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Motion analysis of lumbar vertebrae for different rod materials and flexible rod device – An experimental and finite element study

Rana Masud, Biswas Jayanta Kumar, Roy Sandipan, Biswas Palash, Karmakar Santanu Kumar, Roychowdhury Amit

Biocybernetics and Biomedical Engineering

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2020

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Vol. 40, no. 1

415--425

EN

Different stabilization devices have been used for treating lumbar spine disorders, including fusion, dynamic stabilization devices, flexible rods etc., which possess a different level of limitations. A simple experimental procedure is developed using a prototype lumbar spine specimen (L1-S), to evaluate the biomechanical performance of the lumbar spine. The range of motions (ROM) are tested for pedicle screw made of stainless steel (SS) fixation, using Teflon rod, ultra high molecular weight poly ethylene (UHMWPE) rod, poly ether ether ketone (PEEK) rod and SS flexible rod device (FRD). SS pedicle screw is used for fixation on the prototype lumbar spine. Experimental results are validated and compared with finite element (FE) results. It is observed that, in both flexion and extension, reduction in ROM is higher for Teflon and UHMWPE as compared to PEEK and FRD system. Differences between experimental and numerical results are found to be within an acceptable limit of 5–11%. For flexibility study, both numerical and experimental results support that PEEK rod plays an effective and important role among all the semi-rigid rods. The FRD devices are found to preserve the flexibility of the segment considerably better than PEEK rod.

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A short stem with metaphyseal anchorage reveals a more physiological strain pattern compared to a standard stem : an experimental study in cadavaric bone

Floerkemeier Thilo, Weltin Jennifer, Budde Stefan, Hurschler Christof, Windhagen Henning, Lewinski Gabriela von, Gronewold Jens

Acta of Bioengineering and Biomechanics

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2019

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Vol. 21, no. 2

153--159

EN

The proposed advantages of short stem hip arthroplasties are bone preserving strategies and less soft tissue damage. Bone preserving strategies do not only include a more proximal resection of the femoral neck, but especially for short stem hip arthroplasties with predominantly metaphyseal fixation a presumed more physiologic load transfer and thus a reduction of stress-shielding. However, the hypothesized metaphyseal anchorage associated with the aforementioned benefits still needs to be verified. Unfortunately, mid- to long-term clinical studies are missing. Methods: Therefore, the METHA short stem as a short stem with proposed metaphyseal anchorage and the Bicontact® standard stem were tested biomechanically in three pairs of cadaveric femora while strain gauges monitored their corresponding strain patterns. Results: For the METHA stem, the strains in all tested locations including the region of the calcar were similar to conditions of cadaver without implanted stem. The Bicontact stem showed approximately half of strain of the non-implanted cadaveric femura with slightly increasing strain from proximal to distal. Conclusions: Summarizing, the current study revealed primary metaphyseal anchorage of the METHA short stem and a metaphyseal-diaphyseal anchorage of the Bicontact stem.

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αBSM failed as a carrier of rhBMP-2 to enhance bone consolidation in a sheep model of distraction osteogenesis

Floerkemeier T., Thorey F., Wellmann M., Hurschler C., Budde S., Windhagen H.

Acta of Bioengineering and Biomechanics

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2017

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Vol. 19, no. 4

55--62

EN

One of the problems associated with callus distraction is a long time period needed for consolidation of the newly formed bone. The goal of this study was to determine whether percutaneous injections of rhBMP 2 in BSM would enhance bone consolidation. Methods: A unilateral tibial osteotomy combined with external stabilization was performed in 20 adult sheep. After a latency of four days, distraction was conducted for 20 days. Sheep were divided into three groups: group 1 received rhBMP-2/αBSM injections at day 23 and 30, group 2 buffer/BSM injections at day 23 and 30 and group 3 did not receive any injection. The radiographs and in-vivo torsional stiffness measurements were obtained weekly during the following 50 days. Post-mortem bone densitometry (DXA) and mechanical testing were performed. Results: In-vivo stiffness assessments, DXA values and the maximum torsional moment of the sheep tibia treated with two rhBMP-2 injections were not significantly greater than those of both control groups. Conclusions: Presented application of rhBMP-2 in BSM failed to enhance bone consolidation in distraction osteogenesis.

4

Influence of size and CCD-angle of a short stem hip arthroplasty on strain patterns of the proximal femur : an experimental study

Floerkemeier T., Budde S., Hurschler C., Lewinski G., Windhagen H., Gronewold J.

Acta of Bioengineering and Biomechanics

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2017

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Vol. 19, no. 1

141--149

EN

Purpose: The number of primary total hip arthroplasties (THA) is steadily increasing. Over the last decade numerous so-called short stem hip arthroplasties were introduced on the market. The aim of these implants with a predominantly metaphyseal anchorage is to reduce stress shielding and thereby the risk of aseptic loosening. One of the short stem arthroplasties with predominant metaphyseal fixation is the METHA® short stem (Aesculap, Tuttlingen, Germany). In order to reconstruct the biomechanics the METHA stem is available in different sizes with different centrum-collum-diaphysis-angles (CCD-angle). In this study, we want to address the research question of how the size of the implant and different CCD-angles influence the strain patterns of the proximal femur. Methods: Three different stem sizes (size 2, 3 and 4 – CCD-angle 130°) and three stems with different CCD-angles (size 3 – 120°, 130° and 135° CCD-angle) were successively implanted in a synthetic femur. Eight strain gauges monitored the corresponding strain patterns of the proximal femur. Results: Independent of stem size and CCD-angle only small changes in the strains were recorded around the distal part of the METHA stem when compared to the intact femur. However, all stems increased the strains in the region of the calcar. This was most pronounced by smaller CCD-angles and major sizes. Conclusion: The stem size and CCD-angle primarily influence the region of the calcar. Greater sizes and smaller CCD-angles lead to increased strains at the calcar. The other regions are hardly influenced by the stem size and CCDangle of the femoral component.