Structural Consequences of a Partial Anterior Cruciate Ligament Injury on Remaining Joint Integrity: Evidence for Ligament and Bone Changes Over Time in an Ovine Model.

BACKGROUND: Severe injury to the knee joint often results in accelerated posttraumatic osteoarthritis (PTOA). In an ovine knee injury model, altered kinematics and degradation of the cartilage have been observed at 20 and 40 weeks after partial anterior cruciate ligament (ACL) transection (p-ACL Tx) surgery. However, changes to the integrity of the remaining intact intra-articular ligaments (posterolateral [PL] band and posterior cruciate ligament [PCL]) as well as the subchondral bone after anteromedial (AM) band Tx remain to be characterized. PURPOSE: (1) To investigate histological alterations to the remaining intact intra-articular ligaments, the synovium, and the infrapatellar fat pad (IPFP) and (2) to quantify subchondral bone changes at the contact surfaces of the proximal tibia at 20 and 40 weeks after AM band Tx. STUDY DESIGN: Descriptive laboratory study. METHODS: Mature female Suffolk cross sheep were allocated into 3 groups: nonoperative controls (n = 6), 20 weeks after partial ACL transection (p-ACL Tx; n = 5), and 40 weeks after p-ACL Tx (n = 6). Ligament, synovium, and IPFP sections were stained and graded. Tibial subchondral bone microarchitecture was assessed using high-resolution peripheral quantitative computed tomography. RESULTS: p-ACL Tx of the AM band led to significant change in histological scores of the PL band and the PCL at 20 weeks after p-ACL Tx (P = .031 and P = .033, respectively) and 40 weeks after p-ACL Tx (P = .011 and P = .029) as compared with nonoperative controls. Alterations in inflammatory cells and collagen fiber orientation contributed to the greatest extent of the combined histological score in the PL band and PCL. p-ACL Tx did not lead to chronic activation of the synovium or IPFP. Trabecular bone mineral density was strongly inversely correlated with combined gross morphological damage in the top and middle layers of the subchondral bone in the lateral tibial plateau for animals at 40 weeks after p-ACL Tx. CONCLUSION: p-ACL Tx influences the integrity (biology and structure) of remaining intact intra-articular ligaments and bone microarchitecture in a partial knee injury ovine model. CLINICAL RELEVANCE: p-ACL Tx leads to alterations in structural integrity of the remaining intact ligaments and degenerative changes in the trabecular bone mineral density, which may be detrimental to the injured athlete's knee joint in the long term.

Enumeration and Localization of Mesenchymal Progenitor Cells and Macrophages in Synovium from Normal Individuals and Patients with Pre-Osteoarthritis or Clinically Diagnosed Osteoarthritis.

Osteoarthritis (OA) is a degenerative disorder characterized by chondrocyte apoptosis and degeneration of articular cartilage resulting in loss of mobility and pain. Inflammation plays a key role in the development and progression of OA both on the side of apoptosis and repair, while its exact role in pathogenesis has yet to be fully elucidated. Few studies have examined the cellular composition (inflammatory cells and/or progenitor cells) in the synovium of patients with pre-OA (asymptomatic with cartilage damage). Therefore, in the current study, mesenchymal progenitor cells (MPCs) and macrophages were enumerated within normal, pre-OA and OA synovium. No differences were observed between MPCs in normal vs. pre-OA, however, fewer macrophages were observed in pre-OA vs. normal synovium. Osteoarthritic synovium contained greater numbers of both MPCs and macrophages. Interestingly, the localization of MPCs and macrophages was affected by disease severity. In normal and pre-OA synovium, MPCs and macrophages co-localized, while in OA synovium, MPCs and macrophage populations were spatially distinct. Examining the cellular interactions between MPCs and macrophages in synovium may be essential for understanding the role of these cells in the onset and/or pathogenesis of the disease. This study has provided a first step by examining these cell types both spatially and temporally (e.g., disease severity). Further cellular and molecular studies will be needed to determine the functions of these cells in the context of disease and in relation to each other and the joint as a whole.

The infrapatellar fat pad is affected by injury induced inflammation in the rabbit knee: use of dexamethasone to mitigate damage.

OBJECTIVE AND DESIGN: The health of the infrapatellar fat pad (IFP) has been linked to pain, joint inflammation, and the onset of post-traumatic osteoarthritis. Thus, early inflammation effects on the IFP could have long term sequelae on joint integrity. This study was designed to characterize the natural history of the IFP in a model of surgically induced knee injury and inflammation, and to test the efficacy of one intra-articular (IA) administration of dexamethasone (DEX) immediately following surgery. METHODS: An IA bone drill hole injury to the rabbit knee was conducted and immediately treated with DEX (n = 12). Early and late post-surgical time-points were investigated (48 h and 9 weeks) and the outcome measures were analysis of IFP histology, mRNA levels for relevant molecules, and protein levels for a subset of cytokines. Data were analyzed against a surgical control (injury without treatment; n = 12), a surgical sham (capsular incision only; n = 12), and normal control (n = 6). TREATMENT: Single IA injection of DEX (0.5 mg/kg), administered at the completion of surgery. RESULTS: IFPs from injured joints exhibited significantly increased cellularity and early fibrosis at 48 h post surgery. While the histological inflammation from a capsular incision alone resolved, knee injured animals progressed to a significantly more fibrotic IFP by 9 weeks. DEX significantly lowered histological scores at 48 h, but not at the 9 weeks. DEX did not influence mRNA levels for IL-1ß, 6, and 8, however, protein analysis indicated that IL-8 levels were lower in DEX treated joints. DEX resulted in significantly elevated expression of mRNA for MCP-1, leptin, and VEGF. CONCLUSION: One IA administration of a glucocorticoid appears to mitigate the initial inflammation within the joint, but is not sufficient to protect the joint to 9 weeks post-surgery.

Single intra-articular dexamethasone injection immediately post-surgery in a rabbit model mitigates early inflammatory responses and post-traumatic osteoarthritis-like alterations.

Despite surgical reconstruction of the anterior cruciate ligament, a significant number of patients will still develop post-traumatic osteoarthritis (PTOA). Our objective was to determine if mitigating aspects of the acute phase of inflammation following a defined knee surgery with a single administration of a glucocorticoid could prevent the development of PTOA-like changes within an established rabbit model of surgically induced PTOA. An early and late post-surgical time-point was investigated in this study (48 h and 9 weeks post-surgery) in which the following groups were repeated (each n=6, for a total of 24 rabbits per time-point, and 48 rabbits used in the study): control (age/sex matched), sham (arthrotomy), drill injury (arthrotomy+two drill holes to a non-cartilaginous area of the femoral notch), and drill injury+single intra-articular (IA) injection of dexamethasone (DEX). At 48 h post-surgery, DEX treatment significantly lowered the mRNA levels for a subset of pro-inflammatory mediators, and significantly lowered the histological grade. Nine weeks post surgery, DEX treatment significantly lowered the histological scores (presented as effect size) for synovium (3.8), lateral femoral condyle (3.9), and lateral tibial cartilage (5.1) samples. Thus, DEX likely acts to prevent injury induced inflammation that could contribute to subsequent joint damage.

Alterations in Hoffa's fat pad induced by an inflammatory response following idealized anterior cruciate ligament surgery.

OBJECTIVE: To determine whether inflammation following anterior cruciate ligament (ACL) reconstruction leads to long-term pathological changes in the infrapatellar fat pad (IPFP or Hoffa's fat pad) which could compromise the integrity of the knee joint. MATERIALS AND METHODS: Sixteen mature sheep underwent anatomic idealized ACL reconstruction surgery (ACL-R) and were sacrificed at 2 weeks (n = 9) and 20 weeks (n = 7) post-ACL-R. Five additional animals served as unoperated controls. A histological grading protocol was developed to quantify the changes in the IPFP post-injury. mRNA expression levels for key markers of inflammation, angiogenesis and tissue regeneration were assessed by qPCR. RESULTS: The IPFP exhibited altered cellularity and fibrosis at 2 and 20 weeks post-ACL-R. Immunohistochemistry detected macrophage-like cells in the IPFP which were increased at 20 weeks. Specific pro-inflammatory cytokines and IPFP specific adipokines exhibited changes indicating early inflammation mediated alterations. Elevations in CD105 mRNA levels at 2 weeks corroborated the increases in neovascularization observed in the IPFP following injury. CONCLUSIONS: Sustained long-term pathological changes stemming from inflammation are present in IPFP tissue after ACL-R surgery and may compromise the long-term integrity of the knee joint.

Metabolic profiling of synovial fluid in a unilateral ovine model of anterior cruciate ligament reconstruction of the knee suggests biomarkers for early osteoarthritis.

Joint injuries and subsequent osteoarthritis (OA) are the leading causes of chronic joint disease. In this work, we explore the possibility of applying magnetic resonance spectroscopy-based metabolomics to detect host responses to an anterior cruciate ligament (ACL) reconstruction injury in synovial fluid in an ovine model. Using multivariate statistical analysis, we were able to distinguish post-injury joint samples (ACL and sham surgery) from the uninjured control samples, and as well the ACL surgical samples from sham surgery. In all samples there were 65 metabolites quantified, of which six could be suggested as biomarkers for early post-injury degenerative changes in the knee joints: isobutyrate, glucose, hydroxyproline, asparagine, serine, and uridine. Our results raise a cautionary note indicating that surgical interventions into the knee can result in metabolic alterations that need to be distinguished from those caused by the early onset of OA. Our findings illustrate the potential application of metabolomics as a diagnostic and prognostic tool for detection of injuries to the knee joint. The ability to detect a unique pattern of metabolic changes in the synovial fluid of sheep offers the possibility of extending the approach to precision medicine protocols in patient populations in the future.

Clonal analysis of synovial fluid stem cells to characterize and identify stable mesenchymal stromal cell/mesenchymal progenitor cell phenotypes in a porcine model: a cell source with enhanced commitment to the chondrogenic lineage.

BACKGROUND AIMS: Previous studies have demonstrated that porcine synovial membrane stem cells can adhere to a cartilage defect in vivo through the use of a tissue-engineered construct approach. To optimize this model, we wanted to compare effectiveness of tissue sources to determine whether porcine synovial fluid, synovial membrane, bone marrow and skin sources replicate our understanding of synovial fluid mesenchymal stromal cells or mesenchymal progenitor cells from humans both at the population level and the single-cell level. Synovial fluid clones were subsequently isolated and characterized to identify cells with a highly characterized optimal phenotype. METHODS: The chondrogenic, osteogenic and adipogenic potentials were assessed in vitro for skin, bone marrow, adipose, synovial fluid and synovial membrane-derived stem cells. Synovial fluid cells then underwent limiting dilution analysis to isolate single clonal populations. These clonal populations were assessed for proliferative and differentiation potential by use of standardized protocols. RESULTS: Porcine-derived cells demonstrated the same relationship between cell sources as that demonstrated previously for humans, suggesting that the pig may be an ideal preclinical animal model. Synovial fluid cells demonstrated the highest chondrogenic potential that was further characterized, demonstrating the existence of a unique clonal phenotype with enhanced chondrogenic potential. CONCLUSIONS: Porcine stem cells demonstrate characteristics similar to those in human-derived mesenchymal stromal cells from the same sources. Synovial fluid-derived stem cells contain an inherent phenotype that may be optimal for cartilage repair. This must be more fully investigated for future use in the in vivo tissue-engineered construct approach in this physiologically relevant preclinical porcine model.

Normal sheep synovium has similar appearances and constitutive expression of inflammatory cytokines within and between knee joints: a baseline histological and molecular analysis.

Abstract Clinical evidence suggests that synovium can add to adjacent articular cartilage damage, potentially contributing to the development of osteoarthritis (OA). Inflammation of the synovium (synovitis) is dependent on the type of injury sustained, the time after injury and concomitant changes in other joint tissues. To define the role of synovitis in OA development, there is a need for baseline measures that can reliably distinguish synovial inflammation from normal synovium both within and between joints. This study tested the hypothesis that normal synovium from distinct anatomical locations in young and adult sheep is homogeneous with respect to consistently low molecular expression of the inflammatory mediators - tumour necrosis factor alpha (TNF-α) and interleukins (IL) such as IL-1ß, IL-1Ra, IL-6 and IL-8. Additionally, maturation will not influence the expression of these select inflammatory biomarkers. Samples of synovium from four anatomic locations (medial and lateral margins, suprapatellar pouch (patella region), posterior to the posterior cruciate ligament, from each joint of 5 adult and 4 immature animals were graded histologically or analyzed for mRNA expression of inflammatory cytokines. Histologically, no evidence of synovitis was noted although some variance in sub-intimal fibrosis was observed between sample locations in mature sheep. Molecular expression of all inflammatory mediators was low and homogeneously expressed at constitutive levels in all sample locations. These findings confirm the hypothesis that the normal sheep synovium is a homogeneous tissue throughout the joint and establishes the baseline expression levels for several pro-inflammatory mediators in both immature and mature sheep.

Dexamethasone inhibits inflammation and cartilage damage in a new model of post-traumatic osteoarthritis.

Corticosteroids are used in musculoskeletal diseases, and offer patient relief. Injections of corticosteroids are recommended for management of osteoarthritis (OA). Current data have shown the role of corticosteroids in ameliorating pain. We hypothesized that repeated intra-articular injections of high dose dexamethasone would protect the cartilage from damage in a post-traumatic model of OA. Eighteen female New Zealand White rabbits were used. Twelve underwent surgery to induce OA; six of them received intra-articular injections of dexamethasone every 3 days for 3 weeks. The other six rabbits served as operated controls. Six additional rabbits served as non-operated controls. All animals were euthanized 3 weeks post-surgery. Knees were assessed grossly. Cartilage, synovium, and fat pad were assessed histologically. Synovium and fat pad were analyzed with qPCR and Western blots. Surgical controls had cartilage damage which was supressed with dexamethasone. Dexamethasone significantly decreased synovial expression of interleukin-1ß and collagen I, and a trend to decrease synovial matrix metalloproteinase3 expression. There were also significantly lower levels of interleukin-1ß protein with dexamethasone treatment. Dexamethasone significantly decreased fat pad expression of matrix metalloproteinase13, basic fibroblast growth factor, and interleukin8, and a trend to decrease matrix metalloproteinase3 and transforming growth factorß expression. Dexamethasone decreased joint inflammation and joint tissue degradation and was chondroprotective in this unique model of PTOA.

Kinematic and kinetic interactions during normal and ACL-deficient gait: a longitudinal in vivo study.

The interactions between different tissues within the knee joint and between different kinematic DOF and joint flexion during normal gait were investigated. These interactions change following ACL transection, in both short (4 weeks) and long (20 weeks) term. Ten skeletally mature sheep were used in control (N = 5) and experimental (N = 5) groups. The 6-DOF stifle joint motion was first measured during normal gait. The control group were then euthanized and mounted on a unique robotic testing platform for kinetic measurements. The experimental group underwent ACL transection surgery, and kinematics measurements were repeated 4 and 20 weeks post-operatively. The experimental group were then euthanized and underwent kinetic assessment using the robotic system. Results indicated significant couplings between joint flexion vs. abduction and internal tibial rotation, as well as medial, anterior, and superior tibial translations during both normal and ACL-deficient gait. Distinct kinetic interactions were also observed between different tissues within the knee joint. Direct relationships were found between ACL vs. LM/MM, and PCL vs. MCL loads during normal gait; inverse relationships were detected between ACL vs. PCL and PCL vs. LM/MM loads. These kinetic interaction patterns were considerably altered by ACL injury. Significant inter-subject variability in joint kinematics and tissue loading patterns during gait was also observed. This study provides further understanding of the in vivo function of different tissues within the knee joint and their couplings with joint kinematics during normal gait and over time following ACL transection.

Tendon mineralization is accelerated bilaterally and creep of contralateral tendons is increased after unilateral needle injury of murine achilles tendons.

Heterotopic mineralization may result in tendon weakness, but effects on other biomechanical responses have not been reported. We used a needle injury, which accelerates spontaneous mineralization of murine Achilles tendons, to test two hypotheses: that injured tendons would demonstrate altered biomechanical responses; and that unilateral injury would accelerate mineralization bilaterally. Mice underwent left hind (LH) injury (I; n = 11) and were euthanized after 20 weeks along with non-injured controls (C; n = 9). All hind limbs were examined by micro computed tomography followed by biomechanical testing (I = 7 and C = 6). No differences were found in the biomechanical responses of injured tendons compared with controls. However, the right hind (RH) tendons contralateral to the LH injury exhibited greater static creep strain and total creep strain compared with those LH tendons (p ≤ 0.045) and RH tendons from controls (p ≤ 0.043). RH limb lesions of injured mice were three times larger compared with controls (p = 0.030). Therefore, despite extensive mineralization, changes to the responses we measured were limited or absent 20 weeks postinjury. These results also suggest that bilateral occurrence should be considered where tendon mineralization is identified clinically. This experimental system may be useful to study the mechanisms of bilateral new bone formation in tendinopathy and other conditions.

Characterization of proteoglycan 4 and hyaluronan composition and lubrication function of ovine synovial fluid following knee surgery.

The objective of this study was to determine changes in (1) proteoglycan 4 (PRG4) and hyaluronan (HA) concentration, (2) HA molecular weight (MW) distribution, and (3) cartilage boundary lubricating ability of synovial fluid (SF) from surgical sham (SHAM), anterior cruciate ligament (ACL)/medial collateral ligament (MCL) transection, and lateral meniscectomy (MEN) in a post-knee surgery ovine model. Ovine SF (oSF) was collected at euthanization 20 weeks after surgery, with the contralateral joint serving as the non-operative control. PRG4 and HA concentration in oSF was measured by sandwich enzyme-linked immunosorbent assay, and HA MW distribution by agarose gel electrophoresis. Cartilage boundary lubricating ability of oSF was measured by a cartilage-cartilage friction test. PRG4 and HA concentration in SHAM, ACL/MCL, and MEN oSF were similar in comparison to the contralateral control (CTRL) oSF. The HA MW distribution in the operated oSF for all ranges were similar to the respective CTRL oSF. The kinetic coefficients of friction in operated and CTRL oSF were similar in all groups, and were significantly lower than saline. These results indicate oSF lubricant composition and function at 20 weeks post-knee surgery were similar to contralateral CTRL, and suggest earlier time points post surgery warrant further investigation.

Effect of calcium on the proliferation kinetics of synovium-derived mesenchymal stromal cells.

BACKGROUND AIMS: Synovium-derived mesenchymal stromal cells (S-MSCs) have potential utility in clinical joint repair applications. However, their scarcity in tissues means S-MSCs cannot be isolated in large quantities and need to be expanded in culture. Because synovial tissues in vivo are exposed to higher calcium (Ca(2+)) levels than typically found in culture media, this study examined the impact of Ca(2+) supplementation on the rate of S-MSC proliferation in culture. METHODS: S-MSCs were serially cultured with or without Ca(2+) supplementation. The effect of inhibiting Ca(2+) uptake was assessed using Ca(2+) channel blockers. After extended exposure to elevated Ca(2+) concentrations, S-MSCs were characterized by evaluating surface marker profiles, performing reverse transcriptase quantitative polymerase chain reaction and carrying out tri-lineage differentiation assays. RESULTS: Elevated Ca(2+) concentrations resulted in enhanced S-MSC proliferation. Peak growth occurred at 5.0 mmol/L Ca(2+), with an average fold increase of 4.52 ± 0.65 per passage over 8 passages compared with 2.03 ± 0.46 in un-supplemented medium. Proliferation was inhibited by Ca(2+) channel blockers. Ca(2+)-supplemented cells showed enhanced capacity toward osteogenesis (17.82 ± 4.21 µg Ca(2+) deposited/sample vs. 12.70 ± 2.11 µg Ca(2+) deposited/sample) and adipogenesis (0.47 ± 0.04 mg oil red O/sample vs. 0.352 ± 0.005 mg oil red O/sample) and retained their capacity to undergo chondrogenesis (1.37 ± 0.07 µg glycosaminoglycan/pellet vs. 1.33 ± 0.17 µg glycosaminoglycan/pellet). S-MSCs cultured in elevated Ca(2+) expressed enhanced messenger RNA levels for SOX-9 and peroxisome proliferator activated receptor gamma and depressed levels for collagen I. CONCLUSIONS: S-MSC sensitivity to Ca(2+) has not been reported previously. These findings indicate that S-MSC population expansion rates may be up-regulated by Ca(2+) supplementation without compromising defining cell characteristics. This study exemplifies the need to consider medium composition when culturing stem cells.

New surgical model of post-traumatic osteoarthritis: isolated intra-articular bone injury in the rabbit.

Osteoarthritis (OA) is a leading cause of disability worldwide. We hypothesized that inflammation following isolated intra-articular bone injury can stimulate post-traumatic OA and developed a rabbit model to test that concept. Sixty female New Zealand White Rabbits were used. Twenty-six experimental animals had two holes drilled into their right femoral-notch, 18 rabbits had sham surgery, and 16 were un-operated controls. Rabbits were euthanized in subgroups at 72 h, 3, 6, 9, and 52 weeks. Knees were assessed grossly and tissues collected. Cartilage and synovium were analyzed with histology and qPCR and subgroups compared statistically. All surgical joints showed gross and histological (modified Mankin score) cartilage damage after surgery, with experimentals worsening with time (p < 0.05). Cartilage qPCR showed fivefold increases in TGFß (p < 0.05) expression at 72 h and 3 weeks with sixfold increases in MMP13 (p < 0.025) expression at 72 h. By 6 weeks, expression of these markers was similar to baseline levels. Synovial membrane thickening with increased cellularity was seen at both 9 and 52 weeks (p < 0.05). Short-term synovial inflammatory marker (IL-1ß, IL-Ra, IL-6, and IL-8) expression was three- to fourfold increase in experimentals at 72 h (p < 0.01) returning to baseline levels by 3 weeks. Intra-articular bone injury creates early joint inflammation with some chronic synovial changes and progressive cartilage damage consistent with OA in adult rabbits. This model provides an exciting new avenue to potentially explore some relevant inflammatory drivers of OA without major mechanical variables.

Osteoarthritis develops in the operated joint of an ovine model following ACL reconstruction with immediate anatomic reattachment of the native ACL.

We tested the hypothesis that immediate reattachment of the native anterior cruciate ligament (ACL) can prevent kinematic changes and the development of osteoarthritis (OA). Five sheep underwent anatomic unilateral ACL reconstruction (ACL-R). Animals from a previous study served as sham (n = 7) or non-operated (n = 17) controls. At 4 points of walking gait, 6 degrees of freedom stifle joint kinematics of ACL-R animals were compared with sham controls at 4 and 20 weeks post-surgery. Gross cartilage, bone, and meniscal changes were graded at euthanasia; paired and differential scores were compared. Inter-animal differences were noted in all groups. Of 48 points of gait comparison between ACL-R and sham operated groups, 42 points showed no difference (p > 0.05). Of the six significant differences (p < 0.05), internal rotation in ACL-R animals accounted for three. At 20 weeks, differential scores showed that sham operated joints were morphologically indistinguishable from non-operated controls (p ≥ 0.129) while ACL-R joints had significantly higher combined cartilage and osteophyte scores than those controls (p ≤ 0.003). This method of ACL reconstruction in sheep did not restore normal walking gait kinematics completely and allowed some OA to develop in operated joints. OA may result from relatively subtle mechanical abnormalities, apparently more so in some individuals than others.

Heterotopic mineralization (ossification or calcification) in tendinopathy or following surgical tendon trauma.

Heterotopic tendon mineralization (ossification or calcification), which may be a feature of tendinopathy or which may develop following surgical trauma (repair or graft harvest), has not received much attention. The purpose of this article is to review the prevalence, mechanisms and consequences of heterotopic tendon mineralization and to identify the gaps in our current understanding. We focus on endochondral heterotopic ossification and draw on knowledge of the mechanisms of this process in other tissues and conditions. Finally, we introduce a novel murine Achilles tendon needle injury model, which will enable us to further study the mechanisms and biomechanical consequences of tendon mineralization.

Carrageenan-induced transient inflammation in a rabbit knee model: molecular changes consistent with an early osteoarthritis phenotype.

OBJECTIVE: Inflammation following a knee injury is one of the factors associated with initiation of cartilage degeneration leading to osteoarthritis (OA). The hypothesis tested was that inflammation results in elevated expression of proteinases implicated in OA. METHODS: Mature female rabbits received a single carrageenan injection to the right hind knee and the left knee served as the control. Five animals were killed at time points of 1, 2 and 4 weeks. The synovium and cartilage from both knees were collected and analysed for specific mRNA levels. RESULTS: Interleukin (IL)-1ß and IL-6 mRNA levels peaked at 2 weeks and returned to normal levels in tissues by 4 weeks post-carrageenan treatment. Matrix metalloproteinase (MMP)-13, MMP-1, MMP-3 and cathepsin K followed the trend set by the inflammatory cytokines. Both synovium and cartilage tissues exhibited similar patterns of molecular expression, with cartilage from the tibial plateau responding more strongly than the femoral condyles. CONCLUSIONS: The acute inflammatory milieu controls the transient expression of many degradative proteinases in the knee. However, a single acute exposure to inflammation in the rabbit knee is insufficient to create a chronic inflammatory environment and other complementary factors, such as persistent mechanical instability and/or injury, may contribute to the establishment of OA.

Investigating the potential value of individual parameters of histological grading systems in a sheep model of cartilage damage: the Modified Mankin method.

A total histological grade does not necessarily distinguish between different manifestations of cartilage damage or degeneration. An accurate and reliable histological assessment method is required to separate normal and pathological tissue within a joint during treatment of degenerative joint conditions and to sub-classify the latter in meaningful ways. The Modified Mankin method may be adaptable for this purpose. We investigated how much detail may be lost by assigning one composite score/grade to represent different degenerative components of the osteoarthritic condition. We used four ovine injury models (sham surgery, anterior cruciate ligament/medial collateral ligament instability, simulated anatomic anterior cruciate ligament reconstruction and meniscal removal) to induce different degrees and potentially 'types' (mechanisms) of osteoarthritis. Articular cartilage was systematically harvested, prepared for histological examination and graded in a blinded fashion using a Modified Mankin grading method. Results showed that the possible permutations of cartilage damage were significant and far more varied than the current intended use that histological grading systems allow. Of 1352 cartilage specimens graded, 234 different manifestations of potential histological damage were observed across 23 potential individual grades of the Modified Mankin grading method. The results presented here show that current composite histological grading may contain additional information that could potentially discern different stages or mechanisms of cartilage damage and degeneration in a sheep model. This approach may be applicable to other grading systems.

Ovine synovial membrane-derived mesenchymal progenitor cells retain the phenotype of the original tissue that was exposed to in-vivo inflammation: evidence for a suppressed chondrogenic differentiation potential of the cells.

BACKGROUND: The purpose of this study was to characterize the effect of post-surgery joint inflammation on the chondrogenic differentiation capacity of mesenchymal progenitor cells (MPCs) derived from the synovial membrane (SM). METHODS: Six Suffolk-cross sheep were subjected to experimental anterior cruciate ligament (ACL) core surgeries. After they were killed 2 weeks after surgery, the volume of synovial fluid in the knees was measured and SM was collected for mRNA extraction and cell isolation. Cells were propagated and used for lineage-specific differentiation assays using cell pellet cultures and mRNA extraction. Chondrogenic differentiation assays in the presence of exogenous interleukin-1ß (IL-1ß) were also performed. RESULTS: The volume of synovial fluid from the operated knees was significantly greater than from the contralateral knees. Quantitative RT-PCR revealed that mRNA levels for IL-1ß and matrix metalloproteinases-3 and -13 in SM from the operated knees were significantly higher than those from the contralateral knees. The size of MPC pellets from operated knees (opMPC) cultured in chondrogenic medium were significantly smaller than the corresponding pellets generated with MPCs from contralateral knees (conMPC). Addition of 1-100 ng/ml IL-1ß significantly suppressed the resultant size of chondrogenic cell pellets from normal ovine SM-MPC. DISCUSSION: From these results, we conclude that cells from SM exposed to post-surgical inflammation are compromised by the inflammatory environment and that IL-1ß can inhibit the latent chondrogenic potential of normal MPCs. This suggests that if MPCs from injured joints do contribute to cartilage repair, their endogenous repair potential may become compromised by such post-injury joint inflammation.

Functional outcomes for 2 years comparing hip resurfacing and total hip arthroplasty.

This prospective observational study of 499 patients with hip resurfacing and 255 patients with total hip arthroplasty compared outcomes for 2 years. We used propensity scores to identify matched cohorts of 118 patients with hip resurfacing and 118 patients with total hip arthroplasty. We used these cohorts to compare improvements in the Western Ontario and McMaster University (WOMAC) osteoarthritis index and Medical Outcomes Short-Form 36 physical function component (SF-36 PF) scores at 3 months and at 1 and 2 years postsurgery. Both groups demonstrated significant improvements from baseline in WOMAC and SF-36 PF. Improvements in SF-36 PF were greater for patients with hip resurfacing than for patients with total hip arthroplasty 1 and 2 years postsurgery; improvements in WOMAC were similar for both groups. The clinical significance of this observation needs further investigation.