Osteochondral Grafting: Effect of Graft Alignment, Material Properties, and Articular Geometry

Osteochondral grafting for cartilage lesions is an attractive surgical procedure; however, the clinical results have not always been successful. Surgical recommendations differ with respect to donor site and graft placement technique. No clear biomechanical analysis of these surgical options has been reported. We hypothesized that differences in graft placement, graft biomechanical properties, and graft topography affect cartilage stresses and strains. A finite element model of articular cartilage and meniscus in a normal knee was constructed. The model was used to analyze the magnitude and the distribution of contact stresses, von Mises stresses, and compressive strains in the intact knee, after creation of an 8-mm diameter osteochondral defect, and after osteochondral grafting of the defect. The effects of graft placement, articular surface topography, and biomechanical properties were evaluated. The osteochondral defect generated minimal changes in peak contact stress (3.6 MPa) relative to the intact condition (3.4 MPa) but significantly increased peak von Mises stress (by 110%) and peak compressive strain (by 63%). A perfectly matched graft restored stresses and strains to near intact conditions. Leaving the graft proud by 0.5 mm generated the greatest increase in local stresses (peak contact stresses = 6.7 MPa). Reducing graft stiffness and curvature of articular surface had lesser effects on local stresses. Graft alignment, graft biomechanical properties, and graft topography all affected cartilage stresses and strains. Contact stresses, von Mises stresses, and compressive strains are biomechanical markers for potential tissue damage and cell death. Leaving the graft proud tends to jeopardize the graft by increasing the stresses and strains on the graft. From a biomechanical perspective, the ideal surgical procedure is a perfectly aligned graft with reasonably matched articular cartilage surface from a lower load-bearing region of the knee

Load Bearing Characteristics Of Implants For Osteochondral Defect Repair

Objective: To measure changes in joint contact mechanics, during simulated gait, in the presence of a medial femoral osteochondral defect and after filling the defect using two different polyvinyl alcohol implant configurations. Methods: Seven human cadaveric knees were tested under simulated gait, while the contact stresses on the tibial plateau were recorded using an electronic sensor. Each knee was tested using the following conditions: intact, defect, and after the defect has been filled with either 10% PVA, 20% PVA, 10% PVA + a porous titanium base, or 20% PVA + porous titanium base. Changes in contact area, total force, weight center of contact, and stress pattern differences were measured for each knee. Results: At 14% of the gait cycle, there were no changes in contact area observed between conditions. At 45% of the gait cycle, differences were seen in the meniscal-cartilage contact area with increases in contact area between the intact and 10% PVA as well as 20% PVA scaffolds. At 14% of gait, there was a significant increase in total force between intact and defect conditions and between defect and 20% PVA + pTi in the menical-cartilage region with forces of 179 ± 113 N, 278 ± 113 N, and 193 ± 96 N for the intact, defect, and 20% PVA + pTi respectively. At 45% of gait, there was a significant difference in total force between intact condition and the defect condition in the meniscal-cartilage contact area with average total force of 90 ± 73 N and 148 ± 75 N respectively. Differences were found in the cartilage-cartilage total force at 45% of gait between intact and all other conditions and between defect and 20% PVA + pTi. The total forces were 486 ± 134 N for the intact, 360 ± 158 N for the defect, and 431 ± 177 for the 20% PVA + pTi, and the remaining implants tested having total force values below 412 N. Conclusions: The presence of an osteochondral defect causes an increase in loading on the meniscus. Implants in the range of tissue engineered constructs can partially restore joint loading but cause alterations in contact stress patterns

Investigation of Subchondral Bone Abnormalities associated with Osteoarthritis using Image-Based Biomechanics

Osteoarthritis (OA) is degenerative disease caused by a mechanical failure of bone and cartilage. Common risk factors for developing OA include: being over-weight, female, having joint malalignment, or a history of prior joint injury. Post-traumatic OA is extremely common in the knee as individuals frequently suffer injuries to structures that provide stability to the joint. To enhance our understanding about OA, animal models are employed where the injury can be and monitored in a controlled environment. When used in conjunction with pre-clinical imaging techniques the longitudinal degradation of bone and cartilage can be quantitatively monitored in vivo. Recent evidence has identified cystic lesions within the subchondral bone as the possible source of painful symptoms and accelerated disease progression, but little is known about their etiology. The purpose of this thesis was to improve knowledge regarding the mechanism that causes subchondral cysts. OA was induced in the rodent knee via surgery, and the pathological changes were quantified with micro-CT and MRI. The composition of the cysts was correlated with end-stage histology. Thus, an accurate definition of OA bone cysts was achieved. To assess the effect of cysts in human bone, a study was conducted using a patient data set restrospectively. Using finite element (FE) analysis, higher stress values were found within bone surrounding cysts. Therefore, the probable mechanism of cyst expansion, stress induced resorption, was identified. Finally, the FE models of the bones were combined with soft tissue structures – from a co-registered MRI – to produce comprehensive patient-specific models of the knee

Magnetic Resonance Imaging for the Functional Analysis of Tissues and Biomaterials

Articular cartilage provides mechanical load dissipation and lubrication between joints, and additionally provides protects from abrasion. At present, there are no treatments to cure or attenuate the degradation of cartilage. Early detection and the ability to monitor the progression of osteoarthritis is important for developing effective therapies. However, few reliable imaging biomarkers exist to detect cartilage disease before advanced degeneration in the tissue. One specialized MRI technique, termed displacements under applied loading by MRI (dualMRI), was developed to measure displacements and strain in musculoskeletal tissues, hydrogels and engineered constructs. However, deformation information does not directly describe spatial distributions of tissue properties (e.g. stiffness), which is critical to the understanding of disease progression. To achieve the stiffness measurement, we developed and validated an inverse modeling workflow that combined dualMRI, to directly measure intratissue deformation, with topology optimization in the application of heterogeneous (layered) materials representative of the complex gradient architecture of articular cartilage. We successfully reconstructed bi-layer stiffness from ideal displacements calculated from forward simulation as well as from experimental data measured from dualMRI. To monitor the progression of osteoarthritis, we measured and analyzed biomechanical changes of sheep stifle cartilage after meniscectomy. We found that 2nd principal strain and max shear strain in the femur contact region are sensitive to cartilage degeneration at different stages and compared to more conventional methods like quantitative MRI. To investigate the biomechanical changes in articular cartilage with defect and repair, we implanted decellularized cartilage implant into sheep cartilage defect and evaluate the repair results using quantitative MRI and dualMRI. We found that implants placed in joints demonstrated lower strains compared to joints with untreated defects

Cartilage Repair and Regeneration: Focus on Multi-Disciplinary Strategies

The present book recapitulates the articles published within the Special Issue "Cartilage Repair and Regeneration: Focus on Multi-Disciplinary Strategies", Applied Sciences, MDPI, dealing with the innovative multi-disciplinary therapeutic approaches for musculoskeletal diseases. In particular the published studies space from advanced 3D bioprinting technology to obtain a scaffold with different zonal cell densities, and biphasic scaffold (ChondroMimetic) construction, pass through the comparison of different techniques for cartilage regeneration such as of mosaicplasty and matrix-assisted autologous chondrocyte transplantation (MACT) and histopathological features of osteochondral units, and end with the considerations regarding development of bioreactors able to mimic the biomechanical load on chondrocytes in vitro, giving some interesting insights in this specific scientific field

Effects of Articular Cartilage Defect Size and Shape on Subchondral Bone Contact: Implications for Surgical Cartilage Restoration

Osteoarthritis (OA) progression involves the deterioration of articular cartilage, which, without surgical intervention, will not spontaneously stop. A number of factors influence this progression, two of which are cartilage defect size and subchondral bone changes that occur, such as sclerosis. Microfracture surgery generates mechanically inferior fibrocartilage repair tissue and succeeds in stopping OA progression in small defects, while ACI produces highly organized hyaline-like cartilage that has been shown to restore function and stop OA progression in large defects. The most frequently quoted threshold size to guide defect management is 2 cm2 although there is relatively little clinical or biomechanical data to support this. Therefore, the purpose of this project was to determine the effect of defect size and shape on subchondral bone contact. Experimental biomechanical loading on bovine knees was preformed and defect subchondral bone contact was measured for defects ranging from 5 mm to 25 mm in diameter. Defect shape was also examined using oval – shaped defect. Results indicate that the current 2 cm2 threshold for guiding management of articular cartilage defects may be too conservative, as major subchondral bone contact was not realized in defects below 2.87 cm2 in our study. Furthermore, it was determined that subchondral bone contact was consistently higher in defect on the lateral condyle compared to that of the medial condyle. Preliminary testing of oval defect also suggests that the medial to lateral width of a defect may be more important than the absolute widest dimension of the defect.No embarg

Subject-Specific Finite Element Predictions of Knee Cartilage Pressure and Investigation of Cartilage Material Models

An estimated 27 million Americans suffer from osteoarthritis (OA). Symptomatic OA is often treated with total knee replacement, a procedure which is expected to increase in number by 673% from 2005 to 2030, and costs to perform total knee replacement surgeries exceeded $11 billion in 2005. Subject-specific modeling and finite element (FE) predictions are state-of-the-art computational methods for anatomically accurate predictions of joint tissue loads in surgical-planning and rehabilitation. Knee joint FE models have been used to predict in-vivo joint kinematics, loads, stresses and strains, and joint contact area and pressure. Abnormal cartilage contact pressure is considered a risk factor for incidence and progression of OA. For this study, three subject-specific tibiofemoral knee FE models containing accurate geometry were developed from magnetic resonance images (MRIs). Linear (LIN), Neo-Hookean (NH), and poroelastic (PE) cartilage material models were implemented in each FE model for each subject under three loading cases to compare cartilage contact pressure predictions at each load case. An additional objective was to compare FE predictions of cartilage contact pressure for LIN, NH, and PE material models with experimental measurements of cartilage contact pressure. Because past studies on FE predictions of cartilage contact pressure using different material models and material property values have found differences in cartilage contact pressure, it was hypothesized that different FE predictions of cartilage contact pressure using LIN, NH, and PE material models for three subjects at three different loading cases would find statistically significant differences in cartilage contact pressure between the material models. It was further hypothesized that FE predictions of cartilage contact pressure for the PE cartilage material model would be statistically similar to experimental data, while the LIN and NH cartilage material models would be significantly different for all three loading cases. This study found FE and experimental measurements of cartilage contact pressure only showed significant statistical differences for LIN, NH, and PE predictions in the medial compartment at 1000N applied at 30 degrees, and for the PE prediction in the medial compartment at 500N applied at 0 degrees. FE predictions of cartilage contact pressure using the PE cartilage material model were considered less similar to experimental data than the LIN and NH cartilage material models. This is the first study to use LIN, NH, and PE material models to examine knee cartilage contact pressure predictions using FE methods for multiple subjects and multiple load cases. The results demonstrated that future subject specific knee joint FE studies would be advised to select LIN and NH cartilage material models for the purpose of making FE predictions of cartilage contact pressure

The Effect of High Tibial Osteotomy Correction Angle on Cartilage and Meniscus Loading Using Finite Element Analysis

Medial opening wedge high tibial osteotomy (MOWHTO) is a popular clinical method for curing the osteoarthritis (OA) caused by varus deformity. However, the ideal alignment to maximize osteotomy successful rate and post-operative knee function remains controversial to date. Moreover, the between-patient variability of knee joint biomechanics, particularly during functional tasks, signifies critical importance of conducting patient-specific planning. For this reason, this study introduces a subject-specific modeling procedure to determine the biomechanical effects of simulated different alignments of MOWHTO on tibiofemoral cartilage stress distribution. A 3D finite element (FE) knee model was developed from MRI images of a healthy living subject and used to simulate different alignments following MOWHTO (i.e. 0.2°, 2.7°, 3.9° and 6.6° valgus). Loading and boundary conditions were assigned based on the subject-specific kinematic and kinetic data recorded during gait tests. The compressive and shear stress distributions in the femoral cartilage and tibia cartilage were quantified. It was found that when the loading axis shifted laterally, the peak stresses in the medial compartment decreased, but increased in the lateral compartment. The findings suggest that equal loading between two compartments can be successfully achieved by performing MOWHTO with a HKA angle around 3.9 to 6.6° valgus. More importantly, this patient-specific non-invasive analysis of stress distribution that provided a quantitative insight to evaluate the mechanical responses of the soft tissue within knee joint as a result of adjusting the loading axis, may be used as a preoperative assessment tool to predict the consequential mechanical loading information for surgeon to decide the patient specific optimal angle