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Determination of electrophysical and structural properties of human cancellous bone and synthetic bone substitute material using impedance spectroscopy and X-ray powder diffraction

Haba Y., Köckerling M., Shick Ch., Mittelmeier W., Bader R.

Acta of Bioengineering and Biomechanics

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2018

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Vol. 20, no. 1

11--19

EN

Electrophysical stimulation is used to support fracture healing and bone regeneration. For design optimization of electrostimulative implants, in combination with applied human donor bone or synthetic bone scaffolds, the knowledge of electrophysical properties is fundamental. Hence further investigations of the structural properties of native and synthetic bone is of high interest to improve biofunctionality of bone scaffolds and subsequent healing of the bone defect. The investigation of these properties was taken as an objective of this study. Therefore, surgically extracted fresh cylindrical and consecutively ashed cancellous bone samples from human osteoarthritic femoral heads were characterized and compared to synthetic bone substitute material. Thereby, impedance spectroscopy is used to determine the electrophysical properties and X-ray powder diffraction (XRD) for analysis of structural information of the bone samples. Conductivity and permittivity of fresh and ashed cancellous bone amounted to 1.710–2 S/m and 7.5106 and 210–5 S/m and 7.2103 , respectively. Electrical conductivity and dielectric permittivity of bone scaffold resulted in 1.710–7 S/m and 49. Analysis of the structural properties showed that the synthetic bone scaffolds made of Brushite exhibited some reflections which correspond to the native bone samples. The information in present study of the bone material (synthetic and autologous) could be used for later patient individual application of electrostimulative implants.

2

Comparison of different suture techniques for Achilles tendon repair in rat model using collagen scaffolds

Gabler C., Gierschner S., Tischer T., Bader R.

Acta of Bioengineering and Biomechanics

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2018

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Vol. 20, no. 2

73--77

EN

Tendon injury is an increasing problem in medicine due to aging of the population and increased activity demands. Many rodent animal models are used in order to evaluate tendon reconstruction. Although tendon reruptures are a known problem, the outcomes of tendon repair in animal models are rarely discussed in the literature. The goal of the present experimental study was to compare the primary fixation stability of three suture techniques for repair of Achilles tendon defects in a rat model using a collagen scaffold. Methods: Cadaveric left hind limbs of Sprague-Dawley rats were prepared with an Achilles tendon defect of 3 mm and rejoined using a collagen scaffold. Three suture configurations (simple, simple stitch with additional framing suture, and modified Mason–Allen stitch; n = 5 each) underwent tensile testing until complete failure was observed. Results: Under a load of a mean value of 6.6 N, the failure load of simple stitches was the significantly lowest ( p < 0.01). Both, modified Mason–Allen stitches and simple stitches with additional framing suture showed a mean failure load of more than 14 N. Regardless of the suture technique, most of the samples showed failure of tendon due to suture tear-out. The suture material as well as the scaffold remained mostly intact. Conclusions: Although simple end-toend suture techniques are common in the literature, stitches with more suture strands should be preferred. Using techniques like an additional framing suture or modified Mason–Allen stitch, maximum failure load can be doubled and the risk of tendon rerupture may be decreased in vivo.

3

Experimental analysis of insertion torques and forces of threaded and press-fit acetabular cups by means of ex vivo and in vivo measurements

Vogel D., Rathay A., Teufel S., Ellenrieder M., Zietz C., Sander M., Bader R.

Acta of Bioengineering and Biomechanics

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2017

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Vol. 19, no. 3

155--163

EN

In THA sufficient primary implant stability is the precondition for successful secondary stability. Industrial foams of different densities have been used for primary stability investigations. The aim of this study was to analyse and compare the insertion behaviour of threaded and press-fit cups in vivo and ex vivo using bone substitutes with various densities. Methods: Two threaded (Bicon Plus®, Trident® TC) and one press-fit cup (Trident PSL®) were inserted by orthopaedic surgeons (S1, S2) into 10, 20 and 31 pcf blocks using modified surgical instruments allowing measurements of the insertion forces and torques. Furthermore, the insertion behaviour of two cups were analysed intraoperatively. Results:Torques for the threaded cups increased while bone substitute density increased. Maximum insertion torques were observed for S2 with 102 Nm for the Bicon Plus® in 20 pcf blocks and 77 Nm for the Trident® TC in 31 pcf blocks which compares to the in vivo measurement (85 Nm). The average insertion forces for the press-fit cup varied from 5.2-6.8 kN (S1) and 7.2-11.5 kN (S2) ex vivo. Intraoperatively an average insertion force of 8.0 kN was determined. Conclusions: Implantation behaviour was influenced by acetabular cup design, bone substitute and experience of the surgeon. No specific density of bone substitute could be favoured for ex vivo investigations on the implantation behaviour of acetabular cups. The synthetic bone blocks of high density (31 pcf) led to problems regarding cup orientation and seating. Therefore, bone substitutes used should be critically scrutinized in terms of the comparability to the in vivo situation.

4

Influence of three different preservative techniques on the mechanical properties of the ovine cortical bone

Wieding J., Mick E., Wree A., Bader R.

Acta of Bioengineering and Biomechanics

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2015

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Vol. 17, no. 1

137--146

EN

Purpose: Preservative treatments are necessary for disinfection and long term storage when dealing with biological tissue. Freezing is a gold standard but infectious risk can only be eliminated by using chemical fluids that may alter the mechanical properties, depending on their composition. Therefore, we experimentally evaluated the influence of freezing and of two commonly used preservative fluids (formalin and alcohol) on the intrinsic mechanical properties of ovine cortical bone samples, compared to purely fresh samples. Methods: Prismatic specimens were prepared from the sheep’s metacarpal bones and were divided into four groups (fresh, fresh-frozen, formalin and alcohol). All samples underwent four-point-bending; fresh samples were tested immediately, preserved samples were tested after 14 days. Bending modulus, bending strength, yield strength and energy absorption for the elastic and plastic region were determined. Results: Significant differences were found for the plastic energy absorption for formalin (–41%) and alcohol (+37%) preservation compared to fresh samples. Formalin preservation revealed embrittlement of the cortical bone samples and alcohol preservation revealed higher ability of plastic energy absorption. Conclusions: Our results indicate that freezing has no influence on the mechanical properties of the ovine cortical bone. Preservation with chemical fluids (formalin and alcohol) showed no influence on the elastic properties but it was observed for the ability of plastic energy absorption. Therefore, these methods seem to be suitable for preservation without evident altering of the elastic mechanical properties.

5

Influence of Footwear and Equipment on Stride Length and Range of Motion of Ankle, Knee and Hip Joint

Schulze Ch., Lindner T., Woitge S., Schulz K., Finze S., Mittelmeier W., Bader R.

Acta of Bioengineering and Biomechanics

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2014

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Vol. 16, no. 4

45--51

EN

Purpose: Footwear and equipment worn by military personnel is of importance for them to be able to meet the physical demands specific to their profession daily activities. Aim of the present study was to investigate by means of gait analysis how army-provided footwear and equipment influence the range of motion of hip, knee and ankle joints as well as stride length.Methods: Thirty-two soldiers were subjected to gait analysis on a treadmill by way of video recordings and goniometric measurements. Results: The stride length increased when military shoes are worn. We found no influence on stride length in connection to increased loading. The weight of the shoes represents the decisive factor. Neither shoes nor equipment changed the range of motion of the knee joint.Weight of equipment affected range of motion of the hip joint. The range of motion of the upper and lower ankle joints was mainly influenced by the properties of the shoes. Conclusions: Military footwear and weight of equipment influence stride length and range of motion of joints of the lower extremities in a specific way. Shape of material is the decisive factor.

6

Biomechanical study of the influence of the weight of equipment on selected trunk muscles

Schulze Ch., Lindner T., Woitge S., Glass A., Fimze S., Mittelmeier W., Bader R.

Acta of Bioengineering and Biomechanics

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2013

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Vol. 15, no. 3

45--51

EN

Overexertion and pain of the musculoskeletal system may occur partly owing to load application by the equipment. Both the weight of equipment and the duration of loading are relevant. The aim of the present study was to examine the extent of loading and resultant strain in the trunk muscles. Therefore, the trunk posture of soldiers and muscular activity in reaction to different equipment components (helmet, load-carrying equipment, gun and backpack) were evaluated. Electromyography was performed and a visual assessment of body axis was conducted based on standardised planar images. Data indicate that the activity of the trunk muscles examined (latissimus dorsi, trapezius and pectoralis major) is dependent on the weight and distribution of the equipment components. Activity in the trapezius muscle, for instance, was doubled during specific load application. Moreover, the method of carrying the rifle had a significant influence on the activity of the trapezius muscle (one-sided decrease of activity by 50%). Subjects were able to stabilise the body axis in the coronal plane through increased muscle activity, however, in the sagittal plane a compensatory ventral inclination of the body was observed. Uneven load distribution can lead to an irregular strain on the musculoskeletal system.