Histological and immunohistochemical analyses of articular cartilage during onset and progression of pre- and early-stage osteoarthritis in a rodent model.

Early diagnosis and treatment of pre- and early-stage osteoarthritis (OA) is important. However, the cellular and cartilaginous changes occurring during these stages remain unclear. We investigated the histological and immunohistochemical changes over time between pre- and early-stage OA in a rat model of traumatic injury. Thirty-six male rats were divided into two groups, control and OA groups, based on destabilization of the medial meniscus. Histological and immunohistochemical analyses of articular cartilage were performed on days 1, 3, 7, 10, and 14 postoperatively. Cell density of proteins associated with cartilage degradation increased from postoperative day one. On postoperative day three, histological changes, including chondrocyte death, reduced matrix staining, and superficial fibrillation, were observed. Simultaneously, a compensatory increase in matrix staining was observed. The Osteoarthritis Research Society International score increased from postoperative day seven, indicating thinner cartilage. On postoperative day 10, the positive cell density decreased, whereas histological changes progressed with fissuring and matrix loss. The proteoglycan 4-positive cell density increased on postoperative day seven. These findings will help establish an experimental model and clarify the mechanism of the onset and progression of pre- and early-stage traumatic OA.

Age-related changes in rat joint capsule.

[Purpose] We investigated morphological and histopathological changes in the joint capsule of rats with aging. [Materials and Methods] A total of 18 male Wistar rats were categorized into two groups: the control group (n=8), and the aged group (n=10). The aged group was reared until 75 weeks of age, while the control group was maintained until 11 weeks of age. At the end of the experiment period, the knee joints were sampled, joint capsules were subjected to histopathological analysis, and their thickness was measured. [Results] The joint capsule in the aging group exhibited significantly greater thickness compared to the control group. Histopathological examination revealed distinct differences between the two groups. The control group displayed gaps between the collagen fibers in the posterior joint capsule, along with loosely overlapping connective tissue and the presence of fat cells. Conversely, in the aged group's joint capsule, these gaps between the collagen fibers almost disappeared and fibers became densely packed and thickened. [Conclusion] These results were similar to our previous study in rats with immobilized hindlimb knee joints. Similar findings, including collagen fiber thickening, densification in the joint capsule, and reduced hindlimb knee joint range of motion, were consistent with those observed in the present investigation.

Treadmill Exercise Suppresses Histological Progression of Disuse Atrophy in Articular Cartilage in Rat Knee Joints during Hindlimb Suspension.

OBJECTIVE: The purpose of this study was to determine the preventive effects of treadmill exercise or physiological loading on disuse atrophy in the rat knee joint cartilage and bone during hindlimb suspension. DESIGN: Twenty male rats were divided into 4 experimental groups, including the control, hindlimb suspension, physiological loading, and treadmill walking groups. Histological changes in the articular cartilage and bone of the tibia were histomorphometrically and immunohistochemically evaluated 4 weeks after the intervention. RESULTS: Compared with the control group, the hindlimb suspension group showed thinning of cartilage thickness, decreased matrix staining, and decreased proportion of noncalcified layers. Cartilage thinning, decreased matrix staining, and decreased noncalcified layers were suppressed in the treadmill walking group. The physiological loading group exhibited no significant suppression of cartilage thinning or decreased noncalcified layers, but the decreased matrix staining was significantly suppressed. No significant prevention of bone mass loss or changes in subchondral bone thickness were detected after physiological loading or treadmill walking. CONCLUSION: Disuse atrophy of the articular cartilage caused by unloading conditions could be prevented by treadmill walking in rat knee joints.

Immunohistochemical study on the distribution of telocytes in the knee joint components in a rat osteoarthritis model.

[Purpose] Telocytes are stromal cells that participate in tissue homeostasis. Osteoarthritis is a common degenerative disorder of multiple joint components that causes inflammation; however, the distribution of telocytes in joint components and the impact of osteoarthritis on telocytes is unclear. Therefore, we aimed to clarify the distribution of the telocyte in the joint components and determine the effect of osteoarthritis on telocytes. [Participants and Methods] We divided 30 male rats into control and osteoarthritis groups and surgically induced osteoarthritis by destabilizing the medial meniscus. At two and eight weeks after surgery, we evaluated the changes in CD34-positive and CD31-negative area sizes in the joint components by immunohistochemistry. [Results] The results showed CD34-positive and CD31-negative areas in the loose connective tissue of the lateral meniscus attachment and the infrapatellar fat pad. However, it was not observed in the cartilage, subchondral bone, cruciate ligament, and meniscus. Moreover, there were no significant differences between the CD34-positive and CD31-negative area sizes in control and osteoarthritis groups at both time points. [Conclusion] CD34-positive and CD31-negative cells are distributed in multiple joint components; however, CD34-positive and CD31-negative areas are not affected by the progression of osteoarthritis. This result provides information on telocytes distribution in the knee joint and the impact of osteoarthritis on these cells.

Physiological Reloading Recovers Histologically Disuse Atrophy of the Articular Cartilage and Bone by Hindlimb Suspension in Rat Knee Joint.

OBJECTIVE: This study aimed to clarify physiological reloading on disuse atrophy of the articular cartilage and bone in the rat knee using the hindlimb suspension model. DESIGN: Thirty male rats were divided into 3 experimental groups: control group, hindlimb suspension group, and reloading after hindlimb suspension group. Histological changes in the articular cartilage and bone of the tibia were evaluated by histomorphometrical and immunohistochemical analyses at 2 and 4 weeks after reloading. RESULTS: The thinning and loss of matrix staining in the articular cartilage and the decrease in bone volume induced by hindlimb suspension recovered to the same level as the control group after 2 weeks of reloading. The proportion of the noncalcified and calcified layers of the articular cartilage and the thinning of subchondral bone recovered to the same level as the control group after 4 weeks of reloading. CONCLUSIONS: Disuse atrophy of the articular cartilage and bone induced by hindlimb suspension in the tibia of rats was improved by physiological reloading.

Reduction of knee joint load suppresses cartilage degeneration, osteophyte formation, and synovitis in early-stage osteoarthritis using a post-traumatic rat model.

The purpose of this study was to clarify the histological effect of reducing the loading to knee on cartilage degeneration, osteophyte formation, and synovitis in early-stage osteoarthritis (OA) using a post-traumatic rat model. Ten male rats were randomly allocated into two experimental groups: OA induction by surgical destabilization of medial meniscus (DMM, OA group) and hindlimb suspension after OA induction by DMM (OAHS group). The articular cartilage, osteophyte formation, and synovial membrane in the medial tibiofemoral joint were analyzed histologically and histomorphometrically at 2 and 4 weeks after surgery. The histological scores and changes in articular cartilage and osteophyte formation were significantly milder and slower in the OAHS group than in the OA group. At 2 and 4 weeks, there were no significant differences in cartilage thickness and matrix staining intensity between both the groups, but chondrocytes density was significantly lower in the OA group. Synovitis was milder in OAHS group than in OA group at 2 weeks. Reducing knee joint loading inhibited histological OA changes in articular cartilage, osteophyte formation, and synovial inflammation. This result supports the latest clinical guidelines for OA treatment. Further studies using biochemical and mechanical analyses are necessary to elucidate the mechanism underlying delayed OA progression caused by joint-load reduction.

Disuse Atrophy of Articular Cartilage Induced by Unloading Condition Accelerates Histological Progression of Osteoarthritis in a Post-traumatic Rat Model.

OBJECTIVE: The study aim was to evaluate the histological relationship between osteoarthritis (OA) and articular cartilage in disuse atrophy induced by hindlimb unloading in a post-traumatic OA rat model. DESIGN: Forty male rats were divided into the 4 following experimental groups: control, hindlimb suspension (HS), OA induced by destabilization of the medial meniscus (OA), and OA induction after hindlimb suspension (HS-OA). Histological changes in the articular cartilage of the tibia were evaluated by the Osteoarthritis Research Society International (OARSI) scores and histomorphometrical analyses at 2, 4, and 8 weeks after OA induction. RESULTS: We confirmed that disuse atrophy of the articular cartilage was caused by thinning of the articular cartilage and the decrease in matrix staining for the nonloading period of 4 weeks. The OARSI scores and histomorphological analyses revealed that OA progressed significantly wider and deeper in the HS-OA group than in the OA group over time. In the sham group, disuse atrophy of the articular cartilage recovered at 2 weeks after reloading. CONCLUSIONS: This study revealed that OA progressed faster in cartilage atrophy than in normal articular cartilage. Further studies are required for investigating the mechanisms of disuse atrophy of cartilage and its association with OA using the biochemical and immunohistochemical analysis.

Disuse histological changes of an unloading environment on joint components in rat knee joints.

Objectives: To clarify the effects of mechanical unloading on joint components, including the articular cartilage by knee compartments, synovial membrane, and the infrapatellar fat pad (IFP), using a hindlimb suspension rat model. Design: Twenty-five male rats were divided into the three following experimental groups: the baseline, control (CON), and hindlimb unloading (HU) groups. Rats in the HU group were subjected to periods of hindlimb unloading by tail suspension. The joint components were evaluated by histopathological and histomorphometric analyses. Results: The unloading condition caused articular cartilage thinning and decreased matrix staining. The tendency of these histological changes in articular cartilage was similar between the knee compartments. In general, the unloading environment resulted in no critical histological changes to the synovial membrane and IFP. At 4 weeks, thickening of the synovial membrane and synovial-like tissue invasion were observed in the HU group, but there was no significant change in inflammation. There was no obvious histological change to the IFP caused by unloading. Conclusion: The unloading environment caused disuse histological changes in the articular cartilage; however, the tendency of the changes was similar between compartments. Furthermore, the unloading condition caused no critical histological changes to the synovial membrane or IFP. Clinically, the unloading environment without joint immobilization over a short period may not have caused critical histological changes to the joint components.

Induction of osteoarthritis by injecting monosodium iodoacetate into the patellofemoral joint of an experimental rat model.

This study aimed to investigate the histopathological changes in the patellofemoral joint using a rat model of osteoarthritis that was induced using monosodium iodoacetate, and to establish a novel model of patellofemoral osteoarthritis in a rat model using histopathological analysis. Sixty male rats were used. Osteoarthritis was induced through a single intra-articular injection of monosodium iodoacetate in both knee joints. Animals were equally divided into two experimental groups based on the monosodium iodoacetate dose: 0.2 mg and 1.0 mg. Histopathological changes in the articular cartilage of the patellofemoral joint and the infrapatellar fat pad were examined at 3 days, 1 week, 2 weeks, 4 weeks, 8 weeks, and 12 weeks after the monosodium iodoacetate injection. In the 1.0-mg group, the representative histopathological findings of osteoarthritis were observed in the articular cartilage of the patellofemoral joint over time. Additionally, the Osteoarthritis Research Society International scores of the patellofemoral joint increased over time. The synovitis scores of the infrapatellar fat pad in both groups were highest at 3 days, and then the values decreased over time. The fibrosis score of the infrapatellar fat pad in the 1.0-mg group increased with time, whereas the fibrosis score in the 0.2-mg group remained low. Representative histopathological findings of osteoarthritis were observed in the articular cartilage of the patellofemoral joint in a rat model of osteoarthritis induced using monosodium iodoacetate. With appropriate selection, this model may be regarded as an ideal patellofemoral osteoarthritis model.

Long-term histopathological developments in knee-joint components in a rat model of osteoarthritis induced by monosodium iodoacetate.

[Purpose] This study was performed to evaluate the long-term histopathological changes in knee-joint components including synovial membrane and joint capsule in a rat model of osteoarthritis (OA) induced by monosodium iodoacetate (MIA). [Subjects and Methods] Fifty male rats were used. OA was induced through intra-articular injection of MIA, and ten rats were randomly allocated to each of five groups induced with OA for 1, 2, 4, 6, or 8 weeks. At the end of each period, the knee components were examined histopathologically. [Results] After 1 and 2 weeks, chondrocytes were weakly stained. After 4 weeks, fibrillation, fissuring, and eburnation were observed, whereas after 6 weeks, chondrocyte clustering and osteophyte formation were detected. In the synovial membrane, the proliferation of spindle-shaped cells and a multilayered structure of the surface cells were observed at 1 and 2 weeks, but the degree of these changes decreased over time. In the joint capsule, a narrowing of the space between collagen fiber bundles was observed at 4-8 weeks. [Conclusion] The long-term histopathological changes of the joint components observed in a rat model of OA induced by MIA were similar to those detected in OA, but differed at specific times and tissues.

Differences in Cartilage Repair between Loading and Unloading Environments in the Rat Knee.

We investigated the histopathological and immunohistochemical effects of loading on cartilage repair in rat full-thickness articular cartilage defects. A total of 40 male 9-week-old Wistar rats were studied. Full-thickness articular cartilage defects were created over the capsule at the loading portion in the medial condyle of the femur. Twenty rats were randomly allocated into each of the 2 groups: a loading group and a unloading group. Twenty rats from these 2 groups were later randomly allocated to each of the 2 groups for evaluation at 1 and 2 weeks after surgery. At the end of each period, knee joints were examined histopathologically and immunohistochemically. In both groups at 1 and 2 weeks, the defects were filled with a mixture of granulation tissue and some remnants of hyaline cartilage. The repair tissue was not stained with toluidine blue in both groups. Strong staining of type I collagen was observed in the repair tissue of both groups. The area stained with type I collagen was smaller in the unloading group than in the loading groups, and the stained area was smaller at 2 weeks than at 1 week. In the staining for type II collagen, apparent staining of type II collagen was observed in the repair tissue of both groups at 1 week. At 2 weeks, there was a tendency toward a higher degree of apparent staining in the loading group than in the unloading group. Accordingly, these results indicated that loading and unloading in the early phase of cartilage repair have both merits and demerits.