While 3D metal printing is extensively employed for fabricating honeycomb structures, the evaluation of their printing quality and defects remains challenging due to technical limitations. This work aims to investigate the influence of printing defects, honeycomb geometries, and printing orientations on the compressive mechanical properties of laser powder bed fusion (L–PBF) Ti-6Al-4V cylinders. Honeycomb cylindrical samples were fabricated with the size of Ø5 mm × 10 mm. X-ray microcomputed tomography (micro-CT) was employed to study geometric formation accuracy and printing defects. The printed honeycomb cylinders were then subject to compression testing, and fractured cylinders were rescanned by micro-CT to study the compression-induced failure behaviors. The findings demonstrated that printed Ti-6Al-4V honeycomb cylinders exhibited varying build quality, porosity, dimensional inconsistency, and partially melted or unmelted powder particles. The vertically printed honeycomb cylinder exhibited higher geometry accuracy than the horizontally printed honeycomb cylinder. The designed honeycomb structures and printing orientations had a significant influence on the nominal modulus. Both the vertical and horizontal printing honeycomb cylinders exhibited compression-induced shear failure. This work describes a micro-CT examination technique for investigating the structural integrity and mechanical failures of 3D metal-printed honeycomb structures.

BACKGROUND:Cone-beam computed tomography with multi-source arrays and curved-panel detectors in stationary or semi-stationary configurations (sCBCT) has shown promise for compact, point-of-care imaging systems. Such geometries are subject to high-magnitude, x-ray scatter with complex spatial structure, and variation between source elements. This impedes the use of traditional projection-domain scatter estimators, while reconstruction artifacts hinder volume-based scatter estimators. PURPOSE:In this work, we propose adaptive deep scatter estimation (ADSE), an adaptive projection-domain scatter estimation technique tailored for sCBCT geometries. This technique is intended to overcome the limitations of projection- and volume-domain scatter estimators, which reduce their applicability in sCBCT configurations. METHODS:The scatter-contaminated projections from the sCBCT geometry are transformed into a view-invariant surrogate CBCT geometry. A projection-domain convolutional-neural network-based scatter estimator and scatter fluence weighting operator are applied iteratively, causing the output to converge toward accurate scatter estimates in the surrogate geometry. The final sCBCT scatter estimates are obtained by applying inverse fluence-weighting and re-transformation into the sCBCT geometry. ADSE was assessed in the projection-domain and image-domain via comparison with high-fidelity Monte Carlo (MC) simulations performed on in-silico test phantoms derived from high-quality CT scans of human heads. ADSE was compared to geometry-aware DSE approach trained directly on sCBCT data (gDSE), naïve projection-domain scatter estimation, non-iterative adaptive scatter estimation with a single fluence-weighting, and iterative Monte Carlo (iMC) scatter estimation. In the projection-domain, ADSE was evaluated via pixel value percentage error as a function of projection angle, and global mean absolute percentage error (MAPE). Residual scatter artifacts in the image domain were quantified as the voxelwise error compared to a scatter-free ground truth. A physical anthropomorphic head phantom was used for experimental validation on a sCBCT test bench integrating a curved-panel detector. Metrics included residual cupping, CT number non-uniformity, and recovery of contrast and contrast-to-noise-ratio (CNR) of thirteen embedded spherical inserts, with sizes ranging from 2 to 12 mm and nominal contrast ranging from -329 to 871 HU. RESULTS:In in-silico experiments, ADSE exhibited projection-domain scatter magnitude MAPE of 3.88% for nontruncated projections, compared to iMC (MAPE = 4.42%) and gDSE (MAPE = 5.13%). However, when including truncated projections, MAPE for ADSE increased to 5.18%, while iMC and gDSE remained relatively consistent at 4.32% and 5.26%, respectively. In physical phantom experiments, the embedded spheres in uncorrected reconstructions from the test bench exhibited 58.87% contrast loss and 84.44% CNR loss, compared to an MDCT ground truth. ADSE recovered 48.67% of contrast and 25.03% of CNR, compared to 45.87% and 16.91% using iMC (gDSE, 40.45% and 21.44%). The magnitude of cupping artifacts and CT number non-uniformity decreased by 79% and 71%, respectively, compared to 85% and 53% for iMC (gDSE 114% and 59%). CONCLUSIONS:We present ADSE, aiming to overcome the limitations of volume-domain and projection-domain scatter estimators that reduce their applicability in multisource sCBCT geometries with lateral truncation, angular under-sampling, and large geometrical variation between projection poses. In the presented studies, ADSE outperformed geometry-aware gDSE and volumetric iMC scatter estimation methods, resulting in reduced artifacts and improved image quality. The results illustrate the feasibility of performing scatter compensation in complex stationary CBCT geometries via a combination of conventional scatter estimation methods with geometrical warping operators tailored to the specific sCBCT geometry.

While 3D metal printing is widely used for making complex structures, the printing quality of internal structures and defects are difficult to assess due to technical challenges. This study used X-ray microcomputed tomography (micro-CT) to reveal geometrical accuracies, defects and mechanical failure of Ti-6Al-4V alloys printed by laser powder bed fusion. Ti-alloy cylinders of 10 mm height and 5 mm diameter containing either a circular or a square internal central hole of a cross-sectional area of 1 mm2, were printed horizontally and vertically. The printed metal structures were scanned using high-resolution (7 μm voxel size) micro-CT. The cylinders were then subjected to compression tests to evaluate their compressive mechanical properties, including Young’s modulus, ductility, compressive strength and yield strength. Fractured cylinders were re-scanned by micro-CT to investigate failure behaviors. The results show that all printed Ti-6Al-4V structures had imperfect quality with malforms, dimensional errors, porosities, and unconsolidated powder. Vertical printing achieved higher form and dimension accuracies than horizontal printing. Pore defects and unconsolidated powder concentrated within internal peripheries of printed cylinders. The Young’s moduli and strength were significantly affected by internal structures and defects, and printing directions. Vertically and horizontally printed cylinders with square internal holes exhibited a more ductile brittle fracture mode and suffered from compression-induced catastrophic shear failures compared to the ones with circular internal holes. This research provides a micro-CT detection technique which can be used for the quality assurance of hollow 3D-printed metal structures.

Purpose: Multi-source array (MXA) Computed Tomography systems pose challenges related to sampling and x-ray scatter. We present a semi-stationary head CT system and image formation pipeline including adaptive scatter estimation and image reconstruction based on learned diffusion models. Methods: The CT was evaluated on a robotic bench system including a miniaturized carbon-nanotube x-ray source and a curved-panel detector. Scatter correction was achieved with an Adaptive Deep Scatter Estimation (ADSE) method combining geometry-invariant projection-based scatter estimation with geometry-adaptive registration and scaling. Image reconstruction followed a Diffusion Posterior Sampling method (DPS-Recon) combining an unconditional diffusion model with measured data consistency. Image quality was assessed using anthropomorphic phantoms for a semi-stationary protocol involving a 21-source MXA rotated to three positions. Results: ADSE resulted in 118% mean increase in feature contrast accuracy, 1.75 to 13-fold improvement in CNR for variable contrast features (-337HU to 885HU), and 3.56-fold improvement in CNR for variable size features (2mm-12mm, 110HU) compared to uncorrected reconstructions. Non-uniformity reduced 50% for the three slices. DPS-Recon reduced limited sampling artifacts and improved visualization of soft-tissue structures, particularly in less densely sampled and bony anatomy locations, and further reduced non-uniformity by 20% in the superior brain location. Conclusion: We present first experimental results from a semi-stationary, multi-source CT utilizing CNT x-ray sources and curved-panel detector coupled to an imaging chain that addressed the main challenges inherent to the architecture. Metrics of CT number accuracy, image uniformity, and soft-tissue visualization showed promising performance for visualization of stroke radiological markers with the proposed approach.

Characterization of defects in large 3D printed metals is critical but challenging. This study reports on the X-ray micro-computed tomography (micro-CT) examination of porosities in large-volume 3D-printed and heat-treated titanium (Ti–6Al–4V) alloys, together with their tensile properties and failure mechanisms. Titanium alloy powders were analyzed using scanning electron microscopy (SEM). Laser powder bed fusion (L-PBF) was used to print titanium alloy specimens vertically and horizontally, followed by stress-relieved heat treatment. Micro-CT imaging was performed on printed specimens of 10 × 20 mm3 (diameter × length) to determine their porosities, pore locations and size distributions using an industrial micro-CT system and relevant imaging software. Tensile testing of the processed specimens was conducted to determine their mechanical properties. Optical microscopy and SEM were used to examine the tension-induced failure mechanisms. The results show that porosities, pore sizes and locations were influenced by the build direction, resulting in different mechanical properties. Horizontal printing achieved higher tensile modulus, strength, ductility, resilience and toughness than vertical printing. Heat treatment did not change porosities in horizontally built specimens, but slightly reduced porosities for vertically built ones by 10%. This led to most mechanical properties nearly unchanged for the horizontally printed specimens but remarkably increased yield and tensile strength, and resilience, for the vertically printed ones. All tension-induced fractured surfaces contained pores, possible indicators of failure origins, which should be diminished in advanced processes for higher mechanical reliability.

Background Reverse Shoulder Arthroplasties (RSA) have become a primary choice for improving shoulder function and pain. However, the biomechanical failure mechanism of the humeral component is still unclear. The present study reports a novel protocol for microstructural imaging of the entire humerus implant under load before and after fracture. Methods A humerus specimen was obtained from a 75-year-old male donor. An expert surgeon implanted the specimen with a commonly used RSA implant (Aequalis reversed II, Stryker Orthopaedics, USA) and surgical procedure. The physiological glenohumeral contact force that maximized the distal implant migration was selected from a public repository ( orthoload.com ). Imaging and concomitant mechanical testing were performed using a large-volume micro-CT scanner (Nikon XT H 225 ST) and a custom-made compressive stage. Both when intact and once implanted, the specimen was tested under a pre-load and by imposing a constant deformation causing a physiological reaction load (650 N, 10 degrees adducted). The deformation of the implanted specimen was then increased up to fracture, which was identified by a sudden drop of the reaction force, and the specimen was then re-scanned. Results The specimen’s stiffness decreased from 874 N/mm to 464 N/mm after implantation, producing movements of the bone-implant interface consistent with the implant’s long-term stability reported in the literature. The micro-CT images displayed fracture of the tuberosity, caused by a combined compression and circumferential tension, induced by the distal migration of the implant. Conclusion The developed protocol offers detailed information on implant mechanics under load relative to intact conditions and fracture, providing insights into the failure mechanics of RSA implants. This protocol can be used to inform future implant design and surgical technique improvements.

During cementless total knee arthroplasty (TKA), an overlap between the resected tibia and the implant's geometry, termed interference fit, is introduced to facilitate primary stability and direct bone-implant contact. However, little is known about the actual interference achieved and the resulting mechanical response in the surrounding cancellous bone. The aim of this study was (1) to experimentally quantify the actual interference achieved for a commercially available cementless tibial implant and (2) to assess its effect on the post-impaction cancellous bone strain. Seven human cadaveric tibiae were micro-CT scanned intact (23 µm/pixel), once prepared for TKA (46 µm/pixel) and following implantation (46 µm/pixel). The actual interference across the entire bone-implant interface was quantified and, via digital volume correlation, the compressive strains of bone in contact with the implant and at increasing distance, were extracted. An inhomogeneous actual interference was found across the implant pegs and keel (median ± std dev: 0.70 ± 0.27 mm), which was lower than the intended. Limited interference (0.02 ± 0.12 mm) was found directly under the baseplate, with immediate bone-baseplate contact of 54%. The induced compressive strains were related to the actual interference within 3.14 mm from the bone-implant interface (R2 = 0.269-0.450, p < 0.001), with higher compressive strains corresponding to higher interference, but not being related to the bone volume fraction. Clinical Significance: Insight is provided into the interaction between the variability of the resection and the resulting mechanical environment. A complex relationship is apparent, whereby the actual interference accounted for up to 45% of the variation in induced compressive strain magnitude.

The three-dimensional (3D) microstructure of the cortical and trabecular bone of the proximal ulna has not yet been described by means of high-resolution 3D imaging. An improved characterization can provide a better understanding of their relative contribution to resist impact load. The aim of this study is to describe the proximal ulna bone microstructure using micro-computed tomography (micro-CT) and relate it to gross morphology and function. Five dry cadaveric human ulnae were scanned by micro-CT (17 μm/voxel, isotropic). Both qualitative and quantitative assessments were performed on sagittal image stacks. The cortical thickness of the trochlear notch and the trabecular bone microstructure were measured in the olecranon, bare area and coronoid. Groups of trabecular struts starting in the bare area, spanning towards the anterior and posterior side of the proximal ulna, were observed; within the coronoid, the trabeculae were orthogonal to the joint surface. Consistently among the ulnae, the coronoid showed the highest cortical thickness (1.66 ± 0.59 mm, p = 0.04) and the olecranon the lowest (0.33 ± 0.06 mm, p = 0.04). The bare area exhibited the highest bone volume fraction (BV/TV = 43.7 ± 22.4%), trabecular thickness (Tb.Th = 0.40 ± 0.09 mm) and lowest structure model index (SMI = – 0.28 ± 2.20, indicating plate-like structure), compared to the other regions (p = 0.04). Our microstructural results suggest that the bare area is the region where most of the loading of the proximal ulna is concentrated, whereas the coronoid, together with its anteromedial facet, is the most important bony stabilizer of the elbow joint. Studying the proximal ulna bone microstructure helps understanding its possible everyday mechanical loading conditions and potential fractures. N.A.

Imaging the bone microstructure under progressively increasing loads allows for observing the microstructural failure behavior of bone. Here, we describe a protocol for obtaining a sequence of three-dimensional microstructural images of the entire proximal femur under progressively increasing deformation, causing clinically relevant fractures of the femoral neck. The protocol is demonstrated using four femora from female donors aged 66-80 years at the lower end of bone mineral density in the population (T-score range = -2.09 to -4.75). A radio-transparent compressive stage was designed for loading the specimens replicating a one-leg stance, while recording the applied load during micro-computed tomography (micro-CT) imaging. The field of view was 146 mm wide and 132 mm high, and the isotropic pixel size was 0.03 mm. The force increment was based on finite-element predictions of the fracture load. The compressive stage was used to apply the displacement to the specimen and enact the prescribed force increments. Sub-capital fractures due to opening and shear of the femoral neck occurred after four to five load increments. The micro-CT images and the reaction force measurements were processed to study the bone strain and energy absorption capacity. Instability of the cortex appeared at the early loading steps. The subchondral bone in the femoral head displayed large deformations reaching 16% before fracture, and a progressive increase in the support capacity up to fracture. The deformation energy linearly increased with the displacement up to fracture, while the stiffness decreased to near-zero values immediately before fracture. Three-fourths of the fracture energy was taken by the specimen during the final 25% force increment. In conclusion, the protocol developed revealed a remarkable energy absorption capacity, or damage tolerance, and a synergic interaction between the cortical and trabecular bone at an advanced donor age.

Tomographic systems based on stationary arrangements of compact x-ray sources coupled to curved panel detectors have shown great potential for point-of-care brain imaging, but suffer from large, non-isotropic x-ray scatter. This work presents an adaptive kernel strategy to efficiently estimate scatter in stationary multi-source CT. The adaptive scatter estimation handles non-circular geometries, by the addition of pre- and post-processing steps to projection domain scatter estimators. The method was calibrated and evaluated on simulated data for a previously presented system with 31 x-ray sources on a circular arc coupled to a curved detector. Further assessment was obtained on experimental data obtained with an imaging testbench including a compact CNT-based x-ray source and simulating the scanner geometry. The method achieved accurate air-normalized scatter distributions across x-ray source positions and detector pixels, yielding a mean absolute error of 1.98𝑥10−3 with respect to the Monte-Carlo ground truth. Air-gap compensation had the largest impact on final accuracy. Image quality for simulated data showed consistent mitigation of scatter artifacts and reduction in non-uniformity from NU = 109 HU to 24 HU, with comparable performance for variations in cranium size, ranging in length from 161 mm (NU =14 HU) to 246 mm (NU = 15 HU). The experimental data showed comparable performance with error attributable to slight simulation infidelity. This work presents an adaptive approach to scatter compensation in multi-source, non-circular geometries using warping and weighting operations coupled to kernel-based scatter estimation on a virtual circular geometry, with immediate extension to other projection-based scatter compensation strategies.

Primary stability, the mechanical fixation between implant and bone prior to osseointegration, is crucial for the long-term success of cementless tibial trays. However, little is known about the mechanical interplay between the implant and bone internally, as experimental studies quantifying internal strain are limited. This study employed digital volume correlation (DVC) to quantify the immediate post-implantation strain field of five cadaveric tibiae implanted with a commercially available cementless titanium tibial tray (Attune, DePuy Synthes). The tibiae were subjected to a five-step loading sequence (0-2.5 bodyweight, BW) replicating stair descent, with concomitant time-elapsed micro-CT imaging. With progressive loads, increased compression of trabecular bone was quantified, with the highest strains directly under the posterior region of the tibial tray implant, dissipating with increasing distance from the bone-implant interface. After load removal of the last load step (2.5BW), residual strains were observed in all of the five tibiae, with residual strains confined within 3.14 mm from the boneimplant interface. The residual strain is reflective of the observed initial migration of cementless tibial trays reported in clinical studies. The presence of strains above the yield strain of bone accepted in literature suggests that inelastic properties should be included within finite element models of the initial mechanical environment. This study provides a means to experimentally quantify the internal strain distribution of human tibia with cementless trays, increasing the understanding of the mechanical interaction between bone and implant.

The objectives of this study were to (1) develop a semiautomated method to obtain lesion volume and bone mineral density (BMD) in terms of Hounsfield units from pelvic computed tomography (CT) scans in three regions of interest, and (2) assess accuracy and reliability of the method based on cadaveric CT scans. Image artefacts due to metal implants reduce CT clarity and are more severe with more than one implant in situ. Therefore, accuracy and reliability tests were performed with varying numbers of total hip arthroplasties implanted. To test the accuracy of lesion size measurements, microcomputed tomography was used as a reference. Mean absolute error ranged from 36 to 284 mm3 after five measurements. Intra- and inter-operator reliability of the entire method was measured for a selection of parameters. All coefficient of variation values were good to excellent for CT scans of the native pelvic anatomy and a CT scans of the same pelvis with one and two implants in situ. Accuracy of quantifying lesion volume decreased with decreasing CT image clarity by 0.6%-3.6% mean absolute relative error. Reliability of lesion volume measurement decreased with decreasing CT clarity. This was also the case for reliability of BMD measurements in the region most disrupted by metal artefact. The presented method proposes an approach for quantifying bone loss which has been proven to be accurate, reliable, and clinically applicable.

This study aimed to improve the overall fatigue properties of WAAM-produced SDSS by changing the interpass temperatures. Micro-computed tomography was used to quantitatively characterise the internal defects, such as porosity, in large-volume WAAM-fabricated SDSS materials. An increase in the interpass temperature led to a reduction in the ferrite phase balance by up to 20%. The fatigue anisotropy was still evident, but the fatigue limit in the weakest (transverse) direction was increased to 250 MPa or by approximately 40%. Meanwhile, the increased interpass temperature had no significant effect on fatigue resistance in the longitudinal direction. This study suggests that the interpass temperature can be critical for both achieving isotropic mechanical properties and increasing fatigue life of structural components fabricated with the WAAM method.

Primary stability of press-fit tibial trays is achieved by introducing an interference fit between bone and implant. The internal cancellous bone strains induced during this process and during loading have yet to be quantified experimentally. Advancements in large-gantry micro-CT imaging and digital volume correlation (DVC) allow quantification of such strains. However, before undertaking such a test, experimental requirements and DVC performance need to be examined, particularly considering the presence of a large orthopaedic implant (tibial tray). The aim of this study was to assess the DVC zero-strain accuracy (mean absolute error: MAER) and pre-cision (standard deviation of error: SDER) on a cadaveric human tibia implanted with a titanium press-fit tray across four plausible scanning configurations, using a cabinet micro-CT system (Nikon XT H 225 ST). These varied in rotation step and resulting scanning time (106 min vs. 66 min), presence or absence of a 2 mm-thick aluminium cylinder for mechanical testing, and X-ray tube voltage (150 kVp vs. 215 kVp). One proximal tibia was implanted and micro-CT scanned (42 mu m/pixel), with repeated scanning and specimen repositioning in between. DVC (DaVis, LaVision, direct correlation) was performed on nine cubic volumes of interest (VOIs: 13.4 mm-side) and across the entire proximal tibia. Strain errors were comparable across the four scanning config-urations and sufficiently low for assessing bone within its elastic region in VOIs (MAER=223-540 mu epsilon; SDER=88-261 mu epsilon) and at organ level (MAER=536 mu epsilon; SDER=473 mu epsilon). Whilst the investigated experimental conditions, including a large titanium implant, present added complexity for DVC analysis, scans of sufficient quality can be achieved, reaching a compromise between the DVC requirements and the wanted application. The approach used for choosing the X-ray source settings considering the transmitted X-ray signal intensity and source power, is also discussed.

Gait abnormalities can be caused by natural signs of aging and/or by specific diseases. Therefore, any study that aims to analyze gait in the elderly faces the problem of the interaction between, at least, these two factors. Even if gait analysis nowadays is a solid and well-known tool for research, the interpretation of the results is strongly linked to the interdependence among the different aspects that can affect the subjects in analysis. The most obvious solution to this problem is to focus on narrow studies centered on specific techniques or patients’ conditions. Such studies are important, and in the past have led to several methodological advances. However, not considering age-related factors that are relevant for gait and posture analysis can generate misleading and contradictory results. Contemporary research often suffers from a lack of repeatability, inconsistency of results, and confounding of parameters. These problems can be related to the limited cross-disciplinary approaches applied. Specific studies can appear significant when performed individually, but they can lose significance when included in the wider research context in which they belong. The current research topic presents a Research Topic of studies that tried to cross the borders of current musculoskeletal (MSK) science, setting interdisciplinary goals, merging multiple aspects, and therefore considering the effect that external factors can have over gait and its interpretation. For instance, sight is known to affect posture, stability, and in general, movement in space, and for this reason, studying a combination of factors covering gait and the visual system can allow early detection of a range of various conditions. In the work by Lirani-silva et al., as described in this very topic, eye-tracking systems were used during the gait of subjects with mild traumatic brain injury (mTBI). mTBI can result from several mechanisms and at any age; however, falling, which is a major problem in the elderly, clearly belongs to the possible causes leading to mTBI. The authors find a positive interaction between the condition of the patients and the saccade duration, showing how gait speed can be related to saccade time for people with mTBI. The interaction between the visual system and posture is also studied by Kahya et al. The authors present a relation between postural stability and pupillary response, as an index of cognitive workload during postural control in patients with Parkinson’s disease (PD). PD patients showed a higher level of pupillary response, and therefore higher cognitive workload, together with a higher displacement of the center of pressure, related to reduced stability. The work presents a Edited and reviewed by: Markus O. Heller, University of Southampton, United Kingdom

Solar receivers are an integral part of a concentrated solar power plant and commonly utilise tubular structures to absorb solar energy and transfer the heat into a heat transfer fluid. These systems often contain dissimilar materials joined through welds which are exposed to cyclic temperatures, which can be a locus of failure. A systematic forensic analysis was carried out on a low-pressure CO2 receiver that had developed extensive cracking. Microstructural characterisation using micro-computed tomography was performed to understand the failure mechanism in an area adjacent to a welded section of the two dissimilar alloys Haynes 230 and 253 MA. An electrolytical oxalic acid etch showed grain boundary damage from oxidation. Grain boundary damage through oxidation was confirmed with SEM and energy dispersive X-ray spectroscopy (EDX) analysis as the likely metallurgical degradation mechanism which, combined with thermally induced stress cycles led to the failure of the weaker stainless-steel tube adjacent to the weld.

Postoperative weight bearing has the potential to generate fragmental motion of surgically repaired tibial plateau fractures (TPFs), which may contribute to loss of fracture reduction. The effect of loading on the internal dis-tribution of fragmentary displacements is currently unknown. The aim of this study was to determine the internal displacements of surgically repaired split TPFs due to a three-bodyweight load, using large-volume micro-CT imaging and image correlation. Fractures were generated and surgically repaired for two cadaveric specimens. Load was applied to the specimens inside a large-volume micro-CT system and scanned at 0.046 mm isotropic voxel size. Pre-and post-loading images were paired, co-registered, and internal fragmentary displacements quantified. Internal fragmental displacements of the cadaveric bones were compared to in vivo displacements measured in the lateral split fragments of TPFs in a clinical cohort of patients who had similar surgical repair and were prescribed pain tolerated postoperative weight bearing. The split fragments of cadaveric specimens dis-placed, on average, less than 0.3 mm, consistent with in vivo measurements. Specimen one rotated around the mediolateral axis, while specimen two displaced consistently caudally. Specimen two also had varying dis-placements along the mediolateral axis where, at the fracture site, the fragment displaced caudally and laterally, while the most lateral edge of the tibial plateau displaced caudally and medially. The methods applied in this study can be used to measure internal fragmental motion within TPFs.

Biomechanical factors (e.g., joint loading) have a significant role in the progression of osteoarthritis (OA). However, some relationships between in vivo joint loading indices and tibial cartilage thickness are conflicting. This study investigated relationships between pre-operative in vivo external knee joint moments, joint alignment and regional tibial cartilage thickness using micro-CT in subjects with end-stage knee OA. Tibial plateaus from 25 patients that underwent knee replacement for OA were micro-CT scanned (17 mu m/voxel). Prior to surgery, subjects underwent gait analysis to calculate external knee moments. The mechanical axis deviation (MAD) was obtained from pre-operative radiographs. Cartilage thickness (Cart.Th) was analyzed from micro-CT images, in anteromedial, anterolateral, posteromedial and posterolateral subregions of interest. Medial-to-lateral Cart.Th ratios were also explored. Relationships between Cart.Th and joint loading indices were examined using Pearson's correlations. Significant correlations were found between Cart.Th and joint loading indices, positive anteromedially with the first peak knee adduction moment (r = 0.55, p < 0.01) and external rotation moment (ERM; r = 0.52, p < 0.01), and negative with MAD (r = -0.76, p < 0.001). In the lateral regions, these correlations had opposite signs. The medial-to-lateral Cart.Th ratio correlated strongly with ERM (r = 0.63, p = 0.001) and MAD (r = -0.75, p < 0.001). Joint loading indices correlated with regional cartilage thickness values and their medial-to-lateral ratios in end-stage knee OA subjects, with higher regional loads corresponding to thinner cartilage. These relationships have the opposite sign compared to the subchondral bone microarchitecture found in our previous study on the same specimens, which may suggest a complementary bone-cartilage interplay in response to loading.

This preliminary study quantified tibia cartilage thickness (Cart.Th), subchondral bone plate thickness (SBPl.Th) and subchondral trabecular bone (STB) microarchitecture in subjects with varus- or valgus- malaligned knees diagnosed with end-stage knee osteoarthritis (OA) and compared them to controls (non-OA). Tibial plateaus from 25 subjects with knee-OA (undergoing knee arthroplasty) and 15 cadavers (controls) were micro-CT scanned (17 mu m/voxel). Joint alignment was classified radiographically for OA subjects (varus-aligned n = 18, valgus-aligned n = 7). Cart.Th, SBPl.Th, STB bone volume fraction (BV/TV) and their medial-to-lateral ratios were analyzed in anteromedial, anterolateral, posteromedial and posterolateral subregions. Varus-OA and valgus-OA were compared to controls. Compared to controls (1.19-1.54 mm), Cart.Th in varus-OA was significantly lower anteromedially (0.58 mm, -59%) and higher laterally (2.19-2.47 mm, +60-63%); in valgus-OA, Cart.Th was significantly higher posteromedially (1.86 mm, +56%). Control medial-to-lateral Cart.Th ratios were around unity (0.8-1.1), in varus-OA significantly below (0.2-0.6) and in valgus-OA slightly above (1.0-1.3) controls. SBPl.Th and BV/TV were significantly higher medially in varus-OA (0.58-0.72 mm and 37-44%, respectively) and laterally in valgus-OA (0.60-0.61 mm and 32-37%), compared to controls (0.26-0.47 mm and 18-37%). In varus-OA, the medial-to-lateral SBPl.Th and BV/TV ratios were above unity (1.4-2.4) and controls (0.8-2.1); in valgus-OA they were closer to unity (0.8-1.1) and below controls. Varus- and valgus-OA tibia differ significantly from controls in Cart.Th, SBPl.Th and STB microarchitecture depending on joint alignment, suggesting structural changes in OA may reflect differences in medial-to-lateral load distribution upon the tibial plateau. Here we identified an inverse relationship between cartilage thickness and underlying subchondral bone, suggesting a whole-joint response in OA to daily stimuli.