Acromioclavicular joint suture button repair leads to coracoclavicular tunnel widening.

PURPOSE: Biomechanical evaluation of three different suture button devices used in acromioclavicular joint repair and analysis of their effect on post-testing tunnel widening. METHODS: Eighteen human shoulder girdles were assigned into three groups with a similar mean bone mineral density. Three different single-tunnel acromioclavicular repair devices were tested: (1) AC TightRope® with FiberWire; (2) AC Dog Bone™ Button with FiberTape; (3) Low Profile AC Repair System. Biomechanical testing was performed simulating the complex movement of the distal clavicle as follows. A vertical load of 80 N was applied continuously. The rotation of the clavicle about its long axis was set at 10° anterior and 30° posterior for 2500 cycles at 0.25 Hz. The horizontal translation of the clavicle was set at 6 mm medial and 6 mm lateral for 10,000 cycles at 1 Hz. The coracoclavicular distance was measured before and after testing. After testing, each sample underwent micro-CT analysis. Following 3D reconstruction, the area of the bone tunnels was measured at five defined cross sections. RESULTS: In TightRope® and Dog Bone™ groups, all samples completed testing, whereas in the Low Profile group, three out of six samples showed system failure. The mean absolute difference of coracoclavicular distance after testing was significantly greater in the Low Profile group compared to TightRope® and Dog Bone™ groups (4.3 ± 1.3 mm vs 1.9 ± 0.7 mm vs 1.9 ± 0.8 mm; p = 0.001). Micro-CT analysis of the specimens demonstrated significant tunnel widening in the inferior clavicular and superior coracoid regions in all three groups (p < 0.05). CONCLUSION: Significant tunnel widening can be observed for all devices and is primarily found in the inferior parts of the clavicle and superior parts of the coracoid. The Low Profile AC Repair System showed inferior biomechanical properties compared to the AC TightRope® and AC Dog Bone™ devices. Therefore, clinicians should carefully select the type of acromioclavicular repair device used and need to consider tunnel widening as a complication.

Explant analysis and implant registries are both needed to further improve patient safety.

In the early days of total joint replacement, implant fracture, material problems and wear presented major problems for the long-term success of the operation. Today, failures directly related to the implant comprise only 2-3% of the reasons for revision surgeries, which is a result of the material and design improvements in combination with the standardization of pre-clinical testing methods and the post-market surveillance required by the legal regulation. Arthroplasty registers are very effective tools to document the long-term clinical performance of implants and implantation techniques such as fixation methods in combination with patient characteristics. Revisions due to implant failure are initially not reflected by the registries due to their small number. Explant analysis including patient, clinical and imaging documentation is crucial to identify failure mechanisms early enough to prevent massive failures detectable in the registries. In the past, early reaction was not always successful, since explant analysis studies have either been performed late or the results did not trigger preventive measures until clinical failures affected a substantial number of patients. The identification of implant-related problems is only possible if all failures are reported and related to the number of implantations. A system that analyses all explants from revisions attributed to implant failure is mandatory to reduce failures, allowing improvement of risk assessment in the regulatory process.

Human iPSC-derived renal organoids engineered to report oxidative stress can predict drug-induced toxicity.

Advances in regenerative medicine have led to the construction of many types of organoids, which reproduce important aspects of endogenous organs but may be limited or disorganized in nature. While their usefulness for restoring function remains unclear, they have undoubted usefulness in research, diagnostics, and toxicology. In toxicology, there is an urgent need for better models for human kidneys. We used human iPS-cell (hiPSC)-derived renal organoids to identify HMOX1 as a useful marker of toxic stress via the oxidative stress pathway, and then constructed an HMOX1 reporter in hiPSCs. We used two forms of hiPSC-derived HMOX1-reporter renal organoids to probe their ability to detect nephrotoxicants in a panel of blind-coded compounds. Our results highlight the potential usefulness, and some limitations, of HMOX1-reporter renal organoids as screening tools. The results may guide development of similar stress-reporting organoid assays for other stem-cell-derived organs and tissues.

All-suture anchor pullout results in decreased bone damage and depends on cortical thickness.

PURPOSE: To evaluate the influence of cortical and cancellous bone structure on the biomechanical properties of all-suture and conventional anchors and compare the morphological bone damage after their failure. The hypothesis of the study is that all-suture anchor pullout is less invasive and that the pullout force is influenced by the cortical thickness. METHODS: Thirty human humeri were biomechanically tested as follows: starting with a load cycle from 20 to 50 N, a stepwise increase of the upper peak force by 0.05 N for each cycle at a rate of 1 Hz was performed. Analysis included maximum pullout strength for three different anchor implantation angles (45°, 90°, 110°) of the two anchor types. After anchor pullout, every sample underwent micro-CT analysis. Bone mineral density (BMD) and cortical thickness were determined at the anchor implantation site. Furthermore, the diameter of the cortical defect and the volume of the bone cavity were identified. RESULTS: The maximum pullout strength of all-suture anchors demonstrates a strong correlation to the adjacent cortical thickness (r = 0.82, p ≤ 0.05) with at least 0.4 mm needed to withstand 200 N. No correlation could be seen in conventional anchors. Moreover, no correlation could be detected for local BMD in both anchors. All-suture anchors show a significantly narrower cortical defect as well as a smaller bone cavity following pullout (4.3 ± 1.3 mm vs. 5.3 ± 0.9 mm, p = 0.037; 141 mm3 vs. 212 mm3; p = 0.009). The cortical defect is largest if the anchors are placed at a 45° angle. CONCLUSION: In contrast to conventional anchors, the pullout force of all-suture anchors depends on the thickness of the humeral cortex. Furthermore, all-suture anchors show a significantly smaller cortical defect as well as decreased bone damage in the case of pullout. Therefore, the clinical implication of this study is that all-suture anchors are advantageous due to their bone preserving ability. Also, intraoperative decortication should not be performed and cortical thickness should be preoperatively evaluated to decrease the risk of anchor failure.

Learning metal artifact reduction in cardiac CT images with moving pacemakers.

Metal objects in the human heart such as implanted pacemakers frequently lead to heavy artifacts in reconstructed CT image volumes. Due to cardiac motion, common metal artifact reduction methods which assume a static object during CT acquisition are not applicable. We propose a fully automatic Dynamic Pacemaker Artifact Reduction (DyPAR+) pipeline which is built of three convolutional neural network (CNN) ensembles. In a first step, pacemaker metal shadows are segmented directly in the raw projection data by the SegmentationNets. Second, resulting metal shadow masks are passed to the InpaintingNets which replace metal-affected line integrals in the sinogram for subsequent reconstruction of a metal-free image volume. Third, the metal locations in a pre-selected motion state are predicted by the ReinsertionNets based on a stack of partial angle back-projections generated from the segmented metal shadow mask. We generate the data required for the supervised learning processes by introducing synthetic, moving pacemaker leads into 14 clinical cases without pacemakers. The SegmentationNets and the ReinsertionNets achieve average Dice coefficients of 94.16% ± 2.01% and 55.60% ± 4.79% during testing on clinical data with synthetic metal leads. With a mean absolute reconstruction error of 11.54 HU ± 2.49 HU in the image domain, the InpaintingNets outperform the hand-crafted approaches PatchMatch and inverse distance weighting. Application of the proposed DyPAR+ pipeline to nine clinical test cases with real pacemakers leads to significant reduction of metal artifacts and demonstrates the transferability to clinical practice. Especially the SegmentationNets and InpaintingNets generalize well to unseen acquisition modes and contrast protocols.

Biomechanical comparison of polylactide-based versus titanium miniplates in mandible reconstruction in vitro.

OBJECTIVES: Evaluation of the mechanical integrity and reliability of polylactide-based miniplates for osseous free flap fixation at the mandible in an experimental study setup of a mandible reconstruction model. MATERIAL AND METHODS: 1.0mm titanium miniplates (group TI) (MatrixMandible, DePuy Synthes, Umkirch, Germany) and 1.5mm polylactide miniplates (group PL) (Inion CPS, Inion Oy, Tampere, Finland) were used to fix a polyurethane (PU) fibula segment to a PU mandible reconstruction model using monocortical non-locking screws. Mastication was simulated via unilateral cyclic dynamic loading at 1Hz with increasing loads (+ 0.15N/cycle, Bionix, MTS, USA). A 3D optical tracking system (Aramis, GOM, Braunschweig, Germany) was used to determine interosteotomy movements (IOM). RESULTS: IOM were higher in the polylactide group (distal: P=0.001, mesial: P=0.001). Differences in mean stiffness (titanium: 478±68N/mm; polylactide: 425±38N/mm, P=0.240) and mean force at a vertical displacement of 1.0mm (titanium: 201.6±87.1N; polylactide: 141.3±29.9N, P=0.159) were not significant. CONCLUSIONS: The results of this study suggest that polylactide-based miniplates provide reduced mechanical integrity and higher interosteotomy movements in comparison to titanium miniplates in vitro. Indications for clinical use of polylactide-based miniplates in mandible reconstruction have to be placed critically. Future studies will focus on clinical complications of polylactide-based plates in risk patients.

Motion estimation and correction in cardiac CT angiography images using convolutional neural networks.

Cardiac motion artifacts frequently reduce the interpretability of coronary computed tomography angiography (CCTA) images and potentially lead to misinterpretations or preclude the diagnosis of coronary artery disease (CAD). In this paper, a novel motion compensation approach dealing with Coronary Motion estimation by Patch Analysis in CT data (CoMPACT) is presented. First, the required data for supervised learning is generated by the Coronary Motion Forward Artifact model for CT data (CoMoFACT) which introduces simulated motion to 19 artifact-free clinical CT cases with step-and-shoot acquisition protocol. Second, convolutional neural networks (CNNs) are trained to estimate underlying 2D motion vectors from 2.5D image patches based on the coronary artifact appearance. In a phantom study with computer-simulated vessels, CNNs predict the motion direction and the motion magnitude with average test accuracies of 13.37°±1.21° and 0.77 ±â€¯0.09 mm, respectively. On clinical data with simulated motion, average test accuracies of 34.85°±2.09° and 1.86 ±â€¯0.11 mm are achieved, whereby the precision of the motion direction prediction increases with the motion magnitude. The trained CNNs are integrated into an iterative motion compensation pipeline which includes distance-weighted motion vector extrapolation. Alternating motion estimation and compensation in twelve clinical cases with real cardiac motion artifacts leads to significantly reduced artifact levels, especially in image data with severe artifacts. In four observer studies, mean artifact levels of 3.08 ±â€¯0.24 without MC and 2.28 ±â€¯0.29 with CoMPACT MC are rated in a five point Likert scale.

A calcar collar is protective against early periprosthetic femoral fracture around cementless femoral components in primary total hip arthroplasty: a registry study with biomechanical validation.

AIMS: The aim of this study was to estimate the 90-day risk of revision for periprosthetic femoral fracture associated with design features of cementless femoral stems, and to investigate the effect of a collar on this risk using a biomechanical in vitro model. MATERIALS AND METHODS: A total of 337 647 primary total hip arthroplasties (THAs) from the United Kingdom National Joint Registry (NJR) were included in a multivariable survival and regression analysis to identify the adjusted hazard of revision for periprosthetic fracture following primary THA using a cementless stem. The effect of a collar in cementless THA on this risk was evaluated in an in vitro model using paired fresh frozen cadaveric femora. RESULTS: The prevalence of early revision for periprosthetic fracture was 0.34% (1180/337 647) and 44.0% (520/1180) occurred within 90 days of surgery. Implant risk factors included: collarless stem, non-grit-blasted finish, and triple-tapered design. In the in vitro model, a medial calcar collar consistently improved the stability and resistance to fracture. CONCLUSION: Analysis of features of stem design in registry data is a useful method of identifying implant characteristics that affect the risk of early periprosthetic fracture around a cementless femoral stem. A collar on the calcar reduced the risk of an early periprosthetic fracture and this was confirmed by biomechanical testing. This approach may be useful in the analysis of other uncommon modes of failure after THA. Cite this article: Bone Joint J 2019;101-B:779-786.

[Total hip arthroplasty in young patients : Bearings and custom-made prostheses]. / Hüftendoprothetik beim jungen Patienten : Gleitpaarungen und Individualendoprothesen.

BACKGROUND: Carefully and correctly implanted components are the prerequisite for the lifespan of a prosthesis. Whether higher levels of activity lead to prior failure of total hip arthroplasty in young patients is controversially discussed. The right choice of bearings is still of great relevance. BEARINGS: Ceramic-on-ceramic as well as polyethylene-on-ceramic bearings achieve comparable results, although ceramic-on-ceramic bearings should be avoided in patients with high demands on their range of motion. Polyethylene-on-metal bearings also show good clinical results, if corrosion between head and stem is absent. Metal-on-metal bearings lead to adverse systemic effects due to metal wear and should be implanted in individual cases only, e. g. as hip resurfacing. Alternative bearings have to give proof of effectivity first. Custom-made prostheses constitute an option for young patients with special conditions of hip anatomy. Planning and study results of these prostheses are elucidated in this review article.

Motion artifact recognition and quantification in coronary CT angiography using convolutional neural networks.

Excellent image quality is a primary prerequisite for diagnostic non-invasive coronary CT angiography. Artifacts due to cardiac motion may interfere with detection and diagnosis of coronary artery disease and render subsequent treatment decisions more difficult. We propose deep-learning-based measures for coronary motion artifact recognition and quantification in order to assess the diagnostic reliability and image quality of coronary CT angiography images. More specifically, the application, steering and evaluation of motion compensation algorithms can be triggered by these measures. A Coronary Motion Forward Artifact model for CT data (CoMoFACT) is developed and applied to clinical cases with excellent image quality to introduce motion artifacts using simulated motion vector fields. The data required for supervised learning is generated by the CoMoFACT from 17 prospectively ECG-triggered clinical cases with controlled motion levels on a scale of 0-10. Convolutional neural networks achieve an accuracy of 93.3% ±â€¯1.8% for the classification task of separating motion-free from motion-perturbed coronary cross-sectional image patches. The target motion level is predicted by a corresponding regression network with a mean absolute error of 1.12 ±â€¯0.07. Transferability and generalization capabilities are demonstrated by motion artifact measurements on eight additional CCTA cases with real motion artifacts.

Maximizing the fixation strength of modular components by impaction without tissue damage.

OBJECTIVES: 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. METHODS: A commercially available impaction tool was modified to assemble components in the laboratory using impactor tips with varying stiffness at different applied energy levels. Springs were mounted below the modular components to represent the patient. The pull-off force of the head from the stem was measured to assess stability, and the displacement of the springs was measured to assess the force transmitted to the patient's tissues. RESULTS: The pull-off force of the head increased as the stiffness of the impactor tip increased but without increasing the force transmitted through the springs (patient). Increasing the impaction energy increased the pull-off force but also increased the force transmitted through the springs. CONCLUSIONS: To limit wear and corrosion, manufacturers should maximize the stiffness of the impactor tool but without damaging the surface of the head. This strategy will maximize the stability of the head on the stem for a given applied energy, without influencing the force transmitted through the patient's tissues. Current impactor designs already appear to approach this limit. Increasing the applied energy (which is dependent on the mass of the hammer and square of the contact speed) increases the stability of the modular connection but proportionally increases the force transmitted through the patient's tissues, as well as to the surface of the head, and should be restricted to safe levels.Cite this article: A. Krull, M. M. Morlock, N. E. Bishop. Maximizing the fixation strength of modular components by impaction without tissue damage. Bone Joint Res 2018;7:196-204. DOI: 10.1302/2046-3758.72.BJR-2017-0078.R2.

In vitro surface characteristics and impurity analysis of five different commercially available dental zirconia implants.

BACKGROUND: The aim of this study was to assess surface characteristics, element composition, and surface roughness of five different commercially available dental zirconia implants. Five zirconia implants (Bredent whiteSKY™ (I1), Straumann® PURE Ceramic (I2), ceramic.implant vitaclinical (I3), Zeramex® (I4), Ceralog Monobloc M10 (I5)) were evaluated. METHODS: The evaluation was performed by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and confocal laser scanning microscopy (CLSM). RESULTS: The semi-quantitative element composition showed no significant impurity of any implant tested. Both the machined and the rough areas of the investigated implants were predominated by zirconium, oxygen, and carbon. Roughness values (Sa) showed highest values for I2 and I5. CONCLUSIONS: The investigated zirconia implants showed surface characteristics and roughness values close to those of conventionally produced titanium implants, making them a promising alternative. However, zirconia implants have yet to prove themselves in clinical practice and clinical controlled trials.

Factors influencing taper failure of modular revision hip stems.

Stem 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.

[Endoprostheses in the elderly : Biomaterials, implant selection and fixation technique]. / Endoprothetik des älteren Menschen : Biomaterialien, Implantatwahl, Verankerungstechnik.

The replacement of hip and knee joints is one of the greatest success stories in orthopedics. Due to continuous improvement of biomaterials and implant design, patient-associated problems are now mostly multifactorial and only rarely caused by the implant. Abrasion was significantly reduced by the introduction of highly cross-linked polyethylene (PE), antioxidant stabilized PE, new ceramics and the development of ceramic and protective surfaces. It is assumed that further reduction of frictional resistance will not lead to a significantly better clinical result: however, the problem of periprosthetic infections and implant-related incompatibility is still unsolved and remains challenging for biomaterial research. For the knee joint PE will be irreplaceable for joint articulation even in the future due to the contact situation. Mobile bearings and fixed bearings are two established successful philosophies, which have shown comparably good clinical results. For the hip joint, it is forecasted that ceramic-on-ceramic will be the system of the future if the correct positioning and mounting of the components can be solved so that the problems, such as development of noise and breakage can be reduced to a minimum. An in-depth understanding and detailed knowledge of the biomaterials by the surgeon can prevent implant-related problems. For elderly patients it is assumed that the economic burden on the public healthcare system will have the strongest impact on implant selection.

Clinical and Wear Analyses of 9 Large Metal-on-Metal Total Hip Prostheses.

BACKGROUND: Metal-on-Metal (MoM) total hip arthroplasties (THA) are associated with pseudotumor formation and high revision rates. This prospective study analysed the clinical and wear analyses of 9 large Metal-on-Metal (MoM) total hip arthroplasties (THA) to understand the underlying mechanisms of failure. The MoM bearings were revised for multiple reasons; the main reason was pseudotumor formation. MATERIALS AND METHODS: From 2006 till 2010 the Reinier de Graaf Hospital implanted 160 large head M2a-Magnum™ (Biomet Inc. Warsaw, Indiana, USA) THAs in 150 patients. The first year, 9 bearings were revised and analysed at the Biomechanics Section, Hamburg University of Technology, Germany. We performed clinical (Harris Hip Score, radiographic analysis, blood cobalt and chromium) and wear analysis (implant, tissue and fluid) of the 9 bearings. Since this study did not fall under the scope of the Medical Research Involving Human Subjects Act in The Netherlands, no ethical approval was necessary. In this prospective study all patient details were anonymized by the corresponding author, all other authors were blinded during the research and wear analyses. Patients with bilateral MoM implants were excluded. RESULTS: The 9 bearings had a median (IQR) survival of 41.0 (25) months in situ. From these bearings, three showed no noticeable wear. The median (IQR) head wear volume was 3.2 (3.6) mm3 and maximum wear depth 0.02 (0.02) mm. For the cup the median (IQR) wear volume was 0.23 (0.3) mm3 with a maximum wear depth of 0.03 (0.05) mm. CONCLUSION: An early identification of parameters related to failure of the MoM THA, such as pain, decreased range of motion, radiographic changes and high levels of blood cobalt and chromium is of great importance for patient's quality of life. Especially now patients and surgeons face the long term effects of all these bearings still in situ. This study reports the clinical and wear analyses of 9 MoM THA. In the majority of this group the reason for revision was pseudotumor formation. Most bearings showed signs of wear, however with a great diversity in clinical analysis, in inclination angle, serum cobalt and chromium levels as well as wear analysis. For a better understanding of the underlying mechanisms related with failure, more wear analyses of revised MoM bearings are necessary as well as a frequent follow-up of the patients with a MoM bearing.

Cement augmentation versus extended dorsal instrumentation in the treatment of osteoporotic vertebral fractures: a biomechanical comparison.

AIMS: Loosening of pedicle screws is a major complication of posterior spinal stabilisation, especially in the osteoporotic spine. Our aim was to evaluate the effect of cement augmentation compared with extended dorsal instrumentation on the stability of posterior spinal fixation. MATERIALS AND METHODS: A total of 12 osteoporotic human cadaveric spines (T11-L3) were randomised by bone mineral density into two groups and instrumented with pedicle screws: group I (SHORT) separated T12 or L2 and group II (EXTENDED) specimen consisting of T11/12 to L2/3. Screws were augmented with cement unilaterally in each vertebra. Fatigue testing was performed using a cranial-caudal sinusoidal, cyclic (1.0 Hz) load with stepwise increasing peak force. RESULTS: Augmentation showed no significant increase in the mean cycles to failure and fatigue force (SHORT p = 0.067; EXTENDED p = 0.239). Extending the instrumentation resulted in a significantly increased number of cycles to failure and a significantly higher fatigue force compared with the SHORT instrumentation (EXTENDED non-augmented + 76%, p < 0.001; EXTENDED augmented + 87%, p < 0.001). CONCLUSION: The stabilising effect of cement augmentation of pedicle screws might not be as beneficial as expected from biomechanical pull-out tests. Lengthening the dorsal instrumentation results in a much higher increase of stability during fatigue testing in the osteoporotic spine compared with cement augmentation. Cite this article: Bone Joint J 2016;98-B:1099-1105.

Effects of insulin therapy on porosity, non-enzymatic glycation and mechanical competence in the bone of rats with type 2 diabetes mellitus.

Type 2 diabetes mellitus increases skeletal fragility; however, the contributing mechanisms and optimal treatment strategies remain unclear. We studied the effects of diabetes and insulin therapy on non-enzymatic glycation (NEG), cortical porosity (Ct.Po) and biomechanics of the bone tissue in Zucker Diabetic Fatty (ZDF) rats. Eleven-week old ZDF diabetic and non-diabetic rats were given insulin to achieve glycaemic control or vehicle seven days per week over twelve weeks (insulin dose adapted individually 0.5 international units (IU) at week 1 to 13.0IU at week 12). The right femora were excised, micro-CT scanned, and tested in 3-point bending to measure biomechanics. NEG of the midshaft was determined from bulk fluorescence. Diabetes led to increased NEG (+50.1%, p=0.001) and Ct.Po (+22.9%, p=0.004), as well as to reduced mechanical competence (max. stress: -14.2%, p=0.041, toughness: -29.7%, p=0.016) in the bone tissue. NEG and Ct.Po both correlated positively to serum glucose (NEG: R(2)=0.41, p<0.001, Ct.Po: R(2)=0.34, p=0.003) and HbA1c (NEG: R(2)=0.42, p<0.001, Ct.Po: R(2)=0.28, p=0.008) levels, while NEG correlated negatively with bone biomechanics (elastic modulus: R(2)=0.21, p=0.023, yield stress: R(2)=0.17, p=0.047). Twelve weeks of insulin therapy had no significant effect on NEG or Ct.Po, and was unable to improve the mechanical competence of the bone tissue. A reduction of mechanical competence was observed in the bone tissue of the diabetic rats, which was explained in part by increased collagen NEG. Twelve weeks of insulin therapy did not alter NEG, Ct.Po or bone biomechanics. However, significant correlations between NEG and serum glucose and HbA1c were observed, both of which were reduced with insulin therapy. This suggests that a longer duration of insulin therapy may be required to reduce the NEG of the bone collagen and restore the mechanical competence of diabetic bone.

Effects of parathyroid hormone on cortical porosity, non-enzymatic glycation and bone tissue mechanics in rats with type 2 diabetes mellitus.

Type 2 diabetes mellitus increases skeletal fragility; however, the contributing mechanisms and the efficacy of bone-forming agents are unclear. We studied diabetes and parathyroid hormone (PTH) treatment effects on cortical porosity (Ct.Po), non-enzymatic glycation (NEG) and bone mechanics in Zucker diabetic fatty (ZDF) rats. Eleven-week old ZDF diabetic (DB) and non-diabetic (ND) rats were given 75µg/kg PTH (1-84) or vehicle 5days per week over 12weeks. The right femora and L4 vertebrae were excised, micro-CT scanned, and tested in 3-point bending and uniaxial compression, respectively. NEG of the samples was determined using fluorescence. Diabetes increased Ct.Po (vertebra (vert): +40.6%, femur (fem): +15.5% vs. ND group, p<0.05) but had no effect on NEG. PTH therapy reduced vertebral NEG in the ND animals only (-73% vs untreated group, p<0.05), and increased femoral NEG in the DB vs. ND groups (+63%, p<0.05). PTH therapy had no effect on Ct.Po. Diabetes negatively affected bone tissue mechanics where reductions in vertebral maximum strain (-22%) and toughness (-42%) were observed in the DB vs. ND group (p<0.05). PTH improved maximum strain in the vertebra of the ND animals (+21%, p<0.05) but did not have an effect in the DB group. PTH increased femoral maximum strain (+21%) and toughness (+28%) in ND and decreased femoral maximum stress (-13%) and toughness (-27%) in the DB animals (treated vs. untreated, p<0.05). Ct.Po correlated negatively with maximum stress (fem: R=-0.35, p<0.05, vert: R=-0.57, p<0.01), maximum strain (fem: R=-0.35, p<0.05, vert: R=-0.43, p<0.05) and toughness (fem: R=-0.34, p<0.05, vert: R=-0.55, p<0.01), and NEG correlated negatively with toughness at the femur (R=-0.34, p<0.05) and maximum strain at the vertebra (R=-0.49, p<0.05). Diabetes increased cortical porosity and reduced bone mechanics, which were not improved with PTH treatment. PTH therapy alone may worsen diabetic bone mechanics through formation of new bone with high AGEs cross-linking. Optimal treatment regimens must address both improvements of bone mass and glycemic control in order to successfully reduce diabetic bone fragility. This article is part of a Special Issue entitled "Bone and diabetes".

Quantification of material loss from the neck piece taper junctions of a bimodular primary hip prosthesis. A retrieval study from 27 failed Rejuvenate bimodular hip arthroplasties.

The early failure and revision of bimodular primary total hip arthroplasty prostheses requires the identification of the risk factors for material loss and wear at the taper junctions through taper wear analysis. Deviations in taper geometries between revised and pristine modular neck tapers were determined using high resolution tactile measurements. A new algorithm was developed and validated to allow the quantitative analysis of material loss, complementing the standard visual inspection currently used. The algorithm was applied to a sample of 27 retrievals (in situ from 2.9 to 38.1 months) of the withdrawn Rejuvenate modular prosthesis. The mean wear volumes on the flat distal neck piece taper was 3.35 mm(3) (0.55 to 7.57), mainly occurring in a characteristic pattern in areas with high mechanical loading. Wear volume tended to increase with time to revision (r² = 0.423, p = 0.001). Implant and patient specific data (offset, stem size, patient's mass, age and body mass index) did not correlate with the amount of material loss observed (p > 0.078). Bilaterally revised implants showed higher amounts of combined total material loss and similar wear patterns on both sides. The consistent wear pattern found in this study has not been reported previously, suggesting that the device design and materials are associated with the failure of this prosthesis.