The recent research on multiferroics has provided solid evidence that the breaking of inversion symmetry by spin order can induce ferroelectric polarization P. This type of multiferroics, called ...spin-driven ferroelectrics, often show a gigantic change in P on application of a magnetic field B. However, their polarization (<~0.1 μC cm(-2)) is much smaller than that in conventional ferroelectrics (typically several to several tens of μC cm(-2)). Here we show that the application of external pressure to a representative spin-driven ferroelectric, TbMnO3, causes a flop of P and leads to the highest P (≈ 1.0 μC cm(-2)) among spin-driven ferroelectrics ever reported. We explain this behaviour in terms of a pressure-induced magnetoelectric phase transition, based on the results of density functional simulations. In the high-pressure phase, the application of B further enhances P over 1.8 μC cm(-2). This value is nearly an order of magnitude larger than those ever reported in spin-driven ferroelectrics.
This study examined 1) the clinical relevance of trunk movement asymmetry, which was evaluated using a trunk-mounted inertial measurement unit (IMU), and 2) the relationship between trunk movement ...asymmetry and lower limb muscle strength asymmetry in individuals with knee osteoarthritis (OA).
One-hundred-thirty-one participants (mean age, 74.2 years; 71.8% female; Kellgren and Lawrence K&L grade ≥1) underwent gait analysis at their preferred pace for IMU-based measurement of trunk movement asymmetry (harmonic ratio HR and improved HR). The isometric strength of quadriceps and hip abductors was evaluated using a hand-held dynamometer. Pain and disability level were evaluated using a validated self-reported questionnaire. Multiple regression analyses with covariate adjustment were performed to examine the relationship between trunk movement asymmetry (independent variable) and pain, disability level, or muscle strength asymmetry (dependent variables).
Individuals with severe knee OA (K&L grade ≥3) had increased trunk movement asymmetry in the medio-lateral axis compared to those with a K&L grade of 1. Increased trunk movement asymmetry was associated with a greater knee pain and disability. The increased trunk movement asymmetry was significantly associated with an increase in the asymmetry of quadriceps strength, but not with asymmetry in the strength of hip abductor.
Our findings indicate that increased medio-lateral trunk movement asymmetry may be an indicator of impairment, rather than adaptation, in individuals with knee OA. This preliminary finding warrants validation by future study. Paying close attention to medio-lateral trunk movement asymmetry may be key to our understanding of OA-related pain and disability.
To test the hypothesis that the interaction between low back pain (LBP) and knee pain intensity contributes to the disability level of individuals with knee osteoarthritis (OA).
Community-dwelling ...participants with knee OA (Kellgren/Lawrence K/L grade ≥1) were enrolled. LBP and its severity were identified using questionnaires. Knee pain severity and disability level were evaluated using the Japanese Knee Osteoarthritis Measure (JKOM) subscale. Multiple linear regression analyses were performed to examine the effect of the LBP–knee pain interaction, an independent variable, on disability, a dependent variable.
A total of 260 participants (age, 48–88 years; 77.7% women) were included. Of them, 151 (58.1%) had LBP. The LBP–knee pain interaction was significantly associated with disability after the adjustment for covariates. A post-hoc subgroup analysis revealed that the relationship between knee pain intensity and disability level was higher in individuals with LBP (beta: 0.621 points; 95% confidence interval CI: 0.511 to 0.731 points) than in those without LBP (beta: 0.402 points; 95% CI: 0.316 to 0.487 points).
LBP interacts with knee pain intensity and contributes to disability level in individuals with knee OA. Coexisting LBP and knee pain had a stronger impact on disability level than LBP or knee pain alone. These findings highlight the potential deteriorative effects of the LBP–knee interaction on disability. Maximal treatment effects for disability might be achieved when LBP and knee pain are targeted simultaneously, rather than separately.
Summary Objective Articular cartilage is roughly separated into three areas: the tangential, middle, and deep zones. The structure and molecular components of an additional important zone, the most ...superficial zone (MSZ), which directly faces the joint cavity, have yet to be conclusively elucidated. The purpose of the present study was to use multiple methods to study the MSZ in order to determine its structure. Materials and methods Knees from 16 pigs (age, 6 months) were used. Full-thickness cartilage specimens were harvested from the femoral groove. The MSZ was observed using light microscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM) in combination with histochemical and immunohistochemical methods. Results The combined findings from the three different observational methods indicate that the MSZ is subdivided into three layers. Among these three layers, collagen subtypes I, II, and III are present in the innermost (third) layer of the MSZ. Beneath the third layer, type II collagen is the predominant type, with small amounts of type III collagen. This layer beneath the third layer is considered to be the tangential layer. Conclusions Our observations indicate that the MSZ is subdivided into three layers. Further analysis of the molecular components in each layer may improve our understanding of the structure of the articular surface.
Summary Objective Subchondral bone cyst (SBC) growth, caused by osteoclast activity during early knee osteoarthritis (OA) pathogenesis, should be treated to prevent further progressions of OA. In the ...present study, we evaluated the effects of gentle treadmill walking on subchondral bone and cartilage changes in an experimental rat model of destabilized medial meniscus (DMM). Method Twelve-week-old Wistar rats underwent DMM surgery in their right knee and sham surgery in their left knee and were assigned to either the sedentary group or walking group ( n = 42/group). Animals in the walking group were subjected to treadmill exercise 2 days after surgery, which included walking for 12 m/min, 30 min/day, 5 days/week for 1, 2, and 4 week(s). Subchondral bone and cartilage changes were evaluated by micro-CT analysis, histological analysis, and biomechanical analysis. Results Treadmill walking had a tendency to suppress SBC growth, which was confirmed by micro-CT ( P = 0.06) and positive staining for tartrate-resistant acid phosphatase (TRAP) activity for the osteoclast number per bone surface ( P = 0.09) 4 weeks after surgery. These changes coincide with the prevention of cartilage degeneration as evaluated by the Osteoarthritis Research Society International (OARSI) score ( P < 0.05) and biomechanically softening ( P < 0.05). Furthermore, treadmill walking could suppressed increasing osteocyte deaths ( P < 0.01), which was positively correlated with the OARSI score ( r = 0.77; P < 0.01). Conclusion These results indicate biomechanical and biological links exist between cartilage and subchondral bone; preventive effects of treadmill walking on subchondral bone deterioration might be partly explained by the chondroprotective effects.
Summary Objective This study aimed to investigate subchondral bone changes using micro-computed tomography (micro-CT) and regional differences in articular cartilage degeneration, focusing on changes ...of cartilage covered by menisci, in the early phase using a destabilization of the medial meniscus (DMM) model. Method The DMM model was created as an experimental rat osteoarthritis (OA) model (12 weeks old; n = 24). At 1, 2, and 4 weeks after surgery, the rats were sacrificed, and knee joints were scanned using a Micro-CT system. Histological sections of the medial tibial plateau, which was divided into inner, middle, and outer regions, were prepared and scored using the modified OARSI scoring system. The cartilage thickness was also calculated, and matrix metalloproteinase 13 (MMP13), Col2-3/4c, and vascular endothelial growth factor (VEGF) expression was assessed immunohistochemically. Results Subchondral bone defects were observed in the middle region, in which the cartilage thickness decreased over time after surgery, and these defects were filled with MMP13- and VEGF-expressing fibrous tissue. The OARSI score increased over time in the middle region, and the score was significantly higher in the middle region than in the inner and outer regions at 1, 2, and 4 weeks after surgery. Col2-3/4c and MMP13 expression was observed primarily in the meniscus-covered outer region, in which the cartilage thickness increased over time. Conclusion Loss of meniscal function caused cartilage degeneration and subchondral bone defects in the early phase site-specifically in the middle region. Furthermore, our results might indicate cartilage covered by menisci is easily degraded resulting in osmotic swelling of the cartilage in early OA.
Summary Objective To evaluate the dose–response relationship of exercise loading in the cartilage-subchondral bone (SB) unit in surgically-induced post-traumatic osteoarthritis (PTOA) of the knee. ...Design Destabilized medial meniscus (DMM) surgery was performed on the right knee of 12-week-old male Wistar rats, and sham surgery was performed on the contralateral knee. Four weeks after the surgery, the animals were subjected to moderate (12 m/min) or intense (21 m/min) treadmill exercises for 30 min/day, 5 days/week for 4 weeks. PTOA development in articular cartilage and SB was examined using histological and immunohistochemical analyses, micro-computed tomography (micro-CT) analysis, and biomechanical testing at 8 weeks after surgery. Gremlin-1 was injected to determine the role of bone morphogenetic protein (BMP) signaling on PTOA development following moderate exercise. Results Moderate exercise increased BMP-2, BMP-4, BMP-6, BMP receptor 2, pSmad-5, and inhibitor of DNA binding protein-1 expression in the superficial zone chondrocytes and suppressed cartilage degeneration, osteophyte growth, SB damage, and osteoclast-mediated SB resorption. However, intense exercise had little effect on BMP expression and even caused progression of these osteoarthritis (OA) changes. Gremlin-1 injection following moderate exercise caused progression of the PTOA development down to the level of the non-exercise DMM-operated knee. Conclusions Exercise regulated cartilage-SB PTOA development in DMM-operated knees in a dose-dependent manner. Our findings shed light on the important role of BMP expression in superficial zone chondrocytes in attenuation of PTOA development following physiological exercise loading. Further studies to support a mechanism by which BMPs would be beneficial in preventing PTOA progression are warranted.
Summary Objective This study aimed to determine whether treadmill walking (TW) prevents the progression of post-traumatic osteoarthritic changes in cartilage-subchondral bone unit, and whether the ...exercise timing changes the exercise efficacy in destabilized medial meniscus (DMM) rat knees. Design Twelve-week-old male Wistar rats underwent DMM surgery on their right knees and sham surgery on their left knees and were assigned to either the sedentary ( n = 10) or walking ( n = 24) groups. The rats in the walking group were subjected to TW from day 2 through 4 weeks, from 4 through 8 weeks, or from day 2 through 8 weeks ( n = 8 per group). Osteoarthritic changes of cartilage and subchondral bone were assessed with micro-computed tomography, histology, and immunohistochemistry 8 weeks after surgery. Results TW prevented the progression of cartilage and subchondral bone lesions induced by the DMM, and increased bone morphogenetic protein (BMP)-2 and -6 expressions in superficial zone chondrocytes and bone-lining cells including osteoblasts. Furthermore, the TW-induced increase in BMPs varied with the exercise timing. Beginning TW 4 weeks after DMM surgery was the best option for increasing BMPs, coinciding with the most robust prevention of osteoarthritic changes. Conclusions TW increased the expression of BMPs and prevented the progression of cartilage-subchondral bone lesions in rat knees with a DMM. Selective exercise timing may be a key factor in the development of an exercise regimen for preventing the progression of post-traumatic osteoarthritis (PTOA). Furthermore, exercise may have favorable effects even after the PTOA has been developed.
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