This study aimed to elucidate how rats recover from immobilization-induced knee joint contracture. Rats' right knees were immobilized by an external fixator at a flexion of 140° for 3 weeks. After removal of the fixator, the joints were allowed to move freely (remobilization) for 0, 1, 3, 7, or 14 days (n = 5 each). To distinguish myogenic and arthrogenic contractures, the passive extension range of motion was measured before and after myotomy of the knee flexors. Knee joints were histologically analyzed and the expression of genes encoding inflammatory or fibrosis-related mediators, interleukin-1β (1L-1β), fibrosis-related transforming growth factor-β1 (TGF-β1), and collagen type I (COL1A1) and III (COL3A1), were examined in the knee joint posterior capsules using real-time PCR. Both myogenic and arthrogenic contractures were established within 3 weeks of immobilization. During remobilization, the myogenic contracture decreased over time. In contrast, the arthrogenic contracture developed further during the remobilization period. On day 1 of remobilization, inflammatory changes characterized by edema, inflammatory cell infiltration, and upregulation of IL-1β gene started in the knee joint posterior capsule. In addition, collagen deposition accompanied by fibroblast proliferation, with upregulation of TGF-β1, COL1A1, and COL3A1 genes, appeared in the joint capsule between days 7 and 14. These results suggest the progression of arthrogenic contracture following remobilization, which is characterized by fibrosis development, is possibly triggered by inflammation in the joint capsule. It is therefore necessary to focus on developing new treatment strategies for immobilization-induced joint contracture. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1414-1423, 2017.

Objectives-Enhanced osteoclastogenesis, increased bone resorption, and osteoporosis have been reported in osteoprotegerin-deficient (OPG (Ϫ/Ϫ)) mice. OPG (Ϫ/Ϫ) mice available in Japan usually do not show vascular calcification. We have found that arterial calcification can be quickly induced by a simple procedure in OPG (Ϫ/Ϫ) mice. Methods and Results-Male OPG (Ϫ/Ϫ), OPG (ϩ/Ϫ), and OPG (ϩ/ϩ) mice were fed a high phosphate diet from 6 to 10 weeks after birth, and then 1␣,25-dihydroxyvitamin D3 (calcitriol) was injected for 3 days. We found that severe calcification developed in the media of the aorta in OPG (Ϫ/Ϫ) mice. Under electron microscopy, calcium deposits were observed in the cytoplasm and extracellular matrix of vascular smooth muscle cells (VSMCs Key Words: osteoprotegerin Ⅲ alkaline phosphate Ⅲ vascular smooth muscle cells Ⅲ calcium deposits V ascular calcification, which is frequently observed in patients with end-stage renal disease, diabetes, aging, and osteoporosis, can also lead to cardiovascular diseases and even sudden death. 1-3 Until recently, vascular calcification was considered to be a passive process that occurred as a nonspecific response to tissue injury or necrosis. Now it is becoming increasingly clear that vascular calcification is an actively regulated process that resembles bone metabolism and involves alkaline phosphatase (ALP) and other bonerelated proteins. 4 -7 Osteoprotegerin (OPG) is abundantly produced by osteoblasts at the bone surface and inhibits osteoclast activity, working as a key regulator of bone homeostasis. 8,9 Since it has been reported that OPG (Ϫ/Ϫ) mice exhibit severe osteoporosis attributable to enhanced osteoclastogenesis, OPG is considered to be a protective factor in bone metabolism. 10,11 In the vasculature, the function of OPG is unknown because it is unclear whether vascular calcification takes place in OPG (Ϫ/Ϫ) mice or not. 10,11 Moreover, it was reported that the serum OPG level is associated with the presence and severity of coronary artery disease (CAD). 12 It remains to be clarified whether OPG is involved in the progression of CAD or whether the upregulation of serum OPG concentration is a compensatory mechanism. ALP is a crucial enzyme for initiating mineralization in bone and is present in systemic arteries, arterioles, and some capillaries. 13 It is possible that this enzyme plays a role in arterial calcification by the same mechanism of action as that in bone. 14 Activation of ALP in the arterial wall may result in enhanced vascular calcification.It is well known that either an elevated serum phosphate level or treatment with high doses of vitamin D induces vascular calcification in animal models as well as in humans. 15,16 In the present study, using OPG (Ϫ/Ϫ) mice, we established a mouse model in which arterial calcification can be quickly induced by treatment with a high phosphate diet plus 1␣,25-dihydroxyvitamin D3 (calcitriol) injection, and this model allowed us to perform detailed pathological and biochemical examinations at desired tim...

The purpose of this study was to investigate the chondrogenic potential of magnetically labeled synovium-derived cells (M-SDCs) and examine whether M-SDCs could repair the articular cartilage using an intra-articular magnet after delivery to the lesion. Synovium-derived cells (SDCs) were cultured from the synovium of a rat knee, and were magnetically labeled with ferumoxides. M-SDCs were examined with a transmission electron microscope. A pellet culture system was used to evaluate the chondrogenic potential of M-SDCs in a magnetic field. In a rat model, allogeneic M-SDCs were injected into the knee after we made an osteochondral defect on the patellar groove and implanted an intra-articular magnet at the bottom of the defect. We histologically examined the defects at 48 h, 4 weeks, 8 weeks, and 12 weeks after treatment. Electron microscopy showed the transfection of ferumoxides into SDCs. The pellet cultures revealed the chondrogenic potential of M-SDCs in a magnetic field. M-SDCs accumulated in the osteochondral defect at 48 h after treatment, and we confirmed the regeneration of the articular cartilage at 4 weeks, 8 weeks, and 12 weeks after treatment using an intra-articular magnet. We demonstrated that articular cartilage defects could be repaired using an intra-articular magnet and M-SDCs. We believe that this system will be useful to repair human articular cartilage defects. Keywords: cell delivery system; magnet; synovium; intra-articular injection; cartilage repair Articular cartilage is well known to have very limited self-healing potential. There are many procedures, including drilling, abrasion, microfracture, and distraction, for repairing the articular cartilage.1-7 However, the defects are repaired by fibrous tissues during those procedures, 6,8 and a routine procedure for articular cartilage defect repair has not yet been established.Currently, engineered cartilage tissues are in widespread clinical use, and good clinical results have been achieved with these tissues.9,10 However, this procedure requires the harvesting of a small amount of cartilage tissues from the patient prior to cartilage transplantation. It is therefore necessary to implement a lessinvasive procedure.Recently, synovium-derived cells (SDCs) have been found to have a high potential for both proliferation and differentiation.11-15 Synovial tissues are easy to harvest and may be collected from any joint without damaging the articular cartilage. We therefore evaluated the method of transplanting SDCs for repairing articular cartilage defects.Previous studies have suggested that intra-articular injected mesenchymal stem cells (MSCs) mobilize to the injured tissues. 16 This transplantation was less invasive, but was inefficient because the injected cells spread throughout the joint space. Consequently, we created an intra-articular magnet which had a strong magnetic force, for efficient transplantation. The delivered cells were magnetically labeled with ferumoxides, which is approved by the United States Food and Drug Admi...

Cartilage alterations after SCI would not be explained by only a suppression of mechanical forces by unloading and immobilization, but there may be influences on the cartilage in addition to the change in mechanical forces.

This study was made to elucidate the changes in the periarticular connective tissue that can underlie the contracture after spasticity development. Sixteen Wistar rats underwent a spinal cord injury and 16 rats were either sham- or nonoperated. The periarticular connective tissue of the knee joint was assessed with histological, histomorphometric, immunohistochemical, and biochemical analyses. Histological results showed a smaller synovial intima, a dense subintimal and posterior joint capsule without fibrosis, and a disarranged posterior capsule in the spinal cord-injured knees with the flexion contracture. The synovial intima length was shortened only at the posterior capsule. Neither the distribution nor expression of type I and III collagen was affected. Contractures after spinal cord injuries are characterized by synovial intima adhesions. A dense and disarranged capsule may lead to joint stiffness. The alteration of periarticular connective tissues exhibits properties characteristic of the contracture after spasticity development.