Transection of the anterior cruciate ligament in the dog: a model of osteoarthritis

Early zoledronate treatment inhibits subchondral bone microstructural changes in skeletally-mature, ACL-transected canine knees

Anterior cruciate ligament (ACL) tear leads to post-traumatic osteoarthritis (PTOA), a significant clinical burden worldwide that currently has no cure. Recent studies suggest a role of subchondral bone adaptations in the development of PTOA. Particularly, microstructural changes in the rod-and-plate microstructure of subchondral bone may precede and contribute to OA progression. In this study, we quantified microstructural changes in subchondral trabecular rods and plates after ACL-transection for the first time in the well-established preclinical canine model of PTOA and investigated the therapeutic potentials of a bisphosphonate (zoledronate) and NSAID treatment (meloxicam). Unilateral hindlimb ACL transection was performed on skeletally-mature (2-year-old, N = 20) and juvenile (10-month-old, N = 20) male beagles. Animals were assigned to 4 groups (N = 5): ACLT, un-operated control, ACLT with zoledronate, and ACLT with meloxicam treatment. Subchondral bone microstructure was evaluated by micro-computed tomography and cartilage integrity was evaluated histologically. We found that ACL-induced subchondral bone changes depended on skeletal maturity of animals. In mature animals, significant loss of trabecular plates that resulted in reduced PR ratio occurred at Month 1 and persisted until Month 8. Zoledronate treatment prevented trabecular plate loss while meloxicam treatment did not. Whether cartilage degeneration is also attenuated warrants further investigation. In juvenile animals that have not reached skeletal maturity, transient changes in trabecular plate and rod microstructure occurred at Month 3 but not Month 9. Neither zoledronate nor meloxicam treatment attenuated bone microstructural changes or cartilage damages. Findings from this study suggest that early inhibition of bone resorption by bisphosphonate after injury may be a promising therapeutic approach to prevent alterations in subchondral bone microstructure associated with PTOA. Our results further demonstrate that pathogenesis of PTOA may differ between adolescent and adult patients and therefore require distinct management strategies.

Long-term intake of Lilium lancifolium mitigated osteoarthritic effects by suppressing inflammatory cytokines in a dog model

Background and Aim: Osteoarthritis (OA) is a chronic, painful, degenerative inflammatory disease of the synovial joints. Regular use of nonsteroidal anti-inflammatory drugs to decrease OA pain can have severe side effects, such as gastric irritation, ulcers, and heart problems. Natural products are extensively used to minimize OA-associated pain and inflammatory reactions. Lilium lancifolium is commonly used to alleviate several diseases through its anti-inflammatory effects. This study examined the impact of L. lancifolium extract on alleviating pain and inflammation associated with articular cartilage damage. Materials and Methods: Hydro-ethanol extracts of the L. lancifolium bulb were used. The experimental animals (adult beagle dogs) were divided into four groups: sham, which received neither treatment nor surgery; placebo, which received an empty gelatin capsule; glucosamine, which received glutamine (60 mg/kg); and L. lancifolium, which received an L. lancifolium extract-filled (60 mg/kg) gelatin capsule for 8 weeks. OA was induced by an expert orthopedic surgeon in 2-year-old dogs through resection of cranial cruciate ligament and lateral collateral ligament. Inflammatory cytokines, enzymes, lameness score, radiology, and histological changes were assessed. Results: Our experiments showed that long-term oral therapy with L. lancifolium alleviated inflammation and increased histological damage. L. lancifolium treatment effectively reduced cytokines, such as interleukin-6, metalloproteinase-9, leukotriene-4, prostaglandin, and cyclo-oxygenase in dogs with OA, suggesting the potential to minimize inflammatory reactions in OA. L. lancifolium showed anti-inflammatory qualities in dogs with OA. This effect was comparable with that of glucosamine OA treatment. Conclusion: L. lancifolium supplementation represents a possible therapeutic and management option in this model of OA.

OA foundations - experimental models of osteoarthritis

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.

Intra-articular injection of human synovium-derived mesenchymal stem cells in beagles with surgery-induced osteoarthritis

BACKGROUND

Recently, cell-based tissue engineering approaches using mesenchymal stem cells (MSCs) have been used to treat osteoarthritis (OA). However, the efficacy of human synovium-derived MSCs (hSD-MSCs) has not yet been tested in a canine model of OA. The purpose of this study was to investigate the therapeutic effects of intra-articular hSD-MSC injections in a canine OA model.

METHODS

Sixty beagles underwent surgical manipulation to induce OA and received intra-articular injection 4 weeks after surgery. The dogs were divided into five groups (n = 12) according to the injection material: G1, sham group; G2, control group injected with phosphate-buffered saline; G3, G4, and G5, experimental groups injected with different hSD-MSC dosages (G3, 2.4 × 10⁶ cells; G4, 4.8 × 10⁶ cells; G5, 9.6 × 10⁶ cells). Magnetic resonance imaging (MRI) and histopathological and immunohistochemical examinations were performed 6 and 24 weeks after injection.

RESULTS

MRI revealed significant improvements in synovitis 24 weeks after injection in the hSD-MSC-injected groups (G3-G5). Histopathologic analyses showed that cartilage structure and proteoglycan staining were also significantly improved in these groups (G3-G5) 6 weeks after injection and improved further after 24 weeks. Immunohistochemical analysis revealed significant differences in the levels of collagen types I and II between the hSD-injected groups (G3-G5), indicating a similar extracellular matrix (ECM) composition to naïve articular cartilage.

CONCLUSION

Our study demonstrated for the first time that intra-articular hSD-MSC injection ameliorates the progression of canine OA by restoring cartilage, promoting ECM synthesis, and inhibiting the inflammatory response.

Meniscus Induced Cartilaginous Damage and Non-linear Gross Anatomical Progression of Early-stage Osteoarthritis in a Canine Model

Background:

The predictable outcome of the anterior cruciate ligament transection (ACLT) canine model, and the similarity to naturally occurring osteoarthritis (OA) in humans, provide a translatable method for studying OA. Still, evidence of direct meniscus-induced cartilaginous damage has not been identified, and gross-anatomical blinded scoring of early-stage OA has not been performed.

Objective:

A gross anatomical observation and statistical analysis of OA progression to determine meniscus induced cartilaginous damage, to measure the macroscopic progression of OA, and to address matters involving arthroscopic and surgical procedures of the knee.

Method:

Unblinded assessment and blinded scoring of meniscal, tibial, femoral, and patellar damage were performed for control and at four time points following unilateral ACLT: 3-week (N=4), 8-week (N=4), 12-week (N=5), and 25-week (N=4). Mixed-model statistics illustrates damage (score) progression; Wilcoxon rank-sum tests compared time-point scores; and Wilcoxon signed-rank tests compared ACLT and contralateral scores, and meniscus and tibia scores.

Result:

Damage was manifest first on the posterior aspect of the medial meniscus and subsequently on the tibia and femur, implying meniscal damage can precede, coincide with, and aggravate cartilage damage. Damage extent varied chronologically and was dependent upon the joint component. Meniscal damage was evident at 3 weeks and progressed through 25-weeks. Meniscal loose bodies corresponded to tibial cartilage damage location and extent through 12 weeks, followed by cartilage repair activity after complete meniscal degeneration.

Conclusion:

This study provides additional information for understanding OA progression, identifying OA biomarkers, and arthroscopic and meniscectomy procedures.

The influences of different spatial resolutions on the characteristics of T2 relaxation times in articular cartilage: A coarse-graining study of the microscopic magnetic resonance imaging data

Microscopic magnetic resonance imaging (µMRI) T2 data from canine cartilage at different tibial locations were analyzed to investigate the influences of spatial resolution and pixel position on the T2 sensitivity to osteoarthritis (OA). Five experimental factors were investigated: inaccurate pixel position, different pixel resolutions, different specimen orientations in the magnetic field, topographical variations over the tibial surface, and different OA stages. A number of significant trends were identified in this analysis, which shows the subtle but substantial influences to our abilities of detecting OA due to T2 changes. In particular, any deviation in locating the cartilage pixels may result in erratic values near the cartilage surface. Significant differences were found in T2 values between nearly any two comparison-groups under all resolutions both in the meniscus-covered and -uncovered areas, which were also showed interaction between the OA degradation stages. This multiresolution project should help to improve the detection sensitivities of MRI toward cartilage degeneration. Microsc. Res. Tech. 79:754-765, 2016. © 2016 Wiley Periodicals, Inc.

Change in T2* relaxation time of Hoffa fat pad correlates with histologic change in a rat anterior cruciate ligament transection model

The Hoffa fat pad (infrapatellar fat pad) is a source of post-traumatic anterior knee pain, and Hoffa disease is a syndrome leading to chronic inflammation of the fat pad. Herein, change in T2* relaxation time of the fat pad was measured in a rodent anterior cruciate ligament transection (ACLX) model in order to (i) examine the causal relationship of anterior cruciate ligament (ACL) deficiency and Hoffa disease and (ii) demonstrate the feasibility of using T2* as an imaging biomarker to monitor disease progression. Three groups of male Sprague Dawley rats (n = 6 each group), received either (i) no intervention; (ii) sham surgery at the right knee; or (iii) right ACLX. T2* relaxation time was measured and histology was examined in the Hoffa fat pad after surgery. At 13 and 18 weeks after surgery, T2* values were significantly higher in the right fat pad than the left (p < 0.001) and significantly higher in the ACLX group than the control and sham groups (p < 0.001). Histology showed fibrosis and degeneration of adipocytes in the right knees of the ACLX group. We conclude that ACL deficiency and Hoffa disease are causally related and that MRI T2* value can serve as an imaging biomarker of Hoffa disease progression.

A posteriori comparison of natural and surgical destabilization models of canine osteoarthritis

For many years Canis familiaris, the domestic dog, has drawn particular interest as a model of osteoarthritis (OA). Here, we optimized the dog model of experimental OA induced by cranial cruciate ligament sectioning. The usefulness of noninvasive complementary outcome measures, such as gait analysis for the limb function and magnetic resonance imaging for structural changes, was demonstrated in this model. Relationships were established between the functional impairment and the severity of structural changes including the measurement of cartilage thinning. In the dog model of naturally occurring OA, excellent test-retest reliability was denoted for the measurement of the limb function. A criterion to identify clinically meaningful responders to therapy was determined for privately owned dogs undergoing clinical trials. In addition, the recording of accelerometer-based duration of locomotor activity showed strong and complementary agreement with the biomechanical limb function. The translation potential of these models to the human OA condition is underlined. A preclinical testing protocol which combines the dog model of experimental OA induced by cranial cruciate ligament transection and the Dog model of naturally occurring OA offers the opportunity to further investigate the structural and functional benefits of disease-modifying strategies. Ultimately, a better prediction of outcomes for human clinical trials would be brought.

CIINE Reflects Collagenase-Specific CII Breakdown in Cartilage Explant and Whole Body of Canine

To evaluate collagenase inhibitors for the treatment of osteoarthritis and to correlate them with clinical pathology, canine cartilage explant and anterior cruciate ligament transection (ACLT) models were examined by quantifying the CII neoepitope (CIINE). This peptide is a putative marker for collagenase-specific type II collagen (CII) degradation, which is a critical step in osteoarthritis pathology.

The concentration of CIINE in supernatants of canine cartilage explants showed increase upon IL-1β—stimulation and collagenase inhibitors suppressed this elevation of CIINE. In the canine ACLT model, levels of CIINE in urine (uCIINE) increased as lesions of knee joint cartilage developed and decreased in response to collagenase inhibitors.

Our results suggest that CIINE reflects collagenase-specific CII degradation in canine explants and whole bodies. It is anticipated that these data will establish a tool for clarifying and bridging the efficacy and mechanism of collagenase inhibitors at the preclinical stage of drug discovery.

Tibiofemoral cartilage contact biomechanics in patients after reconstruction of a ruptured anterior cruciate ligament

We investigated the in vivo cartilage contact biomechanics of the tibiofemoral joint in patients after reconstruction of a ruptured anterior cruciate ligament (ACL). A dual fluoroscopic and MR imaging technique was used to investigate the cartilage contact biomechanics of the tibiofemoral joint during in vivo weight-bearing flexion of the knee in eight patients 6 months following clinically successful reconstruction of an acute isolated ACL rupture. The location of tibiofemoral cartilage contact, size of the contact area, cartilage thickness at the contact area, and magnitude of the cartilage contact deformation of the ACL-reconstructed knees were compared with those previously measured in intact (contralateral) knees and ACL-deficient knees of the same subjects. Contact biomechanics of the tibiofemoral cartilage after ACL reconstruction were similar to those measured in intact knees. However, at lower flexion, the abnormal posterior and lateral shift of cartilage contact location to smaller regions of thinner tibial cartilage that has been described in ACL-deficient knees persisted in ACL-reconstructed knees, resulting in an increase of the magnitude of cartilage contact deformation at those flexion angles. Reconstruction of the ACL restored some of the in vivo cartilage contact biomechanics of the tibiofemoral joint to normal. Clinically, recovering anterior knee stability might be insufficient to prevent post-operative cartilage degeneration due to lack of restoration of in vivo cartilage contact biomechanics.

Decreased bone tissue mineralization can partly explain subchondral sclerosis observed in osteoarthritis

For many years, pharmaceutical therapies for osteoarthritis (OA) were focused on cartilage. However, it has been theorized that bone changes such as increased bone volume fraction and decreased bone matrix mineralization may play an important role in the initiation and pathogenesis of OA as well. The mechanisms behind the bone changes are subject of debate, and a better understanding may help in the development of bone-targeting OA therapies. In the literature, the increase in bone volume fraction has been hypothesized to result from mechanoregulated bone adaptation in response to decreased mineralization. Furthermore, both changes in bone volume fraction and mineralization have been reported to be highest close to the cartilage, and bone volume fraction has been reported to be correlated with cartilage degeneration. These data indicate that cartilage degeneration, bone volume fraction, and bone matrix mineralization may be related in OA. In the current study, we aimed to investigate the relationships between cartilage degeneration, bone matrix mineralization and bone volume fraction at a local level. With microCT, we determined bone matrix mineralization and bone volume fraction as a function of distance from the cartilage in osteochondral plugs from human OA tibia plateaus with varying degrees of cartilage degeneration. In addition, we evaluated whether mechanoregulated bone adaptation in response to decreased bone matrix mineralization may be responsible for the increase in bone volume fraction observed in OA. For this purpose, we used the experimentally obtained mineralization data as input for bone adaptation simulations. We simulated the effect of mechanoregulated bone adaptation in response to different degrees of mineralization, and compared the simulation results to the experimental data. We found that local changes in subchondral bone mineralization and bone volume fraction only occurred underneath severely degenerated cartilage, indicating that bone mineralization and volume fraction are related to cartilage degeneration at a local level. In addition, both the experimental data and the simulations indicated that a depth-dependent increase in bone volume fraction could be caused by decreased bone matrix mineralization. However, a quantitative comparison showed that decreased mineralization can only explain part of the subchondral sclerosis observed in OA.

Bone structural changes in osteoarthritis as a result of mechanoregulated bone adaptation: a modeling approach

OBJECTIVE

There are strong indications that subchondral bone may play an important role in osteoarthritis (OA), making it an interesting target for medical therapies. The subchondral bone structure changes markedly during OA, and it has long been assumed that this occurs secondary to cartilage degeneration. However, for various conditions that are associated with OA, it is known that they may also induce bone structural changes in the absence of cartilage degeneration. We therefore aimed to investigate if OA bone structural changes can result from mechanoregulated bone adaptation, independent of cartilage degeneration.

METHOD

With a bone adaptation model, we simulated various conditions associated with OA -without altering the articular cartilage- and we evaluated if mechanoregulated bone remodeling by itself could lead to OA-like bone structural changes.

RESULTS

For each of the conditions, the predicted changes in bone structural parameters (bone fraction, trabecular thickness, trabecular number, and trabecular separation) were similar to those observed in OA.

CONCLUSION

This indicates that bone adaptation in OA can be mechanoregulated with structural changes occurring independent of cartilage degeneration.

Structural and functional changes of the articular surface in a post-traumatic model of early osteoarthritis measured by atomic force microscopy

The functional integrity of the articulating cartilage surface is a critical determinant of joint health. Although a variety of techniques exist to characterize the structural changes in the tissue with osteoarthritis (OA), some with extremely high resolution, most lack the ability to detect and monitor the functional changes that accompany the structural deterioration of this essential bearing surface. Atomic force microscopy (AFM) enables the acquisition of both structural and mechanical properties of the articular cartilage surface, with up to nanoscale resolution, making it particularly useful for evaluating the functional behavior of the macromolecular network forming the cartilage surface, which disintegrates in OA. In the present study, AFM was applied to the articular cartilage surfaces from six pairs of canine knee joints with post-traumatic OA. Microstructure (RMS roughness) and micromechanics (dynamic indentation modulus, E* of medial femoral condyle cartilages were compared between contralateral controls and cruciate-transected knee joints, which develop early signs of OA by three months after surgery. Results reveal a significant increase in RMS roughness and a significant four-fold decrease in E* in cartilages from cruciate-transected joints versus contralateral controls. Compared to previous reports of changes in bulk mechanics, AFM was considerably more sensitive at detecting early cartilage changes due to cruciate-deficiency. The use of AFM in this study provides important new information on early changes in the natural history of OA because of its ability to sensitively detect and measure local structural and functional changes of the articular cartilage surface, the presumptive site of osteoarthritic initiation.

Increased tibiofemoral cartilage contact deformation in patients with anterior cruciate ligament deficiency

OBJECTIVE

To investigate the in vivo cartilage contact biomechanics of the tibiofemoral joint following anterior cruciate ligament (ACL) injury.

METHODS

Eight patients with an isolated ACL injury in 1 knee, with the contralateral side intact, participated in the study. Both knees were imaged using a specific magnetic resonance sequence to create 3-dimensional models of knee bone and cartilage. Next, each patient performed a lunge motion from 0 degrees to 90 degrees of flexion as images were recorded with a dual fluoroscopic system. The three-dimensional knee models and fluoroscopic images were used to reproduce the in vivo knee position at each flexion angle. With this series of knee models, the location of the tibiofemoral cartilage contact, size of the contact area, cartilage thickness at the contact area, and magnitude of the cartilage contact deformation were compared between intact and ACL-deficient knees.

RESULTS

Rupture of the ACL changed the cartilage contact biomechanics between 0 degrees and 60 degrees of flexion in the medial compartment of the knee. Compared with the contralateral knee, the location of peak cartilage contact deformation on the tibial plateaus was more posterior and lateral, the contact area was smaller, the average cartilage thickness at the tibial cartilage contact area was thinner, and the resultant magnitude of cartilage contact deformation was increased. Similar changes were observed in the lateral compartment, with increased cartilage contact deformation from 0 degrees to 30 degrees of knee flexion in the presence of ACL deficiency.

CONCLUSION

ACL deficiency alters the in vivo cartilage contact biomechanics by shifting the contact location to smaller regions of thinner cartilage and by increasing the magnitude of the cartilage contact deformation.

On new bone formation in the pre-osteoarthritic joint

OBJECTIVE

This study investigated the structural alterations in the osteochondral junction, traversing the intact-to-lesion regions, with the aim of elucidating the way in which the pre-osteoarthritic (pre-OA) state progresses to fully developed osteoarthritis (OA).

METHOD

Thirty bovine patellae showing varying degrees of degeneration, with lesions located in the distal-lateral quarter, were used for this study. Cartilage-on-bone blocks were cut along the lateral facet to include both the lesion site in the distal end and the intact site in the proximal end. The blocks were formalin-fixed, mildly decalcified and microtomed to obtain 30 microm - thick osteochondral slices. Using differential interference contrast optics, the tissue microstructure was captured at high resolution in its fully hydrated state.

RESULTS

There were structural changes in the osteochondral junction beneath the still-intact articular cartilage adjacent to the lesion site. The changes observed in traversing from the intact to the lesion site exhibited characteristics that were strikingly similar to those associated with primary bone formation. The evidence suggests that disruption of the cartilage continuum by a lesion has wider mechanobiological consequences at the osteochondral junction.

CONCLUSION

The progression of OA appears to involve new bone formation adjacent to lesion sites. We hypothesise that the new bone spicules that appear in regions beneath intact cartilage adjacent to lesion sites provide a snapshot of the elusive pre-OA state.

Temporal assessment of bone marrow lesions on magnetic resonance imaging in a canine model of knee osteoarthritis: impact of sequence selection

OBJECTIVE

To assess the evolution of bone marrow lesions (BMLs) in a canine model of knee osteoarthritis (OA) using three different magnetic resonance imaging (MRI) sequences.

DESIGN

Three MRI sequences [coronal, T1-weighted three-dimensional fast gradient recalled echo (T1-GRE), sagittal fat-suppressed 3D spoiled gradient echo at a steady state (SPGR), and sagittal T2-weighted fast spin echo with fat saturation (T2-FS)] were performed at baseline, and at week 4, 8 and 26 in five dogs following transection of the anterior cruciate ligament. The same reader scored (0-3) subchondral BMLs twice, in blinded conditions, according to their extent in nine joint subregions, for all imaging sessions, and independently on the three MRI sequences. Correlation coefficients and Bland-Altman plots evaluated intra-reader repeatability. Readings scores were averaged and the nine subregions were summed to generate global BML scores.

RESULTS

BMLs were most prevalent in the central and medial portions of the tibial plateau. Intra-reader repeatability was good to excellent for each sequence (r(s)=0.87-0.97; P<0.001). Maximal intra-reader variability (24%) was reached on T2-FS and was associated to higher scores (P<0.05). Global BML scores increased similarly on all three sequences until week 8 (P<0.05). At week 26, score on T2-FS was decreased, being lower when compared to T1-GRE and SPGR (P<0.05).

CONCLUSION

In this canine OA model, the extent of BMLs varies in time on different MRI sequences. Until the complex nature of these lesions is fully resolved, it is suggested that to accurately assess the size and extent of BMLs, a combination of different sequences should be used.

Complete anterior cruciate ligament tear and the risk for cartilage loss and progression of symptoms in men and women with knee osteoarthritis

OBJECTIVE

To determine whether a complete anterior cruciate ligament (ACL) tear, a frequent incidental finding on magnetic resonance imagings (MRIs) of individuals with established knee osteoarthritis (OA), increases the risk for further knee OA progression.

METHODS

We examined 265 participants (43% women) with symptomatic knee OA in a 30-month, prospective, natural history study of knee OA. The more symptomatic knee was imaged using MRI at baseline, 15 and 30 months. Cartilage was scored at the medial and lateral tibiofemoral joint and at the patellofemoral joint using the Whole-Organ MRI Score (WORMS) semi-quantitative method. Complete ACL tear was determined on baseline MRI. At each visit, knee pain was assessed using a knee-specific visual analog scale and physical function was assessed using the Western Ontario and McMaster Universities (WOMAC) physical function subscale.

RESULTS

There were 49 participants (19%) with complete ACL tear at baseline. Adjusting for age, body mass index, gender and baseline cartilage scores, complete ACL tear increased the risk for cartilage loss at the medial tibiofemoral compartment [odds ratio (OR): 1.8, 95% confidence interval (CI): 1.1, 3.2]. However, following adjustment for the presence of medial meniscal tears, no increased risk for cartilage loss was further seen (OR: 1.1, 95% CI: 0.6, 1.8). Knee pain and physical function were similar over follow-up between those with and without a complete ACL tear.

CONCLUSIONS

Individuals with knee OA and incidental complete ACL tear have an increased risk for cartilage loss that appears to be mediated by concurrent meniscal pathology. The presence of a complete ACL tear did not influence the level of knee pain or physical function over short-term follow-up.

Heberden's nodes and what Heberden could not see: the pivotal role of ligaments in the pathogenesis of early nodal osteoarthritis and beyond

Despite its relatively high prevalence, polyarticular nature, limited treatment options and recognized genetic contribution, the study of generalized OA (GOA) has lagged behind that of isolated knee OA. Whilst the pathogenesis of OA has been viewed in relation to either articular cartilage or bone disease, this article offers a viewpoint on why GOA may, in fact, be primarily a disorder of ligaments, and to a lesser extent tendon and joint capsule dysfunction. A relatively fast presentation of GOA, typically in the perimenopausal period, and its recognition on clinical grounds alone makes this type of OA potentially useful for pathogenic studies in OA, in general. The recent high-resolution MRI studies, microanatomical studies and animal models, in addition to established clinical and radiographic data that support this ligament-centric perspective of disease, are reviewed. The earliest structural abnormalities in GOA may be evident in ligaments and the ligament-associated 'enthesis organ', where degenerative changes are evident. Ligaments also influence the expression of joint damage including Heberden's node and joint erosion formation. Joint inflammation in a 'periarthritis' pattern is well recognized in GOA, and histological studies have shown that the ligament and capsule could represent the epicentre of such inflammatory changes. A perspective is also offered on how ligaments could play a pivotal role in OA in general; for example, the loss of joint space in knee OA due to meniscal extrusion could ultimately be related to derangement of the medial collateral ligament to which the meniscus is anchored.

Ex vivo characterization of articular cartilage and bone lesions in a rabbit ACL transection model of osteoarthritis using MRI and micro-CT

OBJECTIVE

To characterize the rabbit anterior cruciate ligament transection (ACLT) model of osteoarthritis (OA) at various stages of disease using high-resolution 3-D medical imaging systems, which, in turn, will facilitate future longitudinal studies evaluating disease progression and response to therapy in live animals.

METHODS

Degenerative changes in femorotibial cartilage, volumetric bone mineral density (vBMD), bone volume fraction (BV/TV), and osteophyte volume were characterized ex vivo using 4-T magnetic resonance imaging (MRI) and micro-computed tomography (micro-CT) at 4, 8, and 12 weeks post-ACLT. These changes were subsequently correlated to macroscopic joint evaluation.

RESULTS

Macroscopic assessment demonstrated progressive cartilage degeneration post-surgery, which was significantly correlated to MRI evaluation (r=0.82, P<0.0001). Linear regression analysis indicated that vBMD and BV/TV are linearly related such that as vBMD increases, BV/TV increases (P<0.0001). Micro-CT revealed bone loss at 4 and 8 weeks post-ACLT, but recovery to control values at 12 weeks post-ACLT. Volumetric BMD was not strongly correlated with macroscopic assessment of articular cartilage degeneration (r=-0.35, P<0.0001). Quantitative measurement of osteophyte volume demonstrated a statistically significant difference (with respect to control groups) at both 8 and 12 weeks post-ACLT, but not at 4 weeks post-ACLT.

CONCLUSIONS

The rabbit ACLT model of OA demonstrates progressive cartilage degeneration and intermediate bone changes at 4, 8, and 12 weeks post-surgery. Cartilage and bone lesions were characterized ex vivo using 4-T MRI and micro-CT, and MRI assessment of cartilage degeneration was correlated to macroscopic grading.

Influence of tissue maturation and antioxidants on the apoptotic response of articular cartilage after injurious compression

OBJECTIVE

To study the influence of tissue maturation and antioxidants on apoptosis in bovine articular cartilage induced by injurious compression.

METHODS

Bovine articular cartilage disks were obtained from the femoropatellar groove of animals ages 0.5-23 months and placed in culture. Cartilage disks were preincubated overnight with the cell-permeable superoxide dismutase (SOD) mimetic Mn(III) porphyrin (0-12.5 microM) or alpha-tocopherol (0-50 microM) and then injured by a single unconfined compression to a final strain of 50% at a velocity of 1 mm/second. After 4 days of additional incubation, the disks were fixed and embedded for light and electron microscopy. Apoptotic cells were quantified morphologically by the appearance of nuclear blebbing on light microscopy. Biosynthetic activity was demonstrated by incorporation of radiolabeled proline. The antioxidative action of the SOD mimetic was confirmed by histologic examination of cartilage after incubation with nitroblue tetrazolium.

RESULTS

Injurious compression induced significantly more apoptosis in cartilage disks from newborn calves (22% of cells) than in cartilage from more mature cows (2-6%). In cartilage from 22-month-old animals, the SOD mimetic reduced the percentage of apoptotic cells induced by injury in a dose-dependent manner (complete inhibition with 2.5 microM), while alpha-tocopherol had no effect. Neither antioxidant altered protein biosynthesis or cellular ultrastructure.

CONCLUSION

Our data suggest that the apoptotic response of articular cartilage to mechanical injury is affected by maturation and is mediated in part by reactive oxygen species. The antioxidative status of the tissue might be important for the prevention of mechanically induced cell death in articular cartilage.

Indirect injury stimulates scar formation-adaptation or pathology?

In several animal models of osteoarthritis induced by cruciate ligament transection, a dense, scar-like tissue mass forms rapidly on the medial side of the knee joint. This mass mimics clinical fibrosis that sometimes occurs after joint surgery. It is unknown exactly why this medial tissue mass forms and what cells are involved in its formation. This study characterizes this medial mass by histology, biochemistry, and the expression of types I and III collagen mRNA. The medial mass is compared with the medial collateral ligament (MCL) and the MCL epiligament in anterior cruciate-transected and unoperated joints, and to normal skin and skin scar. The morphology of the medial mass resembled the epiligament and skin scar more than the MCL. The concentration of DNA and RNA and the RNA-DNA ratio were elevated dramatically in the medial mass compared with all other tissues including skin scar. However, the mRNA copy number and ratio of collagen types I and III mRNAs did not differ significantly among the medial mass, MCL, epiligament, and skin in either the control or the operated joints. The response of the medial mass, MCL, and MCL epiligament to cruciate transaction involves both hyperplasia and hypertrophy, but without a dramatic shift in cell phenotype. The medial mass may be a useful mimic or model of intraarticular adhesions, hypertrophic scars, ligament sprains, and arthrofibrosis.

Mediation of interleukin-1beta-induced transforming growth factor beta1 expression by activator protein 4 transcription factor in primary cultures of bovine articular chondrocytes: possible cooperation with activator protein 1

OBJECTIVE

Interleukin-1 (IL-1) and transforming growth factor beta1 (TGFbeta1) play major roles in osteoarticular diseases, exerting opposite effects on both the catabolism and anabolism of cartilage matrix. Previous findings suggest that IL-1 and TGFbeta1 could function in a feedback interaction. However, the effect exerted by IL-1 on expression of TGFbeta by articular chondrocytes is, so far, poorly understood. The present study was carried out to determine the influence of IL-1beta on the expression of TGFbeta1 by bovine articular chondrocytes (BACs) in primary culture.

METHODS

BAC primary cultures were treated with IL-1beta, and TGFbeta1 messenger RNA (mRNA) steady-state levels and protein expression were measured by real-time reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. Transient transfection of TGFbeta1 gene promoter constructs was performed to delineate the DNA sequences that mediate the IL-1beta effect. Electrophoretic mobility shift assays (EMSAs) and supershift analysis were used to characterize the transcription factors binding to these sequences.

RESULTS

Cultured BACs responded to IL-1beta exposure by exhibiting an increase of TGFbeta1 expression at both the mRNA and protein levels. The effect was found to be mediated by a major 80-bp sequence located between -732 and -652 upstream of the transcription initiation site. EMSA and supershift analysis revealed that the transcription factors activator protein 4 (AP-4) and AP-1 specifically bound to the -720/-696 part of this sequence under IL-1beta treatment. Overexpression of AP-4 in the BAC cultures resulted in stimulation of the transcriptional activity of the -732/+11 TGFbeta1 promoter construct through the same IL-1beta-responsive element.

CONCLUSION

IL-1beta induces an increase of TGFbeta1 in articular chondrocytes through activation of AP-4 and AP-1 binding to the TGFbeta1 gene promoter. These findings may help us understand the role of IL-1beta in the disease process. Notwithstanding its deleterious effect on cartilage, IL-1 could initiate the repair response displayed by injured cartilage in the early stages of osteoarthritis through its ability to enhance TGFbeta1 expression by local chondrocytes.

Osteoarthritis as an inevitable consequence of the structure of articular cartilage

The hypothesis that osteoarthritis is an inevitable consequence of the structure of articular cartilage is proposed. Cartilage structure is viewed as an evolutionary solution to the optimization of articular cartilage function. A simplified model of the structural elements and constraints will be used to illustrate how the hypothesis leads to a mathematical solution and then a more realistic situation will be described, but not optimized rigorously. The goal for finding a solution will be to optimize the function of articular cartilage subject to the constraints of a biological tissue. In comparison, the structure of genuine articular cartilage will be discussed in the context of an optimal solution to the functional problem and, particularly, in relation to the disease of osteoarthritis.

A potential animal model for creating a controlled and reversible anterior cruciate ligament insufficiency

We developed and tested a device to manipulate the axial position of the tibial anterior cruciate ligament (ACL) insertion in vitro to create a potential animal model that could simulate both ACL insufficiency and 'optimal' ACL reconstruction. This model is based on the concept that controlled incremental proximal displacement of the tibial ACL insertion simulates ACL insufficiency. Replacing the insertion at the joint level and then adjusting its position until the forces recorded equaled those in the ACL-intact knee can simulate 'optimal' ACL reconstruction. Anterior tibial translation (ATT) was quantified in vitro in 24 sheep cadaver knees with the ACL intact and after the ACL was cut or detached (ACL insufficiency). In 8 knees, a bone plug including the tibial ACL insertion was detached, mounted in a specially designed device, and adjusted to reproduce ATT of the ACL-intact knee. ATT was then measured after proximal displacement of the tibial ACL insertion in calibrated 1 mm increments. The results revealed that detaching the ACL increased ATT by 132-700%. Controlled 3 mm proximal displacement of the insertion using this device increased ATT by more than 100%. Comparing the increase in ATT due to controlled displacement of the ACL insertion to that due to detaching the ACL, in only one case was the same magnitude of ACL insufficiency reproduced. Despite the variability between knees, the device was able to reproduce ATT of the ACL-intact knee and to substantially increase ATT with controlled proximal displacement of the tibial ACL insertion. Use of this device, if successful in an in vivo ACL reconstruction model, could help define any quantitative association between altered joint kinematics and degenerative changes in the joint.

The acute structural changes of loaded articular cartilage following meniscectomy or ACL-transection

OBJECTIVE

Meniscectomy and anterior cruciate ligament (ACL) rupture have been identified as precursors of osteoarthrosis (OA) in clinical reviews and animal experiments. In this study, the acute effects of these injuries on articular cartilage matrix deformation, preserved in a loaded state using a cryopreservation technique, were studied by scanning electron microscopy (SEM).

METHOD

Whole knee joints from adult White New Zealand rabbits (N=87) were loaded ex vivo, using a simulated quadriceps pull under static and cyclic loading conditions, following medial meniscectomy or transection of the ACL. Specimens were plunge-frozen while under load, or following a recovery period, and prepared for SEM by cryofixation. Using SEM and photographic images, the medial tibial plateau cartilage was assessed both qualitatively and quantitatively.

RESULTS

After meniscectomy, significantly increased bending and crimping of radial collagen fibers occurred with static loading. Compared to intact knees, the area of tibial cartilage showing an indentation was increased by 80% (P< 0.05), the articular cartilage thickness was significantly more reduced when under load (for high force long duration static loading, intact joints had 53%+/-3 reduction in cartilage thickness compared to 39%+/-4 after meniscectomy, P< 0.05), and it took nearly twice as long for the cartilage thickness to recover following loading. These post-meniscectomy differences were either not present or were minimal when the joint was allowed to extend when loaded. ACL-transection slightly increased collagen deformation in the deeper zones, but only with cyclic loading.

CONCLUSION

The findings indicate that, with static loading, significantly increased deformation of articular cartilage collagen structure can occur following meniscectomy, but is minimized by joint motion. This increased deformation may be relevant to the etiology and progression of joint degeneration.

Long-term outcome of surgery for dogs with cranial cruciate ligament deficiency

Fifty-eight dogs with cranial cruciate ligament deficiency were assessed and treated surgically. At an average of 50 months postoperatively, the functional outcome was assessed by means of an owner-based clinical assessment and a clinical examination. Client-based data were available for 26 dogs and 20 dogs were reassessed after 50 months. The results were compared with the initial values and with data from an assessment 13 months postoperatively. The level of disability at 50 months was judged to be significantly less than initially. However, there were no differences between the initial assessments and those made after 50 months for the perceived 'effect of cold weather' and the dogs' 'ability to jump', despite both measures having improved after 13 months. Age and meniscal injury were identified as poor prognostic indicators for the long-term outcome. The equivalent joint on the contralateral limb deteriorated significantly during the study.

Long-term results of volar ligament reconstruction for symptomatic basal joint laxity

It has been hypothesized that instability of the thumb trapeziometacarpal joint is a major factor in the etiology of degenerative disease. Theoretically, surgically stabilized joints should be subject to less shear force and, hence, will be less likely to develop degenerative changes. The long-term results of volar ligament reconstruction were assessed in 19 patients (24 thumbs). The average age at surgery was 33 years (range, 18-55 years). Twenty-three thumbs were radiographic stage I; a preoperative x-ray was not available in 1. The follow-up period averaged 15 years (range, 10-23 years). At the final follow-up visit 15 thumbs were stage I, 7 were stage II, and 2 were stage III. Fifteen patients were at least 90% satisfied with the results of the surgery. Only 8% of thumbs advanced to radiographic arthritic disease, which compares favorably with the 17% to 33% reported incidence of stage III/IV basal joint arthritis in the general population.

Semiquantitative reverse transcription-polymerase chain reaction analysis of syndecan-1 and -4 messages in cartilage and cultured chondrocytes from osteoarthritic joints

OBJECTIVE

To determine the steady-state of messenger RNA (mRNA) levels of syndecan-1 and syndecan-4 in cartilage samples and chondrocytes derived from human osteoarthritic knee joints.

METHODS

Steady-state levels of gene-specific mRNA (relative to beta-actin) were measured by semiquantitative polymerase chain reaction (PCR).

RESULTS

RT-PCR allowed detection of syndecan-1 (for the first time) and syndecan-4 in both cartilage samples and articular chondrocytes cultured as primary monolayers. The mRNA levels of syndecan-1 were reduced in cartilage tissue from heavily damaged compared to normal-looking areas whereas those of syndecan-4 were significantly increased. In contrast, the expression of syndecan-1 was higher in cultured chondrocytes derived from the fibrillated osteoarthritic cartilage than in cells obtained from intact cartilage, while the syndecan-4 message levels did not differ between the two sites.

CONCLUSION

The expression of the cell-surface syndecans 1 and 4 is altered during the osteoarthritic degradative process of the knee joint. The discoordinate syndecan gene expression, which is probably related to the chondrocyte proliferation and clustering, may contribute to the disorganization of the cartilage and the development of OA processes. Isolation and culturing the chondrocytes as monolayers dramatically change the expression of these genes and cannot reflect the in situ condition.

Effects of the NSAIDs meloxicam and indomethacin on cartilage proteoglycan synthesis and joint responses to calcium pyrophosphate crystals in dogs

NSAIDs are a major cause for concern for their propensity to cause joint deterioration in canine, as in human, patients receiving these drugs for treatment of pain in osteoarthritis and other acute and chronic painful conditions. To determine the potential effects of the new NSAID meloxicam on cartilage integrity, the effects of this drug on proteoglycan biosynthesis in vitro and ex vivo were compared with those of indomethacin, a known inhibitor of sulphated proteoglycans that accelerates joint injury in human osteoarthritis. In vitro cartilage proteoglycan synthesis from a radiosulphate precursor was unaffected by 0.5-10.0 micromol/L meloxicam but was significantly inhibited by 50 micromol/L indomethacin after 6 or 24 h incubation of femoral or tibial cartilage explants in organ culture. This is in accord with previous observations in human or porcine articular cartilage under the same culture conditions. Studies were performed in vivo to establish the effects of the NSAIDs on joint integrity. This involved determining cartilage proteoglycan synthesis ex vivo, leukocyte, fluid and protein accumulation, as well as pain relief. Thus, meloxicam (0.2 mg/kg i.v. x 3 doses) or indomethacin (0.5 mg/kg i.v. x 3 doses) was given for 26 h and the effects were compared with a control (1.0 ml saline i.v. x 3 doses) in dogs in which acute inflammation had been induced by intra-articular (i.a.) injection of calcium pyrophosphate dihydrate (CPPD) crystals into the right stifle joint, an equivalent volume of saline being injected into the left stifle joint as a control. No effects were observed of the treatment with the NSAIDs on ex vivo sulphated proteoglycan synthesis. The lack of the expected inhibitory effects of indomethacin may be related to the relatively low plasma concentrations of this drug obtained during the 26 h period of treatment. The pain response, which was elicited up to 6 h following i.a. injection of CPPD crystals, was totally prevented by the treatment with meloxicam and to a lesser extent with indomethacin. There were no effects from the drug treatment on synovial inflammatory reactions (fluid and cell accumulation), although the protein concentration of the exudate was reduced by meloxicam. This indicates that, at the doses given, it was possible to discriminate the analgesic action from the anti-inflammatory action of the two NSAIDs, this being achieved at relatively low plasma concentrations of these drugs. In conclusion, while relatively high therapeutic concentrations of indomethacin inhibit cartilage proteoglycan synthesis, this is not an effect seen even at high concentrations of meloxicam. Furthermore, the lack of effects on proteoglycan synthesis was evident when these two drugs were given in vivo to dogs. However, the signs of pain, but not the inflammation in the joint, were relieved by low plasma concentrations of the drugs. Meloxicam may thus be safely employed for acute analgesia without the potential risks of joint cartilage damage that occurs with indomethacin given at antiinflammatory doses for long periods of time.

Avocado/soya unsaponifiables enhance the expression of transforming growth factor beta1 and beta2 in cultured articular chondrocytes

OBJECTIVE

Avocado and soya unsaponifiables (ASU) have been reported to exert beneficial effects in the treatment of periodontal and osteoarticular diseases. They are supposed to stimulate deposition and repair of extracellular matrix components, but the mechanisms underlying their action are not well understood. In view of the repair potential of osteoarthritic (OA) cartilage and the role that the transforming growth factor beta (TGFbeta) system could play in that process, we carried out in vitro studies to determine the mechanism of action of ASU on articular chondrocytes that may account for the beneficial effects on cartilage metabolism.

METHODS

Cultured bovine articular chondrocytes were treated with various concentrations of ASU, and the expression of both TGFbeta isoforms, 1 and 2, and their receptors (TGFbetaRI and TGFbetaRII) was determined by Northern blot and reverse transcriptase-polymerase chain reaction. Cell transfection with TGFbeta1 promoter constructs was also used to delineate the cis-acting sequences mediating ASU responsiveness in chondrocytes. The level of plasminogen activator inhibitor 1 (PAI-1) was also evaluated by Northern blotting and protein radiolabeling.

RESULTS

The data indicated that ASU stimulate the expression of TGFbeta1, TGFbeta2, and PAI-1 by articular chondrocytes. In contrast, the levels of TGFbetaRI and TGFbetaRII were not significantly affected by the compound. Treatment of bovine articular chondrocytes transiently transfected with TGFbeta1 promoter constructs suggested that the effect on TGFbeta1 expression is mediated by the region located between -732 and -1132 bp.

CONCLUSION

The results indicate that the ASU-induced stimulation of matrix synthesis previously reported in cultured articular chondrocytes could be explained by the ability to enhance TGFbeta expression in these cells. Further, ASU increase the production of PAI-1, an effect that could help in blocking the plasmin cascade that leads to metalloprotease activation. These data suggest that the compound has properties that might promote TGFbeta-induced matrix repair mechanisms in articular cartilage.

Cell-cycle-dependent expression of transforming growth factor beta type I receptor correlates with differential proliferative effects of TGFbeta1 in articular chondrocytes

We previously found that transforming growth factor beta type 1 (TGFbeta1) had bifunctional effects on articular chondrocytes in culture depending on the proliferative state of the cells. Here, TGFbeta1 responses and the expression of TGFbeta receptors I and II were investigated as a function of growth state in rabbit articular chondrocytes (RAC) and Mv1Lu cells, a cell line which is growth inhibited by TGFbeta1. In contrast to these latter cells, in which DNA synthesis was decreased by TGFbeta1 independently of the cell cycle phases, exponentially growing RAC responded with a stimulation of DNA synthesis while confluent or quiescent cells were growth inhibited. Using synchronized RAC cultures, we showed that inhibitory responses were associated with the G0/G1 phase, whereas proliferative effects were S-phase dependent. Type I receptor mRNA level was severalfold greater in quiescent and slowly proliferating than in exponentially growing cells. In contrast, the expression of type II mRNA did not change. 125I-TGFbeta1 binding to RI in G0/G1-arrested cells was greater than in S-phase, suggesting a correlation with the growth-inhibitory effect of TGFbeta1. Transfection of an RI expression vector in exponentially growing RAC, which normally are growth stimulated by TGFbeta1, induced an inhibitory response, supporting the idea that this effect was due to increased RI expression. These results indicate that the ratio of type I to type II levels is cell cycle dependent and could lead to either negative or positive proliferative responses. In contrast, no influence on the TGFbeta1-induced stimulation of matrix gene transcriptional activity was seen, confirming that TGFbeta cell growth and matrix effects are controlled by separate pathways.

Effects of diacerhein in an accelerated canine model of osteoarthritis

OBJECT

To determine whether diacerhein has a disease-modifying effect in an accelerated canine model of osteoarthritis.

DESIGN

Fourteen adult mongrel dogs underwent unilateral L4-S1 dorsal root ganglionectomy (DRG), followed 3 weeks later by ipsilateral anterior cruciate ligament transection. Seven dogs received diacerhein (15-20 mg/kg) daily throughout the interval between DRG and sacrifice, eight weeks after ligament transection. The other seven dogs served as OA controls.

RESULTS

The mean volume of synovial fluid obtained from the OA knee of the diacerhein-treated dogs was approximately 40% less than that from the OA knee of the controls. In addition, diacerhein appeared to reduce the severity of fibrillation (femoral condyle) and full-thickness ulceration (trochlear ridge) of the articular cartilage and the level of collagenase activity in extracts of the OA cartilage, and to increase net PG synthesis in the OA cartilage, although none of the above changes were statistically significant.

CONCLUSION

The differences between the diacerhein group and untreated OA controls, even though not statistically significant, suggest that diacerhein was active in this rapidly progressive model of OA. Because changes associated with initiation of OA may be different than those associated with progression, whether diacerhein has a disease-modifying effect should be examined in a less rapidly progressive model.

Mono-iodoacetate-induced experimental osteoarthritis: a dose-response study of loss of mobility, morphology, and biochemistry

OBJECTIVE

To characterize the dose-responsiveness of morphologic and biochemical chondral changes relative to mobility in mono-iodoacetate (MIA)-induced osteoarthritis (OA) in rats.

METHODS

Rat mobility was assessed by biotelemetry. Articular lesions were characterized by macroscopic and histologic examinations. Cartilage proteoglycan metabolism was evaluated by the 1,9-dimethylmethylene blue dye binding assay and by radiosulfate incorporation in patellar cartilage.

RESULTS

Spontaneous locomotor activity was rapidly, transiently, and dose-dependently decreased after MIA injection into rat knees (primary response). Thereafter, only high doses (0.3 mg and 3.0 mg) led to a secondary progressive long-term loss of spontaneous mobility on day 15, when subchondral bone was exposed. These 2 doses resulted in significant changes in cartilage proteoglycan concentration at day 15 and a strong inhibition of anabolism in the peripheral patellae by day 2, contrasting with the effects of lower doses (0.01, 0.03, and 0.1 mg).

CONCLUSION

When a sufficient dose of MIA is used, this model can easily and quickly reproduce OA-like lesions and functional impairment in rats, similar to that observed in human disease. These parameters, as well as proteoglycan metabolism, could serve as indicators for studying chondroprotective drugs, or for evaluating the ability of imaging techniques to detect and evaluate chondral lesions.

Eccentric knee flexor torque following anterior cruciate ligament surgery

The purposes of this study were to compare eccentric knee flexor torque and muscle activation in the limbs of normal (NOR) subjects and in subjects who had undergone unilateral ACI, autograft surgical reconstruction (INJ) and to assess the effect of movement speed on EMG/ torque ratios and eccentric-concentric actions. Fourteen subjects (7 NOR and 7 INJ) were tested for knee eccentric flexor torque and EMG activity at four isokinetic speeds (15 degrees, 30 degrees, 45 degrees and 60 degrees.s-1). Results revealed that post-surgical limbs (ACL) produced significantly less (P < 0.05) eccentric torque and flexor EMG activity at 60 degrees.s-1 than uninjured (UNI) contralateral limbs. Eccentric torque rose significantly as speed increased from 45 degrees to 60 degrees.s-1 for surgical group uninjured limbs and NOR group left and right limbs. Eccentric flexor torque increased with speed for both groups and approximated equality with concentric extensor torque at 60 degrees.s-1 for INJ group ACL and UNI limbs. Concentric flexor muscle EMG/torque ratios were 30-191% greater than eccentric muscle actions across groups and speeds. The results suggest that ACL dysfunction may result in reduced eccentric flexor torque at rapid movement speeds, that eccentric flexor torque increases with movement speed and may have the capacity to counter forceful extensor concentric torque, and that eccentric muscle actions produce less muscle activation per unit force than concentric actions which may reflect reduced energy cost.

Effects of fluid-induced shear on articular chondrocyte morphology and metabolism in vitro

This study tested the effects of fluid-induced shear on high density monolayer cultures of adult articular chondrocytes. Fluid-induced shear (1.6 Pa) was applied by cone viscometer to normal human and bovine articular chondrocytes for periods of 24, 48, and 72 hours. At 48 and 72 hours, fluid-induced shear caused individual chondrocytes to elongate and align tangential to the direction of cone rotation. Fluid-induced shear stimulated glycosaminoglycan synthesis by 2-fold (p < 0.05) and increased the length of newly synthesized chains in human and bovine chondrocytes. In human chondrocytes, the hydrodynamic size of newly synthesized proteoglycans also was increased. After 48 hours of fluid-induced shear, the release of prostaglandin E2 from the chondrocytes was increased 10 to 20-fold. In human chondrocytes, mRNA signal levels for tissue inhibitor of metalloproteinase increased 9-fold in response to shear compared with the controls. In contrast, mRNA signal levels for the neutral metalloproteinases, collagenase, stromelysin, and 72 kD gelatinase, did not show such major changes. This study demonstrated that articular chondrocyte metabolism responds directly to physical stimulation in vitro and suggests that mechanical loading may directly influence cartilage homeostasis in vivo.

Mechanical responses of the rabbit patello-femoral joint to blunt impact

Various studies suggest impact trauma may initially soften cartilage, damage subchondral bone, or a combination thereof. The initial damages are commonly thought due to excessive contact pressure generated on cartilage and the underlying bone. The objective of this research was to develop a small animal model for studying post-traumatic OA and to correlate contact pressure with tissue damage. Blunt insult was graded by dropping a rigid mass onto the hyperflexed hind limb of rabbits. Contact pressure in the patello-femoral joint was measured with pressure sensitive film. One, 3, 6, and 14 days later the animals were euthanized. Damage to cartilage and the underlying bone was assessed visually and in microscopic sections. Indentation experiments were performed on the patellar cartilage with a rigid, flat probe. Contact pressures were nonuniform over the articular surfaces and a high frequency of surface fissures were generated on the lateral facet in severe insults. The appearance of surface fissures correlated better with the magnitude of contact pressure gradients in the damage zone than the magnitude of contact pressures on the facet, per se. Blunt trauma causing surface fissures resulted in a measurable degree of softening in the patellar cartilage, especially close to the defects. Surgical intervention of the joint to insert pressure sensitive film, however, also resulted in significant softening of the cartilage.

Animal models for osteoarthritis: processes, problems and prospects

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Osteoarthritis in cynomolgus macaques: a primate model of naturally occurring disease

The objective of the present study was to determine if naturally occurring osteoarthritis of the knee joints that is similar to the condition in humans develops in cynomolgus macaques. Knee joints from 58 young adult (mean age, 7.4 years) female cynomolgus macaques were studied with x-ray densitometry, high-detail radiography, and histology. The animals studied were subjects in a triad designed to examine the effects of the administration of sex steroids on atherosclerosis; except for a control group, the monkeys had been either ovariectomized or treated with sex steroids for 2 years. Therefore, the data were analyzed to determine if these treatments, both of which can influence bone density, affected the severity of osteoarthritis. There was a high prevalence of osteoarthritic lesions, morphologically similar to those seen in humans. Bone changes were more common and severe than cartilage changes and morphologically appeared to precede the cartilage changes. Treatment with testosterone resulted in increased body weight, body mass index, and bone mineral content in the femur and tibia but did not affect the severity of osteoarthritis. These data indicate that naturally occurring osteoarthritis developed in the knee joints of cynomolgus macaques; these animals may be a useful model for the study of osteoarthritis in humans.

Cartilage destruction and osteophytes in instability-induced murine osteoarthritis: role of TGF beta in osteophyte formation?

Osteoarthritis is characterized by focal cartilage destruction and marked formation of osteophytes. We have investigated the possible relationship between site specific occurrence of cartilage damage and osteophytes in the collagenase induced murine osteoarthritis model. The degree of instability of the joint correlated with the amount of cartilage loss. Moreover, cartilage damage in the medial tibial plateau correlated only strongly with the osteophyte at the medial plateau, whereas a similar, site directed trend was noted for lateral damage and lateral osteophytes. A separate study with intraarticular injection of TGF beta 1 in normal murine knee joints revealed that this factor can induce osteophytes at characteristic sites, suggesting a role of endogenous TGF beta in this phenomenon.

Compensation and decompensation of articular cartilage in osteoarthritis

Although contemporary descriptions of the pathology of osteoarthritis emphasize the loss of articular cartilage, in the earlier stages a marked increase in synthetic activity of the chondrocytes can lead to an increase in proteoglycan concentration and commonly, to cartilage hypertrophy. Thus, osteoarthritis exhibits a biphasic course, with an initial "compensatory" phase, during which homeostatic mechanisms may maintain a reasonable articular surface until the second phase, "decompensation" (joint failure), develops. Salicylates interfere with homeostatic repair mechanisms and can markedly truncate the compensatory phase. Polysulfated glycosaminoglycans and tetracyclines prolong the compensatory phase, thereby protecting against joint breakdown.