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.     

The temporal response of the friction coefficient of articular cartilage depends on the contact area

The hypothesis of this study is that the time constant for the transient increase in friction coefficient of articular cartilage under a constant load is proportional to the size of the contact area, as predicated by the dependence of the frictional response on interstitial fluid pressurization. This hypothesis is verified experimentally from measurements of the frictional response of bovine articular cartilage disks of three different diameters (4, 6 and 8mm) against glass. At two different applied stresses (0.127 and 0.254 MPa), the coefficient of determination of a linear regression of the time constant versus the contact area yielded R(2) = 0.892 and R(2) = 0.979 (p < 0.001). The results of this study provide a cogent explanation for the expectation that the friction coefficient in situ will not achieve the elevated equilibrium values observed under common testing conditions.     

Finite element study of a tissue-engineered cartilage transplant in human tibiofemoral joint

Most tissue-engineered cartilage constructs are more compliant than native articular cartilage (AC) and are poorly integrated to the surrounding tissue. To investigate the effect of an implanted tissue-engineered construct (TEC) with these inferior properties on the mechanical environment of both the engineered and adjacent native tissues, a finite element study was conducted. Biphasic swelling was used to model tibial cartilage and an implanted TEC with the material properties of either native tissue or a decreased elastic modulus and fixed charged density. Creep loading was applied with a rigid impermeable indenter that represented the femur. In comparison with an intact joint, compressive strains in the transplant, surface contact stress in the adjacent native AC and load partitioning between different phases of cartilage were affected by inferior properties of TEC. Results of this study may lead to a better understanding of the complex mechanical environment of an implanted TEC.     

Finite element study of a tissue-engineered cartilage transplant in human tibiofemoral joint

Most tissue-engineered cartilage constructs are more compliant than native articular cartilage (AC) and are poorly integrated to the surrounding tissue. To investigate the effect of an implanted tissue-engineered construct (TEC) with these inferior properties on the mechanical environment of both the engineered and adjacent native tissues, a finite element study was conducted. Biphasic swelling was used to model tibial cartilage and an implanted TEC with the material properties of either native tissue or a decreased elastic modulus and fixed charged density. Creep loading was applied with a rigid impermeable indenter that represented the femur. In comparison with an intact joint, compressive strains in the transplant, surface contact stress in the adjacent native AC and load partitioning between different phases of cartilage were affected by inferior properties of TEC. Results of this study may lead to a better understanding of the complex mechanical environment of an implanted TEC.     

Stress distributions and material properties determined in articular cartilage from MRI-based finite strains

The noninvasive measurement of finite strains in biomaterials and tissues by magnetic resonance imaging (MRI) enables mathematical estimates of stress distributions and material properties. Such methods allow for non-contact and patient-specific modeling in a manner not possible with traditional mechanical testing or finite element techniques. Here, we employed three constitutive (i.e. linear Hookean, and nonlinear Neo-Hookean and Mooney-Rivlin) relations with known loading conditions and MRI-based finite strains to estimate stress patterns and material properties in the articular cartilage of tibiofemoral joints. Displacement-encoded MRI was used to determine two-dimensional finite strains in juvenile porcine joints, and an iterative technique estimated stress distributions and material properties with defined constitutive relations. Stress distributions were consistent across all relations, although the stress magnitudes varied. Material properties for femoral and tibial cartilage were found to be consistent with those reported in literature. Further, the stress estimates from Hookean and Neo-Hookean, but not Mooney-Rivlin, relations agreed with finite element-based simulations. A nonlinear Neo-Hookean relation provided the most appropriate model for the characterization of complex and spatially dependent stresses using two-dimensional MRI-based finite strain. These results demonstrate the feasibility of a new and computationally efficient technique incorporating MRI-based deformation with mathematical modeling to non-invasively evaluate the mechanical behavior of biological tissues and materials.     

Subject-specific knee joint geometry improves predictions of medial tibiofemoral contact forces

Estimating tibiofemoral joint contact forces is important for understanding the initiation and progression of knee osteoarthritis. However, tibiofemoral contact force predictions are influenced by many factors including muscle forces and anatomical representations of the knee joint. This study aimed to investigate the influence of subject-specific geometry and knee joint kinematics on the prediction of tibiofemoral contact forces using a calibrated EMG-driven neuromusculoskeletal model of the knee. One participant fitted with an instrumented total knee replacement walked at a self-selected speed while medial and lateral tibiofemoral contact forces, ground reaction forces, whole-body kinematics, and lower-limb muscle activity were simultaneously measured. The combination of generic and subject-specific knee joint geometry and kinematics resulted in four different OpenSim models used to estimate muscle–tendon lengths and moment arms. The subject-specific geometric model was created from CT scans and the subject-specific knee joint kinematics representing the translation of the tibia relative to the femur was obtained from fluoroscopy. The EMG-driven model was calibrated using one walking trial, but with three different cost functions that tracked the knee flexion/extension moments with and without constraint over the estimated joint contact forces. The calibrated models then predicted the medial and lateral tibiofemoral contact forces for five other different walking trials. The use of subject-specific models with minimization of the peak tibiofemoral contact forces improved the accuracy of medial contact forces by 47% and lateral contact forces by 7%, respectively compared with the use of generic musculoskeletal model.     

Chondrocyte damage and contact pressures following impact on the rabbit tibiofemoral joint

Epidemiological studies show that tibial plateau fractures comprise about 10% of all below-knee injuries in car crashes. Studies from this laboratory document that impacts to the tibiofemoral (TF) joint at 50% of the energy producing gross fracture can generate cartilage damage and microcracks at the interface between calcified cartilage and underlying subchondral bone in the tibial plateau. These injuries are suggestive of the initiation for a long term chronic disease, such as osteoarthritis. The disease process may be further encouraged by acute damage to chondrocytes in the cartilage overlying areas of occult microcracking. The hypothesis of the current study was that significant damage to chondrocytes in tibial plateau cartilage could be generated in areas of high contact pressure by a single impact delivered to the rabbit TF joint, without a gross fracture of bone. Three rabbits received a single, 13 J of energy blunt insult to the TF joint, while another three animals were used as controls. Cell viability analyses compared chondrocyte damage in impacted versus control cartilage. Two additional rabbits were impacted to document contact pressures generated in the TF joint. The study showed high contact pressures in uncovered areas of the plateau, with a trend for higher pressures in the lateral versus medial facets. A significantly higher percentage of damaged chondrocytes existed in impacted versus the opposite, nonimpacted limbs. Additionally, more chondrocyte damage was documented in the superficial zone (top 20% of cartilage thickness) of the cartilage compared to middle (middle 50% of thickness) and deep (bottom 30% of thickness) zones. This study showed that a single blunt insult to the in situ rabbit TF joint, generating large areas of contact pressure exceeding 20 MPa, produces significant chondrocyte damage in the tibial articular cartilage, especially in the superficial zone, without gross fracture of bone. Future studies will be needed to investigate the long term, chronic outcome of this blunt force joint trauma.     

Chondrogenesis,joint formation,and articular cartilage regeneration

The repair of joint surface defects remains a clinical challenge, as articular cartilage has a limited healing response. Despite this, articular cartilage does have the capacity to grow and remodel extensively during pre‐ and post‐natal development. As such, the elucidation of developmental mechanisms, particularly those in post‐natal animals, may shed valuable light on processes that could be harnessed to develop novel approaches for articular cartilage tissue engineering and/or regeneration to treat injuries or degeneration in adult joints. Much has been learned through mouse genetics regarding the embryonic development of joints. This knowledge, as well as the less extensive available information regarding post‐natal joint development is reviewed here and discussed in relation to their possible relevance to future directions in cartilage tissue repair and regeneration. J. Cell. Biochem. 107: 383–392, 2009. © 2009 Wiley‐Liss, Inc.     

Comparison of proteoglycans from bovine articular cartilage.

Four bovine articular cartilages have been compared with regard to the chemical composition of the whole cartilages, the amount of proteoglycan selectively extracted with 3 M MGCl2 or with 3 M guanidine-HCl, and the compositions and physical properties of the isolated proteoglycans. The whole cartilages differ but slightly in composition. Occipital condylar cartilage, a thin cartilage from the smallest joint, contains 4% more collagen and proportionately less proteoglycan than proximal humeral, the thickest cartilage from the largest joint. Each cartilage contains a pool of proteoglycan that resists extraction with 3 M MgCl2 but is extracted with 3 M guanidine-HCl. The proteoglycan extracted from each cartilage with 3 M guanidine-HCl contains a high molecular weight proteoglycan-collagen complex demonstrated by analytical ultracentrifugation and by the turbidity of its visible and ultra-violet spectra. The four cartilages appear to differ most remarkably in the fraction of total proteoglycan extracted from each as proteoglycan-collagen complex.     

Determination of real-time in-vivo cartilage contact deformation in the ankle joint

The knowledge of real-time in-vivo cartilage deformation is important for understanding of cartilage function and biomechanical factors that may relate to cartilage degeneration. This study investigated cartilage contact area and peak contact compressive strain of four healthy human ankle joints as a function of time using a combined magnetic resonance (MR) and dual-orthogonal fluoroscopic imaging technique. Each ankle was subjected to a different constant loading (between 700 and 820 N). The cartilage contact deformation was obtained from the first second to 300 s after the load was applied. In all ankle joints studied in this paper, contact strains increased to 24-38% at first 20 s after loading. Beyond 20 s, the change of cartilage contact deformation was relatively small and varied in a rate close to zero beyond 50 s. These data indicated that the cartilage contact areas and contact strain could raise dramatically right after loading and reach a relatively stable condition within 1 min after constant loading. The history of cartilage deformation determined in this study may provide a real-time boundary condition for 3D finite element simulation of in vivo cartilage contact stress in the joint as a function of time.     

An articular cartilage contact model based on real surface geometry

Abnormal, excessive stresses acting on articular joint surfaces are speculated to be one of the causes for joint degeneration. However, articular surface stresses have not been studied systematically, since it is technically difficult to measure in vivo contact areas and pressures in dynamic situations. Therefore, we implemented a numerical model of articular surface contact using accurate surface geometries. The model was developed for the cat patellofemoral joint. We demonstrated that small misalignments of the patella relative to the femur change the joint contact mechanics substantially for a given external load. These results suggest that misalignment might be studied as one of the factors causing articular cartilage disorder and joint degeneration.     

A multiscale synthesis: characterizing acute cartilage failure under an aggregate tibiofemoral joint loading

Biomechanics and Modeling in Mechanobiology - Knee articular cartilage is characterized by a complex mechanical behavior, posing a challenge to develop an efficient and precise model. We argue that...     

Statistical shape model-based prediction of tibiofemoral cartilage

Abstract

Computed tomography is used more routinely to design patient-specific instrumentation for knee replacement surgery. Its moderate imaging cost and simplified segmentation reduce design costs compared with magnetic resonance (MR) imaging, but it cannot provide the necessary cartilage information. Our method based on statistical shape modelling proved to be successful in predicting tibiofemoral cartilage in leave-one-out experiments. The obtained accuracy of 0.54?mm for femur and 0.49?mm for tibia outperforms the average cartilage thickness distribution and reported inter-observer MR segmentation variability. These results suggest that shape modelling is able to predict tibiofemoral cartilage with sufficient accuracy to design patient-specific instrumentation.     

Precision MRI-based joint surface and cartilage density analysis of the knee joint using rapid water-excitation sequence and semi-automatic segmentation algorithm]

The aim of this study was to analyse the precision of three-dimensional joint surface and cartilage thickness measurements in the knee, using a fast, high-resolution water-excitation sequence and a semiautomated segmentation algorithm. The knee joint of 8 healthy volunteers, aged 22 to 29 years, were examined at a resolution of 1.5 mm x 0.31 mm x 0.31 mm, with four sagittal data sets being acquired after repositioning the joint. After semiautomated segmentation with a B-spline Snake algorithm and 3D reconstruction of the patellar, femoral and tibial cartilages, the joint surface areas (triangulation), cartilage volume, and mean and maximum thickness (Euclidean distance transformation) were analysed, independently of the orientation of the sections. The precision (CV%) for the surface areas was 2.1 to 6.6%. The mean cartilage thickness and cartilage volume showed coefficients of 1.9 to 3.5% (except for the femoral condyles), the value for the medial femoral condyle being 9.1%, and for the lateral condyle 6.5%. For maximum thickness, coefficients of between 2.6 and 5.9% were found. In the present study we investigate for the first time the precision of MRI-based joint surface area measurements in the knee, and of cartilage thickness analyses in the femur. Using a selective water-excitation sequence, the acquisition time can be reduced by more than 50%. The poorer precision in the femoral condyles can be attributed to partial volume effects that occur at the edges of the joint surfaces with a sagittal image protocol. Since MRI is non-invasive, it is highly suitable for examination of healthy subjects (generation of individual finite element models, analysis of functional adaptation to mechanical stimulation, measurement of cartilage deformation in vivo) and as a diagnostic tool for follow-up, indication for therapy, and objective evaluation of new therapeutic agents in osteoarthritis.     

Reduced deposition of collagen in the degenerated articular cartilage of dogs with degenerative joint disease

Collagen metabolism in the focal degenerated cartilage from immature dogs with degenerative joint disease was compared with that in the adjacent ‘normal’ cartilage of the same joint surface. The deposition of collagen into the cartilage in vitro as measured by accumulation of hydroxyl [¹⁴C]proline was decreased in the early and in advanced stages of cartilage degeneration. The deposition of collagen into cartilage in vivo as measured by the accumulation of hydroxy[³H]proline (intravenously injected [³H]proline) also was reduced in the degenerated cartilages of a dog with degenerative joint disease. Gel electrophoretic analysis revealed that degenerated cartilage contained less α₁ collagen chains, but increased amounts of larger proteins. Degenerated cartilage contained more water, increased amounts of unidentified, non-collagenous protien. increased collagenolytic enzyme activity and fewer chondrocytes. Decreased deposition of collagen would result in collagen depletion in the foci of degenerated cartilage in joints of dogs with degenerative joint disease.     

MRI-based assessment of hip joint translations

To better understand movement limitations and, to some extent, the pathogenesis of osteoarthritis, it is important to quantitatively measure femoroacetabular translations to assess if any joint subluxation occurs. In this paper, we aim at measuring hip joint displacements from magnetic resonance images (MRI) based on a surface registration technique. Because this measurement is related to the location of the hip joint center (HJC), we investigate and compare different HJC estimation approaches based on patient-specific 3D bone models. We estimate the HJC based on a simulated circumduction while minimizing inter-articular distance changes. Measurements of femoroacetabular translations during low amplitude abductions ($80$ samples) and extreme flexions ($60$ samples) in female professional dancers, which is a population potentially exposed to femoroactebaluar impingements, do not show any significant subluxation.     

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.