Synovial and cartilage responsiveness to peri-operative hyaluronic acid ± dexamethasone administration following a limited injury to the rabbit stifle joint.

Posttraumatic osteoarthritis (PTOA) can develop after an injury to the knee. Previous studies have indicated that an intra-articular (IA) injection of the potent glucocorticoid dexamethasone (DEX) may significantly prevent induction of PTOA. The aim of the present study was to investigate the effectiveness of a single IA injection of hyaluronic acid (HA), alone and in combination with DEX following a localized intra-articular injury as a PTOA-preventing treatment option. An established rabbit model of surgical injury consisting of dual intra-articular (IA) drill holes in a non-cartilaginous area of the femoral notch near the origin of the anterior cruciate ligament (ACL) to allow for bleeding into the joint space was used. Immediately following surgery, subjects were treated with HA, HA + DEX, or received no treatment. An uninjured control group was used for comparison (N = 5/group). Rabbits were sacrificed and investigated at 9 weeks post-injury. At 9 weeks post-injury, there was a significant protective capacity of the single IA treatment of DEX + HA on the histological grade of the synovial tissue, and some variable location-specific effects of HA alone and HA + DEX interactions on cartilage damage. Thus, it is possible that co-treatment with HA may interfere with the effectiveness of the DEX. In vitro friction testing indicated that DEX did not interfere with the lubricating ability of HA or synovial fluid on cartilage. These results suggest that a single IA administration of HA in combination with DEX following an IA injury is not recommended for inhibition of PTOA progression in this model.

High-fat/high-sucrose diet-induced obesity results in joint-specific development of osteoarthritis-like degeneration in a rat model.

OBJECTIVES: Metabolic syndrome and low-grade systemic inflammation are associated with knee osteoarthritis (OA), but the relationships between these factors and OA in other synovial joints are unclear. The aim of this study was to determine if a high-fat/high-sucrose (HFS) diet results in OA-like joint damage in the shoulders, knees, and hips of rats after induction of obesity, and to identify potential joint-specific risks for OA-like changes. METHODS: A total of 16 male Sprague-Dawley rats were allocated to either the diet-induced obesity group (DIO, 40% fat, 45% sucrose, n = 9) or a chow control diet (n = 7) for 12 weeks. At sacrifice, histological assessments of the shoulder, hip, and knee joints were performed. Serum inflammatory mediators and body composition were also evaluated. The total Mankin score for each animal was assessed by adding together the individual Modified Mankin scores across all three joints. Linear regression modelling was conducted to evaluate predictive relationships between serum mediators and total joint damage. RESULTS: The HFS diet, in the absence of trauma, resulted in increased joint damage in the shoulder and knee joints of rats. Hip joint damage, however, was not significantly affected by DIO, consistent with findings in human studies. The total Mankin score was increased in DIO animals compared with the chow group, and was associated with percentage of body fat. Positive significant predictive relationships for total Mankin score were found between body fat and two serum mediators (interleukin 1 alpha (IL-1α) and vascular endothelial growth factor (VEGF)). CONCLUSION: Systemic inflammatory alterations from DIO in this model system may result in a higher risk for development of knee, shoulder, and multi-joint damage with a HFS diet.Cite this article: K. H. Collins, D. A. Hart, R. A. Seerattan, R. A. Reimer, W. Herzog. High-fat/high-sucrose diet-induced obesity results in joint-specific development of osteoarthritis-like degeneration in a rat model. Bone Joint Res 2018;7:274-281. DOI: 10.1302/2046-3758.74.BJR-2017-0201.R2.

Analysis of change in gait in the ovine stifle: normal, injured, and anterior cruciate ligament reconstructed.

BACKGROUND: Many patients who undergo anterior cruciate ligament (ACL) reconstructive surgery develop post-traumatic osteoarthritis (PTOA). ACL reconstructive surgery may not fully restore pre-injury joint biomechanics, thereby resulting in further joint damage and contributing to the development of PTOA. In an ovine model of idealized ACL reconstruction (ACL-R), it has been shown that signs of PTOA develop within surgical joints by 20 weeks post-surgery. The aim of the present study was to investigate whether altered kinematics contribute to early PTOA development within ACL-R joints of the ovine injury model by comparing the gait of these surgical animals to the gait of a stable normal control group, and an unstable injury group in which the ACL and medial collateral ligament (MCL) had been transected. METHODS: Fifteen skeletally mature female sheep were allocated evenly into 3 treatment groups: normal control, ACL-R, and ACL/MCL Tx (each group n = 5). Each animal's gait was recorded at baseline, 4 weeks post injury, and 20 weeks post injury. Principal component analysis (PCA) was used to identify the kinematic patterns that may be discriminant between treatment groups. Results from previous studies were referenced to present the amount of gross PTOA-like changes that occurred in the joints. RESULTS: ACL-R and ACL/MCL transected (Tx) animals developed a similar amount of early PTOA-like changes within the surgical joints, but differed significantly in the amount of kinematic change present at 20 weeks post-surgery. We showed that the stifle joint kinematics of ACL/MCL Tx differed significantly from those of CTRL and the majority of ACL-R animals, while no significant differences in joint kinematic changes were found between ACL-R and CTRL animals. CONCLUSIONS: These results suggest that the early PTOA-like changes reported in the ACL-R model cannot be attributed exclusively to post-surgical kinematic changes, and therefore biologic components in the post-injury environment must be contributing significantly to PTOA development.

Synovial mesenchymal stem cells from osteo- or rheumatoid arthritis joints exhibit good potential for cartilage repair using a scaffold-free tissue engineering approach.

OBJECTIVE: To assess whether synovial mesenchymal stem cells (SMSCs) from patients with osteoarthritis (OA) or rheumatoid arthritis (RA) can be used as an alternative cell source for cartilage repair using allogenic tissue engineered construct (TEC). METHODS: Twenty-five patients (17 female, average age 61.8 years) were divided according to their pathology (control trauma group; N = 6, OA group; N = 6) and RA patients were subdivided into two groups to evaluate the impact of biologics in accordance with whether treated with biologics [Bio(+)RA; N = 7] or not [Bio(-)RA; N = 6]. We compared the following characteristics among these groups: (1) The cell proliferation capacity of SMSCs; (2) The influence of passage number on features of SMSCs; (3) The weight and volume of TEC from the same number of SMSCs; (4) Inflammatory cytokine gene expressions levels of TEC; (5) The chondrogenic potential of TEC; and (6) Osteochondral repair using TEC in athymic nude rats. RESULTS: SMSCs from the four groups exhibited equivalent features in the above evaluation items. In in vivo studies, the TEC-treated repair tissues for all groups exhibited significantly better outcomes than those for the untreated group and no significant differences among the four TEC groups. CONCLUSION: SMSCs from OA or RA patients are no less appropriate for repairing cartilage than those from trauma patients and thus, may be an effective source for allogenic cell-based cartilage repair.

Joint instability leads to long-term alterations to knee synovium and osteoarthritis in a rabbit model.

OBJECTIVES: Joint instability is believed to promote early osteoarthritic changes in the knee. Inflammatory reactions are associated with cartilage degradation in osteoarthritis (OA) but their possible synergistic or additive effects remain largely unexplored. The goal of the present study was to investigate the in vivo effects of Botulinum Toxin A (BTX-A) induced joint instability on intraarticular alterations in an otherwise intact rabbit knee joint model. METHODS: Ten 1-year-old female New Zealand White rabbits (average 5.7 kg, range 4.8-6.6 kg) were randomly assigned to receive three monthly unilateral intramuscular injections of BTX-A (experimental group), or no treatment (control group). After 90 days, all knees were analyzed for specific mRNA levels using RT-qPCR. The synovium and cartilage tissue was assessed for histological alterations using the OARSI scoring system. RESULTS: Cartilage and synovial histology showed significant higher OARSI scores in the BTX-A group animals compared to the untreated controls and contralateral limbs. There were no differences between the untreated control and the contralateral experimental limbs. Gene expression showed significant elevations for collagen I, collagen III, nitric oxide, TGF-ß, IL-1 and IL-6 compared to the healthy controls. CONCLUSION: BTX-A induced joint instability in a muscle weakness model uniquely leads to alterations in gene expression and histological changes in the synovial membranes and cartilage in otherwise intact knee joints. These results lead to the conclusion that joint instability may promote an inflammatory intraarticular milieu, thereby contributing to the development of OA.

Lubricin/Proteoglycan 4 binds to and regulates the activity of Toll-Like Receptors In Vitro.

Proteoglycan 4 (PRG4/lubricin) is secreted by cells that reside in articular cartilage and line the synovial joint. Lubricin may play a role in modulating inflammatory responses through interaction with CD44. This led us to examine if lubricin could be playing a larger role in the modulation of inflammation/immunity through interaction with Toll-like receptors (TLRs). Human Embryonic Kidney (HEK) cells overexpressing TLRs 2, 4 or 5 and surface plasmon resonance were employed to determine if full length recombinant human lubricin was able to bind to and activate TLRs. Primary human synovial fibroblasts were also examined using flow cytometry and Luminex multiplex ELISA. A rat destabilization model of osteoarthritis (OA) was used to determine if lubricin injections were able to regulate pain and/or inflammation in vivo. Lubricin can bind to and regulate the activity of TLRs, leading to downstream changes in inflammatory signalling independent of HA. We confirmed these findings in vivo through intra-articular injections of lubricin in a rat OA model where the inhibition of systemic inflammatory signaling and reduction in pain were observed. Lubricin plays an important role in regulating the inflammatory environment under both homeostatic and tissue injury states.

Relationship between inflammation, the gut microbiota, and metabolic osteoarthritis development: studies in a rat model.

UNLABELLED: Osteoarthritis (OA) may result from intrinsic inflammation related to metabolic disturbance. Obesity-associated inflammation is triggered by lipopolysaccharide (LPS) derived from the gut microbiota. However, the relationship between gut microbiota, LPS, inflammation, and OA remain unclear. OBJECTIVE: To evaluate the associations between gut microbiota, systemic LPS levels, serum and local inflammatory profiles, and joint damage in a high fat/high sucrose diet induced obese rat model. METHODS: 32 rats were randomized to a high fat/high sucrose diet (diet-induced obese (DIO), 40% fat, 45% sucrose, n = 21) or chow diet group (12% fat, 3.7% sucrose n = 11) for 28 weeks. After a 12-week obesity induction period, DIO animals were stratified into Obesity Prone (DIO-P, top 33% by change in body mass, n = 7), and Obesity Resistant groups (DIO-R, bottom 33%, n = 7). At sacrifice, joints were scored using a Modified Mankin Criteria. Blood and synovial fluid analytes, serum LPS, and fecal gut microbiota were analyzed. RESULTS: DIO animals had greater Modified Mankin scores than chow animals (P = 0.002). There was a significant relationship (r = 0.604, p = 0.001) between body fat, but not body mass, and Modified Mankin score. Eighteen synovial fluid and four serum analytes were increased in DIO animals. DIO serum LPS levels were increased compared to chow (P = 0.031). Together, Lactobacillus species (spp.) and Methanobrevibacter spp. abundance had a strong predictive relationship with Modified Mankin Score (r(2) = 0.5, P < 0.001). CONCLUSIONS: Increased OA in DIO animals is associated with greater body fat, not body mass. The link between gut microbiota and adiposity-derived inflammation and metabolic OA warrants further investigation.

Embryonic stem cell-derived osteocytes are capable of responding to mechanical oscillatory hydrostatic pressure.

Osteoblasts can be derived from embryonic stem cells (ESCs) by a 30 day differentiation process, whereupon cells spontaneously differentiate upon removal of LIF and respond to exogenously added 1,25α(OH)2 vitamin D3 with enhanced matrix mineralization. However, bone is a load-bearing tissue that has to perform under dynamic pressure changes during daily movement, a capacity that is executed by osteocytes. At present, it is unclear whether ESC-derived osteogenic cultures contain osteocytes and whether these are capable of responding to a relevant cyclic hydrostatic compression stimulus. Here, we show that ESC-osteoblastogenesis is followed by the generation of osteocytes and then mechanically load ESC-derived osteogenic cultures in a compression chamber using a cyclic loading protocol. Following mechanical loading of the cells, iNOS mRNA was upregulated 31-fold, which was consistent with a role for iNOS as an immediate early mechanoresponsive gene. Further analysis of matrix and bone-specific genes suggested a cellular response in favor of matrix remodeling. Immediate iNOS upregulation also correlated with a concomitant increase in Ctnnb1 and Tcf7l2 mRNAs along with increased nuclear TCF transcriptional activity, while the mRNA for the repressive Tcf7l1 was downregulated, providing a possible mechanistic explanation for the noted matrix remodeling. We conclude that ESC-derived osteocytes are capable of responding to relevant mechanical cues, at least such that mimic oscillatory compression stress, which not only provides new basic understanding, but also information that likely will be important for their use in cell-based regenerative therapies.

Surgical menopause initiates molecular changes that do not result in mechanical changes in normal and healing ligaments.

OBJECTIVES: Ligaments which heal spontaneously have a healing process that is similar to skin wound healing. Menopause impairs skin wound healing and may likewise impair ligament healing. Our purpose in this study was to investigate the effect of surgical menopause on ligament healing in a rabbit medial collateral ligament model. METHODS: Surgical menopause was induced with ovariohysterectomy surgery in adult female rabbits. Ligament injury was created by making a surgical gap in the midsubstance of the medial collateral ligament. Ligaments were allowed to heal for six or 14 weeks in the presence or absence of oestrogen before being compared with uninjured ligaments. Molecular assessment examined the messenger ribonucleic acid levels for collagens, proteoglycans, proteinases, hormone receptors, growth factors and inflammatory mediators. Mechanical assessments examined ligament laxity, total creep strain and failure stress. RESULTS: Surgical menopause in normal medial collateral ligaments initiated molecular changes in all the categories evaluated. In early healing medial collateral ligaments, surgical menopause resulted in downregulation of specific collagens, proteinases and inflammatory mediators at 6 weeks of healing, and proteoglycans, growth factors and hormone receptors at 14 weeks of healing. Surgical menopause did not produce mechanical changes in normal or early healing medial collateral ligaments. With or without surgical menopause, healing ligaments exhibited increased total creep strain and decreased failure stress compared with uninjured ligaments. CONCLUSIONS: Surgical menopause did not affect the mechanical properties of normal or early healing medial collateral ligaments in a rabbit model. The results in this preclinical model suggest that menopause may result in no further impairment to the ligament healing process. Cite this article: Bone Joint Res 2015;4:38-44.

Effect of muscle weakness and joint inflammation on the onset and progression of osteoarthritis in the rabbit knee.

OBJECTIVES: Interactions between mechanical and non-mechanical independent risk factors for the onset and progression of Osteoarthritis (OA) are poorly understood. Therefore, the goal of the present study was to investigate the in vivo effects of muscle weakness, joint inflammation and the combination on the onset and progression of OA in a rabbit knee joint model. MATERIALS AND METHODS: Thirty 1-year-old female New Zealand White rabbits (average 5.7 kg, range 4.8-6.6 kg) were divided into four groups with one limb randomly assigned to be the experimental side: (1) surgical denervation of the vastus lateralis (VL) muscle; (2) muscle weakness induced by intramuscular injection of Botulinum toxin A (BTX-A); (3) intraarticular injection with Carrageenan to induce a transient inflammatory reaction; (4) combination of Carrageenan and BTX-A injection. After 90 days, cartilage histology of the articular surfaces were microscopically analyzed using the Osteoarthritis Research Society International (OARSI) histology scoring system. RESULTS: VL denervation resulted in significantly higher OARSI scores in the patellofemoral joint (group 1). BTX-A administration resulted in significant cartilage damage in all four compartments of the knee (group 2). Carrageenan did not cause significant cartilage damage. BTX-A combined with Carrageenan lead to severe cartilage damage in all four compartments. CONCLUSION: Muscle weakness lead to significant OA in the rabbit knee. A transient local inflammatory stimulus did not promote cartilage degradation nor did it enhance OA progression when combined with muscle weakness. These results are surprising and add to the literature the conclusion that acute inflammation is probably not an independent risk factor for OA in this rabbit model.

Elevated serum soluble CD200 and CD200R as surrogate markers of bone loss under bed rest conditions.

CD200 is a transmembrane protein that belongs to the immunoglobulin family of proteins and is ubiquitously expressed on a variety of cell types. Upon interaction with its receptors (CD200Rs) expressed on myeloid-derived cells and T lymphocytes, an immunoregulatory signal is delivered to receptor-expressing cells. Previous studies have implicated a role for CD200:CD200R in the regulation of the expression of mRNA markers of osteoclastogenesis/osteoblastogenesis, following interaction of CD200 (on osteoblast precursors) with CD200R1 (on osteoclast precursors). Signaling of CD200R1 is hypothesized to attenuate osteoclastogenesis. We have investigated whether levels of soluble forms of CD200 and/or CD200R1 (sCD200, sCD200R1) are altered in volunteers undergoing 6° head down tilt bed rest to mimic conditions of microgravity known to be associated with preferential osteoclastogenesis and whether countermeasures, reported to be beneficial in attenuation of bone loss under microgravity conditions, would lead to altered sCD200 and sCD200R1 levels. Our data suggest that, as predicted, sCD200 levels fall under bed rest conditions while sCD200R1 levels rise. In subjects undergoing 30-minute per day continuous centrifugation protocols, as a countermeasure to attenuate changes which may lead to bone loss, these alterations in sCD200 and sCD200R1 levels seen under conditions of bed rest were abolished or attenuated. Our results suggest that measurement of sCD200 and/or sCD200R1 may prove a useful and rapid means of monitoring subjects at risk of bone loss and/or accessing the efficacy of treatment regimes designed to counter bone loss.

Changes of early post-traumatic osteoarthritis in an ovine model of simulated ACL reconstruction are associated with transient acute post-injury synovial inflammation and tissue catabolism.

The study described here tested the hypothesis that early intra-articular inflammation is associated with the development of post-traumatic osteoarthritis (PTOA) in a sheep model. We extended previously published work in which we investigated joint gross morphology and synovial mRNA expression of inflammatory and catabolic molecules 2 weeks after anatomic Anterior cruciate ligament (ACL) autograft reconstructive surgery (ACL-R). The same variables have been analyzed at 20 weeks post surgery together with new experimental variables at both time points. Animals were sacrificed at 20 weeks post ACL-R surgery and their joints graded for signs of PTOA. Synovial samples were harvested for histological grading plus mRNA and protein analysis for a panel of inflammatory and catabolic molecules. The mRNA expression levels for this panel plus connective tissue matrix turnover molecules were also investigated in cartilage samples. Results of gross morphological assessments at 20 weeks post surgery showed some changes consistent with early OA, but indicated little progression of damage from the 2 week time point. While significant alterations in mRNA levels for synovial inflammatory and catabolic molecules were detected at 2 weeks, values had normalized by 20 weeks. Similarly, all mRNA expression levels for inflammatory and catabolic molecules in articular cartilage had returned to normal levels by 20 weeks post ACL-R surgery. We conclude that synovial inflammatory processes are initiated very early after ACL-R surgery and may instigate events that lead to the gross cartilage and joint abnormalities observed as early as 2 weeks. However, the absence of sustained inflammation and joint instability may prevent OA progression.

A novel approach for in vitro studies applying electrical fields to cell cultures by transformer-like coupling.

The purpose of this study was to develop a new apparatus for in vitro studies applying low frequency electrical fields to cells without interfering side effects like biochemical reactions or magnetic fields which occur in currently available systems. We developed a non-invasive method by means of the principle of transformer-like coupling where the magnetic field is concentrated in a toroid and, therefore, does not affect the cell culture. Next to an extensive characterization of the electrical field parameters, initial cell culture studies have focused on examining the response of bone marrow-derived human mesenchymal stem cells (MSCs) to pulsed electrical fields. While no significant differences in the proliferation of human MSCs could be detected, significant increases in ALP activity as well as in gene expression of other osteogenic markers were observed. The results indicate that transformer-like coupled electrical fields can be used to influence osteogenic differentiation of human MSCs in vitro and can pose a useful tool in understanding the influence of electrical fields on the cellular and molecular level.

Altered cell metabolism in tissues of the knee joint in a rabbit model of Botulinum toxin A-induced quadriceps muscle weakness.

Quadriceps muscle weakness is frequently associated with knee injuries in sports. The influence of quadriceps weakness on knee joint homeostasis remains undefined. We hypothesized that quadriceps weakness will lead to tissue-specific alterations in the cell metabolism of tissues of the knee. Quadriceps weakness was induced with repetitive injections of Botulinum toxin A in six 1-year-old New Zealand White rabbits for 6 months. Five additional animals served as controls with injections of saline/dextrose. Muscle weakness was assessed by muscle wet mass, isometric knee extensor torque, and histological morphology analysis. Cell metabolism was assessed for patellar tendon, medial and lateral collateral ligament, and medial and lateral meniscus by measuring the total RNA levels and specific mRNA levels for collagen I, collagen III, MMP-1, MMP-3, MMP-13, TGF-ß, biglycan, IL-1, and bFGF by reverse transcription and polymerase chain reaction. While the total RNA levels did not change, tissue-specific mRNA levels were lower for relevant anabolic and catabolic molecules, indicating potential changes in tissue mechanical set points. Quadriceps weakness may lead to adaptations in knee joint tissue cell metabolism by altering a subset of anabolic and catabolic mRNA levels corresponding to a new functional and metabolic set point for the knee that may contribute to the high injury rate of athletes with muscle weakness.

The interface of mechanical loading and biological variables as they pertain to the development of tendinosis.

Different tendons are designed to withstand different mechanical loads in their individual environments. Variable physiologic loading ranges and correspondingly different injury thresholds lead to tendon heterogeneity. Also, tendon heterogeneity is evident when examining how different tendons regulate their response to changes in mechanical loading (over- and under-loading). The response of tendons to changes in mechanical loading plays an important role in the induction and progression of tendinosis which is tendon degeneration without inflammation. Tendon overuse injury is likely related to abnormal mechanical loading that deviates from normal mechanical loading in magnitude, frequency, duration and/or direction. Mechanical loading that results in tendon overuse injury can initiate a repair process but, after failed initial repair, non-resolving chronic attempted repair appears to lead to a "smoldering" fibrogenesis. Contributions of regulatory components, including minor components in the "nerve-mast cell-myofibroblast axis", are key features in the development and progression of tendinosis. Hormonal and genetic factors may also influence risk for tendinosis. Further understanding of how tendinosis induction is related to mechanical use/overuse, how tendinosis progression is related to abnormal regulation of attempted repair, and how induction and/or progression are modulated by other risk factors may lead to interventions that mitigate risk and enhance functional repair.

Growth factor and protease expression during different phases of healing after rabbit deep flexor tendon repair.

The purpose of the study was to contribute to the mapping of molecular events during flexor tendon healing, in particular the growth factors insulin-like growth factor-1 (IGF-1), vascular endothelial growth factor (VEGF) and nerve growth factor (NGF), matrix metalloproteinases (MMP-3 and MMP-13) and their inhibitors (tissue inhibitors of metalloproteinases, TIMP-1 and TIMP-3, and the protease cathepsin K. In a rabbit model of flexor tendon injury, the mRNA expression for the growth factors, MMPs and TIMPs were measured in tendon and tendon sheath tissue at several time points (3, 6, 21, and 42 days) representing different phases of the healing process. We found that MMP-13 remained increased during the study period, whereas MMP-3 returned to normal levels within the first week after injury. TIMP-3 was down-regulated in the tendon sheaths. Cathepsin K was up-regulated in tendons and sheaths after injury. NGF was present in both tendons and sheaths, but unaltered. IGF-1 exhibited a late increase in the tendons, while VEGF was down-regulated at the later time points. In conclusion, we have demonstrated the presence of NGF in flexor tendons. MMP-13 expression appears to play a more protracted role in flexor tendon healing than MMP-3. The relatively low levels of endogenous IGF-1 and VEGF mRNA following injury support their potential beneficial role as exogenous modulators to optimize tendon healing and strength without increasing adhesion formation.

New understanding of the complex structure of knee menisci: implications for injury risk and repair potential for athletes.

Menisci help maintain the structural integrity of the knee. However, the poor healing potential of the meniscus following a knee injury can not only end a career in sports but lead to osteoarthritis later in life. Complete understanding of meniscal structure is essential for evaluating its risk for injury and subsequent successful repair. This study used novel approaches to elucidate meniscal architecture. The radial and circumferential collagen fibrils in the meniscus were investigated using novel tissue-preparative techniques for light and electron microscopic studies. The results demonstrate a unique architecture based on differences in the packaging of the fundamental collagen fibrils. For radial arrays, the collagen fibrils are arranged in parallel into ∼10 µm bundles, which associate laterally to form flat sheets of varying dimensions that bifurcate and come together to form a honeycomb network within the body of the meniscus. In contrast, the circumferential arrays display a complex network of collagen fibrils arranged into ∼5 µm bundles. Interestingly, both types of architectural organization of collagen fibrils in meniscus are conserved across mammalian species and are age and sex independent. These findings imply that disruptions in meniscal architecture following an injury contribute to poor prognosis for functional repair.

Alterations to cell metabolism in connective tissues of the knee after ovariohysterectomy in a rabbit model: are there implications for the postmenopausal athlete?

BACKGROUND: Participation in regular exercise and athletic activities across the lifespan is encouraged to maintain the cardiovascular and musculoskeletal systems and general wellbeing. Before the menopause there is an increased risk of anterior cruciate ligament (ACL) injuries in female athletes, whereas there is an increased risk of joint diseases such as knee osteoarthritis after the menopause. Although there are few data regarding alterations in individual connective tissues of the knee in humans either before, during or after the menopause, it is possible to assess changes in experimental models following surgical menopause. OBJECTIVE: To assess changes in cell metabolism in the medial collateral ligament, ACL, patellar tendon, lateral and medial menisci, tibial plateau and femoral condyle articular cartilage and the synovium after surgical menopause in an experimental model system. METHODS: Panels of rabbits were subjected to ovariohysterectomy or sham operations, and RNA from each tissue was assessed for collagen, proteoglycan, proteinase, growth factor, sex hormone receptor and inflammatory mediator messenger RNA levels by reverse transcribed PCR. RESULTS: Unique alterations in cell metabolism were detected 2 months after surgical menopause and the pattern of significant changes was tissue specific (number of mRNA species altered, extent of changes, elevation/depression of changes). CONCLUSIONS: Changes in cell metabolism may alter the set point for the tissues of the knee and subsequently the functioning of the knee after the menopause. Such changes may contribute to an increased risk of injury and/or degenerative conditions. Further studies in pre and postmenopausal women athletes may also shed light on whether the present findings can be extrapolated to human populations.

Changes in mechanical loading lead to tendonspecific alterations in MMP and TIMP expression: influence of stress deprivation and intermittent cyclic hydrostatic compression on rat supraspinatus and Achilles tendons.

BACKGROUND: Tendinopathy commonly occurs in tendons with large in vivo loading demands like the Achilles tendon (AT) and supraspinatus tendon (SST). In addition to differences in their local anatomic environment, these tendons are designed for different loading requirements because of the muscles to which they attach, with the AT experiencing higher loads than the SST. One possible factor in the progression of tendinopathy is the interplay between mechanical loading and the regulation of enzymes that degrade the extracellular matrix (matrix metalloproteinases (MMPs)) and their inhibitors (tissue inhibitor of metalloprotienases (TIMPs)). Thus, overuse injuries may have different biological consequences in tendons designed for different in vivo loading demands. AIM: In this study, the tendon-specific regulation of MMP-13, MMP-3 and TIMP-2 expression in rat AT and SST exposed to two different mechanical environments was investigated. METHODS: Rat AT and SST were exposed to stress deprivation (ie, detached from attachments) and intermittent cyclic hydrostatic compression (with attachments intact). Levels of MMP-13, MMP-3 and TIMP-2 mRNA were evaluated in time-zero control, attached, stressdeprived and "compressed" tendons. RESULTS: Stress deprivation led to elevated expression of MMP-13, MMP-3 and TIMP-2 in both tendons, although the magnitude of the increase was greater for the SST than the AT. Intermittent cyclic hydrostatic compression of attached tendons increased expression of MMP-13 in the SST, but not the AT. CONCLUSIONS: The results of this study suggest that stress deprivation may be one contributor to the progression of tendinopathy in AT and SST, where the tendon designed for the lower in vivo loading demand (SST) was the most affected by a change in mechanical loading. The unique upregulation of MMP-13 with hydrostatic compression supports the impingement injury theory for rotator cuff tears.

Relationship between knee joint laxity and knee joint mechanics during the menstrual cycle.

BACKGROUND: An increase in knee laxity during the menstrual cycle may increase the risk of anterior cruciate ligament injury. OBJECTIVE: To investigate whether changing knee laxity during the menstrual cycle correlates with changing knee joint loads in a cutting manoeuvre. DESIGN: Cross-sectional study. SETTING: Laboratory testing. PARTICIPANTS: 25 healthy women, with a normal menstrual cycle, no history of oral contraceptive use, and no previous knee injury INTERVENTIONS: Serum hormone concentrations were assessed and knee joint laxity at a load of 89 N was measured during the follicular, ovulation and luteal phases. Participants performed 10 trials of a cutting manoeuvre to quantify knee joint mechanics at each test session. MAIN OUTCOME MEASUREMENTS: Knee joint laxity (mm), peak knee angle ( degrees ) and knee joint moment (Nm) and knee joint impulse (Nms). RESULTS: Increased knee laxity was observed during ovulation compared with the luteal phase, but no significant changes in knee mechanics corresponding to menstrual phases were found. A positive correlation was found between changes in knee laxity and changes in knee joint loads (Deltamoment or Deltaimpulse) from the follicular phase to ovulation, and from ovulation to the luteal phase (p<0.05). Women in whom knee laxity increased showed increased knee loads, and those in whom knee laxity decreased showed decreased knee loads during the menstrual cycle. CONCLUSIONS: Knee laxity correlates positively with knee joint loads, and increased knee laxity during the menstrual cycle may be a potential risk factor for anterior cruciate ligament injuries in certain women during sports activity.