Immobilisation causes longlasting matrix changes both in the immobilised and contralateral joint cartilage

Combining biomechanical stimulation and chronobiology: a novel approach for augmented chondrogenesis?

The unique structure and composition of articular cartilage is critical for its physiological function. However, this architecture may get disrupted by degeneration or trauma. Due to the low intrinsic regeneration properties of the tissue, the healing response is generally poor. Low-grade inflammation in patients with osteoarthritis advances cartilage degradation, resulting in pain, immobility, and reduced quality of life. Generating neocartilage using advanced tissue engineering approaches may address these limitations. The biocompatible microenvironment that is suitable for cartilage regeneration may not only rely on cells and scaffolds, but also on the spatial and temporal features of biomechanics. Cell-autonomous biological clocks that generate circadian rhythms in chondrocytes are generally accepted to be indispensable for normal cartilage homeostasis. While the molecular details of the circadian clockwork are increasingly well understood at the cellular level, the mechanisms that enable clock entrainment by biomechanical signals, which are highly relevant in cartilage, are still largely unknown. This narrative review outlines the role of the biomechanical microenvironment to advance cartilage tissue engineering via entraining the molecular circadian clockwork, and highlights how application of this concept may enhance the development and successful translation of biomechanically relevant tissue engineering interventions.

Musculoskeletal research in human space flight - unmet needs for the success of crewed deep space exploration

Based on the European Space Agency (ESA) Science in Space Environment (SciSpacE) community White Paper "Human Physiology - Musculoskeletal system", this perspective highlights unmet needs and suggests new avenues for future studies in musculoskeletal research to enable crewed exploration missions. The musculoskeletal system is essential for sustaining physical function and energy metabolism, and the maintenance of health during exploration missions, and consequently mission success, will be tightly linked to musculoskeletal function. Data collection from current space missions from pre-, during-, and post-flight periods would provide important information to understand and ultimately offset musculoskeletal alterations during long-term spaceflight. In addition, understanding the kinetics of the different components of the musculoskeletal system in parallel with a detailed description of the molecular mechanisms driving these alterations appears to be the best approach to address potential musculoskeletal problems that future exploratory-mission crew will face. These research efforts should be accompanied by technical advances in molecular and phenotypic monitoring tools to provide in-flight real-time feedback.

OA foundations - experimental models of osteoarthritis

Osteoarthritis (OA) is increasingly recognised as a disease of diverse phenotypes with variable clinical presentation, progression, and response to therapeutic intervention. This same diversity is readily apparent in the many animal models of OA. However, model selection, study design, and interpretation of resultant findings, are not routinely done in the context of the target human (or veterinary) patient OA sub-population or phenotype. This review discusses the selection and use of animal models of OA in discovery and therapeutic-development research. Beyond evaluation of the different animal models on offer, this review suggests focussing the approach to OA-animal model selection on study objective(s), alignment of available models with OA-patient sub-types, and the resources available to achieve valid and translatable results. How this approach impacts model selection is discussed and an experimental design checklist for selecting the optimal model(s) is proposed. This approach should act as a guide to new researchers and a reminder to those already in the field, as to issues that need to be considered before embarking on in vivo pre-clinical research. The ultimate purpose of using an OA animal model is to provide the best possible evidence if, how, when and where a molecule, pathway, cell or process is important in clinical disease. By definition this requires both model and study outcomes to align with and be predictive of outcomes in patients. Keeping this at the forefront of research using pre-clinical OA models, will go a long way to improving the quality of evidence and its translational value.

Bone replaces unloaded articular cartilage during knee immobilization. A longitudinal study in the rat

BACKGROUND

Joint immobility results in deleterious changes such as capsule shortening, bone loss and articular cartilage damage. Immobilization of rat knees in flexion for 32 weeks resulted in the distinctive feature of well-established replacement of articular cartilage by bone. Determining the time of onset of bone replacement is critical for the prevention of this likely irreversible complication of joint immobilization.

OBJECTIVES

To determine the onset and progression of bone replacement in the anterior tibial articular cartilage following knee immobilization in flexion.

METHODS

One hundred forty-nine adult male Sprague-Dawley rats were used. The experimental groups had one knee immobilized at 135°of flexion for durations of 2, 4, 8, 16 or 32 weeks and were compared to age-matched controls. The knees were evaluated histologically for the presence and cross-sectional area of bone within the articular cartilage of the tibia. Distance between the anterior aspect of the tibia and intact articular cartilage and cross-sectional bone area of the tibial epiphysis were also measured.

RESULT

Bone replacement in the articular cartilage was observed in 14%, 75%, 95%, 100% and 100% of knees after 2, 4, 8, 16 and 32 weeks of immobilization, respectively. No bone replacement was seen in the control knees. The mean area of bone replacement increased from 0.004 ± 0.007 mm² after 2 weeks to 0.041 ± 0.036 mm²; 0.085 ± 0.077 mm²; 0.092 ± 0.056 mm² and 0.107 ± 0.051 mm² after 4, 8, 16 and 32 weeks of immobilization, respectively, (p < 0.001) largely restricted to the anterior tibial articular cartilage. Mean distance to intact articular cartilage increased from 0.89 ± 0.69 mm at 2 weeks to 1.10 ± 0.35 mm; 1.65 ± 0.77 mm; 1.48 ± 0.63 mm; and 1.78 ± 0.58 mm after 4, 8, 16 and 32 weeks of immobilization, respectively (p = 0.001). Epiphyseal bone cross-sectional area was significantly reduced following 4, 8, and 16 weeks of immobilization compare to controls (all 3 p < 0.05).

CONCLUSION

Knee immobilization in flexion resulted in bone replacement in the anterior tibial articular cartilage that began after 2 weeks and was prevalent after 4 weeks of immobilization. The bone replacement progressed in an anterior-to-posterior direction and stopped at the area of contact between tibia and femur. These findings stress the importance of mobility to maintain joint health.

Protective effect of glucosamine and risedronate (alone or in combination) against osteoarthritic changes in rat experimental model of immobilized knee

This study is aiming to investigate the protective effect of glucosamine, risedronate (alone or in combination) on articular cartilage in experimental model of immobilized rat knee. Twenty-five adult male albino rats were divided into five groups (five rats each): control group, immobilized group, glucosamine-treated group, risedronate-treated group, and group treated by a combination of glucosamine and risedronate. The articular cartilage was obtained for histological, immunohistochemical and morphometric studies. The immobilized group showed manifestations of osteoarthritis in the form of significant decrease of articular cartilage thickness with surface erosions, shrunken chondrocytes with pyknotic nuclei and marked manifested fall of chondrocyte number. There was manifested reduction of collagen contents of the articular cartilage using Masson trichrome stain. Safranin O–Fast Green revealed low proteoglycan contents. The collagen type II was also declined. The manikin score was 7.8. Risedronate improved this manifestation slightly more than glucosamine, but combination of booth drugs caused significant improvement of the damaged articular cartilage caused by immobilization. Oral administration of glucosamine and risedronate improved the degenerative changes of rat knee articular cartilage that follow immobilization. This improvement was more remarkable when both drugs were used in combination.

Physical Activity and Worsening of Radiographic Findings in Persons With or at Higher Risk of Knee Osteoarthritis

OBJECTIVE

The benefits of physical activity among persons with or at higher risk for knee osteoarthritis are well established. However, activity levels in this population are low, in part due to concern that activity will damage the knee joint. We hypothesized that sedentary and moderate-vigorous physical activity are each associated with greater risk of radiographic worsening of knee OA.

METHODS

In Osteoarthritis Initiative participants with or at higher risk for knee OA enrolled in an accelerometer substudy at 48 months (study baseline), physical activity was measured by a uniaxial accelerometer (ActiGraph GT1M). Radiographic progression was defined as any 48 month to 96 month worsening of Kellgren/Lawrence (K/L) grade scores. All analyses were knee-level; we used multivariable logistic regression with generalized estimating equations, adjusting for key covariates.

RESULTS

Of the 1,206 participants, 631 (52%) were female, the mean ± SD age was 64 ± 9 years, and mean ± SD body mass index (BMI) was 28 ± 5. The mean ± SD average daily sedentary activity was 602 ± 86 minutes, average daily light activity was 284 ± 75 minutes, and average daily moderate-vigorous activity was 20 ± 20 minutes. In 1,978 knees, 267 (14%) had worsening of K/L grade scores. In the multivariable model, age, sex, BMI, and pain, were associated with K/L grade worsening, but neither sedentary activity (adjusted odds ratio [OR] 0.99 [95% confidence interval (95% CI) 0.97-1.01]) nor moderate-vigorous activity (adjusted OR 1.00 [95% CI 0.91-1.09]) were associated with K/L grade worsening.

CONCLUSION

In persons with or at higher risk for knee OA, age, sex, BMI, and pain, but not objectively measured average daily minutes of sedentary or moderate-vigorous activity, were associated with subsequent worsening of K/L grade. Whether findings differ in persons with more severe knee OA and/or engaged more frequently in moderate-vigorous activity should be examined in future studies.

Reactive Oxygen Species Mediate Therapeutic Ultrasound-Induced, Mitogen-Activated Protein Kinase Activation in C28/I2 Chondrocytes

Low-intensity pulsed ultrasound (LIPUS) has been used for the treatment of non-healing fractures because of its therapeutic properties of stimulating enhancing endochondral bone formation. However, its mechanism of action remains unclear. In this study, we hypothesized that LIPUS activates mitogen-activated protein kinases through generation of reactive oxygen species. C28/I2 cells were stimulated with LIPUS for 10 and 20 min, while the control group was treated using a sham LIPUS transducer. Through quantitative reverse transcription polymerase chain reaction and immunoblot analyses, we determined that LIPUS application increased reactive oxygen species generation and cell viability in C28/I2 cells. There were increases in the phosphorylation level of ERK1/2 and in expression of SOX9, COL2 A1 and ACAN genes. These effects were reversed when cells were treated with diphenylene iodonium, which is known to inhibit NADPH oxidase. It was concluded that exposure of chondrocytes to LIPUS led to reactive oxygen species generation, which activated MAPK signaling and further increased chondrocyte-specific gene markers involved in chondrocyte differentiation and extracellular matrix formation.

C5a aggravates dysfunction of the articular cartilage and synovial fluid in rats with knee joint immobilization

Degenerative alterations in articular cartilage are involved in the pathogenesis of osteoarthritis. The present study aimed to evaluate the role of complement component 5a (C5a) in osteoarthritic alterations in the articular cartilage and synovialis via a joint immobilization (IM) rat model. Rats were assigned to three groups: Control, IM and IM+anti‑C5a antibody (IM+anti‑C5a) groups. A terminal deoxynucleotidyl transferase dUTP nick end labeling assay and hematoxylin and eosin staining were used to evaluate the morphological alterations in the articular cartilage and synovialis. Reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) analysis, immunohistochemical analysis and western blotting were used to evaluate C5a expression in the articular cartilage and synovialis. An ELISA was used to evaluate C5a‑induced alterations in interleukin (IL)‑1β, IL‑17A and tumor necrosis factor (TNF)‑α levels in the serum and joint fluid. The results demonstrated that knee joint immobilization induced destruction of knee joint synovial fluid and cartilage in the IM and IM+anti‑C5a antibody groups. Immobilization significantly increased the expression levels of C5a in serum and joint fluid in the IM group. Immunohistochemistry, western blotting and RT‑qPCR analysis illustrated markedly increased expression of C5a in the IM group. Immobilization markedly increased the IL‑1β, IL‑17A and TNF‑α expression levels in the serum and joint fluid in the IM group. Anti‑C5a was able to decrease immobilization‑induced alterations in morphology and cytokines compared with the IM group. The expression of C5a was increased in synoviocytes and joint cartilage in the IM model. Pro‑inflammatory cytokines, including TNF‑α and IL‑1β were released in the activated synoviocytes via the induction of C5a, suggesting that C5a serves an important role in joint inflammatory processes.

Influence of Mechanical Unloading on Articular Chondrocyte Dedifferentiation

Due to the limited self-repair capacity of articular cartilage, the surgical restoration of defective cartilage remains a major clinical challenge. The cell-based approach, which is known as autologous chondrocyte transplantation (ACT), has limited success, presumably because the chondrocytes acquire a fibroblast-like phenotype in monolayer culture. This unwanted dedifferentiation process is typically addressed by using three-dimensional scaffolds, pellet culture, and/or the application of exogenous factors. Alternative mechanical unloading approaches are suggested to be beneficial in preserving the chondrocyte phenotype. In this study, we examined if the random positioning machine (RPM) could be used to expand chondrocytes in vitro such that they maintain their phenotype. Bovine chondrocytes were exposed to (a) eight days in static monolayer culture; (b) two days in static monolayer culture, followed by six days of RPM exposure; and, (c) eight days of RPM exposure. Furthermore, the experiment was also conducted with the application of 20 mM gadolinium, which is a nonspecific ion-channel blocker. The results revealed that the chondrocyte phenotype is preserved when chondrocytes go into suspension and aggregate to cell clusters. Exposure to RPM rotation alone does not preserve the chondrocyte phenotype. Interestingly, the gene expression (mRNA) of the mechanosensitive ion channel TRPV4 decreased with progressing dedifferentiation. In contrast, the gene expression (mRNA) of the mechanosensitive ion channel TRPC1 was reduced around fivefold to 10-fold in all of the conditions. The application of gadolinium had only a minor influence on the results. This and previous studies suggest that the chondrocyte phenotype is preserved if cells maintain a round morphology and that the ion channel TRPV4 could play a key role in the dedifferentiation process.

Bone replaces articular cartilage in the rat knee joint after prolonged immobilization

BACKGROUND

Lost joint range of motion (ROM) is common in chronic osteoarthritis, alters regional weight-bearing across the articular surfaces, and contributes to loss of cartilage and bone alterations. Limited data exist on the regional effects on joints subjected to chronic losses of ROM.

OBJECTIVE

To characterize the regional replacement by bone as part of articular cartilage degeneration after prolonged immobilization.

METHODS

Eleven rat knees were rigidly-immobilized in flexion for 32weeks with contralateral and sham-operated (n=6) knees as controls. Sagittal medial tibial epiphysis histological sections assessed the anterior (non-weight-bearing), middle and posterior (both weight-bearing) regions. We quantified the distribution of collagen I, collagen II, cartilage thickness, glycosaminoglycan (GAG) staining, Mankin scoring, and subchondral bone plate cross-sectional area. Using immunohistochemistry (IHC), we visualized blood vessels, osteoblasts, and mesenchymal stem cells (MSCs).

RESULTS

Immobilized cartilage had increased collagen I content in the anterior tibial region with picrosirius red staining (immobilized=61±20%; contralateral=43±12%, p=0.033; sham=20±10%, p=0.028) and collagen I IHC (immobilized=40±10%; contralateral=11±4%, p=0.003; sham=5±3%, p=0.043). Articular cartilage was thinner anteriorly (18±30μm) in immobilized knees versus contralateral (124±40μm, p<0.001) and sham (125±43μm, p=0.043). GAG staining covered 2±4% of the anterior articular area in immobilized knees versus 28±12% contralaterally (p=0.003) and 26±7% in sham (p=0.043). Mankin scores in immobilized knees were 4.7±1.7 versus 0.2±0.4 and 0±0 for contralateral and sham (p=0.003, p=0.042), respectively. The trabecular bone plate area of anterior and posterior regions showed relative loss of cross-sectional area in immobilized knees compared to controls (immobilized/contralateral area ratios of 0.67 and 0.46 respectively, both p=0.003), while the area in the middle region was preserved. Movat's pentachrome stain and CD31 staining showed chondral vascular ingrowth from subchondral bone. Osteocalcin and CD90 MSC staining were decreased in immobilized knees versus contralateral (p=0.003, p=0.036 respectively).

CONCLUSIONS

Bony replacement characterizes articular cartilage degeneration of knees immobilized for 32weeks in the anterior, non-weight bearing region of the tibia. Replacement of cartilage by bone may have been mediated by chondral vascularization, suggesting irreversible changes. These findings stress the importance of weight-bearing and joint motion to maintain cartilage structure.

Thinning of articular cartilage after joint unloading or immobilization. An experimental investigation of the pathogenesis in mice

OBJECTIVE

Moderate mechanical stress generated by normal joint loading and movement is essential for the maintenance of healthy articular cartilage. However, the effects of reduced loading caused by the absence of weight bearing or joint motion on articular cartilage and subchondral bone is still poorly understood. We aimed to characterize morphological and metabolic responses of articular cartilage and subchondral bone to decreased mechanical stress in vivo.

METHODS

Mice were subjected to periods of hindlimb unloading by tail suspension or external fixation of the knee joints. The articular surface was observed with digital microscope and the epiphyseal bone was assessed by micro-CT analysis. Articular cartilage and subchondral bone were further evaluated by histomorphometric, histochemical, and immunohistochemical analyses.

RESULTS

The joint surface was intact, but thickness of both the total and uncalcified layer of articular cartilage were decreased both after joint unloading and immobilization. Subchondral bone atrophy with concomitant marrow expansion predisposed osteoclast activity at bone surface to invade into cartilaginous layer. Uncalcified cartilage showed decreased aggrecan content and increased aggrecanase expression. Alkaline phosphatase (ALP) activity was increased at uncalcified cartilage, whereas decreased at calcified cartilage. The distributions of hypertrophic chondrocyte markers remained unchanged.

CONCLUSION

Thinning of articular cartilage induced by mechanical unloading may be mediated by metabolic changes in chondrocytes, including accelerated aggrecan catabolism and exquisitely modulated matrix mineralization, and cartilage matrix degradation and resorption by subchondral osteoclasts. Cartilage degeneration without chondrocyte hypertrophy under unloading condition indicate the possible existence of mechanism which is different from osteoarthritis pathogenesis.

Meniscus, articular cartilage and nucleus pulposus: a comparative review of cartilage-like tissues in anatomy, development and function

The degradation of cartilage in the human body is impacted by aging, disease, genetic predisposition and continued insults resulting from daily activity. The burden of cartilage defects (osteoarthritis, rheumatoid arthritis, intervertebral disc damage, knee replacement surgeries, etc.) is daunting in light of substantial economic and social stresses. This review strives to broaden the scope of regenerative medicine and tissue engineering approaches used for cartilage repair by comparing and contrasting the anatomical and functional nature of the meniscus, articular cartilage (AC) and nucleus pulposus (NP). Many review papers have provided detailed evaluations of these cartilages and cartilage-like tissues individually but none have comprehensively examined the parallels and inconsistencies in signaling, genetic expression and extracellular matrix composition between tissues. For the first time, this review outlines the importance of understanding these three tissues as unique entities, providing a comparative analysis of anatomy, ultrastructure, biochemistry and function for each tissue. This novel approach highlights the similarities and differences between tissues, progressing research toward an understanding of what defines each tissue as distinctive. The goal of this paper is to provide researchers with the fundamental knowledge to correctly engineer the meniscus, AC and NP without inadvertently developing the wrong tissue function or biochemistry.

Remobilization causes site-specific cyst formation in immobilization-induced knee cartilage degeneration in an immobilized rat model

An understanding of the articular cartilage degenerative process is necessary for the prevention and treatment of joint disease. The present study aimed to examine how long‐term immobilization‐induced cartilage degeneration is aggravated by remobilization. Sixty 8‐week‐old male Wistar rats were used in this study. The unilateral knee joint was immobilized using an external fixator for 8 weeks. The rats were killed at 0 and 3 days, and at 1, 2, 4 and 8 weeks after removing the fixator. After the rats were killed, the maximum knee extension angles were measured. Histological sections at the medial mid‐condylar region (non‐contact, transitional and contact regions of the femur and tibia) were prepared and scored. The cartilage thickness and number of chondrocytes were measured, and CD44 and Col2‐3/4c expression levels were assessed immunohistochemically. The histological assessment revealed progressive aggravation of cartilage degeneration in the transitional region, with a decreased number of chondrocytes and CD44‐positive chondrocytes as well as poor scoring over time, particularly in the tibia. Cyst formation was confirmed in the transitional region of the tibia at 8 weeks post‐remobilization. The cartilage thickness in the transitional region was thicker than that in the contact region, particularly in the tibia. Col2‐3/4c expression was observed in the non‐contact and transitional regions, and the knee extension angle was recovered. In conclusion, immobilization‐induced cartilage degeneration was aggravated by remobilization over time in the transitional region, followed by observations of a decreased number of chondrocytes and morphological disparity between different cartilage regions.

Spatial and temporal changes of subchondral bone proceed to articular cartilage degeneration in rats subjected to knee immobilization

This study was aimed to investigate the spatial and temporal changes of subchondral bone and its overlying articular cartilage in rats following knee immobilization. A total of 36 male Wistar rats (11-13 months old) were assigned randomly and evenly into 3 groups. For each group, knee joints in 6 rats were immobilized unilaterally for 1, 4, or 8 weeks, respectively, while the remaining rats were allowed free activity and served as external control groups. For each animal, femurs at both sides were dissected after sacrificed. The distal part of femur was examined by micro-CT. Subsequently, femoral condyles were collected for further histological observation and analysis. For articular cartilage, significant changes were observed only at 4 and 8 weeks of immobilization. The thickness of articular cartilage and chondrocytes numbers decreased with time. However, significant changes in subchondral bone were defined by micro-CT following immobilization in a time-dependent manner. Immobilization led to a thinner and more porous subchondral bone plate, as well as a reduction in trabecular thickness and separation with a more rod-like architecture. Changes in subchondral bone occurred earlier than in articular cartilage. More importantly, immobilization-induced changes in subchondral bone may contribute, at least partially, to changes in its overlying articular cartilage.

Cartilage matrix changes in contralateral mobile knees in a rabbit model of osteoarthritis induced by immobilization

Background

Many researches have investigated the changes associated with immobilization-induced osteoarthritis (OA). However, there are only few studies focusing on the effect of unilateral knee immobilization on cartilage matrix changes in the contralateral mobile knee. The aim of the present study was to investigate the influence of immobilization on the cartilage matrix in the contralateral mobile knees in a rabbit model of OA induced by immobilization.

Methods

Right knees (experimental knees) of eighteen mature female rabbits were immobilized at an extension of 180° with orthopedic casting tape for 2, 4, or 8 weeks. Left knees (contralateral knees) of the immobilized rabbits were not subjected to immobilization. The knees of six non-immobilized rabbits were designated as control knees. Following immobilization, cartilage specimens from the medial femoral condyle underwent macroscopic, histological, immunohistochemical, and biochemical evaluations.

Results

Roughness of cartilage surface was detected in the experimental knees at 2 weeks, and cartilage degeneration was further developed. In the contralateral knee, cartilage showed degenerative changes after 4 weeks. Safranin-O staining and glycosaminoglycan (GAG) contents were reduced in the experimental knees following immobilization and in the contralateral intact knees after 4 and 8 weeks. Type II collagen staining was gradually reduced, type I collagen accumulation was obviously detected in the upper and middle layers of cartilage in experimental knees after 8 weeks, and the collagen orientation was gradually disorganized in both knees at 4 and 8 weeks. For both experimental and contralateral knees, collagen contents were significantly decreased at 8 weeks, and Mankin and Osteoarthritis Research Society International (OARSI) scores increased over time.

Conclusion

OA developed in the contralateral intact knee with the progress of OA in the immobilized knee in a rabbit model of immobilization-induced OA.

Using 7.0T MRI T2 mapping to detect early changes of the cartilage matrix caused by immobilization in a rabbit model of immobilization-induced osteoarthritis

OBJECTIVE

The goal of this study was to detect early changes in the cartilage matrix caused by immobilization in a rabbit model of immobilization-induced osteoarthritis (OA) by T2 mapping with 7.0T MRI.

MATERIALS AND METHODS

Left knee joints of 28 mature rabbits were immobilized at 180° of extension with orthopedic casting tape for 1, 2, or 3weeks (n=7 rabbits each). No immobilization was performed in the control group (n=7 rabbits). T2 mapping was performed after 1, 2, and 3weeks. Osteochondral specimens harvested from the trochlea groove (TG) and medial femoral condyle (MFC) were subjected to histologic, immunohistochemical, and microscopic evaluation, followed by biochemical assays for water, glycosaminoglycan (GAG), and collagen. The ability of T2 mapping to reveal changes in the cartilage matrix was further assessed.

RESULTS

Rabbits demonstrated elevated T2 values (9.9% in TG, 10.6% in MFC), a dulled cartilage surface, reduced Safranin-O staining, and decreased GAG content (14.2% in TG and MFC) after 2weeks, with cartilage surface softening, irregularity, and markedly reduced GAG content by 3weeks. T2 values were correlated positively with water (r=0.836 in TG, r=0.821 in MFC) and negatively with GAG content (r=-0.945 in TG, r=-0.957 in MFC), but had no discernible relationship with collagen content (r=-0.196 in TG, r=-0.213 in MFC).

CONCLUSIONS

7.0T MRI T2 mapping can be used to detect early changes of the cartilage matrix caused by immobilization in an immobilization-induced OA model.

Alteration of cartilage surface collagen fibers differs locally after immobilization of knee joints in rats

The purpose of this study was to examine the ultrastructural changes of surface cartilage collagen fibers, which differ by region and the length of the experimental period in an immobilization model of rat. Male Wistar rats were randomly divided into histological or macroscopic and ultrastructural assessment groups. The left knees of all the animals were surgically immobilized by external fixation for 1, 2, 4, 8 or 16 weeks (n = 5/time point). Sagittal histological sections of the medial mid-condylar region of the knee were obtained and assessed in four specific regions (contact and peripheral regions of the femur and tibia) and two zones (superficial and deep). To semi-quantify the staining intensity of the collagen fibers in the cartilage, picrosirius red staining was used. The cartilage surface changes of all the assessed regions were investigated by scanning electron microscopy (SEM). From histological and SEM observations, the fibrillation and irregular changes of the cartilage surface were more severe in the peripheral region than in the contact region. Interestingly, at 16 weeks post-immobilization, we observed non-fibrous structures at both the contact and peripheral regions. The collagen fiber staining intensity decreased in the contact region compared with the peripheral region. In conclusion, the alteration of surface collagen fiber ultrastructure and collagen staining intensity differed by the specific cartilage regions after immobilization. These results demonstrate that the progressive degeneration of cartilage is region specific, and depends on the length of the immobilization period.

A non-randomised experimental feasibility study into the immediate effect of three different spinal manipulative protocols on kicking speed performance in soccer players

BACKGROUND

The most utilized soccer kicking method is the instep kicking technique. Decreased motion in spinal joint segments results in adverse biomechanical changes within in the kinematic chain. These changes may be linked to a negative impact on soccer performance. This study tested the immediate effect of lumbar spine and sacroiliac manipulation alone and in combination on the kicking speed of uninjured soccer players.

METHODS

This 2010 prospective, pre-post experimental, single-blinded (subject) required forty asymptomatic soccer players, from regional premier league teams, who were purposively allocated to one of four groups (based on the evaluation of the players by two blinded motion palpators). Segment dysfunction was either localized to the lumbar spine (Group 1), sacroiliac joint (Group 2), the lumbar spine and sacroiliac joint (Group 3) or not present in the sham laser group (Group 4). All players underwent a standardized warm-up before the pre-measurements. Manipulative intervention followed after which post-measurements were completed. Measurement outcomes included range of motion changes (digital inclinometer); kicking speed (Speed Trac™ Speed Sport Radar) and the subjects' perception of a change in kicking speed. SPSS version 15.0 was used to analyse the data, with repeated measures ANOVA and a p-value <0.05 (CI 95%).

RESULTS

Lumbar spine manipulation resulted in significant range of motion increases in left and right rotation. Sacroiliac manipulation resulted in no significant changes in the lumbar range of motion. Combination manipulative interventions resulted in significant range of motion increases in lumbar extension, right rotation and right SI joint flexion. There was a significant increase in kicking speed post intervention for all three manipulative intervention groups (when compared to sham). A significant correlation was seen between Likert based-scale subjects' perception of change in kicking speed post intervention and the objective results obtained.

CONCLUSIONS

This pilot study showed that lumbar spine manipulation combined with SI joint manipulation, resulted in an effective intervention for short-term increases in kicking speed/performance. However, the lack of an a priori analysis, a larger sample size and an unblinded outcome measures assessor requires that this study be repeated, addressing these concerns and for these outcomes to be validated.

In vitro glycation of articular cartilage alters the biomechanical response of chondrocytes in a depth-dependent manner

OBJECTIVE

To determine if increasing cartilage cross-links through in vitro glycation of cartilage explants can alter the biomechanical response of chondrocytes to compressive deformation.

METHOD

Bovine osteochondral explants were either incubated with cell culture solution supplemented with (n = 7) or without (n = 7) ribose for 42 h in order to induce glycation. Deformation-induced changes in cell volume, dimensions and local tissue strains were determined through confocal laser scanning microscopy (CLSM) and the use of a custom built micro-compression device. Osteochondral explants were also utilized to demonstrate changes in depth-wise tissue properties, biomechanical tissue properties and cross-links such as pentosidine (Pent), hydroxylysyl pyridinoline (HP) and lysyl pyridinoline (LP).

RESULTS

The ribose treated osteochondral samples experienced reduced cell volume deformation in the upper tissue zone by ∼ 8% (P = 0.005), as compared the control samples, through restricting cell expansion. In the deeper tissue zone, cell volume deformation was increased by ∼ 12% (P < 0.001) via the transmission of mechanical signals further into the tissue depth. Biomechanical testing of the ribose treated osteochondral samples demonstrated an increase in the equilibrium and dynamic strain dependent moduli (P < 0.001 and P = 0.008, respectively). The biochemical analysis revealed an increase in Pent cross-links (P < 0.001). Depth-wise tissue property analyses revealed increased levels of carbohydrate content, greater levels of fixed charge density and an increased carbohydrate to protein ratio from 6 to 16%, 55-100% and 72-79% of the normalized tissue thickness (from the surface), respectively, in the ribose-treated group (P < 0.05).

CONCLUSION

In vitro glycation alters the biomechanical response of chondrocytes in cartilage differently in upper and deeper zones, offering possible insights into how aging could alter cell deformation behavior in cartilage.

Integrin-mediated mechanotransduction pathway of low-intensity continuous ultrasound in human chondrocytes

Chondrocytes are mechanosensitive cells that require mechanical stimulation for proper growth and function in in vitro culture systems. Ultrasound (US) has emerged as a technique to deliver mechanical stress; however, the intracellular signaling components of the mechanotransduction pathways that transmit the extracellular mechanical stimulus to gene regulatory mechanisms are not fully defined. We evaluated a possible integrin/mitogen-activated protein kinase (MAPK) mechanotransduction pathway using Western blotting with antibodies targeting specific phosphorylation sites on intracellular signaling proteins. US stimulation of chondrocytes induced phosphorylation of focal adhesion kinase (FAK), Src, p130 Crk-associated substrate (p130Cas), CrkII and extracellular-regulated kinase (Erk). Furthermore, pre-incubation with inhibitors of integrin receptors, Src and MAPK/Erk kinase (MEK) reduced US-induced Erk phosphorylation levels, indicating integrins and Src are upstream of Erk in an US-mediated mechanotransduction pathway. These findings suggest US signals through integrin receptors to the MAPK/Erk pathway via a mechanotransduction pathway involving FAK, Src, p130Cas and CrkII.

Orthotic considerations for dense connective tissue and articular cartilage--the need for optimal movement and stress

Orthotic intervention is an essential component of hand rehabilitation, addressing biological factors that affect activity and participation. Functional, pain-free joint mobility requires skeletal stability, healthy articular cartilage, and appropriate extensibility of periarticular dense connective tissues (DCTs). This article addresses basic science underlying clinical reasoning when considering orthoses to maintain or restore structural integrity, mobility and function of DCT structures, and articular cartilage. However, these tissues often have different and sometimes conflicting requirements for the maintenance and restoration of integrity and health. The duration of immobilization, especially at end range, should be carefully considered, as it impairs nutrition of tissues and adversely compresses articular cartilage, causing injury that may not be reversible. Immobilization also reduces extensibility of DCT. Thus, an intermittent orthotic wearing schedule is suggested, allowing movement wherever possible to promote tissue health. To optimize benefits and minimize harmful effects of orthotic intervention, further research on physiological responses of human tissues to immobilization and tension is needed.

Effect of laser acupuncture on disuse osteoarthritis: an ultrasound biomicroscopic study of patellar articular cartilage in rats

To investigate the effect of laser acupuncture (LA) on disuse changes in articular cartilage using ultrasound biomicroscopy (UBM), Eighteen rats were randomly divided into the control group (C), the tail-suspended group (T), and the tail-suspended with LA treatment group (L). During 28-day suspension period, group L were treated with LA at acupoints on the left hindlimb while group T had a sham treatment. Ultrasound roughness index (URI), integrated reflection coefficient (IRC), integrated backscatter coefficient (IBC), cartilage thickness, and ultrasonographic score (US) of articular cartilage at patella were measured by using an ultrasound biomicroscopy system (UBS). Compared with the group C, URI significantly (P < 0.01) increased by 60.9% in group T, increased by 38.1% in group L. In addition, unloading induced a significant cartilage thinning (P < 0.05) in group T, whereas cartilage thickness in group L was 140.22 ± 19.61 μm reaching the level of the control group (147.00 ± 23.99 μm). There was no significant difference in IRC, IBC, and US among the three groups. LA therapy could help to retain the quality of articular cartilage which was subjected to unloading. LA would be a simple and safe nonpharmacological countermeasure for unloading-induced osteoarthritis. The UBM system has potential to be a sensitive, specific tool for quantitative assessment of articular cartilage.

Motion versus fixed distraction of the joint in the treatment of ankle osteoarthritis: a prospective randomized controlled trial

BACKGROUND

Initial reports have shown the efficacy of fixed distraction for the treatment of ankle osteoarthritis. We hypothesized that allowing ankle motion during distraction would result in significant improvements in outcomes compared with distraction without ankle motion.

METHODS

We conducted a prospective randomized controlled trial comparing the outcomes for patients with advanced ankle osteoarthritis who were managed with anterior osteophyte removal and either (1) fixed ankle distraction or (2) ankle distraction permitting joint motion. Thirty-six patients were randomized to treatment with either fixed distraction or distraction with motion. The patients were followed for twenty-four months after frame removal. The Ankle Osteoarthritis Scale (AOS) was the main outcome variable.

RESULTS

Two years after frame removal, subjects in both groups showed significant improvement compared with the status before treatment (p < 0.02 for both groups). The motion-distraction group had significantly better AOS scores than the fixed-distraction group at twenty-six, fifty-two, and 104 weeks after frame removal (p < 0.01 at each time point). At 104 weeks, the motion-distraction group had an overall mean improvement of 56.6% in the AOS score, whereas the fixed-distraction group had a mean improvement of 22.9% (p < 0.01).

CONCLUSION

Distraction improved the patient-reported outcomes of treatment of ankle osteoarthritis. Adding ankle motion to distraction showed an early and sustained beneficial effect on outcome.

Effects of unloading on knee articular cartilage T1rho and T2 magnetic resonance imaging relaxation times: a case series

STUDY DESIGN

Case series.

BACKGROUND

It has been shown in rodent and canine models that cartilage composition is significantly altered in response to long-term unloading. To date, however, no in vivo human studies have investigated this topic. The objective of this case series was to determine the influence of unloading and reloading on T1rho and T2 relaxation times of articular cartilage in healthy young joints.

CASE DESCRIPTION

Ten patients who required 6 to 8 weeks of non-weight bearing (NWB) for injuries affecting the distal lower extremity participated in the study. Quantitative T1rho and T2 imaging of the ipsilateral knee joint was performed at 3 time points: (1) prior to surgery (baseline), (2) immediately after a period of NWB (post-NWB), and (3) after 4 weeks of full weight bearing (post-FWB). Cartilage regions of interest were segmented and overlaid on T1rho and T2 relaxation time maps for quantification. Descriptive statistics are provided for all changes.

OUTCOMES

Increases of 5% to 10% in T1rho times of all femoral and tibial compartments were noted post-NWB. All values returned to near-baseline levels post-FWB. Increases in medial tibia T2 times were noted post-NWB and remained elevated post-FWB. The load-bearing regions showed the most significant changes in response to unloading, with increases of up to 12%.

DISCUSSION

The observation of a transient shift in relaxation times confirms that cartilage composition is subject to alterations based on loading conditions. These changes appear to be mostly related to proteoglycan content and more localized to the load-bearing regions. However, following 4 weeks of full weight bearing, relaxation times of nearly all regions had returned to baseline levels, demonstrating reversibility in compositional fluctuations.

LEVEL OF EVIDENCE

Therapy, level 4.

Effects of immobilization on thickness of superficial zone of articular cartilage of patella in rats

BACKGROUND

Articular cartilage normally functions as a load-bearing resistant material in joints. Patella is composed of hyaline cartilage and spongy bone. Chondrocytes form only 1-5% volume of the articular cartilage. They receive their nutrition by diffusion through the matrix. The alteration in articular cartilage become apparent following immobilization, from 4 to 6 weeks. Until now, focus of research has been the whole cartilage. Zonal changes have not been studied in detail. Since superficial zone bears maximum load and is the first zone to come in contact, the present study was designed to determine changes in thickness on immobilization and remobilization in superficial zone after dividing it into proximal, central, and distal segments.

MATERIALS AND METHODS

Forty male rats belonging to Sprague Dawley strain were divided into two groups. Group 1 (n=20) subdivided into an experimental subgroup of 10 rats that were immobilized in plaster of Paris (POP) for 4 weeks and a control subgroup of 10 that were not immobilized. Group 2 (n=20) subdivided into an experimental subgroup of 10 rats that were immobilized for 4 weeks and remobilized for next 4 weeks and a control subgroup of 10 animals that were not immobilized. At the end of the experimental period, the knee joint was dissected and was cut in sagittal plane. The section was fixed in 10% formalin for 48 hours. Specimen was decalcified using ethylenediaminetetraacetic acid (EDTA). The paraffin blocks of 7 μm sections were cut and stained by H and E stain for routine histology and Alcian blue stain and Mallory Trichrome for fine structural microscopy. The zones were named as superficial transitional, radial, and hypertrophic according to the shape of cells present in each zone. The superficial zone was divided into superior part, central, and inferior parts. These parts were labeled as central, proximal, and distal segments. The calibrated stage micrometer was used to calibrate the ocular micrometer under objectives of different power. The ocular micrometer was placed inside the ocular lens. It was calibrated with the stage micrometer under objective lenses of different power. The number of divisions of ocular covering each zone was calculated. These divisions were converted into micrometer and the actual thickness was calculated.

RESULTS

The significant decrease in thickness of superficial zone in proximal, central and distal segment was observed in experimental group in comparison to control group. When the experimental subgroup of group 2 was compared with experimental subgroup of group 1 (group immobilized for 4 weeks), no significant reversal was seen in superficial zone and instead significant decrease was observed in distal segment. Fibrous connective tissue was increased adjacent to superficial zone.

CONCLUSION

Each segment of superficial zone behaves differentially on immobilization and remobilization. Perhaps a much longer duration of remobilization is required to reverse changes of immobilization in articular cartilage and plays a significant role in knee joint movements.

Biological basis of exercise-based treatments for musculoskeletal conditions

Exercise-based therapies are the cornerstone of rehabilitation programs. While the benefits of exercise on systemic and tissue function are generally accepted, mechanisms underlying these benefits are sometimes poorly understood. An improved understanding of the effects of mechanical loading on molecular and cellular processes has the potential to lead to more disease-specific and efficacious exercise-based therapies. The purpose of this paper is to review the current literature examining the role of mechanical signaling on muscle and cartilage biology.

Oxidative stress in secondary osteoarthritis: from cartilage destruction to clinical presentation?

Due to an increasing life expectance, osteoarthritis (OA) is one of the most common chronic diseases. Although strong efforts have been made to regenerate degenerated joint cartilage, OA is a progressive and irreversible disease up to date. Among other factors the dysbalance between free radical burden and cellular scavenging mechanisms defined as oxidative stress is a relevant part of OA pathogenesis. Here, only little data are available about the mediation and interaction between different joint compartments. The article provides a review of the current literature regarding the influence of oxidative stress on cellular aging, senescence and apoptosis in different joint compartments (cartilage, synovial tissue and subchondral bone). Free radical exposure is known to promote cellular senescence and apoptosis. Radical oxygen species (ROS) involvement in inflammation, fibrosis control and pain nociception has been proven. The data from literature indicates a link between free radical burden and OA pathogenesis mediating local tissue reactions between the joint compartments. Hence, oxidative stress is likely not only to promote cartilage destruction but also to be involved in inflammative transformation, promoting the transition from clinically silent cartilage destruction to apparent OA. ROS induced by exogenous factors such as overload, trauma, local intraarticular lesion and consecutive synovial inflammation cause cartilage degradation. In the affected joint, free radicals mediate disease progression. The interrelationship between oxidative stress and OA etiology might provide a novel approach to the comprehension and therefore modification of disease progression and symptom control.

Physiology and pathophysiology of nitrosative and oxidative stress in osteoarthritic joint destruction

Osteoarthritis (OA) is one of the most common chronic diseases, with increasing importance due to increased life expectancy. On a cellular level, the pathophysiology of joint function impairment and ultimate destruction associated with OA remains poorly understood. Free radicals are highly reactive molecules involved in both normal intracellular signal transduction and degenerative cellular processes. An imbalance between the free radical burden and cellular scavenging mechanisms, defined as oxidative stress, has been identified as a relevant factor in OA pathogenesis. This literature review elucidates the involvement of nitrosative and oxidative stress in cellular ageing in joints, cell senescence, and apoptosis. Free radical exposure is known to promote cellular senescence and apoptosis, and the involvement of radical oxygen species (ROS) in inflammation, fibrosis control, and pain nociception has been proven. A relatively novel approach to OA pathophysiology considers the joint to be a dynamic system consisting of 3, continuously interacting compartments, cartilage, synovial tissue, and subchondral bone. Current knowledge concerning free radical involvement in paracrine signalling in OA is reviewed. The interrelationship between oxidative imbalances and OA pathophysiology may provide a novel approach to the comprehension, and therefore modification, of OA disease progression and symptom control.

Zoologic companion animal rehabilitation and physical medicine

Injury and illness in zoologic companion animals can lead to significant pain and debilitation. Recovery can be slow and sometimes frustrating. By augmenting recovery from trauma or disease with physical medicine and rehabilitation techniques, recovery can be more rapid and complete. Physical medicine techniques, such as massage, can augment recovery from a painful injury or surgery by reducing edema, improving postoperative ileus, and decreasing anxiety. Familiarity with the tools of rehabilitation along with focus on pain management, strengthening, and proprioception improve patient care.

Ultrasound evaluation of site-specific effect of simulated microgravity on articular cartilage

Space flight induces acute changes in normal physiology in response to the microgravity environment. Articular cartilage is subjected to high loads under a ground reaction force on Earth. The objectives of this study were to investigate the site dependence of morphological and ultrasonic parameters of articular cartilage and to examine the site-specific responses of articular cartilage to simulated microgravity using ultrasound biomicroscopy (UBM). Six rats underwent tail suspension (simulated microgravity) for four weeks and six other rats were kept under normal Earth gravity as controls. Cartilage thickness, ultrasound roughness index (URI), integrated reflection coefficient (IRC) and integrated backscatter coefficient (IBC) of cartilage tissues, as well as histological degeneration were measured at the femoral head (FH), medial femoral condyle (MFC), lateral femoral condyle (LFC), patello-femoral groove (PFG) and patella (PAT). The results showed site dependence not significant in all UBM parameters except cartilage thickness (p < 0.01) in the control specimens. Only minor changes in articular cartilage were induced by 4-week tail suspension, although there were significant decreases in cartilage thickness at the MFC and PAT (p < 0.05) and a significant increase in URI at the PAT (p < 0.01). This study suggested that the 4-week simulated microgravity had only mild effects on femoral articular cartilage in the rat model. This information is useful for human spaceflight and clinical medicine in improving understanding of the effect of microgravity on articular cartilage. However, the effects of longer duration microgravity experience on articular cartilage need further investigation.

Vibration training intervention to maintain cartilage thickness and serum concentrations of cartilage oligometric matrix protein (COMP) during immobilization

OBJECTIVE

To test the hypotheses that 1) 14-days of immobilization of young healthy subjects using a 6 degrees -"head-down-tilt-bed-rest"-model (6 degrees -HDT) would reduce cartilage thickness in the knee and serum Cartilage oligometric matrix protein (COMP) concentration and 2) isolated whole body vibration training would counteract the bed rest effects.

METHOD

The study was performed and designed in compliance with the Declaration of Helsinki and is registered as trial DRKS00000140 in the German Clinical Trial Register (register.germanctr.de). Eight male healthy subjects (78.0+/-9.5kg; 179+/-0.96cm, 26+/-5 years) performed 14 days of 6 degrees -HDT. The study was designed as a cross-over-design with two study phases: a training and a control intervention. During the training intervention, subjects underwent 2x5-min whole body vibration training/day (Frequency: 20Hz; amplitude: 2-4mm). Magnetic resonance (MR) images (slice thickness: 2mm; in-plane resolution: 0.35x0.35mm; pixels: 448x512) were taken before and after the 6 degrees -HDT periods. Average cartilage thicknesses were calculated for the load bearing regions on the medial and lateral articulating surfaces in the femur and tibia.

RESULTS

While the control intervention resulted in an overall loss in average cartilage thickness of -8% (pre: 3.08mm+/-0.6mm post: 2.82mm+/-0.6mm) in the weight-bearing regions of the tibia, average cartilage thickness increased by 21.9% (pre: 2.66mm+/-0.45mm post: 3.24mm+/-0.63mm) with the vibration intervention. No significant differences were found in the weight-bearing regions of the femur. During both interventions, reduced serum COMP concentrations were observed (control intervention: -13.6+/-8.4%; vibration intervention: -9.9+/-3.3%).

CONCLUSION

The results of this study suggest that articular cartilage thickness is sensitive to unloading and that vibration training may be a potent countermeasure against these effects. The sensitivity of cartilage to physical training is of high relevance for training methods in space flight, elite and sport and rehabilitation after illness or injury.

Changes in spatial collagen content and collagen network architecture in porcine articular cartilage during growth and maturation

OBJECTIVES

The present study was designed to reveal changes in the collagen network architecture and collagen content in cartilage during growth and maturation of pigs.

METHODS

Femoral groove articular cartilage specimens were collected from 4-, 11- and 21-month-old domestic pigs (n=12 in each group). The animal care conditions were kept constant throughout the study. Polarized light microscopy was used to determine the collagen fibril network birefringence, fibril orientation and parallelism. Infrared spectroscopy was used to monitor changes in the spatial collagen content in cartilage tissue.

RESULTS

During growth, gradual alterations were recorded in the collagen network properties. At 4 months of age, a major part of the collagen fibrils was oriented parallel to the cartilage surface throughout the tissue. However, the fibril orientation changed considerably as skeletal maturation progressed. At 21 months of age, the fibrils of the deep zone cartilage ran predominantly at right angles to the cartilage surface. The collagen content increased and its depthwise distribution changed during growth and maturation. A significant increase of the collagen network birefringence was observed in the deep tissue at the age of 21 months.

CONCLUSIONS

The present study revealed dynamic changes of the collagen network during growth and maturation of the pigs. The structure of the collagen network of young pigs gradually approached a network with the classical Benninghoff architecture. The probable explanation for the alterations is growth of the bone epiphysis with simultaneous adaptation of the cartilage to increased joint loading. The maturation of articular cartilage advances gradually with age and offers, in principle, the possibility to influence the quality of the tissue, especially by habitual joint loading. These observations in porcine cartilage may be of significance with respect to the maturation of human articular cartilage.

Changes of articular cartilage after immobilization in a rat knee contracture model

The objective was to determine the changes of articular cartilage of the knee joint during immobilization in a rat model. The knee joints of adult male rats were immobilized at 150 degrees of flexion using an internal fixator for 3 days, and 1, 2, 4, 8, and 16 weeks. The articular cartilage from the medial midcondylar region of the knee was obtained, divided into three areas (non-contact area, transitional area, contact area), and in each area, a degree of degeneration was evaluated by gross observation, histomorphometric grading, and measurements of thickness and number of chondrocytes. Elasticity of the articular cartilage was estimated by measuring the sound speed with use of scanning acoustic microscopy. Degeneration of the articular cartilage was mainly observed in the contact and transitional areas. Matrix staining intensity by safranin-O and number of chondrocytes were decreased in these two areas. The thickness of the articular cartilage in the non-contact and contact areas was unchanged, but it was increased in the transitional area. Decrease in sound speed was observed in the transitional area of both the femoral and tibial cartilage, indicating the softening of the articular cartilage. The changes of articular cartilage became obvious as early as 1 week after immobilization. These changes may be due to a lack of mechanical stress or a lack of joint fluid circulation during immobilization. Although we do not know the reversibility of these changes of articular cartilage, early mobilization is preferable to avoid these cartilage changes.

Immobilization-induced cartilage degeneration mediated through expression of hypoxia-inducible factor-1alpha, vascular endothelial growth factor, and chondromodulin-I

Immobilization results in thinning of the articular cartilage and cartilage degeneration, although the exact mechanisms are not clear yet. Hypoxia is thought to contribute to the degeneration of articular cartilage. We investigated the roles of hypoxia inducible factor (HIF)-1alpha, vascular endothelial growth factor (VEGF), and the newly cloned antiangiogenic factor, chondromodulin-I (ChM-1), in cartilage degeneration in immobilized joints. Male Wistar rats (n = 30, 12-week-old) were divided randomly into the control group (n = 10), immobilization group (n = 10), and continuous passive motion (CPM) group (n = 10). In the immobilization group, the ankle joints were fixed in full plantar flexion with plaster casts for 4 weeks. In the CPM group, the ankle casts were removed during the immobilization period and the ankle joints were subjected to CPM. Significant thinning of the articular cartilage was noted in the immobilization group but not in the control or CPM group. In the immobilized group, vascular channels were found in the area between the calcified cartilage zone and the subchondral bone. The densities of HIF-1alpha-and VEGF-immunostained cells were higher in the immobilized group than the other two groups. In contrast, low expression of ChM-1 was detected in the articular cartilage of the immobilized group compared with the control and CPM group. Our results showed that immobilization induces thinning of the articular cartilage and appearance of vascular channel, in areas with balanced expression of HIF-1alpha/VEGF and ChM-1.

Oxygen and reactive oxygen species in articular cartilage: modulators of ionic homeostasis

Articular cartilage is an avascular tissue dependent on diffusion mainly from synovial fluid to service its metabolic requirements. Levels of oxygen (O(2)) in the tissue are low, with estimates of between 1 and 6%. Metabolism is largely, if not entirely, glycolytic, with little capacity for oxidative phosphorylation. Notwithstanding, the tissue requires O(2) and consumes it, albeit at low rates. Changes in O(2) tension also have profound effects on chondrocytes affecting phenotype, gene expression, and morphology, as well as response to, and production of, cytokines. Although chondrocytes can survive prolonged anoxia, low O(2) levels have significant metabolic effects, inhibiting glycolysis (the negative Pasteur effect), and also notably matrix production. Why this tissue should respond so markedly to reduction in O(2) tension remains a paradox. Ion homeostasis in articular chondrocytes is also markedly affected by the extracellular matrix in which the cells reside. Recent work has shown that ion homeostasis also responds to changes in O(2) tension, in such a way as to produce significant effects on cell function. For this purpose, O(2) probably acts via alteration in levels of reactive oxygen species. We discuss the possibility that O(2) consumption by this tissue is required to maintain levels of ROS, which are then used physiologically as an intracellular signalling device. This postulate may go some way towards explaining why the tissue is dependent on O(2) and why its removal has such marked effects. Understanding the role of oxygen has implications for disease states in which O(2) or ROS levels may be perturbed.

Shear and Compression Differentially Regulate Clusters of Functionally Related Temporal Transcription Patterns in Cartilage Tissue

Chondrocytes are subjected to a variety of biophysical forces and flows during physiological joint loading, including mechanical deformation, fluid flow, hydrostatic pressure, and streaming potentials; however, the role of these physical stimuli in regulating chondrocyte behavior is still being elucidated. To isolate the effects of these forces, we subjected intact cartilage explants to 1-24 h of continuous dynamic compression or dynamic shear loading at 0.1 Hz. We then measured the transcription levels of 25 genes known to be involved in cartilage homeostasis using real-time PCR and compared the gene expression profiles obtained from dynamic compression, dynamic shear, and our recent results on static compression amplitude and duration. Using clustering analysis, we determined that transcripts for proteins with similar function had correlated responses to loading. However, the temporal expression patterns were strongly dependent on the type of loading applied. Most matrix proteins were up-regulated by 24 h of dynamic compression or dynamic shear, but down-regulated by 24 h of 50% static compression, suggesting that cyclic matrix deformation is a key stimulator of matrix protein expression. Most matrix proteases were up-regulated by 24 h under all loading types. Transcription factors c-Fos and c-Jun maximally responded within 1 h to all loading types. Pre-incubating cartilage explants with either a chelator of intracellular calcium or an inhibitor of the cyclic AMP pathway demonstrated the involvement of both pathways in transcription induced by dynamic loading.

The effect of a passive muscle stretching protocol on the articular cartilage

OBJECTIVE

The aim of this study is to evaluate the articular cartilage alterations of rat ankles, after applying unilateral cyclic passive muscle stretching protocol in previously immobilized rats.

METHODS

Twenty-two male albino rats divided into four groups, I--immobilized; IS--immobilized and stretched; S--stretched and C--control, were used in this experiment. The I and IS groups were immobilized for 4 weeks. In the muscle stretching protocol the treated ankle joint (groups IS and S) was manually full dorsal flexed 10 times for 60s with a 30s interval between each 60s period, 7 days a week for 3 weeks, to stretch the ankle plantar flexors muscle group. The right hind limb was free to move. At the end of the experiment, the ankles were removed, processed in paraffin and stained with hematoxylin-eosin and Safranin-O. Two blinded observers evaluated cellularity, chondrocyte cloning and Safranin-O staining through light microscopy. And a morphometric study was carried out using a hand count of chondrocyte cells and cartilage thickness measurement.

RESULTS

No significant effect of solely muscle stretching concerning cellularity, chondrocyte cloning and Safranin-O staining parameters was detected. However, IS group presented a significantly higher reduction of proteoglycans content than the solely stretched and solely immobilized groups and the morphometric analysis showed significant cellularity increase without thickness alteration compared to control.

CONCLUSIONS

These findings suggest that the stretching protocol used was harmful to the previously immobilized articular cartilage. However, the same stretching protocol did not harm the cartilage of non-immobilized groups.

Cartilage anlagen adapt in response to static deformation

Connective tissue adaptation, including the development of cartilaginous anlagen into bones, is widely believed to be related to dynamic, intermittent load and stress histories. Static stresses, on the other hand, are generally believed deleterious in tissue adaptation. Using serial MRI in a natural human experiment (manipulation and corrective casting of infant clubfoot), we have observed casting produces two effects: (1) the well recognized change in relative positions of the hindfoot anlagen; (2) a newly recognized immediate shape change in the anlagen. These changes seemingly enhance the rate of growth of the anlagen and of the ossific nucleus. The shape change or deformation in the anlagen would occur as a result of alterations in the magnitudes and directions of loading from soft tissue attachments and muscle activity and would necessarily be associated with changes in the stress states within the anlagen and, when present, the ossific nuclei. Given the known role of load and stress history in tissue adaptation, we presume the reduced stress histories influence the enhanced growth rates. These observations contradict some current theories of tissue adaptation since static, rather than dynamic stresses play a crucial role in accelerating the growth and development of anlagen in the infant clubfoot.

Cyclical articular joint loading leads to cartilage thinning and osteopontin production in a novel in vivo rabbit model of repetitive finger flexion

OBJECTIVE

An in vivo rabbit model of repetitive joint flexion and loading was used to characterize the morphological effects of cyclical loading on articular cartilage.

DESIGN

The forepaw digits of eight anesthetized New Zealand White adult female rabbits were repetitively flexed at 1 Hz with a mean peak digit load of 0.42 N for 2 h per day for 60 cumulative hours. Metacarpophalangeal joints were collected from loaded and contra-lateral control limbs, fixed, decalcified, embedded, and thin-sectioned. Serial sections were stained for histology or for immunohistochemistry. Morphometric data including the mean thicknesses of the uncalcified cartilage and of the calcified cartilage were collected from digital photomicrographs of safranin O-stained sections. The number of cells stained with anti-osteopontin antibody was counted.

RESULTS

We observed a decrease in uncalcified cartilage mean thickness with no significant change in calcified cartilage thickness. We also observed a significant increase in the number of cells positive for osteopontin (OPN) in the uncalcified cartilage. These changes occurred without overt cartilage surface degeneration.

CONCLUSIONS

Cyclical loading leads to changes at the tissue and cellular levels in articular cartilage. These changes are suggestive of tidemark advancement and may indicate a reactivation of cartilage mineralization steps analogous to endochondral ossification. This novel in vivo rabbit model of repetitive flexion and loading can be used to investigate the effects of cyclical loading on articular joints.

High hydrostatic pressure inhibits the biosynthesis of eukaryotic elongation factor-2

High continuous hydrostatic pressure is known to inhibit the total cellular protein synthesis. In this study, our goal was to identify pressure-regulated proteins by using two dimensional gel electrophoresis and mass spectrometry. This analysis showed that under 30 MPa continuous hydrostatic pressure the biosynthesis of eukaryotic elongation factor-2 (eEF-2) was inhibited both in HeLa carcinoma and T/C28a4 chondrocytic cell lines. Western blot analysis of HeLa cells revealed that the cellular protein level of eEF-2 decreased by 40%-50% within 12 h of the pressure treatment. However, the steady-state mRNA level of eEF-2 was not affected by the pressure. Cycloheximide addition after 4 h-pressure treatment suggested that the half-life of eEF-2 protein was shorter in pressurized cells. eEF-2 is responsible for the translocation of ribosome along the specific mRNA during translation, and its phosphorylation prevents the ribosomal translocation. Therefore, increased phosphorylation of eEF-2 was considered as one mechanism that could explain the reduced level of protein synthesis in pressurized HeLa cell cultures. However, Western blot analysis with an antibody recognizing the Thr56-phosphorylated form of eEF-2 showed that phosphorylation of eEF-2 was not elevated in pressurized samples. In conclusion, the inhibition of protein synthesis under high pressure occurs independent of the phosphorylation of eEF-2. However, this inhibition may result from the decrease of cellular eEF-2 protein.

Regulation of RANKL by biomechanical loading in fibrochondrocytes of meniscus

OBJECTIVE

We sought to determine whether fibrochondrocytes from menisci express receptor activator of NF-kappaB (RANK), its ligand (RANKL), or osteoprotegerin (OPG) and, if so, whether their expression is modulated by dynamic mechanical loading under inflammatory and normal conditions.

METHODS

Fibrochondrocytes from rat menisci were subjected to cyclic tensile strain (CTS) at various magnitudes and frequencies in the presence or absence of interleukin (IL)-1beta for up to 24 h. In order to determine whether a possible regulatory effect of mechanical loading on RANKL and its receptors under inflamed conditions is sustained, cells were stimulated with IL-1beta for 24 h while being subjected to CTS only for the initial 4 and 8h, respectively. Regulation of RANKL, RANK, and OPG expression and synthesis were determined by semiquantitative and real-time PCR, Western blotting, and immunofluorescence.

RESULT

Fibrochondrocytes constitutively expressed low levels of RANKL and RANK but marked levels of OPG. IL-1beta upregulated expression and synthesis of RANKL and RANK significantly (p<0.05), whereas expression of OPG was unaffected following 4 and 24 h. When fibrochondrocytes were simultaneously subjected to CTS and IL-1beta, expression of RANKL and RANK was significantly (p<0.05) downregulated as compared to that of IL-1beta-stimulated unstretched cells. The inhibitory effect of CTS on the IL-1beta-induced upregulation of RANKL and RANK was sustained as well as magnitude and frequency dependent.

CONCLUSIONS

Our study provides evidence that RANKL and its receptors are expressed in fibrochondrocytes from meniscus. These data also demonstrate that dynamic mechanical loading can modify the expression of RANKL and RANK in inflammatory conditions.

Etiology and pathophysiology of osteoarthritis

Acute or chronic insult, including normal wear and tear, age, obesity, and joint injury, may initiate an imbalance between matrix synthesis and matrix degradation in healthy cartilage that promotes chondral loss and prevents cartilage self-repair. The structure of healthy cartilage and the pathophysiological mechanisms of its degradation are described, followed by descriptions of endogenous and exogenous factors believed to be involved in the progressive course of osteoarthritis. Studies cited include research from the community of sports medicine.

Contrasting alterations of apposed and unapposed articular cartilage during joint contracture formation

OBJECTIVE

To quantify histologic articular cartilage alterations after immobilization, distinguishing between apposed and unapposed sites in an animal model of joint contracture.

DESIGN

Experimental controlled trial.

SETTING

Laboratory, in vivo study.

ANIMALS

Adult male Sprague-Dawley rats (N=128).

INTERVENTIONS

One hundred seventeen animals had 1 knee internally immobilized or sham-operated for 2, 4, 8, 16, or 32 weeks. One knee in 11 nonoperated animals served as controls. Main outcome measures On standardized sections, we identified femur and tibia cartilage sites that were apposed or that were unapposed. We quantified 4 characteristics: number of chondrocytes in the superficial and deep cartilage; matrix staining intensity to toluidine blue; surface irregularity of articular cartilage; and thickness of cartilage.

RESULTS

Immobilized knees harbored fewer chondrocytes in the superficial cartilage at apposed sites and in the deep cartilage at unapposed sites. Matrix staining decreased only at unapposed sites. Cartilage surface became significantly more irregular at both sites but cartilage thickness remained unchanged. Noncartilaginous tissues appeared only at unapposed sites in the superficial and deep cartilage.

CONCLUSIONS

Immobilization led to contrasting patterns of cartilage degeneration at apposed sites compared with unapposed sites. These results suggest distinct pathogenetic pathways for cartilage alterations, possibly through absence of mechanical forces (negative mechanotransduction) at unapposed sites and cyclic pressure at apposed sites. Considering the limited potential for cartilage self-repair, these results support the need for early diagnosis and aggressive mobilization of joints that are developing contractures.