Tendons are force-transmitting structures which facilitate musculoskeletal functioning. Characterizing variations between different anatomical tendons, regions within tendons, as well as between the sexes and with age can improve understanding of tendon physiology and pathology. A systematic search of the literature was conducted to identify and summarize microscopic structural (histological) variations in normal/healthy tendons in relation to these variables (Tendon, Region, Age, Sex, and Other). Regional differences within individual tendons have been investigated in numerous studies, however investigations comparing histological variations between a range of different tendons are sparse, with most focusing on a few select tendons. When injured, ageing tendons typically have a greater degree of pathological changes than younger tendons, but few studies have documented variations in tendon histology throughout typical (uninjured) ageing or across large age spans. Similarly, sex-related observations of tendon structure are underreported. This narrative review summarizes studies on these topics and explores interactions between these variables, as well as the implications of these in the context of selecting control samples for studies of tendon pathology. Future studies should endeavour to improve knowledge of tendon structural variations-specifically focusing on normal tendons-to facilitate understanding of tendon structure-function relationships, physiological mechanisms involved in tendon damage/healing, and to aid clinical research and practice.

Purpose (the aim of the study): Osteoarthritis (OA) affects joints throughout the body with higher incidence in knee (20%), hand (17%) and hip (6%). Although the aetiology of OA is multifactorial, the primary risk factors may differ between joints (e.g. ankle OA is predominantly post-traumatic). The local environment has a critical role and the mechanical properties of tissues are important for maintaining joint structural integrity and function. While cartilage mechanics have been extensively investigated, results are commonly derived from a single joint and/or focus on the most commonly affected joints (e.g.

Tendon allograft and xenograft processing often involves one or more steps of freezing and thawing. As failure strength is an important graft consideration, this study aimed to evaluate effects on failure properties when varying freeze-thaw conditions. Kangaroo tendons, a potential xenograft source, were used to evaluate changes in ultimate tensile strength (UTS), failure strain and elastic modulus after exposure to different freezer-storage temperatures (-20 degrees C vs. -80 degrees C), storage durations (1, 3, 6, 9, or 12 months), number of freeze-thaw cycles (1, 2, 3, 4, 5, or 10), or freeze-thaw temperature ranges (including freezing in liquid nitrogen to thawing at 37 degrees C). Tendons stored for 6 or more months had significantly increased UTS and elastic modulus compared with 1 or 3 months of storage. This increase occurred irrespective of the freezing temperature (-20 degrees C vs. -80 degrees C) or the number of freeze-thaw cycles (1 vs. 10). In contrast, UTS, failure strain and the elastic modulus were no different between storage temperatures, number of freeze-thaw cycles and multiple freeze-thaw cycles across a range of freeze and thaw temperatures. Common freeze-thaw protocols did not negatively affect failure properties, providing flexibility for graft testing, storage, transportation and decellularisation procedures. However, the change in properties with the overall storage duration has implications for assessing the consistent performance of grafts stored for short versus extended periods of time (<6 months vs. >6 months), and the interpretation of data obtained from tissues of varying or unknown storage durations.

BACKGROUND:Methodological heterogeneity hinders data comparisons across isolated studies of tendon and ligament properties, limiting clinical understanding and affecting the development and evaluation of replacement materials. PURPOSE:To create an open-access data set on the morphological, biomechanical, and biochemical properties of clinically important tendons and ligaments of the lower limb, using consistent methodologies, to enable direct tendon/ligament comparisons. STUDY DESIGN:Descriptive laboratory study. METHODS:Nineteen distinct lower limb tendons and ligaments were retrieved from 8 fresh-frozen human cadavers (5 male, 3 female; aged 49-65 years) including Achilles, tibialis posterior, tibialis anterior, fibularis (peroneus) longus, fibularis (peroneus) brevis, flexor hallucis longus, extensor hallucis longus, plantaris, flexor digitorum longus, quadriceps, patellar, semitendinosus, and gracilis tendons; anterior cruciate, posterior cruciate, medial collateral, and lateral collateral ligaments; and 10 mm-wide grafts from the contralateral quadriceps and patellar tendons. Outcomes included morphology (tissue length, ultrasound-quantified cross-sectional area [CSAUS], and major and minor axes), biomechanics (failure load, ultimate tensile strength [UTS], failure strain, and elastic modulus), and biochemistry (sulfated glycosaminoglycan [sGAG] and hydroxyproline contents). Tissue differences were analyzed using mixed-model regression. RESULTS:There was a range of similarities and differences between tendons and ligaments across outcomes. A key finding relating to potential graft tissue suitability was the comparable failure loads, UTS, CSAUS, sGAG, and hydroxyproline present between hamstring tendons (a standard graft source) and 5 tendons not typically used for grafting: fibularis (peroneus) longus and brevis, flexor and extensor hallucis longus, and flexor digitorum longus tendons. CONCLUSION:This study of lower limb tendons and ligaments has enabled direct comparison of morphological, biomechanical, and biochemical human tissue properties-key factors in the selection of suitable graft tissues. This analysis has identified 6 potential new donor tissues with properties comparable to currently used grafts. CLINICAL RELEVANCE:This extensive data set reduces the need to utilize data from incompatible sources, which may aid surgical decisions (eg, evidence to expand the range of tendons considered suitable for use as grafts) and may provide congruent design inputs for new biomaterials and computational models. The complete data set has been provided to facilitate further investigations, with the capacity to expand the resource to include additional outcomes and tissues.

Background: The use of allograft tendons has increased for primary and revision anterior cruciate ligament reconstruction, but allograft supply is currently limited to a narrow range of tendons and donors up to the age of 65 years. Expanding the range of donors and tendons could help offset an increasing clinical demand. Purpose: To investigate the effects of donor age, sex, height, and specific tendon on the mechanical properties of a range of human lower leg tendons. Study Design: Descriptive laboratory study. Methods: Nine tendons were retrieved from 39 fresh-frozen human cadaveric lower legs (35 donors [13 female, 22 male]; age, 49-99 years; height, 57-85 inches [145-216 cm]) including: Achilles tendon, tibialis posterior and anterior, fibularis longus and brevis, flexor and extensor hallucis longus, plantaris, and flexor digitorum longus. Tendons underwent tensile loading to failure measuring cross-sectional area (CSA), maximum load, strain at failure, ultimate tensile strength, and elastic modulus. Results from 332 tendons were analyzed using mixed-effects linear regression, accounting for donor age, sex, height, and weight. Results: Mechanical properties were significantly different among tendons and were substantially greater than the effects of donor characteristics. Significant effects of donor sex, age, and height were limited to specific tendons: Achilles tendon, tibialis posterior, and tibialis anterior. All other tendons were unaffected. The Achilles tendon was most influenced by donor variables: greater CSA in men (β = 15.45 mm2; Šidák adjusted P < .0001), decreased maximum load with each year of increased age (β = −17.20 N per year; adjusted P = .0253), and increased CSA (β = 1.92 mm2 per inch; adjusted P < .0001) and maximum load (β = 86.40 N per inch; adjusted P < .0001) with each inch of increased height. Conclusion: Mechanical properties vary significantly across different human tendons. The effects of donor age, sex, and height are relatively small, are limited to specific tendons, and affect different tendons uniquely. The findings indicate that age negatively affected only the Achilles tendon (maximum load) and challenge the exclusion of donors aged >65 years across all tendon grafts. Clinical Relevance: The findings support including a broader range of tendons for use as allografts for anterior cruciate ligament reconstruction and reviewing the current exclusion criterion of donors aged >65 years.

Purpose: Significant abnormalities in the synovial T-cell profile of osteoarthritis (OA) patients have been found implicating a crucial role for proinflammatory CD4+ T-helper cell subsets, such as Th1 and Th17. Interleukin (IL)12 is not only directly involved in the polarization of Th1 cells, but also promotes polarization of Th17 cells via a shared p40 subunit with IL23, making the IL12 pathway a promising target for immunomodulation. Although evidence exists that highlights the importance of this pathway during the development of rheumatoid arthritis to date the role of this pathway in OA is unknown. We investigated the cellular and histopathological response following IL12 pathway modulation in an unilateral anterior-cruciate-ligament (ACL) rupture model of post-traumatic (pt)OA.

Objectives: Histological scoring remains the gold-standard for quantifying post-traumatic osteoarthritis (ptOA) in animal models, allowing concurrent evaluation of numerous joint tissues. Available systems require scoring multiple sections/joint making analysis laborious and expensive. We investigated if a single section allowed equivalent quantitation of pathology in different joint tissues and disease stages, in three ptOA models.Method: Male 10-12-week-old C57BL/6 mice underwent surgical medial-meniscal-destabilization, anterior-cruciate-ligament (ACL) transection, non-invasive-ACL-rupture, or served as sham-surgical, non-invasive-ACL-strain, or na & iuml;ve/non-operated controls. Mice (n = 12/group) were harvested 1-, 4-, 8-, and 16-week post-intervention. Serial sagittal toluidine-blue/fast-green stained sections of the medial-femoro-tibial joint (n = 7/joint, 84 mu m apart) underwent blinded scoring of 40 histology-outcomes. We evaluated agreement between single-slide versus entire slide-set maximum or median scores (weighted-kappa), and sensitivity/specificity of single-slide versus median/maximum to detect OA pathology.Results: A single optimal mid-sagittal section showed excellent agreement with median (weighted-kappa 0.960) and maximum (weighted-kappa 0.926) scores. Agreement for individual histology-outcomes was high with only 19/240 median and 15/240 maximum scores having a weighted-kappa <= 0.4, the majority of these (16/19 and 11/15) in control groups. Statistically-significant histology-outcome differences between ptOA models and their controls detected with the entire slide-set were reliably reproduced using a single slide (sensitivity >93.15%, specificity >93.10%). The majority of false-negatives with single-slide scoring were meniscal and subchondral bone histology-outcomes (89%) and occurred in weeks 1-4 post-injury (84%).Conclusion: A single mid-sagittal slide reduced the time needed to score diverse histopathological changes by 87% without compromising the sensitivity or specificity of the analysis, across a variety of ptOA models and time-points.(c) 2023 The Author(s). Published by Elsevier Ltd on behalf of Osteoarthritis Research Society International. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Purpose: Osteoarthritis (OA) is a complex heterogeneous joint disease that leads to a chronic pain state. Prevalence is higher in women who suffer worse disease and pain, and exhibit enhanced pain-sensitivity suggesting sex differences in central processing. Sexual dimorphism is also observed in OA animal models, with studies in mice reporting females develop similar or worse pain at milder disease states. These observed sex differences in OA pain-pathology relationships have largely been attributed to differences in neuroimmune interactions peripherally and at the level of the spinal cord. However, the discord between pathology and pain observed in OA patients and animal models highlights the need for further investigation into drivers of OA pain beyond the spinal cord. Using an established model of post-injury OA, we characterised sex differences in OA joint pathology and pain with disease progression, and the associated alterations in central pain processing at the level of the parabrachial nucleus (PBN), a key site of supra-spinal nociceptive signal processing. The aim of this study was to determine if neuronal activation in the PBN following an acute noxious stimulus is altered in mice with injury-induced OA, and whether the level of neuronal activation is different in males and females.

Cite this article:  2022;11(8):514-517.

Purpose: The severity and resolution of synovial inflammation following joint injury have been suggested as potential risk factors for the development of post-traumatic osteoarthritis (ptOA). To date, the majority of studies investigating the innate immune response in the context of ptOA implicate blood-originated (BO) monocyte-derived rather than synovial tissue resident macrophages (STRM) as the main culprit in promoting and sustaining inflammation and disease development. However, whether a targeted depletion of activated (Ly6Chigh) monocytes at the time of joint injury is sufficient to alter this inflammatory response is unknown.

Increasing anterior cruciate ligament (ACL) rupture rates are driving the need for new graft materials which undergo testing to characterize material properties and function. The in vitro collagenase assay is routinely used to determine the degradation rate of collagenous materials. At times, it is used to screen new biomaterials on the basis that results reflect breakdown rates in vivo. However, its predictive potential is inconclusive with no guidelines for acceptable in vitro rates of degradation. Reference data from target tissue/s or existing clinical materials are needed to determine appropriate thresholds. From a summary of reported protocols, the most common bench conditions (bacterial collagenase; unloaded samples) were used to evaluate the in vitro degradation of human tendons used as ACL allografts: patellar, semitendinosus, gracilis, Achilles, tibialis anterior and posterior. Tendons were sectioned in equal volumes and exposed to 100 U collagenase for 1, 2, 4 or 8 h. The change in dry weight was analysed using mixed linear regression. All tendon samples demonstrated a significant reduction in mass over time but the patellar tendon degraded significantly faster than all other tendons ( P ≤ 0.004). As all tendons used in this study are clinically accepted, this study provides a range of human tendon reference data for comparative assessment of new tendon and ligament biomaterials. However, the more rapid degradation of the patellar tendon, one of the most successful ACL graft materials, also highlights the limitations of common collagenase assay conditions for predicting in vivo performance, particularly in the absence of suitable comparative controls.

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

Background: Rupture of the anterior cruciate ligament (ACL) is a well-known risk factor for the development of posttraumatic osteoarthritis (PTOA), but patients with the “same injury” can have vastly different trajectories for the onset and progression of disease. Minor subcritical injuries preceding the critical injury event may drive this disparity through preexisting tissue pathologies and sensory changes. Purpose: To investigate the role of subcritical injury on ACL rupture risk and PTOA through the evaluation of pain behaviors, joint mechanics, and tissue structural change in a mouse model of knee injury. Study Design: Controlled laboratory study. Methods: Ten-week-old male C57BL/6J mice were allocated to naïve control and subcritical knee injury groups. Injury was induced by a single mechanical compression to the right hindlimb, and mice were evaluated using joint histopathology, anteroposterior joint biomechanics, pain behaviors (mechanical allodynia and hindlimb weightbearing), and isolated ACL tensile testing to failure at 1, 2, 4, or 8 weeks after injury. Results: Subcritical knee injury produced focal osteochondral lesions in the patellofemoral and lateral tibiofemoral compartments with no resolution for the duration of the study (8 weeks). These lesions were characterized by focal loss of proteoglycan staining, cartilage structural change, chondrocyte pathology, microcracks, and osteocyte cell loss. Injury also resulted in the rapid onset of allodynia (at 1 week), which persisted over time and reduced ACL failure load ( P = .006; mean ± SD, 7.91 ± 2.01 N vs 9.37 ± 1.01 N in naïve controls at 8 weeks after injury), accompanied by evidence of ACL remodeling at the femoral enthesis. Conclusion: The present study in mice establishes a direct effect of a single subcritical knee injury on the development of specific joint tissue pathologies (osteochondral lesions and progressive weakening of the ACL) and allodynic sensitization. These findings demonstrate a predisposition for secondary critical injuries (eg, ACL rupture) and an increased risk of PTOA onset and progression (structurally and symptomatically). Clinical Relevance: Subcritical knee injuries are a common occurrence and, based on this study, can cause persistent sensory and structural change. These findings have important implications for the understanding of risk factors of ACL injury and subsequent PTOA, particularly with regard to prevention and management strategies following an often underreported event.

Purpose: Osteoarthritis involves disruption of joint homeostasis and the normal mechanobiological cross-talk between different joint tissues. Anterior cruciate ligament (ACL) injury models induce significant pathological change in tissues throughout the knee joint but unique spatial and temporal patterns of OA progression have been observed in different models: surgical versus non-surgical. Understanding the interaction between different tissue pathologies within the joint, and if this differs depending on injury mechanism, may provide important information regarding the onset and progression of post-traumatic OA, as well as considerations for tissue specific treatment targets. Methods: ACL injury was induced in the right hindlimb of 10-week-old, male C57BL/6 mice by either surgical transection (ACLT) or mechanical compression (ACLR). Separate un-injured, naïve mice and sham-surgery controls were included for comparison. At 1, 2, 4 and 8 weeks post-injury, n=7 joints were harvested for histopathological assessment of cartilage degradation, subchondral bone change, osteophytes, synovitis, meniscal pathology and cruciate ligament pathology. OA pathology was evaluated in all 3 knee compartments: medial and lateral tibiofemoral (TF) and patellofemoral (PF). Associations between different histopathological OA disease features within and across compartments were assessed using Kendall's Tau rank partial correlation coefficients with adjustment for time post-injury. Significant associations were determined using the Benjamini-Hochberg procedure with the false discovery rate set to 5%. Results: Across the four models (naïve, sham-operated, ACLT, ACLR), 246 pairwise tissue associations were found to be significant but of these, 153 were determined to be weakly correlated, 30 moderately correlated, and 2 strongly correlated. In general, there were a greater number of within compartment correlations in the medial TF compartment compared with the lateral TF compartment. In the PF compartment only 3 significant correlations were found. As expected, > 80% of the minimally meaningful (i.e. at least weakly correlated) tissue pathology associations were found in the injured joints, however, 73% of these were observed in ACLR whilst only 7% were found in ACLT (Figures 1 and 2). The only consistent correlation across all 4 models was in the lateral TF compartment with a weak to moderate, positive correlation between cartilage proteoglycan loss and cartilage structural damage (τ = 0.4344 - 0.5879, P < 0.0061). For all joints with an intervention (Sham, ACLT, ACLR) there was a weak to moderate positive correlation between subchondral bone sclerosis of the medial and lateral TF compartments (τ = 0.3041-0.5651, P < 0.0063). In the surgical models (Sham and ACLT), the only overlapping correlation was between lateral TF synovitis and PF synovitis (Sham: τ = 0.3823, P = 0.0032; ACLT: τ = 0.5612, P = 0.0033). ACL injured joints (ACLT and ACLR) shared a number of similar associations. For both ACL injury models, medial TF cartilage structural damage was positively associated with: medial TF chondrocyte pathology (ACLT: τ = 0.4600, P = 0.0016; ACLR: τ = 0.5375, P < 0.0001), osteocyte loss (ACLT: τ = 0.3371, P = 0.0025; ACLR: τ = 0.6821, P < 0.0001) and proteoglycan change in the PCL (ACLT: τ = 0.4926, P < 0.0001; ACLR: τ = 0.4091, P = 0.0027). PF enthesophyte severity was also positively correlated with subchondral bone sclerosis in both the medial (ACLT: τ = 0.4473, P < 0.0001; ACLR: τ = 0.3322, P < 0.0042) and lateral (ACLT: τ = 0.3190, P = 0.0067; ACLR: τ = 0.4846, P < 0.0001) TF compartments. Conclusions: The results demonstrate a significant effect of the mechanism of ACL injury on not only the temporal onset and progression of structural PTOA but also the specific tissues affected and the associations between tissues within and across different compartments. Differences in disease trajectory and associations between joint tissue pathologies may have important implications for both the risk of PTOA progression and the success of treatments or interventions, especially those designed to have both direct and indirect effects throughout the joint.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Sex and joint injury are risk factors implicated in the onset and progression of osteoarthritis (OA). In mouse models of post-traumatic OA (ptOA), the pathogenesis of disease is notably impacted by sex (often worse in males) and injury model (e.g. meniscal versus ligament injury). Increasing ptOA progression and severity is often associated with greater relative instability of the joint but few studies have directly quantified changes in joint mechanics after injury and compared outcomes across multiple models in both male and female mice. Passive anterior-posterior knee biomechanics were evaluated in 10-week-old, male and female C57BL/6J mice. PtOA injury models included destabilisation of the medial meniscus (DMM), anterior cruciate ligament transection (ACLT) or mechanical rupture (ACLR), and combined DMM and ACLT (DMM + ACLT). Sham operated and non-operated controls (NOC) were included for baseline comparisons. The test apparatus loaded hindlimbs at 60° flexion between ± 1 N at 0.5 mm/s (build specifications available for download: https://doi.org/10.17632/z754455x3c.1). Measures of joint laxity (range of motion, neutral zone) and stiffness were calculated. Joint laxity was comparable between male and female mice while joint stiffness was greater in females (P ≤ 0.002, correcting for body-mass and injury-model). Anterior-posterior joint mechanics were minimally altered by DMM but significantly affected by loss of the ACL (P < 0.001), with equivalent changes between ACL-injury models despite different injury mechanisms and adjacent meniscal damage. These findings suggest that despite the important role of joint injury; sex- and model-specific differences in ptOA progression and severity are not primarily driven by altered anterior-posterior knee biomechanics.

Purpose: Anterior-cruciate-ligament (ACL) rupture is one of the most common knee injuries, resulting in pain, disability, and increased risk of developing OA. However, only ∼50% of individuals with ACL rupture develop OA, and the factors underlying this variable risk remain unclear. Changes in joint stability as a result of ACL deficiency drive mechanobiological dysfunction and the development of OA. However, specific factors are known to increase OA risk such as concurrent injury to the meniscus, cartilage, and subchondral bone. Also, the degree of initial joint inflammation and its resolution are implicated in long-term outcomes. Surgical and nonsurgical models of ACL rupture in mice result in similar joint instability but distinct risks or trajectories of OA. We used these two models to investigate if differences in synovial inflammatory response are associated with this risk of OA disease progression Methods: Ten-week-old, male C57BL/6 mice were randomly assigned to ACL transection (ACLT), ACL rupture (ACLR), sham-surgery or uninjured groups. Mice in the ACLT and sham-operated groups were subjected to anaesthesia, right unilateral medial arthrotomy, patella luxation, and fat-pad elevation to visualise the ACL, at which time the surgeon was informed to transect or spare the ACL before joint closure. Uninjured and ACLR animals were anaesthetised, the latter having a single compressive load (9-12N) to posteriorly displace the femur and traumatically rupture the ACL. Animals were housed in mixed injury groups (up to 5/cage) and allowed unrestricted activity. At 1, 2, 4 and 8 weeks post-injury, mice were euthanised and joints harvested for fixation, paraffin embedding, sectioning and OA histopathology scoring (n=7/group/timepoint); or synovial tissue (en bloc fat-pad, synovial lining and joint capsule anterior to the collateral ligaments) isolation for RNA extraction and quantitative RT-PCR analysis of cytokines (IL1, IL6, TNF), inflammatory cell markers (CD11b, CD4, CD8), and enzymes implicated in OA pathophysiology (ADAMTS4, ADAMTS5, MMP3, MMP9, MMP13) (n=6/group/time point). Results: ACL injury resulted in progressive OA pathology with cartilage pathology significantly greater in ACLR compared with ACLT at 2 and 4 weeks (p<0.001), but by 8 weeks was equivalent in the two models; posterior osteochondral erosion significantly worse in ACLR than ACLT at 4 and 8 weeks (p<0.01); and osteophyte size (p<0.001) and maturity (p<0.01) greater at 1 and 2 weels in ACLR compared with ACLT. Synovitis was increased acutely in both ACL-injuries and then decreased with time, with ACLT>ACLR (p=0.003) at week-1 but similar thereafter; both still greater than uninjured joints through to week 8 (p<0.001). Sham and ACLT had similar synovitis scores until week 8 when the latter was more severe. Despite histomorphological similarities in synovitis in ACLT and ACLR, there were differences in gene expression patterns. Synovial expression of TNF, CD11b and CD8 was unchanged at any time when comparing between groups. Surgery alone (ACLT and Sham) increased synovial IL6 (week-1: ACLT p=0.02, Sham p<0.001 vs uninjured) while ACLR did not. While CD4 was also increased by surgery (week-1 and -2: ACLT p<0.01, Sham p<0.05 vs uninjured), it was also increased in ACLR versus uninjured at these times (p<0.05; Figure 1). ADAMTS5 expression was not detected in synovial tissue, and MMP9 mRNA did not differ between groups. In contrast, ADAMTS4, MMP3, and MMP13 expression were increased by surgery (ACLT/Sham) and ACLR at week-1 and -2 compared with uninjured joint, although both surgeries>ACLR (Table 1). Conclusions: While both models caused joint instability, OA trajectory and ultimate severity were greater in ACLR. In contrast, surgery induced greater histo-pathological synovitis acutely but was similar in both injuries thereafter. There was a difference in the "phenotype" of the synovial inflammation in the two injury models. In ACLT there was upregulation of IL6 not evident in ACLR but similar to Sham, suggesting this was a response to surgery and wound healing. While helper T-cell (CD4) increase was greater in ACLT and Sham, this also occurred in ACLR suggesting a role of adaptive immunity in OA after nonsurgical injury. Expression of ADAMTS4, MMP3 and MMP13 were similarly increased acutely in both injury models, suggesting synovial tissues as a source of these enzymes implicated in the structural pathology of OA. While their expression was not correlated with ultimate pathological severity they may be broad-spectrum target across varying phenotypes of post-traumatic OA. Our data suggest that synovitis severity per se was not associated with differential OA risk with ACL injury; it likely still contributes to long-term OA structural pathology.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Purpose: The short medium term benefits of intra articular corticosteroids (IAC) are well reported. Recently, we demonstrated the predictive utility of the mouse destabilisation of the medial meniscus (DMM) model for therapeutic outcomes in humans, by measuring the analgesic effect of intra articular triamcinolone acetate (iaTA) when administered at different stages of OA disease. Importantly, the factors that modify efficacy in patients were reflected in this model (better response with more inflammation; less efficacy with worse radiographic OA pathology). Despite the symptom relieving benefits of IAC, the impact of this therapy on OA disease progression is still unclear. Previous animal studies have demonstrated both structural and metabolic effects on articular cartilage (AC). In vitro studies suggest IAC induce chondrocyte apoptosis and inhibit matrix protein expression, thereby promoting cartilage degeneration. However, clinical trials evaluating the effect of IAC on AC and OA progression have produced inconsistent findings. IAC are associated with an increased risk of OA progression, but little is known about how the stage of OA disease at the time of administration impacts long-term joint pathology. The aim of this study was to determine the effect of iaTA on long term joint pathology (OA progression) when administered at three distinct stages of OA disease (post-injury, early established OA, and progressive/chronic OA), using the DMM model of OA. Methods: Male, 10 week C57BL6 mice had unilateral DMM surgery. At week 2, 4 or 8 post surgery, mice received 100mcg iaTA or intra articular saline (n=12 per treatment per time). At week 16 knee joints were harvested for histopathological assessment. Toluidine blue stained, sagittal sections of the tibiofemoral joint were examined microscopically. Global joint pathology was quantified by scoring individual tissue pathology changes. Pathology scores were determined for AC, synovium, subchondral bone (SCB), menisci and osteophytes. Results: There was no significant difference in AC structural damage, cartilage proteoglycan (PG) loss, chondrocyte hyperplasia/apoptosis, SCB or osteophyte pathology, between the 3 time points for saline injection. iaTA did not significantly affect SCB or osteophyte pathology at any injection time, compared to saline injected mice. AC structural damage was significantly increased in week 2 iaTA injected mice, for femur (p=0.03); week 4 injected mice for tibia (p=0.02); and significantly decreased in week 8 iaTA injected mice for both femur (p=0.004) and tibia (p=0.04), compared to saline injected mice. Cartilage PG loss was not affected by iaTA injection at week 2; was significantly increased in week 4 iaTA injected mice (P=0.03) and decreased in week 8 iaTA injected mice (P=0.04) for tibia, compared to saline injected mice. Chondrocyte hypertrophy (apoptosis) was significantly increased in week 4 iaTA injected mice for femur only (P=0.05) compared to saline injected mice. Overall, the greatest long term negative effect on global joint pathology occurred in week 4 injected mice. Consistently, week 4 iaTA injection resulted in increased joint pathology, and week 8 iaTA injection resulted in decreased joint pathology at 16 weeks post DMM, compared to saline injected mice. Interestingly, meniscus was the only joint tissue where pathology scores at week 16 were significantly different between the three time points for saline injection. Week 2 vs. 4 (anterior structural damage), Week 2 vs. 8 (posterior structural damage), and Week 4 vs. 8 (posterior structural damage) all displayed differences for saline injection. Conclusions: In this study we determined for the first time, the effects of corticosteroid treatment given at different times after OA onset, on joint tissue structure in the mouse DMM model. The effect of iaTA on severity of knee OA in this model, at 16 weeks post surgery, varied for different joint tissues and time of injection. The current findings support the idea that both the therapeutic and damaging effects of iaTA vary depending on the stage of OA disease at the time of injection. This may explain the conflicting findings observed in studies that have investigated the effect of IAC on joint tissue degeneration. Importantly, it highlights the need for better patient selection to optimise therapeutic benefit and mitigate risk of further joint damage.

Purpose: Post-traumatic osteoarthritis affects approximately 50% of patients with an anterior cruciate ligament (ACL) tear. The magnitude of joint trauma and destabilisation likely play a role in the risk of OA onset and progression however, the relative effects of low versus high load ACL injuries have not been extensively explored. The aim of this study was to examine OA-related structural and molecular changes in ACL injured joints from two unique murine models of injury: surgical transection (ACLT, no injury load) versus mechanical rupture (ACLR, compressive joint overload). Methods: ACL injury was induced in the right hindlimb of 10-week-old, male C57BL/6 mice by either surgical transection (ACLT) or mechanical compression (ACLR). Separate un-injured mice and sham-surgery controls were included for comparison. At 7, 14, 28 and 56 days post-injury, joints were harvested for histology (n=7) or gene expression using the isolated compartments of the medial and lateral tibial plateau (n=5). The medial and lateral tibial plateaux were evaluated separately for both outcome measures. OA severity was assessed histologically using semi-quantitative scores for: proteoglycan loss, cartilage structural damage and subchondral bone remodelling. Quantitative PCR was performed on the medial and lateral tibial plateaux to investigate key molecules implicated in osteochondral pathology in OA. Results: OA pathology was observed in both the medial and lateral compartments of ACL-injured knees but was typically worse on the medial side of the joint. Tibial cartilage pathology (proteoglycan loss and cartilage structural damage) was more rapid and severe following ACLR compared with ACLT. While subchondral bone remodelling was evident in all groups (especially medially), osteocyte cell loss was only evident after ACL injury, and osteochondral damage was only found in ACLR joints. The spatiotemporal progression of structural OA was paralleled by the upregulation of genes associated with both cartilage and bone pathology: ColX, Adamts4, Mmp2, Mmp13, Timp1, Timp3, Col1, Dmp1, Opg, Hhip and Ptch. Increased expression of Col2 and Adamts5 was only seen after ACLR. Conclusions: ACL-injury induced by mechanical compression (ACLR) resulted in a more rapid and severe degeneration of the knee joint compared to surgically induced ACL tears (ACLT). The differential changes in gene expression between the two models provides further evidence that the initial mechanism of injury (i.e. low versus high load trauma) can significantly alter the biological response of the affected joint tissues. These specific molecular changes and their timing may have important implications for the identification of ACL-injured patients at risk of OA and those most likely to require early intervention.