Influence of age on osteoarthritis progression after anterior cruciate ligament transection in rats

Intra-articular injection of inorganic pyrophosphate improves IL-1β-induced cartilage damage in rat model of knee osteoarthritis in vivo

Objective

Osteoarthritis (OA) is the most common form of chronic joint disease, affecting mainly the elderly population. This disorder is caused by cartilage degeneration with complex changes in the chondrocyte phenotype. Inorganic pyrophosphate (PPi) was shown to counteract the detrimental effect of interleukin (IL)-1β challenging in an in vitro OA model based on rat articular chondrocytes. It also maintained the differentiated articular phenotype, mostly by down regulating wingless-related integration site (Wnt)-5a secretion. These observations suggest a PPi protective role for chondrocyte in vitro.

Methods

To address this hypothesis in vivo, we investigated the impact on knee joint of three intra-articular injection (IAI) of PPi in a rat model of cartilage damage induced by IAI of IL-1β, where cartilage degradation and synovial inflammation are similar to that observed in OA. Cartilage and synovial membrane were collected after 7 days of challenge by IL-1β.

Results

PPi was able to reduce the deleterious effect of IL-1β. This effect was observable on the expression of cartilage extracellular matrix metabolism markers and confirmed by histology with safranin O and hematoxylin-eosin-saffron (HES) staining. Inorganic pyrophosphate also repressed the Wnt5a expression induced by IL-1β. No effect was observed on the inflammatory response of the synovial membrane.

Conclusion

These results demonstrate that PPi improves IL-1β-induced cartilage damage in rat but not the associated inflammation of synovial membrane. Thus, PPi could become a molecule of interest to restrict the progression of this disorder.

CD206+ Trem2+ macrophage accumulation in the murine knee joint after injury is associated with protection against post-traumatic osteoarthritis in MRL/MpJ mice

Post-traumatic osteoarthritis (PTOA) is a painful joint disease characterized by the degradation of bone, cartilage, and other connective tissues in the joint. PTOA is initiated by trauma to joint-stabilizing tissues, such as the anterior cruciate ligament, medial meniscus, or by intra-articular fractures. In humans, ~50% of joint injuries progress to PTOA, while the rest spontaneously resolve. To better understand molecular programs contributing to PTOA development or resolution, we examined injury-induced fluctuations in immune cell populations and transcriptional shifts by single-cell RNA sequencing of synovial joints in PTOA-susceptible C57BL/6J (B6) and PTOA-resistant MRL/MpJ (MRL) mice. We identified significant differences in monocyte and macrophage subpopulations between MRL and B6 joints. A potent myeloid-driven anti-inflammatory response was observed in MRL injured joints that significantly contrasted the pro-inflammatory signaling seen in B6 joints. Multiple CD206+ macrophage populations classically described as M2 were found enriched in MRL injured joints. These CD206+ macrophages also robustly expressed Trem2, a receptor involved in inflammation and myeloid cell activation. These data suggest that the PTOA resistant MRL mouse strain displays an enhanced capacity of clearing debris and apoptotic cells induced by inflammation after injury due to an increase in activated M2 macrophages within the synovial tissue and joint space.

On-demand release of a selective MMP-13 blocker from an enzyme-responsive injectable hydrogel protects cartilage from degenerative progression in osteoarthritis

In osteoarthritis (OA), the degradation of cartilage is primarily driven by matrix metalloprotease-13 (MMP-13). Hence, the inhibition of MMP-13 has emerged as an attractive target for OA treatment. Among the various approaches that are being explored for MMP-13 regulation, blocking of the enzyme with specific binding molecules appears to be a more promising strategy for preventing cartilage degeneration. To enhance effectiveness and ensure patient compliance, it is preferable for the binding molecule to exhibit sustained activity when administered directly into the joint. Herein, we present an enzyme-responsive hydrogel that was designed to exhibit on-demand, the sustained release of BI-4394, a potent and highly selective MMP-13 blocker. The stable and compatible hydrogel was prepared using triglycerol monostearate. The efficacy of the hydrogel to prevent cartilage damage was assessed in a rat model of OA induced by anterior cruciate ligament transection (ACLT). The results revealed that in comparison to the rats administrated weekly with intra-articular BI-4394, the hydrogel implanted rats had reduced levels of inflammation and bone erosion. In comparison to untreated control, the cartilage in animals administered with BI-4394/hydrogel exhibited significant levels of collagen-2 and aggrecan along with reduced MMP-13. Overall, this study confirmed the potential of BI-4394 delivery using an enzyme-responsive hydrogel as a promising treatment option to treat the early stages of OA by preventing further cartilage degradation.

From Inflammation to Resolution: Specialized Pro-resolving Mediators in Posttraumatic Osteoarthritis

PURPOSE OF REVIEW

To provide a comprehensive overview of the inflammatory response following anterior cruciate ligament (ACL) injury and to highlight the relationship between specialized pro-resolving mediators (SPMs) and inflammatory joint conditions, emphasizing the therapeutic potential of modulating the post-injury resolution of inflammation to prevent posttraumatic osteoarthritis (PTOA).

RECENT FINDINGS

The inflammatory response triggered after joint injuries such as ACL tear plays a critical role in posttraumatic osteoarthritis development. Inflammation is a necessary process for tissue healing, but unresolved or overactivated inflammation can lead to chronic diseases. SPMs, a family of lipid molecules derived from essential fatty acids, have emerged as active players in the resolution of inflammation and tissue repair. While their role in other inflammatory conditions has been studied, their relationship with PTOA remains underexplored. Proinflammatory mediators contribute to cartilage degradation and PTOA pathogenesis, while anti-inflammatory and pro-resolving mediators may have chondroprotective effects. Therapies aimed at suppressing inflammation in PTOA have limitations, as inflammation is crucial for tissue healing. SPMs offer a pro-resolving response without causing immunosuppression, making them a promising therapeutic option. The known onset date of PTOA makes it amenable to early interventions, and activating pro-resolving pathways may provide new possibilities for preventing PTOA progression. Harnessing the pro-resolving potential of SPMs may hold promise for preventing PTOA and restoring tissue homeostasis and function after joint injuries.

Pathological Characteristics of Monosodium Iodoacetate-Induced Osteoarthritis in Rats

BACKGROUND

This study aimed to identify pain-related behavior and pathological characteristics of the knee joint in rats with monosodium iodoacetate (MIA)-induced osteoarthritis (OA).

METHODS

Knee joint inflammation was induced by intra-articular injection of MIA (4 mg/50 µL, n = 14) in 6-week-old male rats. Knee joint diameter, weight-bearing percentage on the hind limb during walking, the knee bending score, and paw withdrawal to mechanical stimuli were measured to evaluate edema and pain-related behavior for 28 d after MIA injection. Histological changes in the knee joints were evaluated using safranin O fast green staining on days 1, 3, 5, 7, 14, and 28 after OA induction (n = 3, respectively). Changes in bone structure and bone mineral density (BMD) were examined 14 and 28 d after OA (n = 3, respectively) using micro-computed tomography (CT).

RESULTS

The knee joint diameter and knee bending scores of the ipsilateral joint significantly increased 1 d after MIA injection, and the increased knee joint diameter and knee bending score persisted for 28 d. Weight-bearing during walking and paw withdrawal threshold (PWT) decreased from 1 and 5 d, respectively, and were maintained up to 28 d after MIA. Cartilage destruction started on day 1, and Mankin scores for bone destruction significantly increased for 14 d, as shown by micro-CT imaging.

CONCLUSION

The present study demonstrated that histopathological structural changes in the knee joint due to inflammation started soon after MIA injection, which induced OA pain from inflammation-related acute pain to spontaneous and evoked associated chronic pain.

Early Alterations of Subchondral Bone in the Rat Anterior Cruciate Ligament Transection Model of Osteoarthritis

OBJECTIVE

Advances in research have shown that the subchondral bone plays an important role in the propagation of cartilage loss and progression of osteoarthritis (OA), but whether the subchondral bone changes precede or lead to articular cartilage loss remains debatable. In order to elucidate the subchondral bone and cartilage changes that occur in early OA, an experiment using anterior cruciate ligament transection (ACLT) induced posttraumatic OA model of the rat knee was conducted.

DESIGN

Forty-two Sprague Dawley rats were divided into 2 groups: the ACLT group and the nonoperated control group. Surgery was conducted on the ACLT group, and subsequently rats from both groups were sacrificed at 1, 2, and 3 weeks postsurgery. Subchondral bone was evaluated using a high-resolution peripheral quantitative computed tomography scanner, while cartilage was histologically evaluated and scored.

RESULTS

A significant reduction in the subchondral trabecular bone thickness and spacing was found as early as 1 week postsurgery in ACLT rats compared with the nonoperated control. This was subsequently followed by a reduction in bone mineral density and bone fractional volume at week 2, and finally a decrease in the trabecular number at week 3. These changes occurred together with cartilage degeneration as reflected by an increasing Mankin score over all 3 weeks.

CONCLUSIONS

Significant changes in subchondral bone occur very early in OA concurrent with surface articular cartilage degenerative change suggest that factors affecting bone remodeling and resorption together with cartilage matrix degradation occur very early in the disease.

Transient anabolic effects of synovium in early post-traumatic osteoarthritis: a novel ex vivo joint tissue co-culture system for investigating synovium-chondrocyte interactions

OBJECTIVE

Osteoarthritis (OA) is a serious joint disease with no disease-modifying medical treatment. To develop treatments targeting synovium, we must improve our understanding of the effects of OA-related changes in synovial physiology on joint tissue outcomes. The aim of this study was to investigate the effects of synovial pathology due to post-traumatic OA (PTOA) on articular chondrocyte physiology.

METHODS

We first developed and validated a novel joint tissue co-culture system to model the biological interactions between synovium and articular chondrocytes. Whole-joint synovial tissue from a surgical rat model of PTOA vs sham and surgical-naïve controls was placed into a co-culture system with adult primary articular chondrocytes (n = 4-5). The effects of PTOA synovium on chondrocyte anabolic, inflammatory, and catabolic gene expression and sulfated glycosaminoglycan (sGAG) secretion and aggrecan synthesis were tested, and results from early and later stages of PTOA development were compared.

RESULTS

Synovial injury by arthrotomy (sham surgery) alone decreased primary chondrocyte expression of genes including Col2a1 (0.36 ± 0.15-fold) and Acan (0.41 ± 0.28-fold). Early PTOA synovium rescued the suppression of Acan, induced increased sGAG secretion (3.94 ± 0.44 μg/mL vs surgery-naïve 2.41 ± 0.55 and sham 2.92 ± 0.73 μg/mL controls), and upregulated Mmp3 (3.73 ± 2.62-fold) and Prg4 (4.93 ± 4.29-fold). These effects were lost with later stage PTOA synovium.

CONCLUSIONS

Early PTOA synovium induces transient anabolic responses in articular chondrocytes rather than pro-inflammatory responses that would require inhibition. These results suggest that PTOA synovium plays at least a partially protective role and that loss of these protective effects may contribute to PTOA progression.

Knee osteoarthritis in young growing rats is associated with widespread osteopenia and impaired bone mineralization

Osteoarthritis (OA) leads to joint pain from intraarticular inflammation with articular cartilage erosion, deterioration of joint function and abnormal subchondral bone structure. Besides aging, chronic repetitive joint injury is a common risk factor in young individuals. Nevertheless, whether OA is associated with bone loss at other skeletal sites is unclear. Since OA-associated proinflammatory cytokines-some of which are osteoclastogenic factors-are often detected in the circulation, we hypothesized that the injury-induced knee OA could result in widespread osteopenia at bone sites distant to the injured knee. Here we performed anterior cruciate ligament transection (ACLT) to induce knee OA in one limb of female Sprague-Dawley rats and determined bone changes post-OA induction by micro-computed tomography and computer-assisted bone histomorphometry. We found that although OA modestly altered bone density, histomorphometric analyses revealed increases in bone resorption and osteoid production with impaired mineralization. The bone formation rate was also reduced in OA rats. In conclusions, ACLT in young growing rats induced microstructural defects in the trabecular portion of weight-bearing (tibia) and non-weight-bearing bones (L5 vertebra), in part by enhancing bone resorption and suppressing bone formation. This finding supports the increasing concern regarding the repetitive sport-related ACL injuries and the consequent bone loss.

Effects of Greenshell Mussel (Perna canaliculus) Intake on Pathological Markers of Multiple Phenotypes of Osteoarthritis in Rats

The prevalence of metabolic osteoarthritis has been increasing worldwide, particularly among women. The aim of this study was to investigate the effects of the New Zealand greenshell mussel (Perna canaliculus; GSM) on osteoarthritis (OA) prevention in a rat model. One-hundred-and-eight female rats aged 12 weeks were divided into four test groups, containing 24 rats each, plus an additional control group. Each test group received one of the four experimental diets: normal control diet (ND), normal control diet supplemented with GSM (ND + GSM), high fat/high sugar diet (HFHS), or high fat/high sugar diet supplemented GSM (HFHS + GSM), for 36 weeks (end of the study). After 8 weeks on experimental diets, half of each group was subjected to ovariectomy (OVX) and the remaining half received a sham operation (ovaries left intact). The study evaluated body composition, bone mass, plasma cytokines, adipokines, HbA1c, CTX-II, and knee joint’s histopathology. HFHS diet and OVX significantly induced body weight gain and leptin production. OVX rats lost bone mineral density but increased adiponectin, HbA1C, and MCP-1. The OVX rats fed HFHS showed the highest Mankin scores. Importantly, inclusion of GSM reduced these pathological features. In conclusion, GSM might be beneficial in halting the progression of OA.

Comparison of early-stage changes of osteoarthritis in cartilage and subchondral bone between two different rat models

Osteoarthritis (OA) is a chronic degenerative joint disease and the major cause of joint pain and disability in the elderly. It is mainly characterized by articular cartilage degradation and subchondral bone remodeling. There are two main types of OA: natural occurring OA and secondary OA, mainly associated with aging and trauma, respectively. In this study, we established two OA models in rat knee joints to simulate the two types of OA, using the type II collagenase injection (CI) and anterior cruciate ligament transection (ACLT), respectively. After intervention for 2-6 weeks, cartilage and subchondral bone changes were detected in histological staining, immunochemistry, and micro-CT. Results showed that both models with typical pathology changes of OA were successfully induced, while the development and severity of OA process in the models were different. In ACLT rats, the cartilage damage was milder, lasted for a shorter time, and subchondral bone reconstruction occurred earlier, compared with the changes in CI rats. The cartilage damage was secondary to subchondral bone change in ACLT rats, while subchondral bone change was secondary to cartilage degeneration in CI rats. In conclusion, the interaction between cartilage and subchondral bone is different between the natural-occurring and secondary OA models. These two models not only suggest potential different mechanisms of the two types of OA, but also provide new directions for OA treatment and prevention.

The effects of age on the severity of joint damage and intra-articular inflammation following a simulated medial meniscus injury in 3, 6, and 9 month old male rats

Purpose: Aging is a known risk factor for osteoarthritis (OA). Several transgenic rodent models have been used to investigate the effects of accelerated or delayed aging in articular joints. However, age-effects on the progression of post-traumatic OA are less frequently evaluated. The objective of this study is to evaluate how animal age affects the severity of intra-articular inflammation and joint damage in the rat medial collateral ligament plus medial meniscus transection (MCLT+MMT) model of knee OA.Methods: Forty-eight, male Lewis rats were aged to 3, 6, or 9 months old. At each age, eight rats received either an MCLT+MMT surgery or a skin-incision. At 2 months post-surgery, intra-articular evidence of CTXII, IL1β, IL6, TNFα, and IFNγ was evaluated using a multiplex magnetic capture technique, and histological evidence of OA was assessed via a quantitative histological scoring technique.Results: Elevated levels of CTXII and IL6 were found in MCLT+MMT knees relative to skin-incision and contralateral controls; however, animal age did not affect the severity of joint inflammation. Conversely, histological investigation of cartilage damage showed larger cartilage lesion areas, greater width of affected cartilage, and more evidence of hypertrophic cartilage damage in MCLT+MMT knees with age.Conclusions: These data indicate the severity of cartilage damage subsequent to MCLT+MMT surgery is related to the rat's age at the time of injury. However, despite greater levels of cartilage damage, the level of intra-articular inflammation was not necessarily affected in 3, 6, and 9 month old male rats.

Reactive oxygen species and NADPH oxidase 4 involvement in osteoarthritis

Osteoarthritis (OA) is a degenerative chronic disease affecting >300,000 million people around the world as of 2016. Symptomatic measures exist, but there are hardly any curative treatments available. Disruption of the cartilage homeostasis in favor of catabolism leads to cartilage destruction. ROS-macromolecular-induced damage is significantly greater in OA cartilage and OA is described as low-grade chronic systemic inflammation. This review aimed to assess the critical role of cartilage ageing and oxidative stress in the OA process, focusing in particular on NADPH oxidase and especially Nox4 involvement. With age, hypertrophic senescent cells with an altered redox cell profile accumulated. Chondrocytes are more sensitive to oxidant-mediators and the serum level of pro-inflammatory mediators increases. Age-related advanced glycation end products impact on extra cellular matrix (ECM) properties leading to the apoptosis of chondrocytes. A focus on NADPH oxidase-mediated-ROS signaling highlighted the very specific Nox4 isoform, which plays a role on the final common pathway targeting chondrocyte cells. IL-1β-mediated Nox4 stimulation induced an increase in the levels released by the chondrocyte of MMP-1 and MMP-13 proteins, which are involved in ECM degradation. In comparison with the other Nox isoforms, Nox4 remains unusual, since it is constitutively active, does not depend on cytosolic activator proteins and seems to generate H₂O₂ thanks to the specific conformation of the Nox4 E-loop. Nox4-induced ROS production appears an essential actor in the OA process and it could be relevant to focus on this target in the aim of discovering and developing new therapeutic strategies.

Association of anterior cruciate ligament injury with knee osteoarthritis and total knee replacement: A retrospective cohort study from the Taiwan National Health Insurance Database

Objective

This study aimed to support the potential protective role of anterior cruciate ligament (ACL) reconstruction against the development of osteoarthritis (OA).

Methods

In this retrospective cohort study, the long-term results of ACL reconstruction in Taiwan were evaluated based on data from the National Health Insurance Research Database (NHIRD). In total, 8,769 eligible cases were included from 11,921 ACL-injured patients. The cumulative incidence rates of OA and total knee replacement (TKR) were analyzed using the Kaplan-Meier estimator. Cox proportional hazards models were applied to estimate the hazard ratios (HRs) and 95% confidence intervals (CIs) of OA.

Results

There was a lower cumulative incidence of OA among ACL-reconstructed patients (271, 33.1%) than among non-reconstructed patients (1,874, 40.3%; p < 0.001). Patients who underwent ACL reconstruction had a lower cumulative incidence of TKR during the follow-up period (0.6%) than the non-reconstructed patients (4.6%, p < 0.001). After adjusting for covariates, ACL-injured patients who underwent reconstruction within one month after ACL injury showed a significantly lower risk of OA than those who never underwent reconstruction (adjusted HR = 0.83, 95% CI = 0.69–0.99).

Conclusions

These results indicate that ACL reconstruction might not provide complete protection from OA development after traumatic knee injury but does yield a lower cumulative incidence of OA development and TKR. Moreover, based on the present study, ACL-injured patients should undergo reconstruction as early as possible (within one month) to lower the risk of OA.

Synthetic nanoscale electrostatic particles as growth factor carriers for cartilage repair

The efficient transport of biological therapeutic materials to target tissues within the body is critical to their efficacy. In cartilage tissue, the lack of blood vessels prevents the entry of systemically administered drugs at therapeutic levels. Within the articulating joint complex, the dense and highly charged extracellular matrix (ECM) hinders the transport of locally administered therapeutic molecules. Consequently, cartilage injury is difficult to treat and frequently results in debilitating osteoarthritis. Here we show a generalizable approach in which the electrostatic assembly of synthetic polypeptides and a protein, insulin‐like growth factor‐1 (IGF‐1), can be used as an early interventional therapy to treat injury to the cartilage. We demonstrated that poly(glutamic acid) and poly(arginine) associated with the IGF‐1 via electrostatic interactions, forming a net charged nanoscale polyelectrolyte complex (nanoplex). We observed that the nanoplex diffused into cartilage plugs in vitro and stimulated ECM production. In vivo, we monitored the transport, retention and therapeutic efficacy of the nanoplex in an established rat model of cartilage injury. A single therapeutic dose, when administered within 48 hr of the injury, conferred protection against cartilage degradation and controlled interleukin‐1 mediated inflammation. IGF‐1 contained in the nanoplex was detected in the joint space for up to 4 weeks following administration and retained bioactivity. The results indicate the potential of this approach as an early intervention therapy following joint injury to delay or even entirely prevent the onset of osteoarthritis.

Overweight older adults, particularly after an injury, are at high risk for accelerated knee osteoarthritis: data from the Osteoarthritis Initiative

We explored whether age and body mass index (BMI) can help identify a subset of individuals who are at high risk for accelerated knee osteoarthritis (AKOA) compared with common knee osteoarthritis (KOA). In the Osteoarthritis Initiative, a multicenter observational cohort study of KOA (n = 4796), we studied participants without KOA at baseline (Kellgren-Lawrence (KL) <2). Participants could have one of three outcomes: (1) AKOA, ≥1 knee progressed to end-stage KOA within 48 months; (2) common KOA, ≥1 knee increased in radiographic scoring within 48 months (excluding those with AKOA); and (3) no KOA, no change in KL grade in either knee. After verifying an interaction between age, BMI, and recent knee injury, we determined if we could identify a specific subset of individuals at high risk for AKOA instead of KOA. First, we reviewed three-dimensional graphs with age, BMI, and probability of AKOA versus KOA on the axes. We then conducted a logistic regression with AKOA as the outcome and age-BMI groups as the predictor. In our main analyses, we found that older individuals with a BMI <35 kg/m(2) were more likely to develop AKOA than common KOA (n = 64; mean [SD] BMI = 27.3 [3.1] kg/m(2); odds ratio = 3.47, 95 % confidence interval = 1.70 to 7.10), especially if they had a recent knee injury. While older age and greater BMI are independently associated with AKOA, we found that older individuals who had a higher BMI, particularly if they have an injury, were more likely to develop AKOA than common KOA.

Inflammation in joint injury and post-traumatic osteoarthritis

Inflammation is a variable feature of osteoarthritis (OA), associated with joint symptoms and progression of disease. Signs of inflammation can be observed in joint fluids and tissues from patients with joint injuries at risk for development of post-traumatic osteoarthritis (PTOA). Furthermore, inflammatory mechanisms are hypothesized to contribute to the risk of OA development and progression after injury. Animal models of PTOA have been instrumental in understanding factors and mechanisms involved in chronic progressive cartilage degradation observed after a predisposing injury. Specific aspects of inflammation observed in humans, including cytokine and chemokine production, synovial reaction, cellular infiltration and inflammatory pathway activation, are also observed in models of PTOA. Many of these models are now being utilized to understand the impact of post-injury inflammatory response on PTOA development and progression, including risk of progressive cartilage degeneration and development of chronic symptoms post-injury. As evidenced from these models, a vigorous inflammatory response occurs very early after joint injury but is then sustained at a lower level at the later phases. This early inflammatory response contributes to the development of PTOA features including cartilage erosion and is potentially modifiable, but specific mediators may also play a role in tissue repair. Although the optimal approach and timing of anti-inflammatory interventions after joint injury are yet to be determined, this body of work should provide hope for the future of disease modification tin PTOA.

Weight-bearing asymmetry and vertical activity differences in a rat model of post-traumatic knee osteoarthritis

OBJECTIVE

This study used a rat model of post-traumatic knee osteoarthritis (OA) created by anterior cruciate ligament transection with partial medial meniscectomy (ACLT + pMMx). In this model, mild to moderate structural changes that are typical of knee OA have been observed within 2 and 8 weeks post-surgery. We aimed to determine whether pain-related behaviours can distinguish between an ACLT + pMMx and a sham surgery group.

DESIGN

Three-month old male Sprague-Dawley rats underwent ACLT + pMMx on their right hindlimb within two groups of n = 6 each, and sham surgery within two groups of n = 5 each. Assessments evaluated percent ipsilateral weight-bearing for static weight-bearing and 18 different variables of exploratory motor behaviour at multiple time points between 1 and 8 weeks post-surgery. Histology was performed on the right hindlimbs at 4 and 8 weeks post-surgery.

RESULTS

Histology confirmed mild to moderate knee OA changes in the ACLT + pMMx group and the absence of knee OA changes in the sham group. Compared to the sham group, the ACLT + pMMx group had significantly lower percent ipsilateral weight-bearing from 1 through 8 weeks post-surgery. Compared to the sham group, the ACLT + pMMx group had significantly lower vertical activity (episode count, time, and count) values.

CONCLUSIONS

These findings suggest that ipsilateral weight-bearing deficit and vertical activity limitations resulted from the presence of knee OA-like changes in this model. When using the ACLT + pMMx-induced rat model of knee OA, percent ipsilateral weight-bearing and vertical activity distinguished between rats with and without knee OA changes. These variables may be useful outcome measures in preclinical research performed with this experimental post-traumatic knee OA model.

Animal Models of Osteoarthritis: Comparisons and Key Considerations

Osteoarthritis (OA) is unquestionably one of the most important chronic health issues in humans, affecting millions of individuals and costing billions of dollars annually. Despite widespread awareness of this disease and its devastating impact, the pathogenesis of early OA is not completely understood, hampering the development of effective tools for early diagnosis and disease-modifying therapeutics. Most human tissue available for study is obtained at the time of joint replacement, when OA lesions are end stage and little can be concluded about the factors that played a role in disease development. To overcome this limitation, over the past 50 years, numerous induced and spontaneous animal models have been utilized to study disease onset and progression, as well as to test novel therapeutic interventions. Reflecting the heterogeneity of OA itself, no single "gold standard" animal model for OA exists; thus, a challenge for researchers lies in selecting the most appropriate model to answer a particular scientific question of interest. This review provides general considerations for model selection, as well as important features of species such as mouse, rat, guinea pig, sheep, goat, and horse, which researchers should be mindful of when choosing the "best" animal model for their intended purpose. Special consideration is given to key variations in pathology among species as well as recommended guidelines for reporting the histologic features of each model.

The Relationship between Anterior Cruciate Ligament Injury and Osteoarthritis of the Knee

Anterior cruciate ligament (ACL) tears are a common injury, particularly in the athletic and youth populations. The known association between ACL injury and subsequent osteoarthritis (OA) of the knee merits a more in-depth understanding of the relationship between the ACL-injured knee and osteoarthritis. ACL injury, especially with concomitant meniscal or other ligamentous pathology, predisposes the knee to an increased risk of osteoarthritis. ACL insufficiency results in deterioration of the normal physiologic knee bending culminating in increased anterior tibial translation and increased internal tibial rotation. This leads to increased mean contact stresses in the posterior medial and lateral compartments under anterior and rotational loading. However, surgical reconstruction of the ACL has not been shown to reduce the risk of future OA development back to baseline and has variability based on operative factors of graft choice, timing of surgery, presence of meniscal and chondral abnormalities, and surgical technique. Known strategies to prevent OA development are applicable to patients with ACL deficiency or after ACL reconstruction and include weight management, avoidance of excessive musculoskeletal loading, and strength training. Reconstruction of the ACL does not necessarily prevent osteoarthritis in many of these patients and may depend on several external variables.