Introduction. Osteoarthritis (OA), a painful, debilitating joint disease, often caused by excessive joint stress, is a leading cause of disability (World Health Organisation, 2003) and increases with age and obesity. A 5° varus malalignment increases loading in the medial knee compartment from 70% to 90% (Tetsworth and Paley, 1994). Internal unloading implants, placed subcutaneously upon the medial aspect of the knee joint, are designed to offload the medial compartment of the knee without violating natural joint tissues. The aim of this study is to investigate the effect of an unloading implant, such as the Atlas™ knee system, on stress within the tibiofemoral joint with different grades of cartilage defects. Methods. To simulate surgical treatment of medial knee OA, a three-dimensional computer-aided design of an Atlas™ knee system was virtually fixed to the medial aspect of a validated finite element knee model (Mootanah, 2014), using CATIA v5 software (Dassault Systèmes, Velizy Villacoublay, France). The construct was meshed and assigned material properties and boundary conditions, using Abaqus finite element software (Dassault Systèmes, Velizy Villacoublay, France). A cartilage defect was simulated by removing elements corresponding to 4.7 mm. 2. The international cartilage repair society (ICRS) Grade II and III damage were simulated by normalized defect depth of 33% and 67%, respectively. The femur was mechanically grounded and the tibia was subjected to loading conditions corresponding to the stance phase of walking of a healthy 50-year-old 68-Kg male with anthropometrics that matched those of the cadaver. Finite element analyses were run for peak shear and von Mises stress in the medial and lateral tibiofemoral compartments. Results. Von Mises stress distribution in the tibial cartilage, with ICRS Grade II and III defects, without the unloading implant, at the end of weight acceptance (15% of the gait cycle) were analysed. The internal unloading implant reduces peak von Mises stress by 40% and 43% for Grade II and Grade III cartilage defects, respectively. The corresponding reductions in shear stress are 36% and 40%. Consistent reduction in peak von Mises stress values in the medial cartilage-cartilage and cartilage-meniscus contact areas were predicted throughout the stance phase of the gait cycle for ICRS Grade II defect. Similar results were obtained for Grade III defect and for peak shear stress values. There were no overall increases in peak von Mises stress values in the lateral tibial cartilage. Discussion and Conclusions. The internal unloading implant is capable of reducing von Mises and shear stress values in the medial tibial cartilage with ICRS Grade II and III defects at the cartilage-cartilage and cartilage-meniscus interfaces throughout the stance phase of the gait cycle. This did not result in increased stress values in the lateral tibial cartilage. Our model did not account for the viscoelastic effects of the cartilage and meniscus. Results of this study are based on only one knee specimen. The internal unloading implant may protect the cartilage in individuals with medial knee osteoarthritis, thereby delaying the need for knee replacements

The optimal correction of the weight bearing line during High Tibial Osteotomy has not been determined. We used finite element modelling to simulate the effect that increasing opening wedge HTO has on the distribution of stress and pressure through the knee joint during normal gait. Subject-specific models were developed by combining geometry from 7T MRI scans and applied joint loads from ground reaction forces measured during level walking. Baseline stresses and pressures on the articulating proximal tibial cartilage and menisci were calculated. Progressive osteotomies were then simulated to shift the weight-bearing line from the native alignment towards/into the lateral compartment (between 40 – 80% of medial-lateral tibial width). Changes in calculated stresses and pressures were recorded. Both stress and pressure decreased in the medial compartment and increased in the lateral compartment as increasingly valgus osteotomies were simulated. The models demonstrated a consistent “safe zone” for weight bearing line position at 50%-65% medial-lateral tibial width, outside of which compartment stresses and pressures substantial increased. This study suggests a safe correction zone within which a medial opening wedge HTO can be performed correcting the WBL to 55% medio-lateral width of the tibia

INTRODUCTION:. To avoid the early onset of osteoarthritis after partial meniscectomy an effective replacement of injured meniscal tissue would be desirable. The present study investigates the behaviour of a new silk derived scaffold supplied by Orthox Ltd. (Abingdon, UK) in an in vivo sheep model. METHODS:. The scaffolds where derived from silk fibres by processing into an open porous matrix. Nine sheep (4 ± 1 years) underwent partial meniscectomy at the anterior horn of the medial meniscus followed by implantation of a scaffold. The unoperated contralateral stifle joint served as control. After six months the animals were sacrificed and the joints inspected for inflammation. The Young's modulus of the tibial cartilage, meniscus and scaffold was determined by indentation or confined compression tests. All tissues were fixed in formaldehyde for histology. The data were analysed by a Wilcoxon and Mann-Whitney-U-test. RESULTS:. The sheep were free of lameness 4 days p.o. The macroscopic analysis of the genual region and of the synovial membrane showed no signs of inflammation. This was confirmed by histological sections of synovial membrane, meniscus and scaffold. In histology, amorphous material, some fibroblast-like cell clusters and connective tissue formation was visible inside the pores of the scaffold. There were no statistically significant differences between the Young's moduli of the three measuring points in the operated and unoperated stifle joints. The meniscal tissue showed a higher modulus than the scaffolds. The scaffold's modulus significantly increased after three months implantation. DISCUSSION & CONCLUSIONS:. The presented silk scaffold withstood the loads occurring during the six months implantation period. It showed promising properties concerning biocompatibility and cartilage protection and its mechanical properties started to approach those of meniscal tissue

Introduction. Partial meniscectomy, a surgical treatment for meniscal lesions, allows athletes to return to sporting activities within two weeks. However, this increases knee joint shear stress, which is reported to cause osteoarthritis. The volumes and locations of partial meniscectomy that would result in a substantial increase in knee joint stress is not known. This information could inform surgeons when a meniscus reconstruction is required. Aim. Our aim was to use a previously validated knee finite element (FE) model to predict the effects of different volumes and locations of partial meniscectomy on cartilage shear stress. The functional point of interest was at the end of weight acceptance in walking and running, when the knee is subjected to maximum loading. Method. An FE model of the knee joint was used to simulate walking and running, two of the most common functional activities. Forces and moments, obtained from the gait cycle of a 76.4 kg male subject, were applied at the tibia. Different sizes (0%, 10%, 30%, 60%) and locations (anterior, medial and posterior) of partial meniscectomies were simulated (Figure 1). Maximum cartilage shear stress was determined for the different meniscectomies. Graphs were plotted of the cumulative tibial cartilage volume subjected to stress values above specific thresholds. Results and analysis. Maximum shear stress values for the intact knee during walking were 2.00 MPa medially and 1.71 MPa laterally. During running these magnitudes rose to 3.48 MPa medially and 4.70 MPa laterally. For a 30% anterior, central and posterior meniscectomy during walking shear stress increased by 25.9%, 44.9% and 32.5% medially, and 12.4%, 25.7% and 17.8% laterally. During running shear stress increased by 9.6%, 8.3% and 7.1%, medially and 31.6%, 37.5% and 43.6% laterally. For a 60% meniscectomy, during walking shear stress increased by 47.2% medially and 31.8%, laterally. During running shear stress increased by 10.0%, medially and 51.8%, laterally. The percentage of cartilage volume exposed to shear stress levels above a specified threshold is illustrated in Figure 2 for different volumes and locations of partial meniscectomy. Discussion and conclusions. This is first study that has estimated the volume of cartilage exposed to specific stress thresholds in walking and running as a function of the amount and location of meniscectomy. Maximum shear stress was 100% higher at the end of weight acceptance in running compared to walking. Stress was higher in the lateral compartment during running while higher in the medial compartment during walking. This is because a valgus moment acts at the knee at the end of weight acceptance in running while a varus moment acts at the joint in walking. Clinical significance. The model developed from this research has potential for applications in planning meniscal surgeries and developing rehabilitation strategies for athletes. It could inform surgeons about the safe volume and location of partial meniscectomy that can be performed before meniscus reconstruction becomes necessary. Results of this study also highlight the importance of considering the effect of post-surgical outcomes following different common functional activities

Purpose. It is well known that meniscus extrusion is associated with structural progression of knee OA. However, it is unknown whether medial meniscus extrusion promotes cartilage loss in specific femorotibial subregions, or whether it is associated with a increase in cartilage thickness loss throughout the entire femorotibial compartment. We applied quantitative MRI-based measurements of subregional cartilage thickness (change) and meniscus position, to address the above question in knees with and without radiographic joint space narrowing (JSN). Methods. 60 participants with unilateral medial OARSI JSN grade 1–3, and contralateral knee OARSI JSN grade 0 were drawn from the Osteoarthritis Initiative. Manual segmentation of the medial tibial and weight-bearing medial femoral cartilage was performed, using baseline and 1-year follow-up sagittal double echo steady-state (DESS) MRI, and proprietary software (Chondrometrics GmbH, Ainring, Germany). Segmentation of the entire medial meniscus was performed with the same software, using baseline coronal DESS images. Longitudinal cartilage loss was computed for 5 tibial (central, external, internal, anterior, posterior) and 3 femoral (central, external, internal) subregions. Meniscus position was determined as the % area of the entire meniscus extruding the tibial plateau medially and the distance between the external meniscus border and the tibial cartilage in an image located 4mm posterior to the central image (a location commonly used for semi-quantitative meniscus scoring). The relationship between meniscus position and cartilage loss was assessed using Pearson (r) correlation coefficients, for knees with JSN and without JSN. Results. The percentage of knees showing a quantitative value of >3mm medial meniscus extrusion was 50% in JSN knees, and only 12% in noJSN knees. The 1-year cartilage loss in the medial femorotibial compartment was 74±182µm (2.0%) in JSN knees, and 26±120µm (0.8%) in noJSN knees. There was a significant correlation between cartilage loss throughout the entire femorotibial compartment (MFTC) and extrusion area in JSN knees but not for noJSN knees. Also, the extrusion distance measured 4mm posterior to the central slice was not significantly correlated with MFTC cartilage loss. The strongest (negative) correlation between meniscus position and subregional femorotibial cartilage loss (r=−0.36) was observed for the external medial tibia. In contrast, no significant relationship was seen in the central tibia. No significant relationship was found in other tibial subregions, except for the anterior medial tibia, but only in JSN knees (r=−0.27). Correlation coefficients for the femoral subregions were generally smaller than those for tibial subregions, with only the internal medial weight-bearing femur attaining statistical significance (r =−0.26). Conclusions. The current results show that the relationship between meniscus extrusion and cartilage loss differs substantially between femorotibial subregions. The correlation was strongest for the external medial tibia, a region that is physiologically covered by the medial meniscus. It was less for other tibial and femoral subregions, including the central medial tibia, a region that exhibited similar rates of cartilage loss as the external subregion. The findings suggest that external tibia may be particularly vulnerable to cartilage tissue loss once the meniscus extrudes and the surface is “exposed” to direct, non-physiological, cartilage-cartilage contact

INTRODUCTION. The major loss of articular cartilage in medial osteoarthritis occurs in a central band on the distal femur, and in the center of the tibial plateau (Figure). This is consistent with varus deformity due to cartilage loss and meniscal degeneration, together with the sliding regions in walking. Treatment at an early stage such as KL grade 2 or 3, has the advantages of little bone deformity and cruciate preservation, and could be accomplished by resurfacing only the arthritic areas with Early Intervention (EI) components. Such components would need to be geometrically compatible with the surrounding bearing surfaces, to preserve continuity and stability. However because of the relatively small surface area covered, compared with total knees and even unicompartmentals, it is hypothesized that EI components will be an accurate fit on a population of knees with only a small number of sizes, and that accuracy can be maintained without requiring right-left components. We examined this hypothesis using unique design and methodology. METHODS. Average femur and tibia models, including cartilage, were generated from MRI scans of 20 normal males. The images were imported into Geomagic software. Surface point clouds based on least squares algorithms produced the average models. Averages were also produced from different numbers to determine method validity. Average arthritic models were also generated from 12 KL 1–2 cases, and 13 KL 2–3 cases. The 3 averages were compared by deviation mapping. Using the average from the 20 knees, femoral and tibial implant surfaces were designed using contour matching to fit the arthritic regions, maintaining right-left symmetry. A 5 size system was designed corresponding to large male, average male, small male/large female, average female, small female. For the 20 knees, the components were fitted based on the best possible matching of the contours to the surrounding bearing surfaces. For the femoral component the target was 1 mm projection at the center, matching at the ends. The accuracy of reproducing the cartilage surfaces was then determined by mapping the deviations between the implant surfaces and the cartilage surfaces. RESULTS & DISCUSSION. The average femur and tibia from the 20 knees (Figure) was almost identical no matter what groupings were used to produce the average. Likewise the 2 arthritic and the normal averages were almost identical. The accuracy of fit (Figure) averaged for the 20 normal knees was well below 1mm either above or below the original cartilage surfaces (see table below). This study indicates that such Early Intervention components are a viable method for resurfacing cases with early arthritis, and are likely to show almost normal mechanics due to preserving the original normal geometry. Deviations between tibial cartilage and implant (mm). Above implant mean 0.5 SD 0.2. Max deviation 1.5 SD 0.7. Below implant mean 0.7 SD 0.2. Max deviation 2.0 SD 0.1. Deviations between femoral cartilage and implant (mm). Above implant mean 0.3 SD 0.1. Max deviation 0.8 SD 0.1. Below implant mean 0.3 SD 0.1. Max deviation 0.8 SD 0.3

Objectives

Salubrinal is a synthetic agent that elevates phosphorylation of eukaryotic translation initiation factor 2 alpha (eIF2α) and alleviates stress to the endoplasmic reticulum. Previously, we reported that in chondrocytes, Salubrinal attenuates expression and activity of matrix metalloproteinase 13 (MMP13) through downregulating nuclear factor kappa B (NFκB) signalling. We herein examine whether Salubrinal prevents the degradation of articular cartilage in a mouse model of osteoarthritis (OA).

Treatment for osteoarthritis (OA) has traditionally focused on joint replacement for end-stage disease. An increasing number of surgical and pharmaceutical strategies for disease prevention have now been proposed. However, these require the ability to identify OA at a stage when it is potentially reversible, and detect small changes in cartilage structure and function to enable treatment efficacy to be evaluated within an acceptable timeframe. This has not been possible using conventional imaging techniques but recent advances in musculoskeletal imaging have been significant. In this review we discuss the role of different imaging modalities in the diagnosis of the earliest changes of OA. The increasing number of MRI sequences that are able to non-invasively detect biochemical changes in cartilage that precede structural damage may offer a great advance in the diagnosis and treatment of this debilitating condition.

Cite this article: Bone Joint J 2013;95-B:738–46.