A finite element model of an idealized diarthrodial joint to investigate the effects of variation in the mechanical properties of the tissues

The stiffness of articular cartilage increases dramatically with increasing rate of loading, and it has been hypothesized that increasing the stiffness of the subchondral bone may result in damaging stresses being generated in the articular cartilage. Despite the interdependence of these tissues in a joint, little is understood of the effect of such changes in one tissue on stresses generated in another. To investigate this, a parametric finite element model of an idealized joint was developed. The model incorporated layers representing articular cartilage, calcified cartilage, the subchondral bone plate and cancellous bone. Taguchi factorial design techniques, employing a two-level full-factorial and a four-level fractional factorial design, were used to vary the material properties and thicknesses of the layers over the wide range of values found in the literature. The effects on the maximum values of von Mises stress in each of the tissues are reported here. The stiffness of the cartilage was the main factor that determined the stress in the articular cartilage. This, and the thickness of the cartilage, also had the largest effect on the stresses in all the other tissues with the exception of the subchondral bone plate, in which stresses were dominated by its own stiffness. The stiffness of the underlying subchondral bone had no effect on the stresses generated in the cartilage. This study shows how stresses in the various tissues are affected by changes in their mechanical properties and thicknesses. It also demonstrates the benefits of a structured, systematic approach to investigating parameter variation in finite element models.     

Response of the donor and recipient cells in mesenchymal cell transplantation to cartilage defect

To facilitate the repair of articular cartilage defects, autologous mesenchymal cells from bone marrow or periosteum were transplanted in a rabbit model. Two weeks after the transplantation of the mesenchymal cells, the whole area of the original defect was occupied by cartilage. From the deep area of the reparative cartilage, which contacted with host bone, chondrocytes became hypertrophic and the invasion of bone with vasculature started, until the replacement reached the natural junction of the host cartilage and the subchondral bone about 4 weeks after transplantation. Twelve weeks after the transplantation, the repair cartilage in the defect became a little thinner than the adjacent normal cartilage, which became a little thinner 24 weeks after the transplantation (the longest observation period in the study). Large, full-thickness defects of the weight-bearing region of the articular cartilage were repaired with hyaline-like cartilage after implantation of autologous mesenchymal cells. The repair process by mesenchymal cell transplantation was explained as follows: The donor transplanted cell differentiated into cartilage and the defects were completely filled with cartilage. Then, mesenchymal cells that entered the chondrogenic lineage rapidly progressed through this lineage to the hypertrophic state, which was then the target for erosion and vascular invasion. Although this vasculature and the newly formed bone were considered to be host-derived, there was no evidence to that effect. To prove this, suitable experimental marking of these donor cells is needed. In the case of chondrocyte transplantation, the repair cartilage maintained its thickness to the full depth of the original defect; the tissue derived from the implanted chondrocytes was not invaded by vessels or replaced by subchondral bone.     

Behavior of graft and host cells in underlying subchondral bone after transplantation of osteochondral autograft

Transplantation of osteochondral autograft is widely used as a therapeutic strategy for the defect of articular cartilage. In the repair process, although underlying subchondral bone becomes necrotic and then is followed by bone reconstruction, the fate of graft and host cells during remodeling of underlying subchondral bone has not been elucidated. The objectives of this study were to establish a method to follow graft and host cells after transplantation of osteochondral autograft, and to elucidate the fate of both graft and host cells during remodeling of underlying subchondral bone. For these purposes, autologous transplantation models employing transgenic rats and wild-type rats, which were genetically identical to each other except for transgenes, were used. Two transplantation models were designed so that either the graft or the host cells had transgenes. Model I: transgenic rats were the donor, and wild-type rats were the recipient; model II: conversely, wild-type rats were the donor, and transgenic rats were the recipient. The grafted bone marrow cells and osteocytes in the trabeculae survived in the graft at 3 weeks after transplantation. Invasion of the host bone marrow cells into the graft was also found. Thus, bone marrow cells in the host as well as both bone marrow cells and osteocytes in the graft could potentially participate in the remodeling of underlying subchondral bone. Furthermore, the interface between graft and host was consisted with both graft and host derived cells. Since new bone formation was found in this space, both graft and host cells could have the potential to contribute to remodeling of underlying subchondral bone. The two models of the transplantations using the transgenic rats were found to be beneficial in following graft cells as well as host cells and in understanding their function on healing after autologous transplantation.     

Effects of ageing on the biomechanical properties of rat articular cartilage

Previous studies have demonstrated that male Sprague Dawley (SD) rats experience age-related bone loss with the same characteristics as that in ageing men. As articular cartilage, like bone, is a critical component of the health and function of the musculoskeletal system, the authors hypothesized that articular cartilage in the untreated male SD rats could be a suitable model for studying the age-related deterioration of articular cartilage in men. To test this hypothesis, male SD rats were killed at between 6 and 27 months. The right femur of each rat was removed. The effects of ageing on the structural integrity of the distal femoral articular cartilage were studied by biomechanical testing with a creep indentation apparatus. The aggregate modulus, Poisson's ratio, permeability, thickness, and percentage recovery of articular cartilage were determined using finite element/non-linear optimization modelling. No significant differences were observed in these biomechanical properties of the distal femoral articular cartilage as a function of age. Therefore, untreated male SD rats appear to be unsuitable for studying the age-related changes of articular cartilage as they occur in men. However, and more intriguingly, it is also possible that ageing does not affect the biomechanical properties of articular cartilage in the absence of cartilage pathology.     

Quantitative zonal differentiation of articular cartilage by microscopic magnetic resonance imaging,polarized light microscopy,and Fourier‐transform infrared imaging

This study aimed to synchronize the zonal differentiation of the full‐thickness articular cartilage by three micro‐imaging techniques, namely microscopic magnetic resonance imaging (µMRI), polarized light microscopy (PLM), and Fourier‐transform infrared imaging (FTIRI). Eighteen cartilage‐bone blocks from three canine humeral joints were imaged by: (a) µMRI T₂ relaxation at 0° and 55° orientations in a 7 T magnetic field, (b) PLM optical retardation and azimuthal angle, and (c) FTIRI amide I and amide II anisotropies at 0° and 90° polarizations relative to the articular surface. In addition, µMRI T₁ relaxation was imaged before and after the tissue being immersed in gadolinium (contrast agent) solution, to calculate the proteoglycan concentration. A set of previously established criteria in cartilage imaging was revised. The new criteria could simultaneously correlate the thicknesses of the three consecutive subtissue zones in articular cartilage among these imaging techniques. Microsc. Res. Tech. 76:625–632, 2013. © 2013 Wiley Periodicals, Inc.     

Feasibility of detecting trabecular bone around percutaneous titanium implants in rabbits by in vivo microfocus computed tomography

Objectives: The goal of this study was to examine the feasibility of in vivo imaging of trabecular bone around titanium implants by means of microfocus computed tomography (micro‐CT) and the use of rabbits for this purpose. Materials and Methods: Ten male rabbits type Hollander, received a titanium implant (1.7 mm diameter and 10 mm length) in the trabecular bone of the left tibia. Seven weeks later a micro‐CT scan was taken. Four rabbits were used to monitor potential harmful effects from X‐ray absorption until 4 weeks after scanning. A second group of six rabbits was used for testing the hypothesis that a good correlation exists between in vivo micro‐CT images and histological images of trabecular bone around titanium implants. The six rabbits were scanned and sacrificed immediately. The tibias were extracted and submitted to standard histological procedures. This resulted in a total of 12 histological sections and their corresponding 12 micro‐CT images. Bone area measurements were performed at the left and right side of the implant in three regions: 0–500, 500–1000 and 1000–1500 μm distance from the implant interface. Intra‐class correlations (ICC) were calculated between both techniques. Results: The four rabbits did not show any sign of radiodermatitis 4 weeks after scanning. In the micro‐CT images of the group of six rabbits, trabeculae are visible, but not well defined, due to the presence of noise in the image. The ICC for the right implant side were 0.44 for zone 0–500 μm, 0.48 for zone 500–1000 μm and 0.40 for zone 1000–1500 μm. The ICC for the left implant side could not be calculated. Conclusion: A low agreement was found between the bone measurements from histology and in vivo micro‐CT images. The use of the in vivo micro‐CT for trabecular bone imaging around metallic implants should be restricted to track tendencies in follow‐up studies.     

Application of autofluorescence robotic histology for quantitative evaluation of the 3‐dimensional morphology of murine articular cartilage

Murine models of osteoarthritis (OA) are increasingly important for understating pathogenesis and for testing new therapeutic approaches. Their translational potential is, however, limited by the reduced size of mouse limbs which requires a much higher resolution to evaluate their articular cartilage compared to clinical imaging tools. In experimental models, this tissue has been predominantly assessed by time‐consuming histopathology using standardized semi‐quantitative scoring systems. This study aimed to develop a novel imaging method for 3‐dimensional (3D) histology of mouse articular cartilage, using a robotic system—termed here “3D histocutter”—which automatically sections tissue samples and serially acquires fluorescence microscopy images of each section. Tibiae dissected from C57Bl/6 mice, either naïve or OA‐induced by surgical destabilization of the medial meniscus (DMM), were imaged using the 3D histocutter by exploiting tissue autofluorescence. Accuracy of 3D imaging was validated by ex vivo contrast‐enhanced micro‐CT and sensitivity to lesion detection compared with conventional histology. Reconstructions of tibiae obtained from 3D histocutter serial sections showed an excellent agreement with contrast‐enhanced micro‐CT reconstructions. Furthermore, osteoarthritic features, including articular cartilage loss and osteophytes, were also visualized. An in‐house developed software allowed to automatically evaluate articular cartilage morphology, eliminating the subjectivity associated to semi‐quantitative scoring and considerably increasing analysis throughput. The novelty of this methodology is, not only the increased throughput in imaging and evaluating mouse articular cartilage morphology starting from conventionally embedded samples, but also the ability to add the third dimension to conventional histomorphometry which might be useful to improve disease assessment in the model.     

磁共振显微线圈高分辨成像技术在腕关节病变中的临床应用

目的探讨磁共振显微线圈高分辨成像技术在腕关节病变中的临床应用。方法收集2018年12月至2019年12月45例腕关节类风湿关节炎患者、30例手腕关节骨性关节炎患者、40例腕部撞击综合症损伤患者作为研究对象,分别使用磁共振常规线圈及显微线圈技术对其部位进行扫描。比较分析两种诊断方式的诊断准确率及对软骨侵蚀、关节积液和滑膜增厚的诊出情况。结果显微线圈技术对腕关节类风湿关节炎、手腕关节骨性关节炎、腕部撞击综合症损伤的诊断准确率分别为97.78%、96.67%、97.50%,均显著高于常规线圈技术的60.00%、50.00%、60.00%,差异有统计学意义(P<0.05)。显微线圈技术对软骨侵蚀、关节积液和滑膜增厚的诊出情况显著优于常规线圈技术,差异有统计学意义(P<0.05)。经显微线圈技术MRI增强扫描检测:腕关节类风湿关节炎患者右手近端指间关节周围软组织增厚,关节周围可见少量积液,增强扫描指间关节滑膜呈明显增厚并强化。骨性关节炎患者可见关节面下骨质异常信号,表现为“虫蚀状”或小斑片状软骨下骨质缺损区。结论磁共振显微线圈高分辨成像技术能够显著提高腕关节病变的诊断准确率,提高对软骨侵蚀、关节积液和滑膜增厚的诊出情况,值得广泛推广。     

Development of artificial articular cartilage

Attempts have been made to develop an artificial articular cartilage on the basis of a new viewpoint of joint biomechanics in which the lubrication and load-bearing mechanisms of natural and artificial joints are compared. Polyvinyl alcohol hydrogel (PVA-H), 'a rubber-like gel', was investigated as an artificial articular cartilage and the mechanical properties of this gel were improved through a new synthetic process. In this article the biocompatibility and various mechanical properties of the new improved PVA-H is reported from the perspective of its usefulness as an artificial articular cartilage. As regards lubrication, the changes in thickness and fluid pressure of the gap formed between a glass plate and the specimen under loading were measured and it was found that PVA-H had a thicker fluid film under higher pressures than polyethylene (PE) did. The momentary stress transmitted through the specimen revealed that PVA-H had a lower peak stress and a longer duration of sustained stress than PE, suggesting a better damping effect. The wear factor of PVA-H was approximately five times that of PE. Histological studies of the articular cartilage and synovial membranes around PVA-H implanted for 8-52 weeks showed neither inflammation nor degenerative changes. The artificial articular cartilage made from PVA-H could be attached to the underlying bone using a composite osteochondral device made from titanium fibre mesh. In the second phase of this work, the damage to the tibial articular surface after replacement of the femoral surface in dogs was studied. Pairs of implants made of alumina, titanium or PVA-H on titanium fibre mesh were inserted into the femoral condyles. The two hard materials caused marked pathological changes in the articular cartilage and menisci, but the hydrogel composite replacement caused minimal damage. The composite osteochondral device became rapidly attached to host bone by ingrowth into the supporting mesh. The clinical implications of the possible use of this material in articular resurfacing and joint replacement are discussed.     

Utilizing confocal microscopy to measure refractive index of articular cartilage

This study proposes a method for measuring the refractive index of articular cartilage within a thin and small specimen slice. The cartilage specimen, with a thickness of about 50 μm, was put next to a thin film of immersion oil of similar thickness. Both the articular cartilage and immersion oil were scanned along the depth direction using a confocal microscope. The refractive index mismatch between the cartilage and the immersion oil induced a slight axial deformation in the confocal images of the cartilage specimen that was accurately measured by a subpixel edge‐detection‐based technique. A theoretical model was built to quantify the focal shift of confocal microscopy caused by the refractive index mismatch. With the quantitative deformations of cartilage images and the quantified function of focal shift, the refractive index of articular cartilage was accurately interpolated. At 561 nm, 0.1 MPa and 20 °C, the overall refractive index of the six cartilage plugs was 1.3975 ± 0.0156. The overall coefficient of variation of all cartilage specimens was 0.68%, which indicated the high repeatability of our method. The verification experiments using distilled water showed a minimal relative error of 0.02%.     

In-situ engineering of cartilage repair: a pre-clinical in-vivo exploration of a novel system

This investigation explores a new cartilage repair technique that uses a novel method to secure a non-woven multifilamentous scaffold in the defect site after microfracture. The hypothesis is that a scaffold provides a larger surface area for attachment and proliferation of the mesenchymal stem cells that migrate from the bone marrow. Two in-vivo studies were undertaken in an ovine model. The first study, which lasted for 8 weeks, aimed to compare the new technique with microfracture. Chondral defects, 7 mm in diameter, were created in both femoral medial condyles of five ewes. One defect was treated with the new technique while the contralateral knee was treated with microfracture alone. The results revealed that the quantity of repair tissue was significantly greater in the defects treated with the new system. The second study had two time points, 3 and 6 months, and used 13 ewes. In this study, both defects were treated with the new technique but one received additional subchondral drilling in order to stimulate extra tissue growth. The majority of the implants had good tissue induction, filling 50-100 per cent of the defect volume, while the compressive modulus of the repairs was in the range of 40-70 per cent of that for the surrounding cartilage. In addition, hyaline-like cartilage was seen in all the repairs which had the additional drilling of the subchondral bone.     

The interface region between articular cartilage and bone by μMRI and PLM at microscopic resolutions

This dual-modality microscopic imaging study quantifies the interface region between the noncalcified cartilage and the subchondral bone plate, which includes the deep portion of the noncalcified articular cartilage and the zone of calcified cartilage (ZCC). This interface region is typically not visible in routine MRI but becomes visible in MRI with the application of an ultra-short echo time (UTE) sequence. A number of cartilage-bone blocks from a well-documented canine humeral head were harvested for imaging by microscopic MRI (μMRI) and PLM (polarized light microscopy). In μMRI, T2 anisotropic images were acquired by 2D gradient-echo, magnetization-prepared spin-echo and UTE sequences at the 0° and 55° (the magic angle) orientations at 11.7 μm/pixel resolution. In PLM, quantitative optical retardation (nm) and collagen orientation (°) were mapped from the thin sections from the same μMRI specimens at 0.5–2 μm pixel resolutions. The orientational and organizational architecture of the collagen matrix in this interface region was quantified and correlated between the complementary imaging. The magic angle effect as seen in the noncalcified cartilage was statistically confirmed in ZCC in μMRI, which was further supported by quantitative PLM. With an enhanced understanding of the tissue properties in this important interface region, it will potentially be possible to monitor the changes of this tissue region which is instrumental to the initiation and development of osteoarthritis and other joint diseases.     

Tibiofemoral cartilage thickness distribution and its correlation with anthropometric variables

The objective of this study was to determine tibiofemoral cartilage thickness distribution, and to investigate the relationship between cartilage geometry and anthropometric variables. In this study, 20 magnetic resonance examinations of the knee from normal individuals were reconstructed to provide three-dimensional models of the knee joint, including bony and cartilage surfaces. Three regions were defined on the articular surface, and the cartilage thickness distribution along each of these was determined. Statistically significant differences between femoral and tibial regions were examined using the paired Student t test in Microsoft Excel. Correlations were investigated using the correlation tool in Microsoft Excel. The average tibial cartilage thickness was found to be 2.76 mm and the average femoral cartilage thickness was 2.75 mm. Significant correlations exist between the tibia cartilage thickness and body height (R = 0.60; P < 0.05) and weight (R = 0.64; P < 0.05). Significant correlations exist between the femoral cartilage volume and the body height (R = 0.736; P < 0.01) and weight (R = 0.855; P < 0.01). It is suggested that the distribution and correlations of cartilage distribution indicate adaptation in response to mechanical loading. Information regarding cartilage thickness and volume distribution as found in this study may be useful in diagnosing and monitoring cartilage loss in patients with degenerative joint disease.     

Muscle-ligament interactions at the human knee (II)

In part I of this paper, a three-dimensional model of the human knee joint was incorporated into a detailed human musculoskeletal lower extremity model. The model was used to determine the muscle, ligament, and articular contact forces transmitted at the knee as humans extend/flex in an isometric state. Part II investigates the sensitivity of the model calculations to changes in the parameters which describe the mechanical behavior of cartilage and the ligaments of the knee. The ligament function in the real knee was most sensitive to changes in ligament reference lengths or strains, less sensitive to changes in cartilage stiffness, and least sensitive to changes in ligament stiffness.     

Autologous resurfacing

Background: There is a discrepancy between the interest in joint‐reconstructions and the current knowledge about the healing‐processes involved. Major reconstructions are performed with osteosynthesized allografts and fresh allografts for cartilage. Objectives: The main question to be answered is: what do we know about metaphyseal and epiphyseal cancellous bone healing, contact healing of the subchondral bone and its influence on cartilage healing? Can we achieve healing of all four compartments in contact? Purpose: The purpose is to systematically investigate through animal testing the healing processes of metaphyseal and epiphyseal bone, including the subchondral bone and the healing of cartilage of press‐fit‐inserted grafts, considering nondemineralized high‐resolution histology. Material and Methods: Primary cancellous‐bone healing of osteosynthesized hemi‐osteotomies was studied in 13 canine tibial heads, the contact healing was investigated in 7 dogs and 18 giant‐rabbits comparing contact‐healing of press‐fit‐inserted autologs cylindrical grafts with empty defects applying the wet‐grinding diamond‐technology. Bench‐experiments on the epiphyseal bones of swine including pullout‐tests of cylindrical grafts formed the basis for validation of that press‐fit diamond technology. Results: Primary metaphyseal and epiphyseal contact healing, including hyaline cartilage, was found in all compartments of the meta‐and epiphysis in the precisely performed experiments. The press‐fit principle, which employs cylindrical grafts and diamond instrumentation featuring a difference of 15/100 mm between graft and recipient bed, achieved high loads between 73.48 and 178.95 N (mean value 118.16 and standard deviation 32.79) in the pullout tests. Conclusion: Autologous press‐fit grafting with alignment of the bony baseplate using wet‐grinding precision has attained promising histo‐morphological results. Microsc. Res. Tech., 78:40–51, 2015. © 2014 Wiley Periodicals, Inc.     

Non‐Contact Evaluation of Osmosis‐Induced Shrinkage and Swelling Behavior of Articular Cartilage In‐Situ Using High‐Frequency Ultrasound

Abstract

The aim of the present study was to use high‐frequency ultrasound for the investigation of the transient osmosis‐induced free shrinkage‐swelling behaviors of normal articular cartilage in situ. Full‐thickness cartilage‐bone specimens were prepared from normal bovine patellae. The transient shrinkage and swelling strains of the cartilage induced by changing the bathing solution between physiological saline (0.15 M) and hypertonic saline (2 M) were monitored using a 50 MHz focused ultrasound beam. Both shrinkage and swelling strains showed temporary overshoots, followed by relaxation phases. The absolute peak value of the shrinkage strain (1.01%±0.62%) was significantly larger (p<0.05) than that of the swelling strain (0.40%±0.33%). It was found that the change of the mean ultrasound speed in cartilage could be approximately represented by an exponential function of time after the change of saline concentration.

This study successfully demonstrated that a high‐frequency focused ultrasound beam could be used to monitor the transient osmosis‐induced deformation of articular cartilage in a non‐contact way. Since the osmosis‐swelling behavior of cartilage relates to its compositional and structural characteristics and degeneration status, the reported ultrasound method may have potential for the characterization of cartilage degeneration, such as osteoarthritis.     

Comparison of human and animal femoral head chondral properties and geometries

Investigations into tissue-preserving orthopaedic treatments should consider the tribology of articular cartilage; where simulations using animal joints are a predominant choice. However, very few studies have investigated the differences between human and animal cartilage. The aim of the present study was to characterise the differences in geometry and mechanical properties of human, porcine, bovine and ovine articular cartilage. Creep indentation was performed on osteochondral plugs taken from the superior region of femoral heads of all these species. Cartilage thickness was measured via the resistive force change of a needle descending through cartilage and bone. A biphasic finite element model was used to derive equilibrium elastic modulus and permeability. Results showed that human cartilage was significantly thicker than all other species tested. A positive correlation was found between femoral head diameter and cartilage thickness when comparing between species of quadrupeds. Human cartilage had the largest equilibrium elastic modulus, which was significant when comparing against porcine and bovine. However, porcine cartilage had significantly lower permeability. Significant differences in geometry and mechanical properties of articular cartilage were found between all species tested. It is necessary to consider these variations when choosing animal tissue to represent human.     

Depth-dependent anisotropies of amides and sugar in perpendicular and parallel sections of articular cartilage by Fourier transform infrared imaging

Full thickness blocks of canine humeral cartilage were microtomed into both perpendicular sections and a series of 100 parallel sections, each 6 μm thick. Fourier transform infrared (IR) imaging was used to image each tissue section eleven times under different IR polarizations (from 0° to 180° polarization states in 20° increments and with an additional 90° polarization), at a spatial resolution of 6.25 μm and a wavenumber step of 8 cm^?1. With increasing depth from the articular surface, amide anisotropies increased in the perpendicular sections and decreased in the parallel sections. Both types of tissue sectioning identified a 90° difference between amide I and amide II in the superficial zone (SZ) of cartilage. The fibrillar distribution in the parallel sections from the SZ was shown to not be random. Sugar had a weak but recognizable anisotropy in the upper part of the radial zone (RZ) in the perpendicular sections. The depth‐dependent anisotropic data were fitted with a theoretical equation that contained three signature parameters, which illustrate the arcade structure of collagens with the aid of a fibril model. Fourier‐transform IR imaging of both perpendicular and parallel sections provides the possibility of determining the three‐dimensional macromolecular structures in articular cartilage. Being sensitive to the orientation of the macromolecular structure in healthy articular cartilage aids the prospect of detecting the early onset of the tissue degradation that may lead to pathological conditions such as osteoarthritis. Microsc. Res. Tech. 74:122–132, 2011. © 2010 Wiley‐Liss, Inc.     

Regularized phase tomography enables study of mineralized and unmineralized tissue in porous bone scaffold

Regularized phase tomography was used to image non‐calcified fibrous matrix in in vitro cell‐cultivated porous bone scaffold samples. 3D micro‐architecture of bone and bone scaffold has previously been studied by micro‐computed tomography, synchrotron radiation (SR) micro‐computed tomography and microdiffraction. However, neither of these techniques can resolve the low‐calcified immature pre‐bone fibrous structures. Skelite porous scaffold discs were seeded with osteoblasts, a combination of osteoblast and pre‐osteoclasts and, as controls, with pre‐osteoclasts only, and then cultivated for 8 weeks. They were subsequently imaged using SR propagation‐based phase contrast imaging. Reconstructions using a regularized holographic phase tomography approach were compared to standard (absorption) SR micro‐computed tomography, which show that quantitative analysis, such as volume and thickness measurements, of both the calcified fraction and the immature bone matrix in the reconstructed volumes is enabled. Indications of the effect of this type of culture on Skelite, such as change in mineralization and deposit of mature bone on the walls of the scaffold, are found. The results are verified with a histological study.     

Shear properties of articular cartilage of a bovine knee joint subjected to moderate and high loads: an experimental study.

Freshly excised bovine knee joints were subjected to oscillation under constant load on a specially designed knee joint articulating machine with the joints subjected to moderate and high loadings of 1471.5 and 2943 N respectively. Instantaneous and equilibrium shear moduli of the articular cartilage obtained from the experimental knee joints were measured on a mechanical indentor (DuPont 943 TMA) and compared with the corresponding values of the shear moduli of the cartilage obtained from the control knee joints. At moderate load, both the instantaneous and the equilibrium shear moduli exhibit significant increase in their values. However, at high load the constant shear moduli showed a decrease in its value whereas the value of the equilibrium shear modulus was observed to increase slightly.