Modelling of longitudinally cut carrot curling induced by the vascular cylinder-cortex interference pressure.

Cut carrot pieces are popular convenience foods, which enable the use of misshapen or physiologically imperfect produce. Cut carrots curl due to residual stress, which limits their shelf life and causes unnecessary food waste. The aim of this study is to identify the geometrical and environmental factors which have the most influence on their longevity. An analytical equation was developed using compound cylinder solutions, and this was used to define carrot-specific finite element (FE) models. Over 100 longitudinally cut Lancashire Nantes carrot halves were characterized, each was modelled analytically and verified using FE models. This model was evaluated by comparing predicted curvatures to ones experimentally measured over a week. The average radius of curvature decreased from 1.61 to 1.1 m a week after. A 1.32× reduction in the elastic modulus after 7 days was observed. The moisture content reduction relates to 22% weight loss, correlating to the decreasing radius of curvature. Subsequently, carrots are recommended to be stored in humidity-controlled environments. The experimental results from this study match the predictions made using mechanical principles. The research provides a methodology to predict the deformation of cut root vegetables, and the procedure is likely to be applicable to other plant structures.

Clinically useful finite element models of the natural ankle - A review.

BACKGROUND: Biomechanical simulation of the foot and ankle complex is a growing research area but compared to simulation of joints such as hip and knee, it has been under investigated and lacks consistency in research methodology. The methodology is variable, data is heterogenous and there are no clear output criteria. Therefore, it is very difficult to correlate clinically and draw meaningful inferences. METHODS: The focus of this review is finite element simulation of the native ankle joint and we will explore: the different research questions asked, the model designs used, ways the model rigour has been ensured, the different output parameters of interest and the clinical impact and relevance of these studies. FINDINGS: The 72 published studies explored in this review demonstrate wide variability in approach. Many studies demonstrated a preference for simplicity when representing different tissues, with the majority using linear isotropic material properties to represent the bone, cartilage and ligaments; this allows the models to be complex in another way such as to include more bones or complex loading. Most studies were validated against experimental or in vivo data, but a large proportion (40%) of studies were not validated at all, which is an area of concern. INTERPRETATION: Finite element simulation of the ankle shows promise as a clinical tool for improving outcomes. Standardisation of model creation and standardisation of reporting would increase trust, and enable independent validation, through which successful clinical application of the research could be realised.

Chemical stability of oil-infused polyethylene.

Ultra-high molecular weight polyethylene (UHMWPE) can be made radiopaque for medical imaging applications through the diffusion of an iodised oil-based contrast agent (Lipiodol Ultra Fluid). A similar process is used for Vitamin E incorporated polyethylene which provides antioxidant properties. This study aimed to investigate the critical long-term properties of oil-infused medical polyethylene after 4 weeks of accelerated thermal ageing. Samples treated with an oil (Vitamin E or Lipiodol) had a higher oxidation stability than currently used medical grade polyethylene, indicated by a smaller increase in oxidation index after ageing (Vitamin E + 36%, Lipiodol +40%, Untreated +136%, Thermally treated +164%). The tensile properties of oil treated polyethylene after ageing were significantly higher than the Untreated and Thermally treated controls (p<0.05) indicating less mechanical degradation. There was also no alteration in the percentage crystallinity of oil treated samples after ageing, though the radiopacity of the Lipiodol treated samples reduced by 54% after ageing. The leaching of oil with time was also investigated; the leaching of Lipiodol and Vitamin E followed the same trend and reached a steady state by two weeks. Overall, it can be concluded that the diffusion of an oil-based fluid into polyethylene not only increases the oxidative and chemical stability of polyethylene but also adds additional functionality (e.g. radiopacity) providing a more suitable material for long-term medical applications.

Characterisation of the physical, chemical and mechanical properties of a radiopaque polyethylene.

Ultra-high molecular weight polyethylene has a low X-ray attenuation, hence, the performance of the polyethylene implants used for joint replacements cannot be directly investigated using X-ray-based imaging techniques. In this study, the X-ray attenuation of polyethylene was increased by diffusing an FDA-approved oil-based contrast agent (Lipiodol ultra fluid) into the surface of the samples, and the suitability of this novel radiopaque ultra-high molecular weight polyethylene for clinical applications was examined. Different levels of radiopacity were created by controlling the diffusion parameters, and the level of radiopacity was quantified from computed tomography scans and reported in Hounsfield units. The physical, chemical and tensile properties of the radiopaque ultra-high molecular weight polyethylene were examined and compared to untreated and thermally treated controls. The results of this study confirmed that for the samples treated at 115°C or less the diffusion of the contrast agent did not significantly alter the crystallinity (p = 0.7) or melting point (p = 0.4) of the polyethylene. Concomitantly, the tensile properties were not significantly different from the control samples (p > 0.05 for all properties). In conclusion, the radiopaque ultra-high molecular weight polyethylene treated for less than 18 h at a temperature of 115°C or below is a promising candidate for joint replacement applications as it can be identified in a standard X-ray while retaining the tensile properties of clinically used radiolucent ultra-high molecular weight polyethylene.

Minimising tibial fracture after unicompartmental knee replacement: A probabilistic finite element study.

BACKGROUND: Periprosthetic tibial fracture after unicompartmental knee replacement is a challenging post-operative complication. Patients have an increased risk of mortality after fracture, the majority undergo further surgery, and the revision operations are less successful. Inappropriate surgical technique increases the risk of fracture, but it is unclear which technical aspects of the surgery are most problematic and no research has been performed on how surgical factors interact. METHODS: Firstly, this study quantified the typical variance in surgical cuts made during unicompartmental knee replacement (determined from bones prepared by surgeons during an instructional course). Secondly, these measured distributions were used to create a probabilistic finite element model of the tibia after replacement. A thousand finite element models were created using the Monte Carlo method, representing 1000 virtual operations, and the risk of tibial fracture was assessed. FINDINGS: Multivariate linear regression of the results showed that excessive resection depth and making the vertical cut too deep posteriorly increased the risk of fracture. These two parameters also had high variability in the prepared synthetic bones. The regression equation calculated the risk of fracture from three cut parameters (resection depth, vertical and horizonal posterior cuts) and fit the model results with 90% correlation. INTERPRETATION: This study introduces for the first time the application of a probabilistic approach to predict the aetiology of fracture after unicompartmental knee replacement, providing unique insight into the relative importance of surgical saw cut variations. Targeted changes to operative technique can now be considered to seek to reduce the risk of periprosthetic fracture.

High Variability of Acetabular Offset in Primary Hip Osteoarthritis Influences Acetabular Reaming-A Computed Tomography-Based Anatomic Study.

BACKGROUND: The objectives of the present study were to (1) evaluate the accuracy and reliability of native acetabular offset (AO) measurements performed on conventional supine anterior-posterior (ap) pelvis radiographs with reference to computed tomography (CT) in patients with end-stage hip osteoarthritis (OA); (2) determine the minimum and maximum amount of medialization of the center of rotation (COR) simulating different reaming techniques; and (3) identify patients at increased risk of excessive medialization of the COR. METHODS: A consecutive series of corresponding 131 CT scans and radiographs of patients with primary hip OA was evaluated using validated software for three-dimensional acetabular and femoral measurements. We simulated the implantation of a hemispherical press-fit cup comparing anatomic and conventional reaming techniques and assessed corresponding changes in AO. RESULTS: Standardized ap pelvis radiographs allowed for an accurate and reliable assessment of AO compared with CT. Cup placement in the most lateral position (anatomic reaming technique) resulted in a mean implant-related medialization of 5.9 ± 3.4 mm. Anatomic cup placement did not require reaming to the true floor in 64 hips (49%). With the conventional reaming technique, the total medialization of the COR (implant-related and reaming-related) was 6.8 ± 2.9, with 34% of cases having a medialization ≥8 mm. CONCLUSION: The present study highlights the variability of acetabular anatomy in patients with primary OA. AO can be accurately and reliably determined on conventional radiographs and appears to be independent of femoral shape and geometry. Depending on the preferred reaming technique a substantial number of patients appear at risk for excessive cup medialization.

Posterior Bearing Overhang Following Medial and Lateral Mobile Bearing Unicompartmental Knee Replacements.

This study explores the extent of bearing overhang following mobile bearing Oxford unicompartmental knee replacement (OUKR) (Oxford Phase 3, Zimmer Biomet). The Oxford components are designed to be fully congruent, however knee movements involve femoral rollback, which may result in bearing overhang at the posterior margin of the tibial implant, with potential implications for; pain, wear, and dislocation. Movement is known to be greater, and therefore posterior overhang more likely to occur, with; lateral compared to medial implants, anterior cruciate ligament (ACL) deficiency (ACLD) compared to ACL intact (ALCI), and at extremes of movement. Twenty-four medial, and 20 domed lateral, OUKRs underwent sagittal plane knee fluoroscopy during step-up and forward lunge exercises. The bearing position was inferred from the relative position of the femoral and tibial components. On the basis of the individual component sizes and geometry the extent the posterior part of the bearing which overhung the posterior part of the tibial component was calculated. There was no significant posterior overhang in knees with medial implants. Knees with lateral domed implants exhibited overhang at flexion angles beyond 60°, the magnitude of which increased with increasing flexion angle, reaching a maximum of 50% of the bearing length at 140° (range 0-140°). This demonstrates a clear difference between the kinematics, and prevalence and extent of posterior bearing overhang between medial and lateral OUKRs. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1938-1945, 2019.

Reduced Bearing Excursion After Mobile-Bearing Unicompartmental Knee Arthroplasty is Associated With Poor Functional Outcomes.

BACKGROUND: A small proportion of patients with mobile unicompartmental knee arthroplasty (UKA) report poor functional outcomes in spite of optimal component alignment on postoperative radiographs. The purpose of this study is to assess whether there is a correlation between functional outcome and knee kinematics. METHODS: From a cohort of consecutive cases of 150 Oxford medial UKA, patients with fair/poor functional outcome at 1-year postsurgery (Oxford Knee Score [OKS] < 34, n = 15) were identified and matched for age, gender, preoperative clinical scores, and follow-up period with a cohort of patients with good/excellent outcome (OKS ≥ 34, n = 15). In vivo kinematic assessment was performed using step-up and deep knee bend exercises under fluoroscopic imaging. The fluoroscopic videos were analyzed using MATLAB software to measure the variation in time taken to complete the exercises, patellar tendon angle, and bearing position with knee flexion angle. RESULTS: Mean OKS in the fair/poor group was 29.9 and the mean OKS in the good/excellent group was 41.1. The tibial slope, time taken to complete the exercises, and patellar tendon angle trend over the flexion range were similar in both the groups; however, bearing position and the extent of bearing excursion differed significantly. The total bearing excursion in the OKS < 34 group was significantly smaller than the OKS ≥ 34 group (35%). Furthermore, on average, the bearing was positioned 1.7 mm more posterior on the tibia in the OKS < 34 group. CONCLUSION: This study provides evidence that abnormal knee kinematics, in particular bearing excursion and positioning, are associated with worse functional outcomes after mobile UKA.

An open source software tool to assign the material properties of bone for ABAQUS finite element simulations.

A new software tool to assign the material properties of bone to an ABAQUS finite element mesh was created and compared with Bonemat, a similar tool originally designed to work with Ansys finite element models. Our software tool (py_bonemat_abaqus) was written in Python, which is the chosen scripting language for ABAQUS. The purpose of this study was to compare the software packages in terms of the material assignment calculation and processing speed. Three element types were compared (linear hexahedral (C3D8), linear tetrahedral (C3D4) and quadratic tetrahedral elements (C3D10)), both individually and as part of a mesh. Comparisons were made using a CT scan of a hemi-pelvis as a test case. A small difference, of -0.05kPa on average, was found between Bonemat version 3.1 (the current version) and our Python package. Errors were found in the previous release of Bonemat (version 3.0 downloaded from www.biomedtown.org) during calculation of the quadratic tetrahedron Jacobian, and conversion of the apparent density to modulus when integrating over the Young׳s modulus field. These issues caused up to 2GPa error in the modulus assignment. For these reasons, we recommend users upgrade to the most recent release of Bonemat. Processing speeds were assessed for the three different element types. Our Python package took significantly longer (110s on average) to perform the calculations compared with the Bonemat software (10s). Nevertheless, the workflow advantages of the package and added functionality makes 'py_bonemat_abaqus' a useful tool for ABAQUS users.

Sagittal kinematics of mobile unicompartmental knee replacement in anterior cruciate ligament deficient knees.

BACKGROUND: There is a greater risk of tibial component loosening when mobile unicompartmental knee replacement is performed in anterior cruciate ligament deficient knees. We previously reported on a cohort of anterior cruciate ligament deficient patients (n=46) who had undergone surgery, but no difference was found in implant survivorship at a mean 5-year follow-up. The purpose of this study was to examine the kinematic behaviour of a subcohort of these patients. METHODS: The kinematic behaviour of anterior cruciate deficient knees (n=16) after mobile unicompartmental knee replacement was compared to matched intact knees (n=16). Sagittal plane knee fluoroscopy was taken while patients performed step-up and forward lunge exercises. The patellar tendon angle, knee flexion angle and implant position was calculated for each video frame. FINDINGS: The patellar tendon angle was 5° lower in the deficient group, indicating greater anterior tibial translation compared to the intact group between 30 and 40° of flexion. Large variability, particularly from 40-60° of flexion, was observed in the bearing position of the deficient group, which may represent different coping mechanisms. The deficient group took 38% longer to perform the exercises. INTERPRETATION: Kinematic differences were found between the deficient and intact knees after mobile unicompartmental knee replacement; but these kinematic changes do not seem to affect the medium-term clinical outcome. Whether these altered knee kinematics will have a clinical impact is as yet undetermined, but more long-term outcome data is required before mobile unicompartmental knee replacement can be recommended for an anterior cruciate ligament deficient patient.

Topographical and chemical effects of electrochemically assisted deposited hydroxyapatite coatings on osteoblast-like cells.

A recently commercialised hydroxyapatite electrochemically assisted chemical deposition technique (BoneMaster) has been shown to induce increased bone apposition; whether this response is caused by the surface topography or chemistry is unknown. An in-vitro examination using human osteoblast-like cells was performed on a series of BoneMaster-coated surfaces. The chemistry was separated from the topography using a thin gold coating; Thermanox coverslips were used as a control. BoneMaster surfaces showed significantly greater alkaline phosphatase activity and osteocalcin production compared with controls; however, no difference was found between the gold-coated and uncoated BoneMaster samples, indicating topography is the main contributing factor.

Fracture of mobile unicompartmental knee bearings: a parametric finite element study.

Cases of fractured mobile unicompartmental knee bearings have recently been reported. The purpose of this study was to understand the mechanics behind these fractures and to examine the influence of different design modifications. A parametric finite element model was used to examine the influence of different geometrical factors on the stresses within the bearing. Crack initiation occurred clinically in the centre of the bearing; this correlated with the position of the maximum von Mises stress. Tensile stresses, thought to propagate the fatigue crack, were maximal at the medial-lateral sides of the bearing, and the tensile vectors were normal to the fracture direction observed clinically. Fully congruent femoral articulation on the bearing, use of a thicker bearing size, and minimising wear of the component reduced the risk of fracture. For example, an unworn 6.5-mm-thick bearing (no clinical fractures reported) had 21.6% lower medial-lateral tensile stress compared to an unworn 3.5 mm bearing (five clinical fractures reported). In turn, an unworn 3.5 mm bearing had 34.3% lower tensile stress compared to a 3.5 mm bearing after 1.9 mm wear (average linear wear reported for clinically fractured bearings). The fracture risk was also reduced when the radio-opaque marker wire was positioned further from the centre of the bearing, and when marker balls were used instead of marker wires (19% reduction in tensile stress in some regions). These results indicate the importance of minimising component wear; the data also support the current component design which uses posterior marker balls instead of marker wires, and the continuing use of a congruous femoral component.

Individual motion patterns during gait and sit-to-stand contribute to edge-loading risk in metal-on-metal hip resurfacing.

The occurrence of pseudotumours (soft tissue masses relating to the hip joint) following metal-on-metal hip resurfacing arthroplasty has been associated with higher than normal bearing wear and high serum metal ion levels although both these findings do not necessarily coexist. The purpose of this study was to examine patient activity patterns and their influence on acetabular component edge loading in a group of subjects with known serum metal ion levels. Fifteen subjects with metal-on-metal hip resurfacing arthroplasty (eight males and seven females) were recruited for motion analysis followed by computed tomography scans. They were divided into three groups based on their serum metal ion levels and the orientation of their acetabular component: well-positioned acetabular component with low metal ions, mal-positioned acetabular component with low metal ions and mal-positioned acetabular component with high ions. A combination of motion analysis, subject-specific modelling (AnyBody Modeling System, Aalborg, Denmark) and computed tomography measurements was used to calculate dynamically the contact patch-to-rim distance for each subject during gait and sit-to-stand. The contact-pitch-to-rim distance for the high ion group was significantly lower (p<0.001) than for the two low ion groups (well-positioned and mal-positioned) during the stance phase of gait (0%-60%) and loading phase of sit-to-stand (20%-80%). The results of this study, in particular, the significant difference between the two mal-positioned groups, suggest that wear of metal-on-metal hip resurfacing arthroplasty is not only affected by acetabular cup orientation but also influenced by individual patient activity patterns.

Knee replacement for osteoarthritis.

Knee replacement is one of the commonest surgical procedures performed in older adults, and its incidence is increasing rapidly. It is the only curative procedure for knee osteoarthritis, and it has excellent outcomes overall in terms of reoperation, functional outcomes and cost-effectiveness. However, a significant proportion of patients are dissatisfied after knee replacement surgery and there is a growing body of research into predictors of poor outcome and dissatisfaction.In this review, we discuss the place of total knee replacement (TKR) in the management of osteoarthritis, together with operative and non-operative alternatives to TKR. We discuss the different ways in which outcome can be measured, and the influence of patient and surgical factors on the success or failure of knee replacement surgery.

Evaluation of factors affecting tibial bone strain after unicompartmental knee replacement.

Persistent pain is an important cause of patient dissatisfaction after unicompartmental knee replacement (UKR) and has been correlated with localized tibial strain. However, the factors that influence these strains are not well understood. To address this issue, we created finite element models to examine the effect on tibial strain of: (1) muscle forces (estimated using instrumented knee data) acting on attachment sites on the proximal tibia, (2) UKR implantation, (3) loading position, and (4) changes in gait pattern. Muscle forces acting on the tibia had no significant influence on strains within the periprosthetic region, but UKR implantation increased strain by 20%. Strain also significantly increased if the region of load application was moved >3 mm medially. The strain within the periprosthetic region was found to be dependent on gait pattern and was influenced by both medial and lateral loads, with the medial load having a greater effect (regression coefficients: medial = 0.74, lateral = 0.30). These findings suggest that tibial strain is increased after UKR and may be a cause of pain. It may be possible to reduce pain through modification of surgical factors or through altered gait patterns.

Mono-functional aminosilanes as primers for peptide functionalization.

When covalently attaching biomolecules to surfaces such as titanium, trifunctional silanes are commonly used as primers to produce surface amine groups. However, these primed surfaces are rarely uniform in structure due to networking of the silane. Mono-functional aminosilanes may result in more uniform structures, although their long-term stability and effect on osteoblast cell responses are possible issues for orthopedic applications. This study examines for the first time the optimization of peptide coupling to titanium using mono-functional aminosilane reaction chemistry. The resultant surface topography, chemistry, and thicknesses were characterized showing improved surface uniformity compared with trifunctional silanized surfaces. The stability of the coatings was examined over a period of 8 days in environments of varying pH, temperature, and humidity. In addition, human osteosarcoma (HOS) cell adhesion and spreading on the samples was examined; adhesion was minimal on silanized surfaces, but after functionalization with cysteine the cell density was greater than the titanium control and showed no overall detrimental effect on initial cell responses.