Alteration in articular cartilage of rat knee joints after spinal cord injury

Effects of different combinations of mechanical loading intensity, duration, and frequency on the articular cartilage in mice

BACKGROUND

Understanding how healthy articular cartilage responds to mechanical loading is critical. Moderate mechanical loading has positive effects on the cartilage, such as maintaining cartilage homeostasis. The degree of mechanical loading is determined by a combination of intensity, frequency, and duration; however, the best combination of these parameters for knee cartilage remains unclear. This study aimed to determine which combination of intensity, frequency, and duration provides the best mechanical loading on healthy knee articular cartilage in vitro and in vivo.

METHODS AND RESULTS

In this study, 33 male mice were used. Chondrocytes isolated from mouse knee joints were subjected to different cyclic tensile strains (CTSs) and assessed by measuring the expression of cartilage matrix-related genes. Furthermore, the histological characteristics of mouse tibial cartilages were quantified using different treadmill exercises. Chondrocytes and mice were divided into the control group and eight intervention groups: high-intensity, high-frequency, and long-duration; high-intensity, high-frequency, and short-duration; high-intensity, low-frequency, and long-duration; high-intensity, low-frequency, and short-duration; low-intensity, high-frequency, and long-duration; low-intensity, high-frequency, and short-duration; low-intensity, low-frequency, and long-duration; low-intensity, low-frequency, and short-duration. In low-intensity CTSs, chondrocytes showed anabolic responses by altering the mRNA expression of COL2A1 in short durations and SOX9 in long durations. Furthermore, low-intensity, low-frequency, and long-duration treadmill exercises minimized chondrocyte hypertrophy and enhanced aggrecan synthesis in tibial cartilages.

CONCLUSION

Low-intensity, low-frequency, and long-duration mechanical loading is the best combination for healthy knee cartilage to maintain homeostasis and activate anabolic responses. Our findings provide a significant scientific basis for exercise and lifestyle instructions.

Effects of sex differences on osteoarthritic changes after anterior cruciate ligament reconstruction in rats

The prevalence of primary osteoarthritis is higher in females than males. However, it remains unclear if there are sex differences in the incidence of post-traumatic osteoarthritis after anterior cruciate ligament (ACL) reconstruction. In this study, we aimed to investigate the effects of sex on osteoarthritic changes after ACL reconstruction using an animal model. Rats were divided into the following four groups: male control, male ACL reconstruction, female control, and female ACL reconstruction. ACL reconstruction surgery was performed on the right knees of rats in the ACL reconstruction groups, while rats in the control groups did not undergo knee surgery. At 1, 4, and 12 weeks after surgery, cartilage degeneration in the medial tibial plateau and osteophyte formation in the proximal tibia were histologically assessed. After ACL reconstruction, an increase in the Mankin score, cartilage fissures, and osteophyte formation were detected within 12 weeks in both male and female rats, with similar degrees of these changes between males and females. However, changes in cartilage thickness and chondrocyte density after ACL reconstruction differed between males and females. Cartilage thickening was observed in male rats but not in female rats. The increase in chondrocyte density in the anterior region was detected in both males and females but was more pronounced in female rats. In conclusion, osteoarthritic changes were observed after ACL reconstruction in both male and female rats, but differences in changes in cartilage thickness and chondrocyte density were observed between males and females.

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.

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.

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.

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.

Spaceflight and hind limb unloading induces an arthritic phenotype in knee articular cartilage and menisci of rodents

Reduced knee weight-bearing from prescription or sedentary lifestyles are associated with cartilage degradation; effects on the meniscus are unclear. Rodents exposed to spaceflight or hind limb unloading (HLU) represent unique opportunities to evaluate this question. This study evaluated arthritic changes in the medial knee compartment that bears the highest loads across the knee after actual and simulated spaceflight, and recovery with subsequent full weight-bearing. Cartilage and meniscal degradation in mice were measured via microCT, histology, and proteomics and/or biochemically after: (1) ~ 35 days on the International Space Station (ISS); (2) 13-days aboard the Space Shuttle Atlantis; or (3) 30 days of HLU, followed by a 49-day weight-bearing readaptation with/without exercise. Cartilage degradation post-ISS and HLU occurred at similar spatial locations, the tibial-femoral cartilage-cartilage contact point, with meniscal volume decline. Cartilage and meniscal glycosaminoglycan content were decreased in unloaded mice, with elevated catabolic enzymes (e.g., matrix metalloproteinases), and elevated oxidative stress and catabolic molecular pathway responses in menisci. After the 13-day Shuttle flight, meniscal degradation was observed. During readaptation, recovery of cartilage volume and thickness occurred with exercise. Reduced weight-bearing from either spaceflight or HLU induced an arthritic phenotype in cartilage and menisci, and exercise promoted recovery.

Transcutaneous Carbon Dioxide Improves Contractures After Spinal Cord Injury in Rats

BACKGROUND

Joint contractures are a major complication in patients with spinal cord injuries. Positioning, stretching, and physical therapy are advocated to prevent and treat contractures; however, many patients still develop them. Joint motion (exercise) is crucial to correct contractures. Transcutaneous carbon dioxide (CO2) therapy was developed recently, and its effect is similar to that of exercise. This therapy may be an alternative or complementary approach to exercise.

QUESTION/PURPOSES

Using an established model of spinal cord injury in rats with knee flexion contractures, we sought to clarify whether transcutaneous CO2 altered (1) contracture, as measured by ROM; (2) muscular and articular factors contributing to the loss of ROM; (3) fibrosis and fibrosis-related gene expression in muscle; and (4) the morphology of and fibrosis-related protein expression in the joint capsule.

METHODS

Thirty-six Wistar rats were divided into three equal groups: caged control, those untreated after spinal cord injury, and those treated with CO2 after spinal cord injury. The rats were treated with CO2 from either the first day (prevention) or 15th day (treatment) after spinal cord injury for 2 or 4 weeks. The hindlimbs of rats in the treated group were exposed to CO2 gas for 20 minutes once daily. Knee extension ROM was measured with a goniometer and was measured again after myotomy. We calculated the muscular and articular factors responsible for contractures by subtracting the post-myotomy ROM from that before myotomy. We also quantified histologic muscle fibrosis and evaluated fibrosis-related genes (collagen Type 1, α1 and transforming growth factor beta) in the biceps femoris muscle with real-time polymerase chain reaction. The synovial intima's length was measured, and the distribution of fibrosis-related proteins (Type I collagen and transforming growth factor beta) in the joint capsule was observed with immunohistochemistry. Knee flexion contractures developed in rats after spinal cord injuries at all timepoints.

RESULTS

CO2 therapy improved limited-extension ROM in the prevention group at 2 weeks (22° ± 2°) and 4 weeks (29° ± 1°) and in the treatment group at 2 weeks (31° ± 1°) compared with untreated rats after spinal cord injuries (35° ± 2°, mean difference, 13°; 39° ± 1°, mean difference, 9°; and 38° ± 1°, mean difference, 7°, respectively) (95% CI, 10.50-14.86, 8.10-10.19, and 4.73-9.01, respectively; all p < 0.001). Muscular factors decreased in treated rats in the prevention group at 2 weeks (8° ± 2°) and 4 weeks (14°± 1°) and in the treatment group at 2 weeks (14 ± 1°) compared with untreated rats (15° ± 1°, 4.85-9.42; 16° ± 1°, 1.24-3.86; and 17° ± 2°, 1.16-5.34, respectively; all p < 0.05). The therapy improved articular factors in the prevention group at 2 weeks (4° ± 1°) and 4 weeks (6° ± 1°) and in the treatment group at 2 weeks (8° ± 1°) compared with untreated rats (10° ± 1°, 4.05-7.05; 12° ± 1°, 5.18-8.02; and 11° ± 2°, 1.73-5.50, respectively; all p < 0.05). CO2 therapy decreased muscle fibrosis in the prevention group at 2 weeks (p < 0.001). The expression of collagen Type 1, α1 mRNA in the biceps femoris decreased in treated rats in the prevention group at 2 and 4 weeks compared with untreated rat (p = 0.002 and p = 0.008, respectively), although there was little difference in the expression of transforming growth factor beta (p > 0.05). CO2 therapy did not improve shortening of the synovial intima at all timepoints (all p > 0.05). CO2 therapy decreased transforming growth factor beta immunolabeling in joint capsules in the rats in the prevention group at 2 weeks. The staining intensity and Type I collagen pattern showed no differences among all groups at all timepoints.

CONCLUSION

CO2 therapy may be useful for preventing and treating contractures after spinal cord injuries. CO2 therapy particularly appears to be more effective as a prevention and treatment strategy in early-stage contractures before irreversible degeneration occurs, as shown in a rat model.

CLINICAL RELEVANCE

Our findings support the idea that CO2 therapy may be able to improve the loss of ROM after spinal cord injury.

Effects of hypertonia on contracture development in rat spinal cord injury

STUDY DESIGN

Experimental animal study.

OBJECTIVES

Spastic hypertonia is originally believed to cause contractures from clinical observations. Botulinum toxin is effective for the treatment of spasticity and is widely used in patients who have joints with contractures. Using an established rat model with knee contractures after spinal cord injuries, we aimed to verify whether hypertonia contributes to contracture development, and the botulinum toxin improves structural changes in muscles and joint components responsible for contractures.

SETTING

University laboratory in Japan.

METHODS

To evaluate the effect of hypertonia on contracture development, the rats received botulinum toxin injections after spinal cord injuries. Knee extension motion was measured with a goniometer applying a standardized torque under anesthesia, and the contribution by muscle or non-muscle structures to contractures were calculated by measuring joint motion before and after the myotomies. We quantitatively measured the muscle atrophy, muscle fibrosis, and synovial intima length.

RESULTS

Botulinum toxin injections significantly improved contractures, whereas did not completely prevent contracture development. Botulinum toxin was effective in improving the muscular factor, but little difference in the articular factor. Spinal cord injuries induced muscle atrophy, and botulinum toxin significantly accelerated muscle atrophy and fibrosis. The synovial intima length decreased significantly after spinal cord injuries, and botulinum toxin did not improve this shortening.

CONCLUSIONS

This animal study provides new evidence that hypertonia is not the sole cause rather is the partial contributor of contractures after spinal cord injuries. Furthermore, botulinum toxin has adverse effects in the muscle.

Diffusion tractography of the rat knee at microscopic resolution

PURPOSE

To evaluate whole knee joint tractography, including articular cartilage, ligaments, meniscus, and growth plate using diffusion tensor imaging (DTI) at microscopic resolution.

METHODS

Three rat knee joints were scanned using a modified 3D diffusion-weighted spin echo pulse sequence with 90- and 45-μm isotropic spatial resolution at 9.4T. The b values varied from 250 to 1250 s/mm² with 4 times undersampling in phase directions. Fractional anisotropy (FA) and mean diffusivity (MD) were compared at different spatial resolution and b values. Tractography was evaluated at multiple b values and angular resolutions in different connective tissues, and compared with conventional histology. The mean tract length and tract volume in various types of tissues were also quantified.

RESULTS

DTI metrics (FA and MD) showed consistent quantitative results at 90- and 45-μm isotropic spatial resolutions. Tractography of various connective tissues was found to be sensitive to the spatial resolution, angular resolution, and diffusion weightings. Higher spatial resolution (45 μm) supported tracking the cartilage collagen fiber tracts from the superficial zone to the deep zone, in a continuous and smooth progression in the transitional zone. Fiber length and fiber volume in the growth plate were strongly dependent on angular resolution and b values, whereas tractography in ligaments was found to be less dependent on spatial resolution.

CONCLUSION

High spatial and angular resolution DTI and diffusion tractography can be valuable for knee joint research because of its visualization capacity for collagen fiber orientations and quantitative evaluation of tissue's microscopic properties.

Mechanoadaptation: articular cartilage through thick and thin

The articular cartilage is exquisitely sensitive to mechanical load. Its structure is largely defined by the mechanical environment and destruction in osteoarthritis is the pathophysiological consequence of abnormal mechanics. It is often overlooked that disuse of joints causes profound loss of volume in the articular cartilage, a clinical observation first described in polio patients and stroke victims. Through the 1980s, the results of studies exploiting experimental joint immobilisation supported this. Importantly, this substantial body of work was also the first to describe metabolic changes that resulted in decreased synthesis of matrix molecules, especially sulfated proteoglycans. The molecular mechanisms that underlie disuse atrophy are poorly understood despite the identification of multiple mechanosensing mechanisms in cartilage. Moreover, there has been a tendency to equate cartilage loss with osteoarthritic degeneration. Here, we review the historic literature and clarify the structural, metabolic and clinical features that clearly distinguish cartilage loss due to disuse atrophy and those due to osteoarthritis. We speculate on the molecular sensing pathways in cartilage that may be responsible for cartilage mechanoadaptation.

Mechanical Stress by Spasticity Accelerates Fracture Healing After Spinal Cord Injury

Accelerated fracture healing in patients with spinal cord injuries (SCI) is often encountered in clinical practice. However, there is no distinct evidence in the accelerated fracture healing, and the mechanisms of accelerated fracture healing in SCI are poorly understood. We aimed to determine whether SCI accelerated fracture healing in morphology and strength, to characterize the healing process with SCI, and to clarify the factors responsible for accelerated fracture healing. In total, 39 male Wistar rats were randomly divided into healthy control without intervention, SCI only, fracture with SCI, botulinum toxin (BTX) A-treated fracture with SCI, and propranolol-treated fracture with SCI groups. These rats were assessed with computed microtomography, histological, histomorphological, immunohistological, and biomechanical analyses. Both computed microtomography and histological analyses revealed the acceleration of a bony union in animals with SCI. The strength of the healed fractures after SCI recovered to the same level as that of intact bones after SCI, while the healed bones were weaker than the intact bones. Immunohistology revealed that SCI fracture healing was characterized by formation of callus with predominant intramembranous ossification and promoting endochondral ossification. The accelerated fracture healing after SCI was attenuated by BTX injection, but did not change by propranolol. We demonstrated that SCI accelerate fracture healing in both morphology and strength. The accelerated fracture healing with SCI may be due to predominant intramembranous ossification and promoting endochondral ossification. In addition, our results also suggest that muscle contraction by spasticity accelerates fracture healing after SCI.

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.

Stretching After Heat But Not After Cold Decreases Contractures After Spinal Cord Injury in Rats

BACKGROUND

Contractures are a prevalent and potentially severe complication in patients with neurologic disorders. Although heat, cold, and stretching are commonly used for treatment of contractures and/or spasticity (the cause of many contractures), the sequential effects of these modalities remain unclear.

QUESTIONS/PURPOSES

Using an established rat model with spinal cord injury with knee flexion contracture, we sought to determine what combination of heat or cold before stretching is the most effective for treatment of contractures derived from spastic paralyses and investigated which treatment leads to the best (1) improvement in the loss of ROM; (2) restoration of deterioration in the muscular and articular factors responsible for contractures; and (3) amelioration of histopathologic features such as muscular fibrosis in biceps femoris and shortening of the joint capsule.

METHODS

Forty-two adolescent male Wistar rats were used. After spasticity developed at 2 weeks postinjury, each animal with spinal cord injury underwent the treatment protocol daily for 1 week. Knee extension ROM was measured with a goniometer by two examiners blinded to each other's scores. The muscular and articular factors contributing to contractures were calculated by measuring ROM before and after the myotomies. We quantitatively measured the muscular fibrosis and the synovial intima length, and observed the distribution of collagen of skeletal muscle. The results were confirmed by a blinded observer.

RESULTS

The ROM of heat alone (34° ± 1°) and cold alone (34° ± 2°) rats were not different with the numbers available from that of rats with spinal cord injury (35° ± 2°) (p = 0.92 and 0.89, respectively). Stretching after heat (24° ± 1°) was more effective than stretching alone (27° ± 3°) at increasing ROM (p < 0.001). Contrastingly, there was no difference between stretching after cold (25° ± 1°) and stretching alone (p = 0.352). Stretching after heat was the most effective for percentage improvement of muscular (29%) and articular (50%) factors of contractures. Although quantification of muscular fibrosis in the rats with spinal cord injury (11% ± 1%) was higher than that of controls (9% ± 0.4%) (p = 0.01), no difference was found between spinal cord injury and each treatment protocol. The total synovial intima length of rats with spinal cord injury (5.9 ± 0.2 mm) became shorter than those of the controls (7.6 ± 0.2 mm) (p < 0.001), and those of stretching alone (6.9 ± 0.4 mm), stretching after heat (7.1 ± 0.3 mm), and stretching after cold (6.7 ± 0.4 mm) increased compared with rats with spinal cord injury (p = 0.01, p = 0.001, and p = 0.04, respectively). The staining intensity and pattern of collagen showed no difference among the treatment protocols.

CONCLUSIONS

This animal study implies that heat or cold alone is ineffective, and that stretching is helpful for the correction of contractures after spinal cord injury. In addition, we provide evidence that heat is more beneficial than cold to increase the effectiveness of stretching.

CLINICAL RELEVANCE

Our findings tend to support the idea that stretching after heat can improve the loss of ROM and histopathologic features of joint tissues. However, further studies are warranted to determine if our findings are clinically applicable.

Effect of muscle contractions on cartilage: morphological and functional magnetic resonance imaging evaluation of the knee after spinal cord injury

Objective

To evaluate the effect of complete absence of muscle contractions on normal human cartilage in the presence of joint motion.

Methods

Patients with complete acute spinal cord injuries were enrolled. All patients underwent magnetic resonance imaging (MRI) on both knees as soon as their medical condition was stable and at six months after the primary lesion. All patients received rehabilitation treatment that included lower-limb passive motion exercises twice a day. The MRIs were analyzed by two radiologists with expertise in musculoskeletal disorders. A region of interest was established at the patellar facets and trochlea, and T2 relaxation times were calculated. The area under the cartilage T2 relaxation time curve was calculated and standardized.

Results

Fourteen patients with complete spinal cord injuries were enrolled, but only eight patients agreed to participate in the study and signed the informed consent statement. Two patients could not undergo knee MRI due to their clinical conditions. Initial knee MRIs were performed on six patients. After six months, only two patients underwent the second bilateral knee MRI. Both patients were neurologically classified as Frankel A. An increase in T2 values on the six-month MRI was observed for both knees, especially in the patellofemoral joint.

Conclusion

The absence of muscle contractions seems to be deleterious to normal human knee cartilage even in the presence of a normal range of motion. Further studies with a larger number of patients, despite their high logistical complexity, must be performed to confirm this hypothesis.

Use of micro-computed tomography to evaluate the effects of exercise on preventing the degeneration of articular cartilage in tail-suspended rats

Space flight has been shown to induce bone loss and muscle atrophy, which could initiate the degeneration of articular cartilage. Countermeasures to prevent bone loss and muscle atrophy have been explored, but few spaceflight or ground-based studies have focused on the effects on cartilage degeneration. In this study, we investigated the effects of exercise on articular cartilage deterioration in tail-suspended rats. Thirty-two female Sprague-Dawley rats were randomly divided into four groups (n=8 in each): tail suspension (TS), tail suspension plus passive motion (TSP), tail suspension plus active exercise (TSA), and control (CON) groups. In the TS, TSP, and TSA groups, the rat hindlimbs were unloaded for 21 days by tail suspension. Next, the cartilage thickness and volume, and the attenuation coefficient of the distal femur were evaluated by micro-computed tomography (μCT). Histological analysis was used to assess the surface integrity of the cartilage, cartilage thickness, and chondrocytes. The results showed that: (1) the cartilage thickness on the distal femur was significantly lower in the TS and TSP groups compared with the CON and TSA groups; (2) the cartilage volume in the TS group was significantly lower compared with the CON, TSA, and TSP groups; and (3) histomorphology showed that the chondrocytes formed clusters where the degree of matrix staining was lower in the TS and TSP groups. There were no significant differences between any of these parameters in the CON and TSA groups. The cartilage thickness measurements obtained by μCT and histomorphology correlated well. In general, tail suspension could induce articular cartilage degeneration, but active exercise was effective in preventing this degeneration in tail-suspended rats.

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.

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.

Severe Spinal Cord Injury Causes Immediate Multi-cellular Dysfunction at the Chondro-Osseous Junction

Spinal cord injury is associated with rapid bone loss and arrested long bone growth due to mechanisms that are poorly understood. In this study, we sought to determine the effects of severe T10 contusion spinal cord injury on the sublesional bone microenvironment in adolescent rats. A severe lower thoracic (vertebral T10) spinal cord injury was generated by weight drop (10 g×50 mm). Severely injured and body weight-matched uninjured male Sprague-Dawley rats were studied. At 3 and 5 days post-injury, we performed histological analysis of the distal femoral metaphysis, TUNEL assay, immunohistochemistry, real-time PCR, and western blot analysis compared to uninjured controls. We observed severe hindlimb functional deficits typical of this model. We detected uncoupled remodeling with increased osteoclast activity in the absence of osteoblast activity. We detected osteoblast, osteocyte, and chondrocyte apoptosis with suppressed osteoblast and chondrocyte proliferation and growth plate arrest due to spinal cord injury. We also detected altered gene expression in both whole bone extracts and bone marrow monocytes following spinal cord injury. We conclude that spinal cord injury results in altered gene expression of key regulators of osteoblast and chondrocyte activity. This leads to premature cellular apoptosis, suppressed cellular proliferation, growth plate arrest, and uncoupled bone remodeling in sublesional bone with unopposed osteoclastic resorption.

Amount of torque and duration of stretching affects correction of knee contracture in a rat model of spinal cord injury

BACKGROUND

Joint contractures are a common complication of many neurologic conditions, and stretching often is advocated to prevent and treat these contractures. However, the magnitude and duration of the stretching done in practice usually are guided by subjective clinical impressions.

QUESTIONS/PURPOSES

Using an established T8 spinal cord injury rat model of knee contracture, we sought to determine what combination of static or intermittent stretching, varied by magnitude (high or low) and duration (long or short), leads to the best (1) improvement in the limitation in ROM; (2) restoration of the muscular and articular factors leading to contractures; and (3) prevention and treatment of contracture-associated histologic alterations of joint capsule and articular cartilage.

METHODS

Using a rat animal model, the spinal cord was transected completely at the level of T8. The rats were randomly assigned to seven treatment groups (n = 4 per group), which were composed of static or intermittent stretching in combination with different amounts of applied torque magnitude and duration. We assessed the effect of stretching by measuring the ROM and evaluating the histologic alteration of the capsule and cartilage.

RESULTS

Contractures improved in all treated groups except for the low-torque and short-duration static stretching conditions. High-torque stretching was effective against shortening of the synovial membrane and adhesions in the posterosuperior regions. Collagen Type II and VEGF in the cartilage were increased by stretching.

CONCLUSIONS

High-torque and long-duration static stretching led to greater restoration of ROM than the other torque and duration treatment groups. Stretching was more effective in improving articular components of contractures compared with the muscular components. Stretching in this rat model prevented shortening and adhesion of the joint capsule, and affected biochemical composition, but did not change morphologic features of the cartilage.

CLINICAL RELEVANCE

This animal study tends to support the ideas that static stretching can influence joint ROM and histologic qualities of joint tissues, and that the way stretching is performed influences its efficacy. However, further studies are warranted to determine if our findings are clinically applicable.

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.

Effects of aging and exercise training on the histological and mechanical properties of articular structures in knee joints of male rat

The impact of aging on joints can have a profound effect on an individual's functioning. Our objectives were to assess the histological and mechanical properties of the knee joint capsule and articular cartilage with aging, and to examine the effects of exercise on age-related changes in the knee joint. 2-year-old Wistar rats were divided into a sedentary control group and an exercise-trained group. 10-week-old animals were used to investigate the changes with aging. The joint capsule and cartilage were evaluated with histological, histomorphometric, immunohistochemical, and mechanical analyses. Severe degenerative changes in articular cartilage were observed with aging, whereas exercise apparently did not have a significant effect. The articular cartilage of aged rats was characterized by damage to the cartilage surface, cell clustering, and an abnormal cartilage matrix. Histomorphometric analysis further revealed changes in cartilage thickness as well as a decreased number of chondrocytes. Aging led to stiffness of the articular cartilage and reduced the ability to dissipate the load and distribute the strain generated within the joint. Joint stiffness with aging was independent of capsular stiffness and synovitis was not a characteristic feature of the aging joint. This study confirms that aging alone eventually leads to joint degeneration in a rat model. The lack of recovery in aging joint changes may be due to several factors, such as the duration of the intervention and the regeneration ability of the cartilage.

A phenomenological mathematical model of the articular cartilage damage

Articular cartilage (AC) is a biological tissue that allows the distribution of mechanical loads and movement of joints. The presence of these mechanical loads influences the behavior and physiological condition of AC. The loads may cause damaged by fatigue through injuries due to repeated accumulated stresses. The aim of this work is to introduce a phenomenological mathematical model of damage caused by mechanical action. It is considered that tissue failure is a consequence of chondrocyte death and matrix loss, taking into account factors modifying fatigue resistance such as age, body mass index (BMI) and metabolic activity. The model was numerically implemented using the finite elements method and the results obtained allowed us to predict tissue failure at different loading frequencies, different damage sites and variations in damage magnitude. Qualitative concordance between numerical results and experimental data led us to conclude that the model may be useful for physicians and therapists as a prediction tool for prescribing physical exercise and prognosis of joint failure.

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.

Expression of collagen types I and II on articular cartilage in a rat knee contracture model

The purpose of our study was to clarify the expression patterns of collagen types I and II on articular cartilage after immobilization in a rat knee contracture model in 3 specific areas (noncontact area, transitional area, contact area). The unilateral knee joints of adult male rats were rigidly immobilized at 150 degrees of flexion using screws and a rigid plastic plate. Sham-operated animals had holes drilled in the femur and the tibia and screws inserted but were not plated. The expression patterns of collagen types I and II in each area were evaluated by in situ hybridization (ISH), immunohistochemistry (IHC), and quantitative real-time polymerase chain reaction (qPCR). The expression of collagen type II in the noncontact area was decreased by ISH but appeared unchanged when examined by IHC. In the transitional and contact areas, the expression of collagen type II was initially shown to have decreased and then increased at the hypertrophic chondrocytes by ISH but appeared decreased by IHC. Quantitative PCR revealed the decreased expression of type II collagen in the contact area. Immunostaining of collagen type I was increased at the noncontact area and transitional areas. Alterations of collagen types I and II expression may also affect the degeneration of articular cartilage after immobilization and the changes were different in the three areas.

Skeletal unloading induces a full-thickness patellar cartilage defect with increase of urinary collagen II CTx degradation marker in growing rats

Mechanical stress plays an important role in tissue morphogenesis and extracellular matrix metabolism. However, little is known about the effects of reduced loading without restriction of joint motion on the patella. We investigated the effects of long-term skeletal unloading on patellar cartilage and subchondral bone and systemic collagen II metabolism. Nine-week-old male F344/N rats (n=128) were randomly divided into two groups: caged control (C) and tail suspended (TS). Hindlimbs of the TS rats were subjected to unloading for up to 12 weeks. Sequential changes in the patellar cartilage and subchondral bone were analyzed macroscopically, by pathological findings and histomorphologically. All animals received double tidemark fluorochrome labeling prior to sacrifice. Glycosaminoglycan (GAG) content in patellar cartilage, cross-linked C-telopeptide of type II collagen (CTx-II) in 24-h urine and type II procollagen-C-peptide (pCol-II-C) in sera were also measured by DMB assay, ELISA and EIA, respectively. In the TS group, GAG content was significantly reduced only during the first 3 weeks. No further significant decrease was found. Alkaline phosphatase (ALP) activity was increased, especially at the deep zone. Tidemark mineral apposition rate (MAR) was temporally increased, which resulted in an increase in the ratio of calcified cartilage to the entire cartilage. In the medial part, in addition, thickness of the entire cartilage was decreased by temporal acceleration of subchondral ossification advancement and, in the medial margin, a full-thickness cartilage defect was revealed in 88.6% of TS rats. However, the remaining articular surface was free from fibrillation. While urinary CTx-II was significantly increased during the experimental periods, serum pCol-II-C was significantly decreased at the early phase. There were significant correlations between the urinary CTx-II levels and tidemark MAR. Our results provided evidence that skeletal unloading increased ALP activity at the deep zone and temporally accelerated tidemark advancement associated with a decrease in proteoglycan content. In addition, skeletal unloading temporally accelerated subchondral ossification advancement in the medial part of the patella and finally induced a full-thickness patellar cartilage defect without any fibrillation at the remaining articular surface by additional subchondral bone modeling and possible retarded cartilage growth, which was through a different mechanism than overloading.

Contrasting alteration patterns of different cartilage plates in knee articular cartilage after spinal cord injury in rats

STUDY DESIGN

Experimental, controlled trial, animal study.

OBJECTIVE

To assess morphologic changes in different cartilage plates after spinal cord injury and identify the localization of these alterations.

SETTING

Saitama, Japan.

METHODS

A total of 16 Wistar rats were used. Eight rats underwent a spinal cord injury and eight rats had no intervention as control. The cartilage alterations of the knee joint were evaluated with radiography and histomorphometric analysis. To quantify cartilage alterations, we selected the histologic characteristics: thickness of the articular cartilage, number of chondrocytes, matrix staining to toluidine blue as a reflection of proteoglycan content and surface irregularity.

RESULTS

No differences in knee joints were found between the groups by radiography. In the medial knee joint, cartilage thickness of spinal-cord-injured knees increased at the anterior femoral region and decreased at the tibial and posterior femoral regions; however, in the lateral knee, that of spinal cord injuries did not change compared with control knees. Spinal cord injuries decreased the number of chondrocytes, especially at the anterior femoral regions. Matrix staining increased partially at the tibial regions. Surface irregularity of spinal-cord-injured knees was comparable to that of control knees in all cartilage plates.

CONCLUSION

The present findings exhibit characteristics of the cartilage after spinal cord injury. These alterations were different in nature between the medial and lateral regions. Future studies should assess separately different cartilage plates, to overestimate these severities when the changes at the medial knee were examined and to underestimate when the changes at the lateral knee were examined.