kN) and afterwards an increasing torque was applied until the head disconnected. The maximal torque off value was used as a measure for the taper strength.


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. 99-B, Issue SUPP_4 | Pages 85 - 85
1 Feb 2017
Kretzer J Schroeder M Mueller U Sonntag R Braun S
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The numbers of anatomic total shoulder joint replacements (ATSR) is increasing during the past years with encouraging clinical results. However, the survivorship of ATSR is lower as compared to total knee and hip replacements. Although the reasons for revision surgery are multifactorial, wear-associated problems like loosening are well-known causes for long-term failure of ATSR. Furthermore there is lack of valid experimental wear tests for ATSR. Therefore the purpose of this study was to define experimental wear testing parameters for ATSR and to perform a wear study comparing ceramic and metallic humeral heads.

Kinetic and kinematic data were adopted from in-vivo loading measurements of the shoulder joint (orthoload.com) and from several clinical studies on shoulder joint kinematics. As activity an ab/adduction motion of 0 to 90° in combination with an ante/retroversion while lifting a load of 2 kg has been chosen. Also a superior-inferior translation of the humeral head has been considered. The wear assessment was performed using a force controlled AMTI joint simulator for 3×106 cycles (Fig. 1) and polyethylene wear has been assed gravimetrically.

The studied ATSR (TuronTM, DJO Surgical, USA) resulted in a polyethylene wear rate of 62.75 ± 1.60 mg/106 cycles in combination with metallic heads. The ceramic heads significantly reduced the wear rate by 26.7 % to 45.99 ± 1.31 mg/106 (p<0.01). The wear scars dimensions were in good agreement to clinical retrievals.

This study is the first that experimentally studied the wear behavior of ATSR based on clinical and biomechanical data under load controlled conditions. In term of wear the analyzed ATSR could clearly benefit from ceramic humeral heads. However, in comparison to experimental wear studies of total knee and hip replacements the wear rate of the studied ATSR was relatively high. Therefore further research may focus on optimized wear conditions of ATSR and the hereby described method may serve as a tool to evaluate a wear optimization process.


Orthopaedic Proceedings
Vol. 98-B, Issue SUPP_9 | Pages 61 - 61
1 May 2016
Mueller U Kretzer J
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Introduction

Taper corrosion has been identified to be major problem in total hip replacement during the past years. Patients may suffer from adverse local tissue reactions (ALTR) due to corrosion products that are released from modular taper connection. So far, the mechanism that leads to taper corrosion in taper connections is not fully understood. Some retrieval studies tried to correlate implant related design parameters to the incidence and the severeness of taper corrosion. For example Kocagöz et al.[1] have not seen an influence of the taper clearance to taper corrosion. Hothi et al.[2] showed that shorter and rougher tapers increase taper corrosion. One limitation of retrieval studies may be that the analysed tapers are used and may have been altered during in vivo service. Beside the effect of taper corrosion many surgeons are not aware that the tapers may vary among different manufactors. With our study we want to provide taper related data that may be used for comparison and correlation (e.g. retrieval studies). Therefore we aimed to assess and compare geometric and topographic design parameters of currently available hip stem tapers from different manufacturers.

Material

For comparison well established cementless hip stems made of titanium alloy were choosen. All of them have a 12/14-taper. The analysed implants are shown in Fig. 1. As geometrical parameters the taper angle, the opening taper diameter and the taper length were measured using a coordinate measuring machine (CMM) (MarVision MS 222, Mahr, Göttingen, Germany; accuracy: ±2.3 µm). Several topographical parameters (e.g. Ra, Rz, etc.) were determined using a tactil roughness measurement instrument (Perthometer M2, Mahr, Göttingen, Germany; accuracy: 12 nm). Three independent samples of each taper were measured five times.


Orthopaedic Proceedings
Vol. 98-B, Issue SUPP_9 | Pages 60 - 60
1 May 2016
Mueller U Reinders J Kretzer J
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Introduction

Temporary use of antibiotic-impregnated polymethylmethacrylate (PMMA) bone cement spacers in two-stage revisions is considered to be standard of care for patients with a chronic infection of a joint replacement. Spacers should be wear resistant and load-bearing to avoid prolonged immobilisation of the patient and to reduce morbidity.

Most cement spacers contain barium sulphate or zirconium dioxide as radio-opaque substrate. Both are quite hard materials that may negatively influence the wear behaviour of the spacer.

Calcium carbonate is another radio-opaque substrate with lower hardness potentially increasing the wear resistance of the spacer materials.

The purpose of the study was to compare a prototype PMMA knee spacer (calcium carbonate loaded) with a commercially available spacer (containing barium sulphate) regarding the wear performance and particle release in a knee wear simulator.

Material and Methods

Spacer K (TECRES, Italy) was used as barium sulphate (10%) containing spacer material. A prototype material (Heraeaus Medical, Germany) with 15% calcium carbonate was compared. Both were gentamicin impregnated, ready-made for clinical application (preformed) and consist of a tibial and a femoral component.

Force-controlled simulation was carried out on an AMTI knee simulator. The test parameters were in accordance to ISO 14243–1 with a 50% reduced axial force (partial weight bearing). Tests were carried out at 37 °C in closed chambers filled with calf serum. Tests were run for 500,000 cycles at a frequency of 1 Hz. For wear analysis, gravimetric wear measurements according to ISO 14243–2 and wear particle analysis according to ASTM F1877–05 were performed.


Orthopaedic Proceedings
Vol. 88-B, Issue SUPP_I | Pages 81 - 81
1 Mar 2006
Granes R Maurer T Mueller U Ochsner P
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Introduction: Intramedullary reaming has its selected indication in osteomyelitis of long bones when remnants of dead infected bone are intramedullary embedded in a endostal new bone formation. The validity of this method has not yet been proven in long-term follow-ups. We reevaluated our patients in a 10 to 15 years follow-up to look at the recurrence rate of osteomyelitis after intramedullary reaming. We were also interested in the level of activity and the ability of working in our patients today.

Study design: From 1984 till 1992 forty-three patients with forty-four locations of chronic osteomyelitits of long bones were treated by intramedullary reaming. The collective consisted of 38 men and 5 women. The mean duration of the infection was 13.2 years. The causes of osteomyelitis were in 37 cases posttraumatic, in 6 cases haematogenous and one patient suffered from chronic osteomyelitis after removal of a total hip. Main locations of the focus were the diaphysis of the tibia and the femur. Intramedullary reaming was performed in patients with a infection centrally located in the bone protected by a thick periosteal new bone formation. In important endosteal bone formation a window was needed in order to pass with the guide wire for medullary reaming. Reaming went up to 18mm leaving a important cortical thickness of 6 to 10mm. Thorough irrigation focused a total removal of reaming mill. The treatment included a antibiotic therapy from 6 to 12 weeks. Staph. aureus was the most frequent micro-organism. The follow-up data was based on a continously documented clinical observation. Next to visits in our outpatient clinic we received informations by having designed a questionnaire booklet which was answered by the patients.

Results: In the 10 year follow-up in 37 cases (83%) osteomyelitis had never reoccurred. 5 patients needed a revision. 23 patients worked full-time, 3 had a reduced ability of work and 8 had been retired. 27 patients were pain-free, in 7 cases mild pain was found and 1 patient had moderate pain during working or walking. We have reevaluted 21 patients in a 15years follow-up, 7 patients will be followed up by 10/2004. Fifteen patients had died.

Discussion: Intramedullary reaming of the diaphysis of long bones after posttraumatic or haematogenous osteomyelitis proves to be a valuable treatment. The constitution of the bone, the reaming technique and the antibiotic therapy are influencing factors for a positive outcome.