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On customization of orthopedic implants - from design and additive manufacturing to implementation
Mid Sweden University, Faculty of Science, Technology and Media, Department of Quality Technology and Management, Mechanical Engineering and Mathematics.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This doctoral thesis is devoted to studying the possibilities of using additive manufacturing (AM) and design based on computed tomography (CT), for the production of patient-specific implants within orthopedic surgery, initially in a broad perspective and, in the second part of the thesis focusing on customized clavicle osteosynthesis plates. The main AM method used in the studies is the Electron Beam Melting (EBM) technology. Using AM, the parts are built up directly from 3D computer models, by melting or in other ways joining thin layers of material, layer by layer, to build up the part. Over the last 20 years, this fundamentally new way of manufacturing and the rapid development of software for digital 3D reconstruction of anatomical models from medical imaging, have opened up entirely new opportunities for the design and manufacturing of patient-specific implants. Based on the information in a computed tomography (CT) scan, both digital and physical models of the anatomy can be created and of implants that are customized based on the anatomical models.

 

The main method used is a number of case studies performed, focusing on different parts of the production chain, from CT-scan to final implant, and with several aims: learning about the details of the different steps in the procedure, finding suitable applications, developing the method and trying it out. The first study was on customized hip stems, focusing on the EBM method and its special preconditions and possibilities. It was followed by a study of bone plates, designed to follow the patient-specific bone contour, in this case a tibia fracture including the whole production chain. Further, four cases of patient-specific plates for clavicle fracture fixation were performed in order to develop and evaluate the method. The plates fit towards the patient’s bone were tested in cooperation with an orthopedic surgeon at Östersund hospital. In parallel with the case studies, a method for finite element (FE) analysis of fixation plates placed on a clavicle bone was developed and used for the comparative strength analysis of different plates and plating methods. The loading on the clavicle bone in the FE model was defined on a muscle and ligament level using multibody musculoskeletal simulation for more realistic loading than in earlier similar studies. 

 

The initial studies (papers I and II) showed that the EBM method has great potential, both for the application of customized hip stems and bone plates; in certain conditions EBM manufacturing can contribute to significant cost reductions compared to conventional manufacturing methods due to material savings and savings in file preparation time. However, further work was needed in both of the application areas before implementation. The studies on the fracture fixation using patient-specific clavicle plates indicated that the method can facilitate the work for the surgeon both in the planning and in the operating room, with the potential of a smoother plate with a better fit and screw positioning tailored to the specific fracture (paper VI). However, a large clinical trial is required to investigate the clinical benefit of using patient-specific plates. The FE simulations showed similar stress distributions and displacements in the patient-specific plates and the commercial plates (papers III to VI).

 

To summarize: the results of this thesis contribute to the area of digital design and AM in patient-specific implants with broad basis of knowledge regarding the technologies used and areas in which further work is needed for the implementation of the technology on a larger scale. Further, a method has been developed and initially evaluated for implementation in the area of clavicle fracture fixation, including an approach for comparing the strength of different clavicle plates.

Place, publisher, year, edition, pages
Sundsvall, Sweden: Kopieringen, Mid Sweden University , 2014. , 60 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 191
Keyword [en]
Patient-specific implants, Additive manufacturing, Electron beam melting, Multibody musculoskeletal analysis, Orthopedic implants, Clavicle, Finite element analysis, Computer aided design, Osteosynthesis plate, Hip stem implants
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:miun:diva-22902ISBN: 978-91-87557-63-7 (print)OAI: oai:DiVA.org:miun-22902DiVA: diva2:745912
Supervisors
Available from: 2014-09-15 Created: 2014-09-11 Last updated: 2015-03-13Bibliographically approved
List of papers
1. Production of Customized Hip Stem Prostheses: a Comparison Between Machining and Additive Manufacturing
Open this publication in new window or tab >>Production of Customized Hip Stem Prostheses: a Comparison Between Machining and Additive Manufacturing
2013 (English)In: Rapid prototyping journal, ISSN 1355-2546, E-ISSN 1758-7670, Vol. 19, no 5, 365-372 p.Article in journal (Refereed) Published
Abstract [en]

Purpose - The purpose of this paper is to study the use of the additive manufacturing (AM) method, electron beam melting (EBM), for manufacturing of customized hip stems. The aim is to investigate EBM's feasibility and commercial potential in comparison with conventional machining, and to map out advantages and drawbacks of using EBM in this application. One part of the study concerns the influence on the fatigue properties of the material, when using the raw surface directly from the EBM machine, in parts of the implant.Design/methodology/approach - The research is based on a case study of manufacturing a batch of seven individually adapted hip stems. The stems were manufactured both with conventional machining and with EBM technology and the methods were compared according to the costs of materials, time for file preparation and manufacturing. In order to enhance bone ingrowths in the medial part of the stem, the raw surface from EBM manufacturing is used in that area and initial fatigue studies were performed, to get indications on how this surface influences the fatigue properties.Findings - The cost reduction due to using EBM in this study was 35 per cent. Fatigue tests comparing milled test bars with raw surfaced bars indicate a reduction of the fatigue limit by using the coarse surface.Originality/value - The paper presents a detailed comparison of EBM and conventional machining, not seen in earlier research. The fatigue tests of raw EBM-surfaces are interesting since the raw surface has shown to enhance bone ingrowths and therefore is suitable to use in some medical applications.

Keyword
Orthopedic implants, hip stem, electron beam melting, additive layer manufacturing
National Category
Medical Materials
Identifiers
urn:nbn:se:miun:diva-14391 (URN)10.1108/RPJ-07-2011-0067 (DOI)000323021700008 ()2-s2.0-84881395614 (Scopus ID)
Available from: 2011-08-24 Created: 2011-08-24 Last updated: 2016-09-21Bibliographically approved
2. Implementation of digital design and solid free-form fabrication for customization of implants in trauma orthopaedics
Open this publication in new window or tab >>Implementation of digital design and solid free-form fabrication for customization of implants in trauma orthopaedics
2012 (English)In: Journal of medical and biological engineering, ISSN 1609-0985, Vol. 32, no 2, 91-96 p.Article in journal (Refereed) Published
Abstract [en]

Bone plates for the fixation of complex fractures in proximity to joints often have to be reshaped to follow the bone contour. Good adhesion of the screws in areas where the bone is osteoporotic is also a challenge. One possible solution to these issues is to tailor-make plates by creating a digital three-dimensional model of the fracture from a computed tomography (CT) scan, digitally reducing the fracture, designing a plate, and finally manufacturing it directly from the digital model with solid free-form fabrication (SFF) technology. This study designs a custom plate for a distal tibia fracture, and investigates and refines the procedure from the CT scan to the final implant, with the aim of making it usable in trauma orthopaedics. The bone plate is manufactured using electron beam melting (EBM) technology. The challenges of bone plate design using digitalization and SFF are discussed. The virtual models created by the engineer while digitally reducing the fracture and modeling the plate are valuable for the physician while planning the surgery. A combination of surgery planning and digital plate design improves the surgeon's preparations and ensures correspondence between the plan and the designed implant. The proposed procedure, with the approximate required time in brackets, includes the separation of bone in the DICOM file (60 min), the reduction of fracture (5-30 min), revision (30 min), modelling of the plate (30-120 min), confirmation (30 min), manufacturing with SFF (10 h), post-processing (60 min), and finally cleaning and sterilization (90 min). The whole procedure requires about three working days.

Keyword
Bone plate; Electron beam melting; Orthopaedic implant; Solid free-form fabrication; Trauma
National Category
Biomedical Laboratory Science/Technology
Identifiers
urn:nbn:se:miun:diva-14393 (URN)10.5405/jmbe.883 (DOI)000303147300003 ()2-s2.0-84864007060 (Scopus ID)
Available from: 2011-08-24 Created: 2011-08-24 Last updated: 2014-09-15Bibliographically approved
3. Combined finite element and multibody musculoskeletal investigation of a fractured clavicle with reconstruction plate
Open this publication in new window or tab >>Combined finite element and multibody musculoskeletal investigation of a fractured clavicle with reconstruction plate
2015 (English)In: Computer Methods in Biomechanics and Biomedical Engineering, ISSN 1025-5842, E-ISSN 1476-8259, Vol. 18, no 7, 740-748 p.Article in journal (Refereed) Published
Abstract [en]

This paper addresses the evaluation of clavicle fixation devices, by means of computational models. The aim was to develop

a method for comparison of stress distribution in various fixation devices, to determine whether the use of multibody

musculoskeletal input in such model is applicable and to report the approach. The focus was on realistic loading and the

motivation for the work is that the treatment can be enhanced by a better understanding of the loading of the clavicle and

fixation device. The method can be used to confirm the strength of customised plates, for optimisation of new plates and to

complement experimental studies. A finite element (FE) mesh of the clavicle geometry was created from computed

tomography data and imported into the FE solver where the model was subjected to muscle forces and other boundary

conditions from a multibody musculoskeletal model performing a typical activity of daily life. A reconstruction plate and

screws were also imported into the model. The combination models returned stresses and displacements of plausible

magnitudes in all included parts and the result, upon further development and validation, may serve as a design guideline for

improved clavicle fixation.

Keyword
clavicle, finite element analysis, multibody simulation, bone plate
National Category
Engineering and Technology
Identifiers
urn:nbn:se:miun:diva-20515 (URN)10.1080/10255842.2013.845175 (DOI)000345141700006 ()24156391 (PubMedID)2-s2.0-84911987251 (Scopus ID)
Note

Published online 24 Oct 2013.

Available from: 2013-12-09 Created: 2013-12-09 Last updated: 2014-12-11Bibliographically approved
4. Strength analysis of clavicle fracture fixation devices and fixation techniques using finite element analysis with musculoskeletal force input
Open this publication in new window or tab >>Strength analysis of clavicle fracture fixation devices and fixation techniques using finite element analysis with musculoskeletal force input
2015 (English)In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 53, no 8, 759-769 p.Article in journal (Refereed) Published
Abstract [en]

In the cases, when clavicle fractures are treated with a fixation plate,opinions are divided about the best position of the plate, type of plateand type of screw units. Results from biomechanical studies of claviclefixation devices are contradictory, probably partly because ofsimplified and varying load cases used in different studies. The anatomyof the shoulder region is complex, which makes it difficult andexpensive to perform realistic experimental tests; hence, reliablesimulation is an important complement to experimental tests. In thisstudy, a method for finite element simulations of stresses in theclavicle plate and bone is used, in which muscle and ligament force dataare imported from a multibody musculoskeletal model. The stressdistribution in two different commercial plates, superior and anteriorplating position and fixation including using a lag screw in thefracture gap or not, was compared. Looking at the clavicle fixation froma mechanical point of view, the results indicate that it is a majorbenefit to use a lag screw to fixate the fracture. The anterior platingposition resulted in lower stresses in the plate, and the anatomicallyshaped plate is more stress resistant and stable than a regularreconstruction plate.

Keyword
Clavicle, Finite element analysis, Multibody simulation, Bone plates, Fixation techniques
National Category
Medical Engineering
Identifiers
urn:nbn:se:miun:diva-22982 (URN)10.1007/s11517-015-1288-5 (DOI)000356371000008 ()2-s2.0-84931576402 (Scopus ID)
Available from: 2014-09-15 Created: 2014-09-15 Last updated: 2015-08-13Bibliographically approved
5. Modeling of fractured clavicles and reconstruction plates using CAD, finite element analysis and real musculoskeletal forces input
Open this publication in new window or tab >>Modeling of fractured clavicles and reconstruction plates using CAD, finite element analysis and real musculoskeletal forces input
2013 (English)In: WIT Transactions on Biomedicine and Health, WIT Press, 2013, 235-243 p.Conference paper, (Refereed)
Abstract [en]

This study focuses on the treatment options for clavicle fractures, more specifically the cases with a need for internal fixation: non-unions and some complex fractures. Enhancing the understanding of the loading of the bone and fixation device enables treatment options to be improved. The aim of the study was to develop a method for the realistic simulation of stresses and displacements in the bone and fixation device and to use this method to make comparisons between a conventional reconstruction plate and a customized plate, designed from patient-specific computed tomography (CT) data. In an earlier study, a finite element (FE) mesh of the clavicle geometry was created from CT data, subjected to muscle forces and other boundary conditions from a multibody musculoskeletal model and imported into the FE solver. In this study, a solid 3D model of the same clavicle geometry was created and the mesh was replaced by the solid model to make the FE-model more suitable for the comparison of different plates. An LCP Reco-Plate 3.5 straight, 6 holes (by Synthes) was compared with a customized plate which was designed to follow the anatomy of the bone. The LCP-Reco plate has tapered reconstruction segments throughout the plate to allow for the plate reshaping during surgery. The customized plate was designed without such segments and with a lower width than the LCP plate. The two different plates showed stresses and displacements of similar magnitudes. The customized plate had a more even stress distribution while the LCP plate had higher stress concentrations in the middle of the plate and on the edges of the tapered reconstruction segments. To the authors' best knowledge, this is the first FE model of a clavicle bone with plate and it may, upon further development, serve as a useful instrument for improved clavicle fixation.

Place, publisher, year, edition, pages
WIT Press, 2013
Series
WIT Transactions on Biomedicine and Health, ISSN 1743-3525 ; 17
Keyword
Bone plate, CAD, Clavicle, Finite element analysis, Modeling
National Category
Biomedical Laboratory Science/Technology
Identifiers
urn:nbn:se:miun:diva-19364 (URN)10.2495/BIO130211 (DOI)2-s2.0-84878022216 (Scopus ID)9781845647063 (ISBN)
Conference
10th International Conference on Modelling in Medicine and Biology, BIOMED 2013; Budapest; Hungary; 24 April 2013 through 26 April 2013; Code 97013
Available from: 2013-08-26 Created: 2013-06-19 Last updated: 2014-09-15Bibliographically approved
6. Patient-specific bone plates for clavicle fractures: Design, manufacturing and strength analysis
Open this publication in new window or tab >>Patient-specific bone plates for clavicle fractures: Design, manufacturing and strength analysis
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Medical Engineering
Identifiers
urn:nbn:se:miun:diva-22983 (URN)
Available from: 2014-09-15 Created: 2014-09-15 Last updated: 2014-09-15Bibliographically approved

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