Effect of superficial collagen patterns and fibrillation of femoral articular cartilage on knee joint mechanics-a 3D finite element analysis

Collagen fibrils of articular cartilage have specific depth-dependent orientations and the fibrils bend in the cartilage surface to exhibit split-lines. Fibrillation of superficial collagen takes place in osteoarthritis. We aimed to investigate the effect of superficial collagen fibril patterns and collagen fibrillation of cartilage on stresses and strains within a knee joint. A 3D finite element model of a knee joint with cartilage and menisci was constructed based on magnetic resonance imaging. The fibril-reinforced poroviscoelastic material properties with depth-dependent collagen orientations and split-line patterns were included in the model. The effects of joint loading on stresses and strains in cartilage with various split-line patterns and medial collagen fibrillation were simulated under axial impact loading of 1000 N. In the model, the collagen fibrils resisted strains along the split-line directions. This increased also stresses along the split-lines. On the contrary, contact and pore pressures were not affected by split-line patterns. Simulated medial osteoarthritis increased tissue strains in both medial and lateral femoral condyles, and contact and pore pressures in the lateral femoral condyle. This study highlights the importance of the collagen fibril organization, especially that indicated by split-line patterns, for the weight-bearing properties of articular cartilage. Osteoarthritic changes of cartilage in the medial femoral condyle created a possible failure point in the lateral femoral condyle. This study provides further evidence on the importance of the collagen fibril organization for the optimal function of articular cartilage.     

Mathematical reconstruction of human femoral condyles

There is a direct correlation between ligament function and the articulating surface of the normal knee, and changes to any of these structures can affect the other. This is also true for knee replacements, where the articulating surface is greatly changed compared to the natural knee. This study investigated the morphometry of healthy knees and proposes a method to predict original normal knee profiles. A variety of mathematical techniques are compared in terms of the accuracy with which they can represent the original knee joint geometry. Additionally, a method of predicting the irregular femoral condyle geometry for an individual knee is described by making use of the mathematical techniques presented, and the accuracy of this method is also investigated. The mathematical approach using B-splines provides flexibility and can accurately describe the complex geometry of the femoral condyles in both the sagittal and transverse planes. It was further found that the condyles are highly asymmetrical; therefore simpler methods cannot portray the condyles sufficiently and are especially inaccurate in representing the lateral condyle. The study proposes a method for predicting the geometry of the femoral condyles with good accuracy. The B-spline model showed best results.     

Anisotropy and inter-condyle heterogeneity of cartilage under large-strain shear

We were the first to examine the mechanical responses of skeletally mature bovine femoral cartilage under large-strain simple shear (up to ±20%) using a multiaxial shear testing device. Since shear loading is critical in both tissue failure and chondrocyte responses, we aimed to probe (1) anisotropy with respect to the split-line direction (principal alignment of the collagen fibers near the articulating surface), (2) heterogeneity between femoral condyles, and (3) the influence of local cartilage thickness. We harvested a total of 48 cuboid cartilage specimens from four bovine knee joints. With each specimen we applied shear strains both parallel and perpendicular to the local split-line direction at a rate of 75 μm/min and calculated the peak-to-peak shear stresses, shear strain–energy dissipation densities, and peak effective shear moduli. The Wilcoxon signed rank test revealed that the medial condyle was anisotropic in some mechanical measures at applied shear strains above 5%, while the lateral condyle was mechanically isotropic at all applied shear strains. The Kruskal–Wallis test revealed no significant differences in the median mechanical behavior of the lateral and medial condyles. Spearman׳s rank correlations revealed statistically significant negative monotonic correlations among thickness and most of our mechanical measures for both lateral and medial condyles at most applied strains and directions of applied shear. These results suggest that large-strain analyses account for nonlinear, anisotropic and location-dependent effects not fully realized at small strains. Our findings may inspire new experiments and models that consider anisotropy and heterogeneity of cartilage in ways previously ignored.     

A spatial mechanism with higher pairs for modelling the human knee joint

By generalizing a previous model proposed in the literature, a new spatial kinematic model of the knee joint passive motion is presented. The model is based on an equivalent spatial parallel mechanism which relies upon the assumption that fibers within the anterior cruciate ligament (ACL), the medial collateral ligament (MCL) and the posterior cruciate ligament (PCL) can be considered as isometric during the knee flexion in passive motion (virtually unloaded motion). The articular surfaces of femoral and tibial condyles are modelled as 3-D surfaces of general shapes. In particular, the paper presents the closure equations of the new mechanism both for surfaces represented by means of scalar equations that have the Cartesian coordinates of the points of the surface as variables and for surfaces represented in parametric form. An example of simulation is presented in the case both femoral condyles are modelled as ellipsoidal surfaces and tibial condyles as spherical surfaces. The results of the simulation are compared to those of the previous models and to measurements. The comparison confirms the expectation that a better approximation of the tibiofemoral condyle surfaces leads to a more accurate model of the knee passive motion.     

Application of a semi-automatic cartilage segmentation method for biomechanical modeling of the knee joint

Manual segmentation of articular cartilage from knee joint 3D magnetic resonance images (MRI) is a time consuming and laborious task. Thus, automatic methods are needed for faster and reproducible segmentations. In the present study, we developed a semi-automatic segmentation method based on radial intensity profiles to generate 3D geometries of knee joint cartilage which were then used in computational biomechanical models of the knee joint. Six healthy volunteers were imaged with a 3T MRI device and their knee cartilages were segmented both manually and semi-automatically. The values of cartilage thicknesses and volumes produced by these two methods were compared. Furthermore, the influences of possible geometrical differences on cartilage stresses and strains in the knee were evaluated with finite element modeling. The semi-automatic segmentation and 3D geometry construction of one knee joint (menisci, femoral and tibial cartilages) was approximately two times faster than with manual segmentation. Differences in cartilage thicknesses, volumes, contact pressures, stresses, and strains between segmentation methods in femoral and tibial cartilage were mostly insignificant (p > 0.05) and random, i.e. there were no systematic differences between the methods. In conclusion, the devised semi-automatic segmentation method is a quick and accurate way to determine cartilage geometries; it may become a valuable tool for biomechanical modeling applications with large patient groups.     

Discrepancies in knee joint moments using common anatomical frames defined by different palpable landmarks

The aim was to investigate the effects of three anatomical frames using palpable anatomical landmarks of the knee on the net knee joint moments. The femoral epicondyles, femoral condyles, and tibial ridges were used to define the different anatomical frames and the segment end points of the distal femur and proximal tibia, which represent the origin of the tibial coordinate system. Gait data were then collected using the calibrated anatomical system technique (CAST), and the external net knee joint moments in the sagittal, coronal, and transverse planes were calculated based upon the three anatomical frames. Peak knee moments were found to be significantly different in the sagittal plane by approximately 25% (p 相似文献   

Load sharing between solid and fluid phases in articular cartilage: I--Experimental determination of in situ mechanical conditions in a porcine knee.

The in situ mechanical conditions of cartilage in the articulated knee were quantified during joint loading. Six porcine knees were subjected to a 445 N compressive load while cartilage deformations and contact pressures were measured. From roentgenograms, cartilage thickness before and during loading allowed the calculation of tissue deformation on the lateral femoral condyle at different times during the loading process. Contact pressures on the articular surface were measured with miniature fiber-optic pressure transducers. Results showed that the medial side of the lateral femoral condyle had higher contact pressures, as well as deformations. To begin to correlate the pressures and resulting deformations, the intrinsic material properties of the cartilage on the lateral condyle were obtained from indentation tests. Data from four normal control specimens indicated that the aggregate modulus of the medial side was significantly higher than in other areas of the condyle. These experimental measures of the in situ mechanical conditions of articular cartilage can be combined with theoretical modeling to obtain valuable information about the relative contributions of the solid and fluid phases to supporting the applied load on the cartilage surface (see Part II).     

Use of 3D geometry modeling of osteochondrosis-like iatrogenic lesions as a template for press-and-fit scaffold seeded with mesenchymal stem cells

Computed tomography (CT) is an effective diagnostic modality for three-dimensional imaging of bone structures, including the geometry of their defects. The aim of the study was to create and optimize 3D geometrical and real plastic models of the distal femoral component of the knee with joint surface defects. Input data included CT images of stifle joints in twenty miniature pigs with iatrogenic osteochondrosis-like lesions in medial femoral condyle of the left knee. The animals were examined eight and sixteen weeks after surgery. Philips MX 8000 MX and View workstation were used for scanning parallel plane cross section slices and Cartesian discrete volume creation. On the average, 100 slices were performed in each stifle joint. Slice matrices size was 512 x 512 with slice thickness of 1 mm. Pixel (voxel) size in the slice plane was 0.5 mm (with average accuracy of +/-0.5 mm and typical volume size 512 x 512 x 100 voxels). Three-dimensional processing of CT data and 3D geometrical modelling, using interactive computer graphic system MediTools formerly developed here, consisted of tissue segmentation (raster based method combination and 5 % of manual correction), vectorization by the marching-cubes method, smoothing and decimation. Stifle- joint CT images of three individuals of different body size (small, medium and large) were selected to make the real plastic models of their distal femurs from plaster composite using rapid prototyping technology of Zcorporation. Accuracy of the modeling was +/- 0.5 mm. The real plastic models of distal femurs can be used as a template for developing custom made press and fit scaffold implants seeded with mesenchymal stem cells that might be subsequently implanted into iatrogenic joint surface defects for articular cartilage-repair enhancement.     

Knee joint kinematics during walking influences the spatial cartilage thickness distribution in the knee

The regional adaptation of knee cartilage morphology to the kinematics of walking has been suggested as an important factor in the evaluation of the consequences of alteration in normal gait leading to osteoarthritis. The purpose of this study was to investigate the association of spatial cartilage thickness distributions of the femur and tibia in the knee to the knee kinematics during walking. Gait data and knee MR images were obtained from 17 healthy volunteers (age 33.2 ± 9.8 years). Cartilage thickness maps were created for the femoral and tibial cartilage. Locations of thickest cartilage in the medial and lateral compartments in the femur and tibia were identified using a numerical method. The flexion-extension (FE) angle associated with the cartilage contact regions on the femur, and the anterior-posterior (AP) translation and internal-external (IE) rotation associated with the cartilage contact regions on the tibia at the heel strike of walking were tested for correlation with the locations of thickest cartilage. The locations of the thickest cartilage had relatively large variation (SD, 8.9°) and was significantly associated with the FE angle at heel strike only in the medial femoral condyle (R(2)=0.41, p<0.01). The natural knee kinematics and contact surface shapes seem to affect the functional adaptation of knee articular cartilage morphology. The sensitivity of cartilage morphology to kinematics at the knee during walking suggests that regional cartilage thickness variations are influenced by both loading and the number of loading cycles. Thus walking is an important consideration in the analysis of the morphological variations of articular cartilage, since it is the dominant cyclic activity of daily living. The sensitivity of cartilage morphology to gait kinematics is also important in understanding the etiology and pathomechanics of osteoarthritis.     

Deformation of the distal femur: a contribution towards the pathogenesis of osteochondrosis dissecans in the knee joint.

Osteochondrosis dissecans (OD) is a process of subchondral bone necrosis occurring predominantly in young individuals at specific sites. The aetiology of this disease remains controversial with mechanical processes due to trauma and/or ischaemic factors being proposed. This study aims at explaining the aetiology of OD in the knee joint as a result of the particular deformation of the condyles. A finite element analysis of the distal third of the femur was performed. A three-dimensional model was developed based on computed tomography scans of a normal femur, consisting of cortical bone, cancellous bone and articular cartilage. This model was subjected to physiological loads at 0, 30, 60 and 90 degrees of knee flexion. A complex deformation was found within each condyle as well as between the two condyles. Both medial and lateral condyles are deformed in the medio-lateral direction and at the same time compressed between the patella and the tibia in the antero-posterior direction. This effect is highest at 60 degrees of knee flexion. In both planes, the medial condyle is distorted more than the lateral one. Strain concentration in the subchondral bone facing the patella varies with flexion, especially for angles exceeding 60 degrees. The deformation of the femur in the predominant locus of OD in the medial condyle exceeds that of the lateral condyle considerably. The analysis shows that repeated vigorous exercise including extreme knee flexion may produce rapidly changing strains which in turn could ultimately be responsible for local subchondral bone collapse.     

In vivo tibiofemoral contact analysis using 3D MRI-based knee models

This paper quantified the motion of the tibiofemoral contact points during in vivo weight bearing flexion using MRI- based 3D knee models and two orthogonal fluoroscopic images. The contact points on the medial and lateral tibial plateau were calculated by finding the centroid of the intersection of the tibial and femoral cartilage layers and by using the bony geometry alone. Our results indicate that the medial femoral condyle remains in the central portion of the tibial plateau and the lateral condyle translates posteriorly with increasing flexion. Using the bony contact model increased the total translation of the medial and lateral condyles by 250 and 55%, respectively, compared to the cartilage contact model. These results suggest that using the bony geometry alone may not accurately represent the articular surfaces of the knee. Articular cartilage geometry may have to be used to accurately quantify tibiofemoral contact.     

Tibiofemoral kinematics and condylar motion during the stance phase of gait

Accurate knowledge of the dynamic knee motion in-vivo is instrumental for understanding normal and pathological function of the knee joint. However, interpreting motion of the knee joint during gait in other than the sagittal plane remains controversial. In this study, we utilized the dual fluoroscopic imaging technique to investigate the six-degree-of-freedom kinematics and condylar motion of the knee during the stance phase of treadmill gait in eight healthy volunteers at a speed of 0.67 m/s. We hypothesized that the 6DOF knee kinematics measured during gait will be different from those reported for non-weightbearing activities, especially with regards to the phenomenon of femoral rollback. In addition, we hypothesized that motion of the medial femoral condyle in the transverse plane is greater than that of the lateral femoral condyle during the stance phase of treadmill gait. The rotational motion and the anterior–posterior translation of the femur with respect to the tibia showed a clear relationship with the flexion–extension path of the knee during the stance phase. Additionally, we observed that the phenomenon of femoral rollback was reversed, with the femur noted to move posteriorly with extension and anteriorly with flexion. Furthermore, we noted that motion of the medial femoral condyle in the transverse plane was greater than that of the lateral femoral condyle during the stance phase of gait (17.4±2.0 mm vs. 7.4±6.1 mm, respectively; p<0.01). The trend was opposite to what has been observed during non-weightbearing flexion or single-leg lunge in previous studies. These data provide baseline knowledge for the understanding of normal physiology and for the analysis of pathological function of the knee joint during walking. These findings further demonstrate that knee kinematics is activity-dependent and motion patterns of one activity (non-weightbearing flexion or lunge) cannot be generalized to interpret a different one (gait).     

Tibio-femoral movement in the living knee. A study of weight bearing and non-weight bearing knee kinematics using 'interventional' MRI

The aim of this study was to image tibio-femoral movement during flexion in the living knee. Ten loaded male Caucasian knees were initially studied using MRI, and the relative tibio-femoral motions, through the full flexion arc in neutral tibial rotation, were measured. On knee flexion from hyperextension to 120 degrees , the lateral femoral condyle moved posteriorly 22 mm. From 120 degrees to full squatting there was another 10 mm of posterior translation, with the lateral femoral condyle appearing almost to sublux posteriorly. The medial femoral condyle demonstrated minimal posterior translation until 120 degrees . Thereafter, it moved 9 mm posteriorly to lie on the superior surface of the medial meniscal posterior horn. Thus, during flexion of the knee to 120 degrees , the femur rotated externally through an angle of 20 degrees . However, on flexion beyond 120 degrees , both femoral condyles moved posteriorly to a similar degree. The second part of this study investigated the effect of gender, side, load and longitudinal rotation. The pattern of relative tibio-femoral movement during knee flexion appears to be independent of gender and side. Femoral external rotation (or tibial internal rotation) occurs with knee flexion under loaded and unloaded conditions, but the magnitude of rotation is greater and occurs earlier on weight bearing. With flexion plus tibial internal rotation, the pattern of movement follows that in neutral. With flexion in tibial external rotation, the lateral femoral condyle adopts a more anterior position relative to the tibia and, particularly in the non-weight bearing knee, much of the femoral external rotation that occurs with flexion is reversed.     

Effects of joint unloading and reloading on human cartilage morphology and function, muscle cross-sectional areas, and bone density - a quantitative case report

Recent studies have shown that thinning of human cartilage occurs with unloading, but no data are available on the effect of remobilization (after immobilization) on knee joint cartilage status in humans. We examined a 36-year-old patient after 6 weeks of unilateral immobilization. Knee joint cartilage morphology (patella and tibia), patellar cartilage deformation, and thigh muscle cross-sectional areas were assessed with quantitative MR imaging and bone density with peripheral quantitative computed tomography (pQCT) during 24 months of remobilization. The immobilized limb displayed lower muscle cross-sectional areas (MCSA) of the knee extensors (-36%), lower bone density of the femur and tibia (-12/-6%), lower patellar cartilage thickness (-14%), but no side differences of tibial cartilage thickness. During remobilization, side differences decreased to -4% for knee extensor MCSAs, to -6%/-3% for femoral and tibial BMD, and to -8% for patellar cartilage thickness. No change was observed in tibial cartilage. Patellar deformation decreased from 9% to 4% after 15 months. In conclusion, we observed substantial changes of thigh MCSAs, but little (patella) to no (tibia) change in cartilage thickness during remobilization. These preliminary results indicate that human cartilage macro-morphology may be less adaptive to variations of the mechanical loading than muscle and bone.     

The movement of the normal tibio-femoral joint

This review describes the anatomy of the articular surfaces and their movement in the normal tibio-femoral joint, together with methods of measurement in volunteers. Forces and soft tissues are excluded. To measure movement, the articular surfaces and natural or inserted movement markers must be imaged by some combination of MRI, CT, RSA or fluoroscopy. With the aid of computer-imaging, the movements can then be related to an anatomy-based co-ordinate system to avoid kinematic cross-talk. Methods of depicting these movements which are understandable to engineers and clinicians are discussed. The shapes of the articular surfaces are reported. They are relevant to landmarks and co-ordinate systems and form a basis for inferring the nature of the movements which take place in the knee. The movements of the condyles are described from hyperextension to full passive flexion. Medially the condyle hardly moves antero-posteriorly from 0 degrees to 120 degrees but the contact area transfers from an anterior pair of tibio-femoral surfaces at 10 degrees to a posterior pair at about 30 degrees . Thus because of the shapes of the bones, the medial contact area moves backwards with flexion to 30 degrees but the condyle does not. Laterally the femoral condyle and the contact area move posteriorly but to a variable extent in the mid-range causing tibial internal rotation to occur with flexion around a medial axis. From 120 degrees to full flexion both condyles roll back onto the posterior horn so that the tibio-femoral joint subluxes.     

Effects of increased chronic loading on articular cartilage material properties in the Lapine tibio-femoral joint

Methods of producing relevant and quantifiable load alterations in vivo with which to study load-induced cartilage degeneration analogous to osteoarthritis are limited. An animal model was used to investigate the effects of increased chronic loads on articular cartilage. Mature rabbits were randomized into one of three experimentally loaded groups and a fourth unoperated control group. A mechanical-loading device was skeletally fixed to the hind limb of animals in the loaded groups. Engaging the device resulted in an additional load of 0%, +22% or +44% body weight to the medial compartment of the experimental knee, while allowing normal joint function. Following a 12-week loading protocol, a creep-indentation test and needle probe test were used to determine the biphasic material properties and thickness of the cartilage at four locations of each femoral and tibial condyle of the experimental and contralateral limbs. Analyses of covariance were performed to compare outcome measures across the treatment groups. The effect of increased load was site and load-level specific with alterations of material properties and thickness most prominent in the posterior region of the medial compartment of the tibia. At this site, permeability increased 128% and thickness increased 28% in the +44% body weight group relative to the 0% body weight group. This model of altered chronic loading initiated changes in the material properties to the articular cartilage at the sites of increased load over 12-weeks that were consistent with early degenerative changes suggesting that increased tibio-femoral loading may be responsible for the alterations. This work begins to elucidate the chronic-load threshold and the time course of cartilage degeneration at different levels of altered loading.     

In vivo patellar tracking and patellofemoral cartilage contacts during dynamic stair ascending

The knowledge of normal patellar tracking is essential for understanding the knee joint function and for diagnosis of patellar instabilities. This paper investigated the patellar tracking and patellofemoral joint contact locations during a stair ascending activity using a validated dual-fluoroscopic imaging system. The results showed that the patellar flexion angle decreased from 41.9° to 7.5° with knee extension during stair ascending. During first 80% of the activity, the patella shifted medially about 3.9mm and then slightly shifted laterally during the last 20% of the ascending activity. Anterior translation of 13mm of the patella was measured at the early 80% of the activity and the patella slightly moved posteriorly by about 2mm at the last 20% of the activity. The path of cartilage contact points was slightly lateral on the cartilage surfaces of patella and femur. On the patellar cartilage surface, the cartilage contact locations were about 2mm laterally from heel strike to 60% of the stair ascending activity and moved laterally and reached 5.3mm at full extension. However, the cartilage contact locations were relatively constant on the femoral cartilage surface (～5mm lateral). The patellar tracking pattern was consistent with the patellofemoral cartilage contact location pattern. These data could provide baseline knowledge for understanding of normal physiology of the patellofemoral joint and can be used as a reference for clinical evaluation of patellofemoral disorders.     

A finite element model of the human knee joint for the study of tibio-femoral contact

As a step towards developing a finite element model of the knee that can be used to study how the variables associated with a meniscal replacement affect tibio-femoral contact, the goals of this study were 1) to develop a geometrically accurate three-dimensional solid model of the knee joint with special attention given to the menisci and articular cartilage, 2) to determine to what extent bony deformations affect contact behavior, and 3) to determine whether constraining rotations other than flexion/extension affects the contact behavior of the joint during compressive loading. The model included both the cortical and trabecular bone of the femur and tibia, articular cartilage of the femoral condyles and tibial plateau, both the medial and lateral menisci with their horn attachments, the transverse ligament, the anterior cruciate ligament, and the medial collateral ligament. The solid models for the menisci and articular cartilage were created from surface scans provided by a noncontacting, laser-based, three-dimensional coordinate digitizing system with an root mean squared error (RMSE) of less than 8 microns. Solid models of both the tibia and femur were created from CT images, except for the most proximal surface of the tibia and most distal surface of the femur which were created with the three-dimensional coordinate digitizing system. The constitutive relation of the menisci treated the tissue as transversely isotropic and linearly elastic. Under the application of an 800 N compressive load at 0 degrees of flexion, six contact variables in each compartment (ie., medial and lateral) were computed including maximum pressure, mean pressure, contact area, total contact force, and coordinates of the center of pressure. Convergence of the finite element solution was studied using three mesh sizes ranging from an average element size of 5 mm by 5 mm to 1 mm by 1 mm. The solution was considered converged for an average element size of 2 mm by 2 mm. Using this mesh size, finite element solutions for rigid versus deformable bones indicated that none of the contact variables changed by more than 2% when the femur and tibia were treated as rigid. However, differences in contact variables as large as 19% occurred when rotations other than flexion/extension were constrained. The largest difference was in the maximum pressure. Among the principal conclusions of the study are that accurate finite element solutions of tibio-femoral contact behavior can be obtained by treating the bones as rigid. However, unrealistic constraints on rotations other than flexion/extension can result in relatively large errors in contact variables.     

The load-bearing area in the knee joint

Measurements were made of the location and size of the contact areas in cadaver knee joints, for a load of 150 Kgf applied for 5 sec down the long axis of the tibia. Results were obtained from a total of 4 knees, considering flexion angles from 0 to 120°. The methods used were to measure directly from castings of the joint cavity; and to calculate from measurements of radii of curvature and joint deflection. Average contact areas for lateral and medial condyles were 1·4 and 1·8 cm² respectively. Areas for the medial condyle were greater than for the lateral condyle and also the areas diminished as flexion angle increased. The implications of the results to contact stresses, joint lubrication and ‘condylar replacement’ knee prosthesis design were discussed.     

Ex vivo thickness measurement of cartilage covering the temporomandibular joint

Articular cartilage covers the temporomandibular joint (TMJ) and provides smooth and nearly frictionless articulation while distributing mechanical loads to the subchondral bone. The thickness of the cartilage is considered to be an indicator of the stage of development, maturation, aging, loading history, and disease. The aim of our study was to develop a method for ex vivo assessment of the thickness of the cartilage that covers the TMJ and to compare that with two other existing methods. Eight porcine TMJ condyles were used to measure cartilage thickness. Three different methods were employed: needle penetration, micro-computed tomography (micro-CT), and histology; the latter was considered the gold standard. Histology and micro-CT scanning results showed no significant differences between thicknesses throughout the condyle. Needle penetration produced significantly higher values than histology, in the lateral and anterior regions. All three methods showed the anterior region to be thinner than the other regions. We concluded that overestimated thickness by the needle penetration is caused by the penetration of the needle through the first layer of subchondral bone, in which mineralization is less than in deeper layers. Micro-CT scanning method was found to be a valid method to quantify the thickness of the cartilage, and has the advantage of being non-destructive.