This study was supported in part by a JSPS KAKENHI grant (numbers JP18H03129 and JP18K19739). 
This research also received funding from the Alliance for Regenerative Rehabilitation Research &#38; Training (AR3T), which is supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institute of Neurological Disorders and Stroke (NINDS), and National Institute of Biomedical Imaging and Bioengineering (NIBIB) of the National Institutes of Health under Award Number P2CHD086843. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

The protocol was approved by the Animal Research Committee of Kyoto University (approval number: Med kyo 17616).
1. Perform in vivo cyclic compression on the rat knee
<ol>
	<li>Induce experimental animal anesthesia
	<ol>
		<li>Induce anesthesia in a 12-week-old Wistar rat (256.8 &#177; 8.7 g) by inhalation of 5% isoflurane solution in the anesthesia box.</li>
		<li>Intraperitoneally inject a mixture of three anesthetic agents9, including medetomidine, midazolam, and butorphanol, at 2 mg/kg of the rat body weight, and shave the area around the right knee joint. Confirm sufficient anesthetization by lack of pedal reflex to a toe-pinch.</li>
	</ol>
	</li>
	<li>Mount the anesthetized rat on the fixation device.
	<ol>
		<li>Place the anesthetized rat lying on their belly on the baseplate (Figure 1), with the right knee attached to a small piece of resin with a concave groove. Place the right hind limb in the hip extension, knee flexion, and ankle extension positions, with the knee flexed at approximately 140&#176;. Accommodate the heel of the rat on the wedge-shaped groove on the movable fixture.</li>
		<li>Move the fixation device to the stress/tensile testing instrument (see the Table of Materials). After ensuring that there are no contacts with the load cell, open the stress/tensile testing instrument control software (Table of Materials) and click on the Calibration button. After calibration, attach the top of the frame to the load cell carefully. To keep the knee joint closely attached to the frame, turn on the rotary knob on the movable main operational panel slowly until the pre-load reaches 5 N.</li>
	</ol>
	</li>
	<li>Build a loading method and set up the compressive test.
	<ol>
		<li>On the Main menu, click on Create a new method | System label. Set Test Mode to Cycle, and Test Type to Compression. Click on the Sensor label and select the Test tab to check that the limit is within 60 N. In addition, select the Stroke tab and check that the limit is within 500 mm. 
		NOTE: The above step will stop the operation immediately if there is a large displacement on the stress point.</li>
		<li>Under the Testing control label, select Origin of growth to start the main program with 0.3%/full scale. Of the four sections in a loading cycle, set the Stroke speed in control in the 1st and 3rd sections to 1 mm/s. Set the Maximum testing force in the 2nd section to 20 N, and the Minimum testing force in the 4th section to 5 N. Set &#34;the Duration of hold&#34; to 0.5 s for the peak load and 10 s for the minimum load (Figure 2). 
		NOTE: As this step defines every cycle, ensure that the joint surfaces are in contact with each other and are moving at a reasonable speed and that the motion is maintained.</li>
		<li>In the Pre-load tab at the bottom of the page, ensure that On is checked, the Speed of deflection removal is set to 100 mm/min, and maximum force is 5 N. In the Specimen label, set the Material as Metal. 
		NOTE: These detailed settings may be specific for each manufacturer.</li>
		<li>In the Main menu, under the Select method and test section, select the method that was just built, and click on Start to begin the test. 
		NOTE: The table at the bottom shows the actual measurements of the peak load and displacement.</li>
		<li>Set the number of cycles to 60. 
		&#8203;NOTE: The entire loading session includes 60 cycles, which lasts approximately 12 min. In the control group, rats underwent 5 N pre-loading for 12 min pre-load under the same conditions.</li>
	</ol>
	</li>
	<li>After loading, return the rat to its cage and monitor until full recovery. Maintain a 12-12 h light-dark schedule in the cage with sufficient space and food ad libitum. After the required experimental periods, sacrifice the rats with an overdose of the mixture of the three anesthetic agents injected intraperitoneally or carbon dioxide inhalation for analysis (1 h-8 weeks).</li>
</ol>

<ol><li>De Souza, R. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Non-invasive+axial+loading+of+mouse+tibiae+increases+cortical+bone+formation+and+modifies+trabecular+organization%3A+a+new+model+to+study+cortical+and+cancellous+compartments+in+a+single+loaded+element%5BTitle%5D)+AND+%22Bone%22%5BJournal%5D)">Non-invasive axial loading of mouse tibiae increases cortical bone formation and modifies trabecular organization: a new model to study cortical and cancellous compartments in a single loaded element.</a> Bone. 37 (6), 810-818 (2005).</li>
<li>Poulet, B., Hamilton, R. W., Shefelbine, S., Pitsillides, A. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Characterizing+a+novel+and+adjustable+noninvasive+murine+joint+loading+model%5BTitle%5D)+AND+%22Arthritis+and+Rheumatism%22%5BJournal%5D)">Characterizing a novel and adjustable noninvasive murine joint loading model.</a> Arthritis and Rheumatism. 63 (1), 137-147 (2011).</li>
<li>Wu, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Early+response+of+mouse+joint+tissue+to+noninvasive+knee+injury+suggests+treatment+targets%5BTitle%5D)+AND+%22Arthritis+and+Rheumatism%22%5BJournal%5D)">Early response of mouse joint tissue to noninvasive knee injury suggests treatment targets.</a> Arthritis and Rheumatism. 66 (5), 1256-1265 (2014).</li>
<li>Poulet, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Intermittent+applied+mechanical+loading+induces+subchondral+bone+thickening+that+may+be+intensified+locally+by+contiguous+articular+cartilage+lesions%5BTitle%5D)+AND+%22Osteoarthritis+Cartilage%22%5BJournal%5D)">Intermittent applied mechanical loading induces subchondral bone thickening that may be intensified locally by contiguous articular cartilage lesions.</a> Osteoarthritis Cartilage. 23 (6), 940-948 (2015).</li>
<li>Ko, F. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Progressive+cell-mediated+changes+in+articular+cartilage+and+bone+in+mice+are+initiated+by+a+single+session+of+controlled+cyclic+compressive+loading%5BTitle%5D)+AND+%22Journal+of+Orthopaedic+Research%22%5BJournal%5D)">Progressive cell-mediated changes in articular cartilage and bone in mice are initiated by a single session of controlled cyclic compressive loading.</a> Journal of Orthopaedic Research. 34 (11), 1941-1949 (2016).</li>
<li>Adebayo, O. O., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Role+of+subchondral+bone+properties+and+changes+in+development+of+load-induced+osteoarthritis+in+mice%5BTitle%5D)+AND+%22Osteoarthritis+Cartilage%22%5BJournal%5D)">Role of subchondral bone properties and changes in development of load-induced osteoarthritis in mice.</a> Osteoarthritis Cartilage. 25 (12), 2108-2118 (2017).</li>
<li>Ko, F. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((In+vivo+cyclic+compression+causes+cartilage+degeneration+and+subchondral+bone+changes+in+mouse+tibiae%5BTitle%5D)+AND+%22Arthritis+and+Rheumatism%22%5BJournal%5D)">In vivo cyclic compression causes cartilage degeneration and subchondral bone changes in mouse tibiae.</a> Arthritis and Rheumatism. 65 (6), 1569-1578 (2013).</li>
<li>Ji, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Effects+of+in+vivo+cyclic+compressive+loading+on+the+distribution+of+local+Col2+and+superficial+lubricin+in+rat+knee+cartilage%5BTitle%5D)+AND+%22Journal+of+Orthopaedic+Research%22%5BJournal%5D)">Effects of in vivo cyclic compressive loading on the distribution of local Col2 and superficial lubricin in rat knee cartilage.</a> Journal of Orthopaedic Research. 39 (3), 543-552 (2021).</li>
<li>Kawai, S., Takagi, Y., Kaneko, S., Kurosawa, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Effect+of+three+types+of+mixed+anesthetic+agents+alternate+to+ketamine+in+mice%5BTitle%5D)+AND+%22Experimental+Animals%22%5BJournal%5D)">Effect of three types of mixed anesthetic agents alternate to ketamine in mice.</a> Experimental Animals. 60 (5), 481-487 (2011).</li>
<li>Iijima, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Destabilization+of+the+medial+meniscus+leads+to+subchondral+bone+defects+and+site-specific+cartilage+degeneration+in+an+experimental+rat+model%5BTitle%5D)+AND+%22Osteoarthritis+Cartilage%22%5BJournal%5D)">Destabilization of the medial meniscus leads to subchondral bone defects and site-specific cartilage degeneration in an experimental rat model.</a> Osteoarthritis Cartilage. 22 (7), 1036-1043 (2014).</li>
</ol>

The authors declare no conflicts of interest.

For the first time, the current protocol shows how to establish a model of loading-induced cartilage lesion on the lateral femoral condyle in rats, similar to the intra-articular damage model in smaller rodents such as the mouse2. However, the loading protocol in mice caused severe osteophyte formation and cruciate ligament lesions, which was not ideal for evaluating the effects of cyclic compression. The current protocol created a focal cartilage lesion in rats with a much lower loading force. Correct loading method settings are critical for the protocol because only the appropriate magnitude, speed, and duration of stress can destroy the cartilage without damaging the bone tissue.
Setting the displacement limit (protocol step 1.3.1) is also crucial as it immediately stops the instrument in case of ligament rupture or if the rat wakes up from anesthesia during the loading session. The optimal maximum load and the age of the rat remain to be determined. However, in the preliminary experiments, a load of over 50 N resulted in a high probability of ACL rupture in the rat&#39;s knees. Moreover, the current model is difficult to reproduce in older (&#62;36 weeks old) rats, possibly due to the stiffness of the cartilage as growth occurs.
Although the destructive load threshold for younger rats was not determined, it is believed that future studies should keep the maximum load under 20 N to observe any anabolic effects on the cartilage. The scope and localization of the lesion area were relatively straightforward to establish, even for those new to the field, as estimated by the chondrocyte-degenerative volume in each sample, which potentially focused on the subsequent evaluation of the intervention to a relatively narrow cartilage area.
Histological staining demonstrated that the scope of the lesion area was relatively steady during the 8-week observation period. However, Mankin&#39;s scores deteriorated continuously while the matrix staining and cell distribution scores increased in the affected area. Moreover, there was an obvious color deviation between the middle layer and the calcified cartilage, which illustrated that only the cartilage above the tidemark was affected by the interarticular compression.
On the contrary, apart from mild fibrillation in rare samples, the integrity of the cartilage remained largely intact throughout the entire observational period, which is different from progressive OA injury models10. Therefore, a non-surgical model may be better for the assessment of cartilage interface collision-induced focal lesions, which are more common in sports injuries. In the future, the current model will be used to assess the effects of medication or physical therapy, such as hyperthermia therapy and aerobic joint exercise, on traumatic cartilage damage. Moreover, chondrocyte anabolism and catabolism in response to cyclic mechanical stimulation could also be validated in vivo in animals&#160;using this model.
The current protocol had several limitations. First, only cartilage lesions on the lateral femoral condyle were investigated. The lesion on the lateral tibia should also be evaluated in future studies. Second, the lesioned part of the articular cartilage studied in the current protocol was not the main loading-bearing region during walking. Due to the heterogeneity of cartilage, the stiffness of the intra-articular cartilage may differ from the part examined in the current study. Thus, these findings can only be used as a reference. Finally, the model did not show any significant progression of cartilage degeneration, which is an important feature of OA development. Further studies could combine invasive surgery with pre-loaded lesions to observe spatiotemporal changes.

Traditionally, anterior cruciate ligament (ACL) transection or destabilization of the medial meniscus has been considered optimal for investigating post-traumatic osteoarthritis (PTOA) in small animals. In recent years, non-invasive cyclic compression models have been used to study PTOA. This model was originally designed to investigate the cancellous bone response to mechanical loading1 and was then modified as a non-surgical animal model for PTOA studies2,3,4,5,6. The rationale is to collide&#160;the articular cartilage by applying a periodic external force, which triggers a series of inflammatory responses. However, this model has only been applied to mice, and the appropriate magnitude of loading on larger animals has not been discussed.
Another problem with the previous model is that the high-volume protocol included too many cycles, which caused excessive thickening of the subchondral bone, an unwanted side effect, in several samples7. Therefore, a novel method of cyclic compression with the appropriate magnitude for large animals and a lower loading side effect was developed8. The overall goal of the current article is to describe the protocol of the non-invasive cyclic compression model in rats and observe the representative results of cartilage degeneration. The current protocol would help readers interested in the application of the non-invasive cyclic compression model on rats.

<table><tbody><tr><td>Anesthetic Apparatus for Small Animals</td><td>SHINANO MFG CO.,LTD.</td><td>SN-487-0T</td><td></td></tr><tr><td>Autograph AG-X</td><td>Shimadzu Corp</td><td>N.A.</td><td>Precision Universal / Tensile Tester</td></tr><tr><td>Fluoview FV10i microscope</td><td>Olympus Corp</td><td>N.A.</td><td>A fully automated confocal laser-scanning microscope</td></tr><tr><td>ISOFLURANE Inhalation Solution</td><td>Pfizer Japan Inc.</td><td>(01)14987114133400</td><td></td></tr><tr><td>LIVE/DEA Viability/Cytotoxicity Kit</td><td>Thermo Fisher Scientific Japan Inc</td><td>L3224</td><td>A quick and easy two-color assay to determine viability of cells</td></tr><tr><td>TRAPEZIUM X Software</td><td>Shimadzu Corp</td><td>N.A.</td><td>Data processing software for Autograph AG-X</td></tr></tbody></table>

a non-invasive method for generating the cyclic loading-induced intra-articular cartilage lesion model of the rat knee

The pathophysiology of primary osteoarthritis (OA) remains unclear. However, a specific subclassification of OA in relatively younger age groups is likely correlated with a history of articular cartilage damage and ligament avulsion. Surgical animal models of OA of the knee play an important role in understanding the onset and progression of post-traumatic OA and aid in the development of novel therapies for this disease. However, non-surgical models have been recently considered to avoid traumatic inflammation that could affect the evaluation of the intervention. 
In this study, an intra-articular cartilage lesion rat model induced by in vivo cyclic compressive loading was developed, which allowed researchers to (1) determine the optimal magnitude, speed, and duration of load that could cause focal cartilage damage; (2) assess post-traumatic spatiotemporal pathological changes in chondrocyte vitality; and (3) evaluate the histological expression of destructive or protective molecules that are involved in the adaptation and repair mechanisms against joint compressive loads. This report describes the experimental protocol for this novel cartilage lesion in a rat model.

A representative result of the short-term changes (1 h and 12 h) in chondrocyte viability in samples subjected to 20 N cyclic loading was obtained. As shown in Figure 3, the number of dead chondrocytes (red fluorescence) increased at 12 h post-trauma. Conversely, the number of living chondrocytes (green fluorescence) continued to decrease, with some samples containing no live chondrocytes in the affected area.
Histology showed that the articular cartilage of the rat knees that underwent 20 N dynamic loading was damaged, and one focal lesion zone was confirmed in the lateral femoral condyle in all the samples (Figure 4). However, the lesion size did not progressively increase during the 8-week observational period. The border that corresponded to the interface of the lesion and the unaffected cartilage could be observed in the affected area.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/62660/62660fig01.jpg" /> 
Figure 1: The fixation device consists of a baseplate and a fixation apparatus. The base plate (length: 27.5 cm, width: 13 cm) has a resin concave groove (length: 0.8 cm, width: 0.4 cm) on the posterior side to accommodate the flexed knee joint of the rat. The fixation apparatus has a wedge-shaped groove (groove width: 1.5 cm, groove depth: 1 cm) that accommodates the rat&#39;s heel, which is nested in the baseplate between two metal bars. The top of the fixation apparatus will be in direct contact with the load cell of the stress/tensile testing instrument. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62660/62660fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/62660/62660fig02.jpg" /> 
Figure 2: Load profile for one cycle of loading. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62660/62660fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/62660/62660fig03.jpg" /> 
Figure 3: Spatiotemporal assessment of chondrocyte viability in the lesion area. After sacrifice, the knee joint was dissected and separated using small forceps and scissors. Solutions of calcein AM and EthD-1 stains were prepared by diluting the original kit (Table of Materials) at 1:500 and 1:4,000 in 5 mL of PBS, respectively. The samples were incubated for 20 min at room temperature. Control samples were immersed in PBS under the same conditions. Fluorescence images were obtained using a fluorescence microscope (Table of Materials) using fluorescein isothiocyanate (495 nm/519 nm) and propidium Iodide (535 nm/617 nm) channels. The vital chondrocytes displayed green fluorescence, whereas dead cells fluoresced red. Compared to the chondrocytes in control samples (A), the number of dead chondrocytes on the loaded rat knee was increased at 1 h (B) and occupied most of the area in the affected region at 12 h (C). Green and red fluorescence represent the regions of the live and dead chondrocytes, respectively. Scale bars = 100 &#181;m. Abbreviations: calcein AM = calcein acetoxymethyl ester; EthD-1 = ethidium homodimer-1; PBS= phosphate-buffered saline. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62660/62660fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/62660/62660fig04.jpg" /> 
Figure 4: Representative safranin O staining of the femoral condyle in the loaded knee. A slide showing the sagittal sections of the lateral femoral condyle, which were stained with a safranin O/Fast Green and hematoxylin solution. Compared to the control, the safranin O staining intensity in the affected area was decreased after loading, and a clear border (arrow) of the upper/calcified cartilage was observed. Scale bars = 100 &#181;m. Abbreviation: w = week.<a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62660/62660fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about A Non-Invasive Method for Generating the Cyclic Loading-Induced Intra-Articular Cartilage Lesion Model of the Rat Knee at JoVE.com

A Non-Invasive Method for Generating the Cyclic Loading-Induced Intra-Articular Cartilage Lesion Model of the Rat Knee

Here, we present the cyclic loading-induced intra-articular cartilage lesion model of the rat knee, generated by 60 cyclic compressions over 20 N, resulting in damage to the femoral condylar cartilage in rats.

The pathophysiology of primary osteoarthritis (OA) remains unclear. However, a specific subclassification of OA in relatively younger age groups is likely ...

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2.1K Views.  Kyoto University. Here, we present the cyclic loading-induced intra-articular cartilage lesion model of the rat knee, generated by 60 cyclic compressions over 20 N, resulting in damage to the femoral condylar cartilage in rats.

Video: A Non-Invasive Method for Generating the Cyclic Loading-Induced Intra-Articular Cartilage Lesion Model of the Rat Knee

In Vivo Tracking of Human Adipose-derived Mesenchymal Stem Cells in a Rat Knee Osteoarthritis Model with Fluorescent Lipophilic Membrane Dye

In order to support the clinical application of human adipose-derived mesenchymal stem cell (haMSC) therapy for knee osteoarthritis (KOA), we examined the efficacy of cell persistence and biodistribution of haMSCs in animal models. We demonstrated a method to label the cell membrane of haMSCs with lipophilic fluorescent dye. Subsequently, intra-articular injection of the labeled cells in rats with surgically induced KOA was monitored dynamically by an in vivo imaging system. We employed the lipophilic carbocyanines DiD (DilC18 (5)), a far-red fluorescent Dil (dialkylcarbocyanines) analog, which utilized a red laser to avoid excitation of the natural green autofluorescence from surrounding tissues. Furthermore, the red-shifted emission spectra of DiD allowed deep-tissue imaging in live animals and the labeling procedure caused no cytotoxic effects or functional damage to haMSCs. This approach has been shown to be an efficient tracking method for haMSCs in a rat KOA model. The application of this method could also be used to determine the optimal administration route and dosage of MSCs from other sources in pre-clinical studies.

In Vivo Tracking of Human Adipose-derived Mesenchymal Stem Cells in a Rat Knee Osteoarthritis Model with Fluorescent Lipophilic Membrane Dye

This protocol describes an efficient way to monitor the cell persistence and biodistribution of human adipose-derived mesenchymal stem cells (haMSCs) by far-red fluorescence labeling in a rat knee osteoarthritis (KOA) model via intra-articular (IA) injection.

In order to support the clinical application of human adipose-derived mesenchymal stem cell (haMSC) therapy for knee osteoarthritis (KOA), we examined the ...

Developmental Biology

Athymic Rat Model for Evaluation of Engineered Anterior Cruciate Ligament Grafts

Anterior cruciate ligament (ACL) rupture is a common ligamentous injury that often requires surgery because the ACL does not heal well without intervention. Current treatment strategies include ligament reconstruction with either autograft or allograft, which each have their associated limitations. Thus, there is interest in designing a tissue-engineered graft for use in ACL reconstruction. We describe the fabrication of an electrospun polymer graft for use in ACL tissue engineering. This polycaprolactone graft is biocompatible, biodegradable, porous, and is comprised of aligned fibers. Because an animal model is necessary to evaluate such a graft, this paper describes an intra-articular athymic rat model of ACL reconstruction that can be used to evaluate engineered grafts, including those seeded with xenogeneic cells. Representative histology and biomechanical testing results at 16 weeks postoperatively are presented, with grafts tested immediately post-implantation and contralateral native ACLs serving as controls. The present study provides a reproducible animal model with which to evaluate tissue engineered ACL grafts, and demonstrates the potential of a regenerative medicine approach to treatment of ACL rupture.

Animal models are important tools for the evaluation of tissue-engineered grafts. This paper presents the protocol for preparing an electrospun biodegradable polymer graft for use in anterior cruciate ligament tissue engineering, as well as a surgical protocol for implantation in a rat model.

Anterior cruciate ligament (ACL) rupture is a common ligamentous injury that often requires surgery because the ACL does not heal well without ...

Bioengineering

Real-time Visualization and Analysis of Chondrocyte Injury Due to Mechanical Loading in Fully Intact Murine Cartilage Explants

Homeostasis of articular cartilage depends on the viability of resident cells (chondrocytes). Unfortunately, mechanical trauma can induce widespread chondrocyte death, potentially leading to irreversible breakdown of the joint and the onset of osteoarthritis. Additionally, maintenance of chondrocyte viability is important in osteochondral graft procedures for optimal surgical outcomes. We present a method to assess the spatial extent of cell injury/death on the articular surface of intact murine synovial joints after application of controlled mechanical loads or impacts. This method can be used in comparative studies to investigate the effects of different mechanical loading regimens, different environmental conditions or genetic manipulations, as well as different stages of cartilage degeneration on short- and/or long-term vulnerability of in situ articular chondrocytes. The goal of the protocol introduced in the manuscript is to assess the spatial extent of cell injury/death on the articular surface of murine synovial joints. Importantly, this method enables testing on fully intact cartilage without compromising native boundary conditions. Moreover, it allows for real-time visualization of vitally stained articular chondrocytes and single image-based analysis of cell injury induced by application of controlled static and impact loading regimens. Our representative results demonstrate that in healthy cartilage explants, the spatial extent of cell injury depends sensitively on load magnitude and impact intensity. Our method can be easily adapted to investigate the effects of different mechanical loading regimens, different environmental conditions or different genetic manipulations on the mechanical vulnerability of in situ articular chondrocytes.

We present a method to assess the spatial extent of cell injury/death on the articular surface of intact murine joints after application of controlled mechanical loads or impacts. This method can be used to investigate how osteoarthritis, genetic factors and/or different loading regimens affect the vulnerability of in situ chondrocytes.

Homeostasis of articular cartilage depends on the viability of resident cells (chondrocytes). Unfortunately, mechanical trauma can induce widespread ...

Cyclic Mechanical Loading for Inducing Tendinopathy in Rat Achilles Tendon

A Passive Ankle Dorsiflexion Testing System for an In Vivo Model of Overuse-induced Tendinopathy

Tendinopathy is a chronic tendon condition that results in pain and loss of function and is caused by repeated overload of the tendon and limited recovery time. This protocol describes a testing system that cyclically applies mechanical loads via passive dorsiflexion to the rat Achilles tendon. The custom-written code consists of pre- and post-cyclic loading measurements to assess the effects of the loading protocol along with the feedback control-based cyclic fatigue loading regimen. 
We used 25 Sprague-Dawley rats for this study, with 5 rats per group receiving either 500, 1,000, 2,000, 3,600, or 7,200 cycles of fatigue loads. The percentage differences between the pre- and post-cyclic loading measurements of the hysteresis, peak stress, and loading and unloading moduli were calculated. The results demonstrate that the system can induce varying degrees of damage to the Achilles tendon based on the number of loads applied. This system offers an innovative approach to apply quantified and physiological varying degrees of cyclic loads to the Achilles tendon for an in vivo model of fatigue-induced overuse tendon injury.

Author Spotlight: Integrating Mechanical and Biological Analysis in Tendinopathy Research 

This protocol presents a testing system used to induce quantifiable and controlled fatigue injuries in a rat Achilles tendon for an in-vivo model of overuse-induced tendinopathy. The procedure consists of securing the rat's ankle to a joint actuator that performs passive ankle dorsiflexion with a custom-written MATLAB script.

Tendinopathy is a chronic tendon condition that results in pain and loss of function and is caused by repeated overload of the tendon and limited recovery ...

Osteoarthritis Pain Model Induced by Intra-Articular Injection of Mono-Iodoacetate in Rats

The current animal models of osteoarthritis (OA) can be divided into spontaneous models and induced models, both of which aim to simulate the pathophysiological changes of human OA. However, as the main symptom in the late stage of OA, pain affects the patients&#39; daily life, and there are not many available models. The mono-iodoacetate (MIA)-induced model is the most widely used OA pain model, mainly used in rodents. MIA is an inhibitor of glyceraldehyde-3-phosphate dehydrogenase, which causes chondrocyte death, cartilage degeneration, osteophyte, and measurable changes in animal behavior. Besides, expression changes of matrix metalloproteinase (MMP) and pro-inflammatory cytokines (IL1 &#946; and TNF &#945;) can be detected in the MIA-induced model. Those changes are consistent with OA pathophysiological conditions in humans, indicating that MIA can induce a measurable and successful OA pain model. This study aims to describe the methodology of intra-articular injection of MIA in rats and discuss the resulting pain-related behaviors and histopathological changes.

This study describes the method of intra-articular injection of mono-iodoacetate in rats and discusses the resulting pain-related behaviors and histopathological changes, which provide references for future applications.

The current animal models of osteoarthritis (OA) can be divided into spontaneous models and induced models, both of which aim to simulate the ...

Destabilization of the Medial Meniscus and Cartilage Scratch Murine Model of Accelerated Osteoarthritis

Osteoarthritis is the most prevalent musculoskeletal disease in people over 45, leading to an increasing economic and societal cost. Animal models are used to mimic many aspects of the disease. The present protocol describes the destabilization and cartilage scratch model (DCS) of post-traumatic osteoarthritis. Based on the widely used destabilization of the medial meniscus (DMM) model, DCS introduces three scratches on the cartilage surface. The current article highlights the steps to destabilize the knee by transecting the medial meniscotibial ligament followed by three intentional superficial scratches on the articular cartilage. The possible analysis methods by dynamic weight-bearing, microcomputed tomography, and histology are also demonstrated. While the DCS model is not recommended for studies that focus on the effect of osteoarthritis on the cartilage, it enables the study of osteoarthritis development in a shorter time window, with special focus on (1) osteophyte formation, (2) osteoarthritic and injury pain, and (3) the effect of cartilage damage in the whole joint.

The present protocol describes the controlled microblade scratches on the surface of the articular cartilage after destabilizing the mouse knee by cutting the medial miniscotibial ligament. This animal model presents an accelerated form of osteoarthritis (OA) suitable for studying osteophyte formation, osteosclerosis, and early-stage pain.

Osteoarthritis is the most prevalent musculoskeletal disease in people over 45, leading to an increasing economic and societal cost. Animal models are ...

Development and Evaluation of a Rat Model of Full-Thickness Cartilage Defects

Cartilage defects of the knee joint caused by trauma are a common sports joint injury in the clinic, and these defects result in joint pain, impaired movement, and eventually, knee osteoarthritis (kOA). However, there is little effective treatment for cartilage defects or even kOA. Animal models are important for developing therapeutic drugs, but the existing models for cartilage defects are unsatisfactory. This work established a full-thickness cartilage defects (FTCD) model by drilling holes in the femoral trochlear groove of rats, and the subsequent pain behavior and histopathological changes were used as readout experiments. After surgery, the mechanical withdrawal threshold was decreased, chondrocytes at the injured site were lost, matrix metalloproteinase MMP13 expression was increased, and type II collagen expression decreased, consistent with the pathological changes observed in human cartilage defects. This methodology is easy and simple to perform and enables gross observation immediately after the injury. Furthermore, this model can successfully mimic clinical cartilage defects, thus providing a platform for studying the pathological process of cartilage defects and developing corresponding therapeutic drugs.

This protocol establishes a full-thickness cartilage defects (FTCD) model by drilling holes in the femoral trochlear groove of rats and measuring the subsequent pain behavior and histopathological changes.

Cartilage defects of the knee joint caused by trauma are a common sports joint injury in the clinic, and these defects result in joint pain, impaired ...

Standardized Tuina Manipulation for Knee Osteoarthritis in Rats

Tuina Manipulation to Reduce Inflammation and Cartilage Loss in Knee Osteoarthritis Rats

Clinical trials suggest that Tuina manipulation is effective in treating knee osteoarthritis (KOA), while further studies are required to discover its mechanism. Therefore, the manipulation of animal models of knee osteoarthritis is critical. This protocol provides a standard process for Tuina manipulation on KOA rats and a preliminary exploration of the mechanism of Tuina for KOA. The press and kneading manipulation method (a kind of Tuina manipulation that refers to pressing and kneading the specific area of the body surface) is applied on 5 acupoints around the knee joint of rats. The force and frequency of the manipulation were standardized by finger pressure recordings, and the position of the rat during manipulation is described in detail in the protocol. The effect of manipulation can be measured by pain behavior tests and microscopic findings in synovial and cartilage. KOA rats showed significant improvement in pain behavior. The synovial tissue inflammatory infiltration was reduced in the Tuina group, and the expression of tumor necrosis factor (TNF)-&#945; was significantly lower. Compared to the control group, chondrocyte apoptosis was less in the Tuina group. This study provides a standardized protocol for Tuina manipulation on KOA rats and preliminary proof that the therapeutic effects of Tuina may be related to reducing synovial inflammation and delayed chondrocyte apoptosis.

Author Spotlight: Understanding the Mechanism of Tuina Manipulation in Rats 

We present a protocol for Tuina manipulation performed on plaster-immobilized-induced knee osteoarthritis rats. Based on the preliminary results, it suggested that the efficacy of the method relied on the reduction of inflammation and cartilage loss.

Clinical trials suggest that Tuina manipulation is effective in treating knee osteoarthritis (KOA), while further studies are required to discover its ...

Impact of Non-Invasive ACL Injury and Surgery on Protease Activity in Mice

Non-Invasive Compression-Induced Anterior Cruciate Ligament (ACL) Injury and In Vivo Imaging of Protease Activity in Mice

Traumatic joint injuries such as anterior cruciate ligament (ACL) rupture or meniscus tears commonly lead to post-traumatic osteoarthritis (PTOA) within 10-20 years following injury. Understanding the early biological processes initiated by joint injuries (e.g., inflammation, matrix metalloproteinases (MMPs), cathepsin proteases, bone resorption) is crucial for understanding the etiology of PTOA. However, there are few options for in vivo measurement of these biological processes, and the early biological responses may be confounded if invasive surgical techniques or injections are used to initiate OA. In our studies of PTOA, we have used commercially available near-infrared protease activatable probes combined with fluorescence reflectance imaging (FRI) to quantify protease activity in vivo following non-invasive compression-induced ACL injury in mice. This non-invasive ACL injury method closely recapitulates clinically relevant injury conditions and is completely aseptic since it does not involve disrupting the skin or the joint capsule. The combination of these injury and imaging methods allows us to study the time course of protease activity at multiple time points following a traumatic joint injury.

Author Spotlight: Investigating Early Events and Long-Term Effects of ACL Injuries for Osteoarthritis Progression

Non-invasive ACL injury is a reliable and clinically relevant method for initiating post-traumatic osteoarthritis (PTOA) in mice. This injury method also allows for in vivo quantification of protease activity in the joint at early time points post-injury using protease-activatable near infrared probes and fluorescence reflectance imaging.

Traumatic joint injuries such as anterior cruciate ligament (ACL) rupture or meniscus tears commonly lead to post-traumatic osteoarthritis (PTOA) within ...

A Reproducible Cartilage Impact Model to Generate Post-Traumatic Osteoarthritis in the Rabbit

Post-traumatic osteoarthritis (PTOA) is responsible for 12% of all osteoarthritis cases in the United States. PTOA can be initiated by a single traumatic event, such as a high-impact load acting on articular cartilage, or by joint instability, as occurs with anterior cruciate ligament rupture. There are no effective therapeutics to prevent PTOA currently. Developing a reliable animal model of PTOA is necessary to better understand the mechanisms by which cartilage damage proceeds and to investigate novel treatment strategies to alleviate or prevent the progression of PTOA. This protocol describes an open, drop tower-based rabbit femoral condyle impact model to induce cartilage damage. This model delivered peak loads of 579.1 &plusmn; 71.1 N, and peak stresses of 81.9 &plusmn; 10.1 MPa with a time-to-peak load of 2.4 &plusmn; 0.5 ms. Articular cartilage from impacted medial femoral condyles (MFCs) had higher rates of apoptotic cells (p = 0.0058) and possessed higher Osteoarthritis Research Society International (OARSI) scores of 3.38 &plusmn; 1.43 compared to the non-impacted contralateral MFCs (0.56 &plusmn; 0.42), and other cartilage surfaces of the impacted knee (p &lt; 0.0001). No differences in OARSI scores were detected among the non-impacted articular surfaces (p &gt; 0.05).

The open medial femoral condyle impact model in rabbits is reliable for studying post-traumatic osteoarthritis (PTOA) and novel therapeutic strategies to mitigate PTOA progression. This protocol generates an isolated cartilage defect of the posterior medial femoral condyle in rabbits using a carriage-based drop tower with an impactor head.

Post-traumatic osteoarthritis (PTOA) is responsible for 12% of all osteoarthritis cases in the United States. PTOA can be initiated by a single traumatic ...

A Non-Invasive Method for Generating the Cyclic Loading-Induced Intra-Articular Cartilage Lesion Model of the Rat Knee

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