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Item type:Publication, Access status: without files , Development of a fully implantable EMG measurement system : status report on the MyoPlant project(De Gruyter, 2014); ; ; ; MyoPlant is a publicly funded research project that developed a fully implantable EMG measurement system. The system consists of a central implant, and single silicone electrodes that are placed on the muscles of choice. Electrodes are connected by means of subcutaneous cables. While electrodes were tested in rats, the complete system was tested in sheep and rhesus macaques. Electrodes showed good handling during surgery and were well tolerated by all animals without adverse reactions. No electrode defects were observed during the runtime of the project. Data from the animal trials showed that electrodes are well encapsulated after approximately eight weeks. The custom designed chip in the central implant performed as intended. Data transmission and inductive energy supply worked as designed. The latter was susceptible to coil misalignment. Electromyographic signals recorded with the system showed very good separation between electrodes, no cross-talk and no 50Hz noise. Amplitudes were consistent between sessions. Overall, we were able to demonstrate the technical feasibility of a fully implantable EMG measurement system. The recorded signals seem well suited to control modern myoelectric arm prostheses with multiple degrees of freedom in the future.Publicationtype: Journal Article58 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Effects of long-term alendronate treatment on bone mineralisation, resorption parameters and biomechanics of single human vertebral trabeculae(University of Wales, 2014); ; ; ; Due to their well-established fracture risk reduction, bisphosphonates are the most frequently used therapeutic agent to treat osteoporosis. Bisphosphonates reduce fracture risk by suppressing bone resorption, but the lower bone turnover could have a negative impact on bone quality at the tissue level. Here, we directly assess the structural and mechanical characteristics of cancellous bone from the lumbar vertebrae (L5) in non-treated osteoporotic controls (n = 21), mid-term alendronate-treated osteoporotic patients (n = 6), and long-term alendronate-treated osteoporotic patients (n = 7). The strength and toughness of single trabeculae were evaluated, while the structure was characterised through measurements of microdamage accumulation, mineralisation distribution, and histological indices. The alendronate-treated cases had a reduced eroded surface (ES/BS, p < 0.001) and a higher bone mineralisation in comparison to non-treated controls (p = 0.037), which is indicative of low turnover associated with treatment. However, the amount of microdamage and the mechanical properties were similar among the control and treatment groups. As the tissue mineral density (TMD) increased significantly with alendronate treatment compared to non-treated osteoporotic controls, the reduction in resorption cavities could counterbalance the higher TMD allowing the alendronate-treated bone to maintain its mechanical properties and resist microdamage accumulation. A multivariate analysis of the possible predictors supports the theory that multiple factors (e.g., body mass index, TMD, and ES/BS) can impact the mechanical properties. Our results suggest that long-term alendronate treatment shows no adverse impact on mechanical cancellous bone characteristics.Publicationtype: Journal ArticleScopus© Citations 15 63 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Cementation and interface analysis of early failure cases after hip-resurfacing arthroplasty(Springer, 2012-01-11); ; ; ; Purpose: The use of inappropriate cementation techniques has been suggested as an adverse factor for the long-term survival of hip-resurfacing arthroplasty. Inadequate initial fixation, thermal osteonecrosis and interface biological reactions are possible causes of failure. We analysed morphological changes associated with the cementation technique in a large collection of retrieved femoral components. Methods: One hundred and fifty femoral components (mean time to failure of 8.3 months±11.0) obtained at revision surgery were analysed morphometrically and histopathologically. Cement mantle and penetration were quantified in six different regions of interest. Histopathological analysis of the bone-cement interface was performed on undecalcified processed bone tissue. Results: The vast majority of the cases differed substantially from laboratory-based cement-penetration depth recommendations. Fifty-nine cases had a fibrous membrane at the cement-bone interface. This membrane was significantly thicker in cases with osteonecrosis compared to cases viable bone. Conclusions: Our results demonstrate that most failures were cemented inappropriately. We suggest that poor cementation was an important adverse factor; however, the cause of the failures was obviously multifactorial. The thickness of the fibrous membrane at the cement-bone interface differed significantly between cases with osteonecrosis and specimens with viable bone tissue.Publicationtype: Journal Article7 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , 9 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Analysis of retrieved hip resurfacing arthroplasties reveals the interrelationship between interface hyperosteoidosis and demineralization of viable bone trabeculae(Elsevier, 2011-12-16); ; ; ; Retrieved hip resurfacing arthroplasties (HRA) revised for causes other than osteonecrosis enable further insights into bone-cement interactions within the interface with only minimal biomechanical stresses. Our primary objective was to investigate the mineralization changes at the trabecular bone interface in retrieved hips using bright field and polarized light microscopy and by quantitative backscattered electron imaging. Because superficial seams of non-mineralized bone tissue varied substantially, we defined hyperosteoidosis as an osteoid seam of more than 20μm thickness. We hypothesized that interface hyperosteoidosis might be caused by the demineralization of previously mineralized bone tissue. One hundred and thirty-one retrieved HRAs with viable bone remnant tissue were analyzed. Bone mineral density distribution obtained from backscattered signal intensities of the trabecular bone at the bone-cement interface was assessed in cases with and without interface hyperosteoidosis. In cases with interface hyperosteoidosis, the degree of trabecular mineralization was also analyzed in deeper areas of the femoral remnants. Thirty-four cases showed hyperosteoidosis at the bone-cement interface, mostly in female patients. Bone trabeculae with hyperosteoidosis displayed a mineral density distribution pattern suggestive of the demineralization of a previously mineralized bone matrix. Our results demonstrate the localized disorder of the mineralization pattern of bone trabeculae at the bone-cement interface in a group of retrieved HRAs. In previously well-fixed femoral components, potential adverse effects on the load-bearing bone due to a decreased degree of mineralization at the bone-cement interface may affect the durability of the implant's function. © 2011 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.Publicationtype: Journal Article184 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Femoral component loosening after hip resurfacing arthroplasty(Springer, 2010-08-01); ; ; ; Objective: Before the re-introduction of the current generation of total hip resurfacing arthroplasty, component loosening and osteolysis were of great concern to the orthopaedic community. Early, mid- and long-term clinical results are encouraging, but component loosening still exists. Materials and Methods: Macroscopic, contact radiographic and histopathological analyses after undecalcified preparation of bone tissue specimens were performed. To investigate the frequency and morphological patterns of the loosening of the femoral component, we analysed a series of 190 retrieved femoral remnants that were revised for aseptic failures. Results: Thirty-five (18.4%) hips were revised for clinical and/or radiographic loosening of the femoral component. Pseudoarthrosis (n=17; median in situ time: 16 weeks, interquartile range [IQR]: 9 to 34), collapsed osteonecrosis (n=5; median in situ time: 79 weeks, IQR: 63 to 97), cement-socket debonding (n=3; median in situ time: 89 weeks, IQR: 54 to 97) and at later follow-up bone-cement loosening (n=10; median in situ time: 175 weeks; IQR 112 to 198; p=0.005) were distinct patterns of the femoral remnant-implant loosening. Fibrocartilaginous metaplasia of interface bone trabeculae (n=38; median in situ time: 61 weeks, IQR: 32 to 138) was strongly associated with femoral component loosening (p=0.009). Both the trabecular hyperosteoidosis (n=32; median in situ time: 71 weeks, IQR 50 to 129) and excessive intraosseous lymphocyte infiltration (n=12; median in situ time: 75 weeks, IQR 51 to 98) at the bone-cement interface correlated strongly with fibrocartilaginous metaplasia (p=0.001 and p=0.016 respectively) and all three lesions were associated with the female gender (p=0.021, p=0.009, and p=0.051). Conclusion: Femoral component loosening at early follow-up was mostly caused by pathological changes of the femoral remnant bone tissue: pseudoarthrosis and collapsed osteonecrosis. Fibrocartilaginous metaplasia was frequently observed in hips with femoral component loosening. The potential role of interface hyperosteoidosis as a precursor lesion of bone-cement loosening and its possible association with delayed type hypersensitivity reaction are discussed. © 2010 ISS.Publicationtype: Journal Article4 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Morphologic analysis of periprosthetic fractures after hip resurfacing arthroplasty(Wolters Kluwer Health, 2010-02-01); ; ; ; Domarus, Christoph vonBackground: Periprosthetic fractures have long been recognized as one of the major complications of hip resurfacing arthroplasty. The objective of this study was to develop a systematic and morphologic classification of the fracture mode based on pathogenesis. Methods: One hundred and seven retrieved specimens consisting of the femoral remnant and the femoral component of a total hip resurfacing arthroplasty that had failed as a result of a periprosthetic fracture were analyzed with regard to the morphologic failure mode. The location of the fracture line was used to differentiate the fractures. The fractures were also classified histopathologically as acute biomechanical, acute postnecrotic, or chronic biomechanical. Results: Fifty-nine percent (sixty-three) of the fractures occurred within the bone inside the femoral component. Fifty-one percent (fifty-five) of the fractures were classified morphologically as acute postnecrotic; 40% (forty-three), as chronic biomechanical; and 8% (nine), as acute biomechanical. Acute biomechanical fractures were found exclusively in the femoral neck and occurred earlier (mean time [and standard deviation] between implantation and revision, 41 ± 57 days) than acute postnecrotic fractures (mean time between implantation and revision, 149 ± 168 days; p = 0.002) or chronic biomechanical fractures (mean time between implantation and revision, 179 ± 165 days; p = 0.001). The latter two fracture types both occurred predominantly in the bone inside the femoral component. Conclusions: Three distinct fracture modes were characterized morphologically. Osteonecrosis was the most frequent cause of fracture-related failures. We suggest that an intraoperative mechanical injury of the femoral neck such as notching and/or malpositioning of the femoral component might lead to changes in the loading pattern or in the resistance to fracture of the femoral neck and may result in both acute and chronic biomechanical femoral neck fractures. These findings may serve as feedback information for the surgeon and possibly influence future therapeutic strategies.Publicationtype: Journal Article4 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Intraosseous lymphocytic infiltrates after hip resurfacing arthroplasty : a histopathological study on 181 retrieved femoral remnants(Springer, 2009-05-01); ; ; To identify a possible role of lymphocytic infiltrates in failure mechanism of the metal-on-metal hip resurfacing arthroplasty, the extent of lymphocytic infiltration was compared with reasons for prosthesis failure in a series of retrieval specimens. One hundred eighty-one femoral head and neck remnants were subjected to thorough analysis of histological findings and clinical data. Lymphocytic infiltrates were considered weak to moderate in 52 (28.7%) and excessive in ten (5.5%) cases. Six cases with excessive lymphocytic infiltrates belonged to the group of 33 (18.2%) revisions without obvious cause (periprosthetic fracture, component loosening, and infection) for prosthesis failure. Excessive lymphocytic infiltrates were strongly linked to the presence of proliferative desquamative synovitis (p∈<∈0.0001). Both the excessive lymphocytic infiltrates and proliferative desquamative synovitis were associated with female gender (p∈<∈0.05). We hypothesize that a specific cause of groin pain might be related to excessive intraosseous lymphocytic infiltrates and explained possibly by the hypersensitivity reaction of the delayed type after the hip resurfacing arthroplasty. Proliferative desquamative synovitis might constitute another morphologic feature associated with the delayed type hypersensitivity reaction.Publicationtype: Journal Article16 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Modes of implant failure after hip resurfacing : morphological and wear analysis of 267 retrieval specimens.(Wolters Kluwer Health, 2008-08); ; ; ; BACKGROUND: Resurfacing of the hip joint is experiencing a revival due to improvements in materials, design, and manufacturing techniques. Despite good midterm outcomes, the high early rate of failure and concerns about metal debris require a detailed morphological and wear analysis of retrieved resurfacing implants in order to understand failure mechanisms. METHODS: A worldwide collection of hip resurfacing revision devices was initiated, and 267 components were received. Devices were analyzed by patient demographics, radiographic positioning, and wear, as well as morphologically and histologically. Specimens were grouped into four different failure types. They were also stratified into rim-loaded or non-rim-loaded groups. Failures were also assessed by surgeon learning-curve effects. RESULTS: Time to failure was significantly different between the four revision-type groups: Specimens with fractures involving the implant rim were most common (46%) and failed earliest after surgery (mean of ninety-nine days), followed by fractures inside the femoral head (20%, 262 days) and loose cups (9%, 423 days). Revisions not due to fractures or cup loosening (25%) occurred at a mean of 722 days after surgery. Rim-loaded implants exhibited an average twenty-one to twenty-sevenfold higher wear rate than implants without rim-loading. Rim-loaded implants also showed a steeper mean cup inclination than their non-rim-loaded counterparts (59 degrees compared with 50 degrees ). Most failures occurred during the learning curve of the surgeon (the first fifty to 100 implantations). CONCLUSIONS: Failures on the femoral side usually occur within the first nine months after surgery and appear to be most directly related to the implantation technique or patient selection. Later failures are observed mainly due to acetabular problems, either due to dramatically increased wear or poor cup anchorage. Improper cup anteversion may be similar to or more important than cup inclination in producing excessive wear.Publicationtype: Journal Article9 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Reasons for failure of hip resurfacing implants : a failure analysis based on 250 revision specimens(Springer, 2008-07-01); ; ; ; Hip resurfacing has been experiencing a revival over the last 5-10 years. Early failure rates are higher than for conventional primary hip arthroplasty. Fractures of the femoral neck or head, cup loosening and persistent pain are the most frequently observed reasons for early revision. In this international retrospective uncontrolled study, 256 revision specimens (219 resurfacing heads, 37 cups) were analysed radiologically, tribologically, morphologically and histologically in order to investigate the failure mechanism. Of the head revisions, 70% were due to neck (median: 67 days after implantation) and head fractures (161 days), 9% were due to cup loosening (350 days) and 21% due to other reasons (602 days). Implants with rim loading (22% of all retrievals, cup inclination 58.0±10.9°) exhibited a head wear rate of 7.1±5.2 mm3/year. Non-rim loaded implants exhibited a head wear rate of 0.24±0.53 mm3/year (cup inclination 49.0±4.0°). The failure rate was highest during the first 16 weeks after surgery and for the first ten operations performed by a surgeon. Revisions based on problems on the femoral side such as notching and high implantation forces occurred earlier than revisions based on problems on the acetabular side such as cup loosening and high wear due to suboptimal cup position.Publicationtype: Journal Article15