8 results
Now showing1 - 8 of 8
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , 45 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Factors influencing taper failure of modular revision hip stemsStem modularity of revision hip implant systems offers the advantage of the restoration of individual patient geometry but introduces additional interfaces, which are subjected to repetitive bending loading and have a propensity for fretting corrosion. The male stem taper is the weakest part of the modular junction due to its reduced cross section compared to the outside diameter of the stem. Taper fractures can be the consequence of overloading in combination with corrosion. The purpose of this study was to assess the influence of implant design factors, patient factors, and surgical factors on the risk of taper failure of the modular junction of revision stems. An analytical bending model was used to estimate the strength of the taper connection for pristine, fatigued and corroded conditions. Additionally, a finite element contact model of the taper connection was developed to assess the relative motion and potential for surface damage at the taper interface under physiological loading for varyied assembly and design parameters. Increasing the male taper diameter was shown to be the most effective means for increasing taper strength but would require a concurrent increase in the outer implant diameter to limit a greater risk of total surface damage for a thinner female taper wall. Increasing the assembly force decreases the total surface damage but not local magnitudes, which are probably responsible for crack initiation. It is suggested that in unfavourable loading conditions a monobloc implant system will reduce the risk of failure.Publicationtype: Journal ArticleScopus© Citations 21 249 769 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Maximizing the fixation strength of modular components by impaction without tissue damage(British Editorial Society of Bone and Joint Surgery, 2018-02-24); ; Taper junctions between modular hip arthroplasty femoral heads and stems fail by wear or corrosion which can be caused by relative motion at their interface. Increasing the assembly force can reduce relative motion and corrosion but may also damage surrounding tissues. The purpose of this study was to determine the effects of increasing the impaction energy and the stiffness of the impactor tool on the stability of the taper junction and on the forces transmitted through the patient's surrounding tissues.Publicationtype: Journal ArticleScopus© Citations 15 233 295 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , The Influence of Contamination and Cleaning on the Strength of Modular Head Taper Fixation in Total Hip Arthroplasty(2017-10); ; Background Intraoperative interface contamination of modular head-stem taper junctions of hip implants can lead to poor fixation strength, causing fretting and crevice corrosion or even stem taper fracture. Careful cleaning before assembly should help to reduce these problems. The purpose of this study was to determine the effect of cleaning (with and without drying) contaminated taper interfaces on the taper fixation strength. Methods Metal or ceramic heads were impacted onto titanium alloy stem tapers with cleaned or contaminated (fat or saline solution) interfaces. The same procedure was performed after cleaning and drying the contaminated interfaces. Pull-off force was used to determine the influence of contamination and cleaning on the taper strength. Results Pull-off forces after contamination with fat were significantly lower than those for uncontaminated interfaces for both head materials. Pull-off forces after application of saline solution were not significantly different from those for uncontaminated tapers. However, a large variation in taper strength was observed, pull-off forces for cleaned and dried tapers were similar to those for uncontaminated tapers for both head materials. Conclusion Intraoperative contamination of taper interfaces may be difficult to detect but has a major influence on taper fixation strength. Cleaning of the stem taper with saline solution and drying with gauze directly before assembly allows the taper strength of the pristine components to be achieved. Not drying the taper results in a large variation in pull-off forces, emphasizing that drying is essential for sufficient and reproducible fixation strength.Publicationtype: Journal Article146 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of the compliance of a patient's body on the head taper fixation strength of modular hip implants(2017-07-01); ; ; ; Background The strength of the modular fixation between head and stem taper of total hip replacement implants should be sufficient to minimise relative motion and prevent corrosion at the interface. Intraoperatively the components are assembled by impaction with a hammer. It is unclear whether the effective compliance of the patient's body modifies the strength of the taper interface under impaction assembly. The purpose of this study was to assess the influence of the compliance of the patient's body on the taper fixation strength. Methods Cobalt-chrome and ceramic femoral heads were assembled with titanium alloy stem tapers in the laboratory under impaction. Impaction forces were applied with a constant energy, defined by the drop height of the impactor, according to standard experimental procedure. The compliance of the patient was simulated in the laboratory by varying the stiffness of springs mounted below the stem taper. Pull-off forces between head and neck were measured to determine fixation strength. Findings Decreasing spring stiffness had no effect on the applied peak impaction forces during assembly or on the pull-off forces. Pull-off forces showed no difference between metal and ceramic head materials. Interpretation Pull-off forces and impaction forces were independent of the spring stiffness below the stem taper, indicating that the compliance of the patient has no effect on the taper fixation strength. Impaction testing in the laboratory can therefore be performed under rigid fixation, without accounting for the compliance of the patient.Publicationtype: Journal Article128 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Parallel N- and C-Terminal Truncations Facilitate Purification and Analysis of a 155-kDa Cold-Adapted Type-I PullulanaseThe cold-adapted pullulanase Pul13A is an industrial useful amylolytic enzyme, but its low solubility is the major bottleneck to produce the protein in recombinant form. In a previous approach, a complex and time-consuming purification strategy including a step-wise dialysis procedure using decreasing concentrations of urea to renature the insoluble protein from inclusion bodies had been established. In this study, a truncation strategy was developed to facilitate the purification and handling of the type-I pullulanase. Pul13A has a size of 155-kDa with a multidomain architecture that is composed of the following predicted modules: CBM41/E-set/Amy-Pul/DUF3372/E-set/E-set/E-set, with CBM and E-set domains being putative carbohydrate-binding modules, Amy-Pul is the catalytic region and DUF is a domain of unknown function. Consecutive N- and C-terminal deletions of domains were applied to construct minimized enzyme variants retaining pullulanase activity and exhibiting improved renaturation efficiencies. A total of seven truncation constructs were generated and tested, which still led to the production of inclusion bodies. However, the parallel deletion of the exterior CBM41 and E-set domain enabled the direct refolding of active enzymes during one-step dialysis in urea-free buffer. Catalytic properties of truncation construct Pul13A-N1/C1 were not impaired indicating that this enzyme variant may be superior for industrial applications over the full-length pullulanase.Publicationtype: Journal Article97 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Stem taper mismatch has a critical effect on ceramic head fracture risk in modular hip arthroplasty(2017-01); ; ; ; Background Modular total hip prostheses with ceramic heads are well established in orthopedic surgery and widely used. With the variety of different manufacturers and available designs, components are at risk for mismatch. Several case studies show the potentially devastating effects of mismatch. Methods The aim of this study was to investigate the outcome of one arbitrary component mismatch with commercially available components that appear to provide a stable fixation during assembly. A biomechanical in-vitro analysis of fracture strength (n = 5) was carried out in accordance with ISO 7206-10. “Type1” Bi-Metric®-stems were mismatched with “V40” Al2O3 ceramic heads. Findings Mean fracture strength was reduced to about 50% of the recommended FDA minimum by the mismatch (Mean 23.68 kN, SD 2.35 kN). A small contact area between head and stem taper was identified as a potential key parameter. Interpretation Mixing and matching components can put a patient at greater risk for ceramic head fracture and must be avoided.Publicationtype: Journal Article251 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , The influence of stem taper re-use upon the failure load of ceramic heads(2015-06-01); ; ; Ceramic components are frequently used in total hip replacement due to their good tribological properties. In revision of broken ceramic heads clinical uncertainties arise, whether the taper of the stem can be re-used with a new ceramic head, especially if the stem is well fixed. Ceramic is a brittle material. Even small damage on the male stem taper can lead to stress concentrations causing premature failure of a new ceramic head. As a consequence, manufactures strictly prohibit stem taper re-use for ceramic heads. The aim of this study was to determine the fracture strength of ceramic heads assembled to re-used male stem tapers, which were subjected to prior head fracture. Five 12/14 Ti6Al4V male tapers and 15 Al2O3 ceramic heads (BIOLOXforte® θ 28mm, L) were used for three consecutive fracture tests. Before and after every fracture test, all components were inspected visually and the surface geometry was analyzed. Mean fracture force (52.5kN) did not decrease with the number of taper re-uses (p≥0.77) but the range increased significantly from initially 4.1kN to 31.8kN for the first and 52.6kN for the second re-use due to some components failing at very low loads. Visual inspection was not sufficient to predict the reduced failure loads. Ceramic heads should therefore not be put on used male tapers without metal adapter sleeves.Publicationtype: Journal Article116