Importance of subchondral bone to articular cartilage in health and disease

Orthotic considerations for dense connective tissue and articular cartilage--the need for optimal movement and stress

Orthotic intervention is an essential component of hand rehabilitation, addressing biological factors that affect activity and participation. Functional, pain-free joint mobility requires skeletal stability, healthy articular cartilage, and appropriate extensibility of periarticular dense connective tissues (DCTs). This article addresses basic science underlying clinical reasoning when considering orthoses to maintain or restore structural integrity, mobility and function of DCT structures, and articular cartilage. However, these tissues often have different and sometimes conflicting requirements for the maintenance and restoration of integrity and health. The duration of immobilization, especially at end range, should be carefully considered, as it impairs nutrition of tissues and adversely compresses articular cartilage, causing injury that may not be reversible. Immobilization also reduces extensibility of DCT. Thus, an intermittent orthotic wearing schedule is suggested, allowing movement wherever possible to promote tissue health. To optimize benefits and minimize harmful effects of orthotic intervention, further research on physiological responses of human tissues to immobilization and tension is needed.

Elevated cross-talk between subchondral bone and cartilage in osteoarthritic joints

Osteoarthritis (OA) is a degenerative joint disease and one of the leading causes of disability in the United States and across the world. As a disease of the whole joint, OA exhibits a complicated etiology with risk factors including, but not limited to, ageing, altered joint loading, and injury. Subchondral bone is hypothesized to be involved in OA development. However, direct evidence supporting this is lacking. We previously detected measurable transport of solute across the mineralized calcified cartilage in normal joints, suggesting a potential cross-talk between subchondral bone and cartilage. Whether this cross-talk exists in OA has not been established yet. Using two models that induced OA by either ageing or surgery (destabilization of medial meniscus, DMM), we tested the hypothesis that increased cross-talk occurs in OA. We quantified the diffusivity of sodium fluorescein (mol. wt. 376Da), a marker of small-sized signaling molecules, within calcified joint matrix using our newly developed fluorescence loss induced by photobleaching (FLIP) method. Tracer diffusivity was found to be 0.30±0.17 and 0.33±0.20μm(2)/s within the calcified cartilage and 0.12±0.04 and 0.07±0.03μm(2)/s across the osteochondral interface in the aged (20-24-month-old, n=4) and DMM OA joints (5-month-old, n=5), respectively, which were comparable to the control values for the contralateral non-operated joints in the DMM mice (0.48±0.13 and 0.12±0.06μm(2)/s). Although we did not detect significant changes in tissue matrix permeability in OA joints, we found i) an increased number of vessels invading the calcified cartilage (and sometimes approaching the tidemark) in the aged (+100%) and DMM (+50%) joints relative to the normal age controls; and ii) a 60% thinning of the subchondral bone and calcified cartilage layers in the aged joints (with no significant changes detected in the DMM joints). These results suggested that the capacity for cross-talk between subchondral bone and articular cartilage could be elevated in OA. Further studies are needed to identify the direction of the cross-talk, the signaling molecules involved, and to test whether subchondral bone initiates OA development and could serve as a pharmaceutical target for OA treatment. This article is part of a Special Issue entitled "Osteoarthritis".

Prediction of progression of radiographic knee osteoarthritis using tibial trabecular bone texture

OBJECTIVE

To develop a system for predicting the progression of radiographic knee osteoarthritis (OA) using tibial trabecular bone texture.

METHODS

We studied 203 knees with (n = 68) or without (n = 135) radiographic tibiofemoral OA in 105 subjects (90 men and 15 women with a mean age of 54 years) in whom 2 sets of knee radiographs were obtained 4 years apart. We determined medial and lateral compartment tibial trabecular bone texture using an automated region selection method. Three texture parameters were calculated: roughness, degree of anisotropy, and direction of anisotropy based on a signature dissimilarity measure method. We evaluated tibiofemoral OA progression using a radiographic semiquantitative outcome: an increase in the medial joint space narrowing (JSN) grade. We examined the predictive ability of trabecular bone texture in knees with and those without preexisting radiographic OA, with adjustment for age, sex, and body mass index, using logistic regression (generalized estimating equations) and receiver operating characteristic curves.

RESULTS

The prediction of increased medial JSN in knees with or without preexisting radiographic OA was the most accurate for medial trabecular bone texture; the area under the curve (AUC) was 0.77 and 0.75, respectively. For lateral trabecular bone texture, the AUC was 0.71 in knees with preexisting OA and 0.72 in knees without preexisting OA.

CONCLUSION

We have developed a system, based on analyzing tibial trabecular bone texture, which yields good prediction of loss of tibiofemoral joint space. The predictive ability of the system needs to be further validated.

Analysis of osteoarthritis in a mouse model of the progeroid human DNA repair syndrome trichothiodystrophy

The increasing average age in developed societies is paralleled by an increase in the prevalence of many age-related diseases such as osteoarthritis (OA), which is characterized by deformation of the joint due to cartilage damage and increased turnover of subchondral bone. Consequently, deficiency in DNA repair, often associated with premature aging, may lead to increased pathology of these two tissues. To examine this possibility, we analyzed the bone and cartilage phenotype of male and female knee joints derived from 52- to 104-week-old WT C57Bl/6 and trichothiodystrophy (TTD) mice, who carry a defect in the nucleotide excision repair pathway and display many features of premature aging. Using micro-CT, we found bone loss in all groups of 104-week-old compared to 52-week-old mice. Cartilage damage was mild to moderate in all mice. Surprisingly, female TTD mice had less cartilage damage, proteoglycan depletion, and osteophytosis compared to WT controls. OA severity in males did not significantly differ between genotypes, although TTD males had less osteophytosis. These results indicate that in premature aging TTD mice age-related changes in cartilage were not more severe compared to WT mice, in striking contrast with bone and many other tissues. This segmental aging character may be explained by a difference in vasculature and thereby oxygen load in cartilage and bone. Alternatively, a difference in impact of an anti-aging response, previously found to be triggered by accumulation of DNA damage, might help explain why female mice were protected from cartilage damage. These findings underline the exceptional segmental nature of progeroid conditions and provide an explanation for pro- and anti-aging features occurring in the same individual.

Subchondral bone remodeling is related to clinical improvement after joint distraction in the treatment of ankle osteoarthritis

OBJECTIVE

In osteoarthritis (OA), subchondral bone changes alter the joint's mechanical environment and potentially influence progression of cartilage degeneration. Joint distraction as a treatment for OA has been shown to provide pain relief and functional improvement through mechanisms that are not well understood. This study evaluated whether subchondral bone remodeling was associated with clinical improvement in OA patients treated with joint distraction.

METHOD

Twenty-six patients with advanced post-traumatic ankle OA were treated with joint distraction for 3 months using an Ilizarov frame in a referral center. Primary outcome measure was bone density change analyzed on computed tomography (CT) scans. Longitudinal, manually segmented CT datasets for a given patient were brought into a common spatial alignment. Changes in bone density (Hounsfield Units (HU), relative to baseline) were calculated at the weight-bearing region, extending subchondrally to a depth of 8mm. Clinical outcome was assessed using the ankle OA scale.

RESULTS

Baseline scans demonstrated subchondral sclerosis with local cysts. At 1 and 2 years of follow-up, an overall decrease in bone density (-23% and -21%, respectively) was observed. Interestingly, density in originally low-density (cystic) areas increased. Joint distraction resulted in a decrease in pain (from 60 to 35, scale of 100) and functional deficit (from 67 to 36). Improvements in clinical outcomes were best correlated with disappearance of low-density (cystic) areas (r=0.69).

CONCLUSIONS

Treatment of advanced post-traumatic ankle OA with 3 months of joint distraction resulted in bone density normalization that was associated with clinical improvement.

Multimodal imaging demonstrates concomitant changes in bone and cartilage after destabilisation of the medial meniscus and increased joint laxity

OBJECTIVE

Alterations in joint mechanics can cause osteoarthritis, which results in degeneration of both cartilage and bone tissue. The objective of this work is to measure changes in the laxity of the mouse knee joint after destabilisation of the medial meniscus (DMM) and to visualise and quantify the resulting three-dimensional changes in the bone and cartilage.

METHODS

Skeletally mature C57Bl6 male mice underwent DMM surgery in the right leg. Animals were sacrificed immediately 0 weeks (n=15), 4 weeks (n=11) or 8 weeks (n=12) after surgery. For the 0-week group, the anterior-posterior (AP) and varus-valgus laxity of the DMM limb were compared to the contralateral limb. For 4 and 8-week groups, tibiae were scanned with micro-computed tomography (μCT) to quantify and visualise bone changes and with confocal scanning laser microscopy (CSLM) to measure changes in cartilage.

RESULTS

Laxity testing measured an increase in AP range of motion, particularly in the anterior direction. The DMM limbs showed a decrease in epiphyseal trabecular bone at 8 weeks and a decrease in cartilage volume, primarily on the posterior medial plateau, compared to the contralateral limb. Significant bone remodelling was observed at the periphery of the joint and in severe cases, osteolysis extended through the growth plate.

CONCLUSION

Multimodal imaging allowed quantifiable 3D assessment of bone and cartilage and indicated extensive changes in the tissues. The increase in AP laxity suggests that DMM surgery redistributes loading posteriorly on the medial plateau, resulting in bone and cartilage loss primarily on the posterior portion of the medial plateau.

Magnetic resonance imaging evaluation of weight-bearing subchondral trabecular bone in the knee

OBJECTIVE

Changes in weight-bearing subchondral bone are central to osteoarthritis (OA) pathophysiology. Using MR, knee trabecular bone is typically assessed in the axial plane, however partial volume artifacts limit the utility of MR methods for femorotibial compartment subchondral bone analysis. Oblique-coronal acquisitions may enable direct visualization and quantification of the expected increases in femorotibial subchondral trabecular bone.

METHODS

MR acquisition parameters were first optimized at 3 Tesla. Thereafter, five volunteers underwent axial and coronal exams of their right knee. Each image series was evaluated visually and quantitatively. An anatomically standardized region-of-interest was placed on both the medial and lateral tibial plateaus of all coronal slices containing subchondral bone. Mean and maximum marrow signal was measured, and "bone signal" was calculated.

RESULTS

The MR acquisition had spatial resolution 0.2 × 0.2 × 1.0 mm and acquisition time 10.5 min. The two asymptomatic knees exhibited prominent horizontal trabeculae in the tibial subchondral bone, while the one confirmed OA knee had disorganized subchondral bone and absent horizontal trabeculae. The subchondral bone signal was 8-14% higher in both compartments of the OA knee than the asymptomatic knees.

CONCLUSION

The weight-bearing femorotibial subchondral trabecular bone can be directly visualized and changes quantified in the coronal-oblique plane. Qualitative and quantitative assessments can be performed using the resultant images and may provide a method to discriminate between the healthy and OA knees. These methods should enable a quantitative evaluation of the role of weight-bearing subchondral bone in the natural history of knee OA to be undertaken.

The bone-cartilage unit in osteoarthritis

Osteoarthritis (OA) refers to a group of mechanically-induced joint disorders to which both genetic and acquired factors contribute. Current pathophysiological concepts focus on OA as a disease of the whole joint. Within these models, the functional unit formed by the articular cartilage and the subchondral bone seems to be of particular interest. Cartilage and bone receive and dissipate the stress associated with movement and loading, and are therefore continuously challenged biomechanically. Recent data support the view that cartilage and bone can communicate over the calcified tissue barrier; vessels reach out from bone into the cartilage zone, patches of uncalcified cartilage are in contact with bone, and microcracks and fissures further facilitate transfer of molecules. Several molecular signaling pathways such as bone morphogenetic proteins and Wnts are hypothesized to have a role in OA and can activate cellular and molecular processes in both cartilage and bone cells. In addition, intracellular activation of different kinase cascades seems to be involved in the molecular crosstalk between cartilage and bone cells. Further research is required to integrate these different elements into a comprehensive approach that will increase our understanding of the disease processes in OA, and that could lead to the development of specific therapeutics or treatment strategies.

Similarities and discrepancies in subchondral bone structure in two differently induced canine models of osteoarthritis

In osteoarthritis (OA), cartilage degradation is accompanied by subchondral bone changes. The pathogenesis and physiology of bone changes in OA are still unclear. The changes in subchondral bone architecture and cartilage damage were compared in differently induced experimental models of OA. Experimental OA was induced bilaterally by anterior cruciate ligament transection (ACLT) or by cartilage trauma (Groove model); bilateral sham surgery served as control. Lysylpyridinoline (LP, bone resorption) and C-telopeptide of type II collagen (CTX-II, cartilage breakdown) were measured over time. At 20 weeks after surgery, the subchondral cortical plate and trabecular bone of the tibia were analyzed by micro-computed tomography (microCT) and cartilage degeneration was analyzed histologically and biochemically. In both models, cartilage degeneration and cortical subchondral plate thinning were present. CTX-II levels were elevated over time in both models. Subchondral trabecular bone changes were observed only in the ACLT model, not in the Groove model. Correspondingly, LP levels were elevated over time in the ACLT model and not in the Groove model. Interestingly, the trabecular bone changes in the ACLT model were extended to the metaphyseal area. The early decrease in plate thickness, present in both models, as was cartilage damage, suggests that plate thinning is a phenomenon that is intrinsic to the process of OA independent of the cause/induction of OA. On the other hand, trabecular changes in subchondral and metaphyseal bone are not part of a common pathway of OA development and may be induced biomechanically in the destabilized and less loaded ACLT joint.

Targeting subchondral bone for treating osteoarthritis: what is the evidence?

Over the past few decades, significant progress has been made with respect to new concepts about the pathogenesis of osteoarthritis (OA). This article summarises some of the knowledge we have today on the involvement of the subchondral bone in OA. It provides substantial evidence that changes in the metabolism of the subchondral bone are an integral part of the OA disease process and that these alterations are not merely secondary manifestations, but are part of a more active component of the disease. Thus, a strong rationale exists for therapeutic approaches that target subchondral bone resorption and/or formation, and data evaluating the drugs targeting bone remodelling raise the hope that new treatment options for OA may become available.

The basic science of the subchondral bone

In the past decades, considerable efforts have been made to propose experimental and clinical treatments for articular cartilage defects. Yet, the problem of cartilage defects extending deep in the underlying subchondral bone has not received adequate attention. A profound understanding of the basic anatomic aspects of this particular site, together with the pathophysiology of diseases affecting the subchondral bone is the key to develop targeted and effective therapeutic strategies to treat osteochondral defects. The subchondral bone consists of the subchondral bone plate and the subarticular spongiosa. It is separated by the cement line from the calcified zone of the articular cartilage. A variable anatomy is characteristic for the subchondral region, reflected in differences in thickness, density, and composition of the subchondral bone plate, contour of the tidemark and cement line, and the number and types of channels penetrating into the calcified cartilage. This review aims at providing insights into the anatomy, morphology, and pathology of the subchondral bone. Individual diseases affecting the subchondral bone, such as traumatic osteochondral defects, osteochondritis dissecans, osteonecrosis, and osteoarthritis are also discussed. A better knowledge of the basic science of the subchondral region, together with additional investigations in animal models and patients may translate into improved therapies for articular cartilage defects that arise from or extend into the subchondral bone.

Vascularized osteochondral graft from the medial femoral trochlea: anatomical study and clinical perspectives

PURPOSE

Few donor sites for vascularized reconstruction of convex joint surfaces have been described. We studied the feasibility of a convex vascularized osteochondral graft harvested from the medial femoral condyle and trochlea, on an anatomical and practical point of view.

METHODS

An injection-corrosion technique was used on 16 fresh cadaver specimens, and completed by a modified Spalteholz clearing. The extra- and intraosseous vascularization of the medial femoral condyle was systematized and the luminal diameter of the arteries was microscopically measured. Radii of curvature of the medial trochlea and of the carpal bones were measured on arthro-CT-scanner reconstructed images.

RESULTS

The periosteal vessels of the medial condyle are responsible for the whole peripheral intraosseous vascularization, without any watershed region. They are fed by the articular branch of the descending genicular artery and/or the superomedial genicular artery. Several constant vascular axes can be found, and may serve as a pedicle for a vascularized osteochondral graft from the medial femoral trochlea. The radii of curvature of this graft do fit those of the proximal carpal row. A simple surgical approach is suggested.

CONCLUSIONS

A vascularized graft harvested on the medial femoral trochlea is a technically feasible procedure that could represent a new reconstructive tool for convex joint surfaces. Osteonecrosis of the proximal pole of the scaphoid or Kienböck's disease are among several situations where such a graft could be beneficial.

Local leptin production in osteoarthritis subchondral osteoblasts may be responsible for their abnormal phenotypic expression

INTRODUCTION

Leptin is a peptide hormone with a role in bone metabolism and rheumatic diseases. The subchondral bone tissue plays a prominent role in the pathophysiology of osteoarthritis (OA), related to abnormal osteoblast (Ob) differentiation. Although leptin promotes the differentiation of Ob under normal conditions, a role for leptin in OA Ob has not been demonstrated. Here we determined if endogenous leptin produced by OA Ob could be responsible for the expression of the abnormal phenotypic biomarkers observed in OA Ob.

METHODS

We prepared primary normal and OA Ob from subchondral bone of tibial plateaus removed for knee surgery of OA patients or at autopsy. We determined the production of leptin and of the long, biologically active, leptin receptors (OB-Rb) using reverse transcriptase-polymerase chain reaction, ELISA and Western blot analysis. We determined the effect of leptin on cell proliferation by BrdU incorporation and 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays, and we determined by Western blot analysis phospho 42/44 MAPK (p42/44 Erk1/2) and phospho p38 levels. We then determined the effect of the addition of exogenous leptin, leptin receptor antagonists, inhibitors of leptin signaling or siRNA techniques on the phenotypic features of OA Ob. Phenotypic features of Ob were determined by measuring alkaline phosphatase activity (ALP), osteocalcin release (OC), collagen type 1 production (CICP) and of Transforming Growth Factor-beta1 (TGF-beta1).

RESULTS

Leptin expression was increased approximately five-fold and protein levels approximately two-fold in OA Ob compared to normal. Leptin stimulated its own expression and the expression of OB-Rb in OA Ob. Leptin dose-dependently stimulated cell proliferation of OA Ob and also increased phosphorylated p42/44 Erk1/2 and p38 levels. Inactivating antibodies against leptin reduced ALP, OC, CICP and TGF-beta1 levels in OA Ob. Tyrphostin (AG490) and piceatannol (Pce), inhibitors of leptin signaling, reproduced this effect. Inhibition of endogenous leptin levels using siRNA for leptin or inhibiting leptin signaling using siRNA for OB-Rb expression both reduced ALP and OC about 60%. Exogenous leptin addition stimulated ALP, yet this failed to further increase OC or CICP.

CONCLUSIONS

These results suggest that abnormal production of leptin by OA Ob could be responsible, in part, for the elevated levels of ALP, OC, collagen type 1 and TGF-beta1 observed in these cells compared to normal. Leptin also stimulated cell proliferation, and Erk 1/2 and p38 signaling. Taken together, these data suggest leptin could contribute to abnormal osteoblast function in OA.

ADAMTS5-/- mice have less subchondral bone changes after induction of osteoarthritis through surgical instability: implications for a link between cartilage and subchondral bone changes

OBJECTIVE

Osteoarthritis (OA) is characterized by damaged articular cartilage and changes in subchondral bone. Previous work demonstrated aggrecanase-2 deficient (ADAMTS5-/-) mice to be protected from cartilage damage induced by joint instability. This study analyzed whether this protective effect on cartilage is also reflected in the subchondral bone structure.

METHODS

Right knee joints from 10-week old male wild type (WT) and ADAMTS5-/- mice received transection of the medial meniscotibial ligament to induce OA, whereas left knees were left unoperated. After 8 weeks knee joints were scanned by micro-CT. The proximal tibia was selected for further analysis. Histology was performed to evaluate cartilage damage and osteoclast presence.

RESULTS

ADAMTS5-/- joints had a significantly thinner subchondral plate and less epiphyseal trabecular bone compared to WT joints. Histology confirmed previous findings that ADAMTS5-/- mice have significantly less cartilage damage than WT in the instability-induced OA model. Although the subchondral bone plate became significantly thicker at the medial tibial plateau in operated joints of both genotypes, the percentage increase was significantly smaller in ADAMTS5-/- mice (WT: 20.7+/-4.7%, ADAMTS5-/-: 8.3+/-1.2% compared to the left unoperated control joint). In ADAMTS5-/- animals a significant decrease was found in both Oc.N./BS and Oc.S./BS. Finally, in WT but not in ADAMTS5-/- mice a significant correlation was found between medial subchondral bone plate thickness and cartilage damage at the medial tibial plateau.

CONCLUSION

ADAMTS5-/- joints that were protected from cartilage damage showed minor changes in the subchondral bone structure, in contrast to WT mice where substantial changes were found. This finding suggests links between the process of cartilage damage and subchondral bone changes in instability-induced OA.

Chondrocyte survival in articular cartilage

The aim of this study was to determine whether subchondral bone influences in situ chondrocyte survival. Bovine explants were cultured in serum-free media over seven days with subchondral bone excised from articular cartilage (group A), subchondral bone left attached to articular cartilage (group B), and subchondral bone excised but co-cultured with articular cartilage (group C). Using confocal laser scanning microscopy, fluorescent probes and biochemical assays, in situ chondrocyte viability and relevant biophysical parameters (cartilage thickness, cell density, culture medium composition) were quantified over time (2.5 hours vs seven days). There was a significant increase in chondrocyte death over seven days, primarily within the superficial zone, for group A, but not for groups B or C (p < 0.05). There was no significant difference in cartilage thickness or cell density between groups A, B and C (p > 0.05). Increases in the protein content of the culture media for groups B and C, but not for group A, suggested that the release of soluble factors from subchondral bone may have influenced chondrocyte survival. In conclusion, subchondral bone significantly influenced chondrocyte survival in articular cartilage during explant culture.

The extrapolation of bone-cartilage interactions in vitro to the clinical situation must be made with caution, but the findings from these experiments suggest that future investigation into in vivo mechanisms of articular cartilage survival and degradation must consider the interactions of cartilage with subchondral bone.

Multinuclear NMR and microscopic MRI studies of the articular cartilage nanostructure

Studies of the structure of articular cartilage by a number of NMR spectroscopic and imaging techniques are reviewed. Advantage is taken of the fact that the NMR investigations can be done non-invasively on the intact tissue and do not require sectioning, slicing and decalcification as in the case of electron microscopy. The different contributions to 1H T2 relaxation are described and it is pointed out that ignoring the biexponential behavior of the transverse relaxation can lead to serious errors in the proton density measurements and the T2 characterization of the articular cartilage. A way to slow the transverse relaxation and to minimize its angular dependence by the use of dipolar echo is described. 2H double quantum filtered spectroscopic MRI is a powerful technique to follow the orientation and density of the collagen fibers in articular cartilage. Using this technique, it was found that attachment of the cartilage to the bone has a stabilizing effect on the collagen matrix and that the hydroxyapatite in the calcified zone resides near the collagen fibers but does not contribute to their order. In response to mechanical pressure, it was shown that the collagen fibers flatten near the surface and become crimped near the bone. A number of NMR techniques have been described for the measurement of 23Na residual quadrupolar interaction. It was found that this can serve as a very sensitive measure of the depletion of proteoglycans. Finally, a combination of the above techniques was used to study a maturation of articular cartilage in pigs. The increased order and density of the collagen fibers from newborn to adult pigs revealed itself as a shortening of T2 and significant increase of the residual quadrupolar interaction of both 2H and 23Na nuclei.

The effect of decalcification on the microstructure of articular cartilage assessed by 2H double quantum filtered spectroscopic MRI

2H quadrupolar splitting of deuterated water molecules is a sensitive measure of the order and density of the collagen fibers in articular cartilage. In the calcified zone, near the bone, two pairs of quadrupolar split satellites were previously observed. To examine whether the large splitting observed originates from the presence of calcium ions and hydroxyapatite, one-dimensional 2H single and double quantum filtered spectroscopic imaging were performed on articular cartilage-bone plugs before and after decalcification. After decalcification, the magnitude splitting of the two pairs of satellites did not change and orientation dependency was kept. However, the intensity of the large splitting was greatly enhanced. According to these results the two pairs of satellites do not stem from the presence of calcium ions and hydroxyapatite but originate from the presence of two groups of collagen fibers with different degrees of hydration. The enhanced intensity of the large splitting is attributed to an increased amount of water molecules that fill the void, resulting from the removal of hydroxyapatite, which resides near the fibers responsible for the large splitting. The quadrupolar splitting observed in the trabecular bone was not orientation-dependent, indicating a random orientation of the collagen fibers in that tissue.

Osteoblasts from the sclerotic subchondral bone downregulate aggrecan but upregulate metalloproteinases expression by chondrocytes. This effect is mimicked by interleukin-6, -1beta and oncostatin M pre-treated non-sclerotic osteoblasts

OBJECTIVE

To determine the effects of osteoarthritic (OA) subchondral osteoblasts on the metabolism of human OA chondrocytes in alginate beads.

METHODS

Human chondrocytes were isolated from OA cartilage and cultured in alginate beads for 4 days in the absence or in the presence of osteoblasts isolated from non-sclerotic (N) or sclerotic (SC) zones of human OA subchondral bone in monolayer (co-culture system). Before co-culture, osteoblasts were incubated for 72 h with or without 1.7ng/ml interleukin (IL)-1beta, 100 ng/ml IL-6 with its soluble receptor (50 ng/ml) or 10 ng/ml oncostatin M (OSM). Aggrecan (AGG) and matrix metalloproteases (MMP)-3 and -13 mRNA levels in chondrocytes were quantified by real-time polymerase chain reaction. AGG production was assayed by a specific enzyme amplified sensitivity immunoassay.

RESULTS

SC, but not N, osteoblasts induced a significant inhibition of AGG production and AGG gene expression by human OA chondrocytes in alginate beads, and significantly increased MMP-3 and MMP-13 gene expression by chondrocytes. When they were pre-incubated with IL-1beta, IL-6 or OSM, N osteoblasts inhibited AGG synthesis and increased MMP-3 and -13 gene expression by chondrocytes in alginate beads in a same order of magnitude as SC osteoblasts.

CONCLUSIONS

These results demonstrate that SC OA subchondral osteoblasts could contribute to cartilage degradation by stimulating chondrocytes to produce more MMP and also by inhibiting AGG synthesis.

The relationships between bone mineral density in the spine, hip, distal femur and proximal tibia and medial minimum joint space width in the knees of healthy females

OBJECTIVE

To investigate the relationships between bone mineral density (BMD) in the hip, spine, distal femur and proximal tibia and minimum joint space width (mJSW) in the knees of healthy women.

METHODS

Women 22-68 years old without a history of knee pain, bone or joint disease or injury underwent a single, fixed-flexion knee X-ray. Radiographs were graded according to the Kellgren-Lawrence scale and analyzed for mJSW using a computer algorithm. Dual X-ray absorptiometry scans of the spine, hip, distal femur and proximal tibia were also acquired for each participant. Femur and tibia scans were acquired and analyzed using a modified version of the lumbar spine software.

RESULTS

Forty-five females, mean [standard deviation (SD)] age and body mass index (BMI) of 40.1 (13.9) years and 24.6 (4.5)kg/m(2), respectively, participated. The mean (SD) mJSW was 4.64 (0.68)mm. Linear regression analyses controlling for age and BMI revealed that BMD in the femoral trochanter and the central two regions of the tibia (T2 and T3) was significantly related to mJSW in the knee. A backwards regression analysis performed to determine which region of interest is most significantly related to mJSW revealed that femoral trochanter BMD (beta-value=0.416) is the most significant.

CONCLUSIONS

In contrast to the suggestion that BMD is negatively correlated with mJSW in the knees of osteoarthritic individuals, these results suggest that increasing BMD in the femoral trochanter and tibia is significantly associated with increasing mJSW in healthy females. Further investigation of this relationship is warranted.

Pharmaceutical and nutraceutical management of canine osteoarthritis: present and future perspectives

Osteoarthritis (OA) is one of the most common chronic musculoskeletal diseases and causes of lameness in the dogs. The osteoarthritic disease process involves the entire synovial joint, encompassing the synovium, cartilage and underlying bone. Joint failure results from an abnormal mechanical strain causing damage to normal tissue or failure of pathologically impaired articular cartilage and bone under the influence of normal physiological strain or a combination of both. In both cases, the end point is cartilage loss and joint impairment. Osteoarthritic chondrocytes show an altered phenotype characterised by an excess production of catabolic factors, including metalloproteinases and reactive oxygen species. These factors constitute potential therapeutic targets and some new drugs and nutraceuticals have been proposed to promote the return to homeostasis. Until now, the therapeutic management of OA in dogs has been dominated by nonsteroidal anti-inflammatory drugs, but some new compounds, including diacerhein, with potential structure-modifying effects, are already used to treat OA in humans and could be helpful to manage OA in the dog. In addition, novel nutraceuticals, such as avocado/soybean unsaponifiable substances, have shown symptomatic effects in knee OA in humans, and could offer an alternative to prevent OA progression. This paper provides an overview of recent discoveries in the pathophysiology and in the therapeutic management of osteoarthritis in dogs.

The effect of detachment of the articular cartilage from its calcified zone on the cartilage microstructure, assessed by 2H-spectroscopic double quantum filtered MRI

Most studies on articular cartilage properties have been conducted after detachment of the cartilage from the bone. In the present work we investigated the effect of detachment on collagen fiber architecture. We used one-dimensional (2)H double quantum filtered MRI on cartilage bone plugs equilibrated in deuterated saline. The quadrupolar splittings observed in the different zones were related to the degree of order and the density of the collagen fibers. The method is non-destructive, allowing for measurements on the same plug without the need for fixation, dehydration, sectioning and decalcification. Detachment of the radial from the calcified zone resulted in swelling of the cartilage plug in physiological saline and a concomitant decrease in the quadrupolar splitting. The effect of mechanical pressure on the (2)H quadrupolar splittings for the detached cartilage and for the calcified zone-bone plugs were compared with those of the same zones in the intact cartilage-bone plug. The splitting in the radial zone of the detached cartilage collapsed at much smaller loads compared to the intact cartilage-bone plug. The effect of the load on the size of the cartilage was also greater for the detached plug. These results indicate that anchoring of the cartilage to the bone through the calcified zone plays an important role in retaining the order of the collagen fibers. The water (2)H quadrupolar splitting in intact and proteoglycan-depleted cartilage was the same, indicating that the proteoglycans do not contribute to the ordering of the collagen fibers.

Alterations in mineral composition observed in osteoarthritic joints of cynomolgus monkeys

Osteoarthritis (OA) is a prevalent joint disease that affects more than 40 million Americans and is characterized by degeneration of the articular cartilage and thickening of the underlying subchondral bone. Although subchondral bone thickening has been implicated in articular cartilage degeneration, very little is known about the composition of subchondral bone in OA. In the present study, infrared microspectroscopy (IRMS) was used to determine the chemical composition of the calcified cartilage-subchondral bone plate in a monkey model of OA. Specifically, the levels of mineralization (mineral/protein ratio), carbonate accumulation (carbonate/protein ratio), crystallinity, and collagen structure were determined as a function of animal age and OA severity. OA severity was assessed using a grading scheme that included scores or measurements for several histomorphometric parameters including articular cartilage fibrillation or clefting, subchondral bone thickness, and numbers of tidemarks and chondrocyte clones. Individual scores and measurements were summarized using principal components (factor) analysis. Results demonstrated that the level of mineralization and carbonate content increased as a function of animal age. In addition, bone mineralization level increased as subchondral bone thickness increased. Dramatic increases in the mineralization level and carbonate accumulation were also observed as a function of the number of tidemarks. The presence of multiple tidemarks indicates the occurrence of one or more additional phases of cartilage calcification, suggesting that the observed compositional changes are due to cartilage mineralization. Our results support a reactivation of endochondral ossification that occurs with age, which is more pronounced in OA. No relationships were observed between mineral crystallinity and collagen cross-linking as a function of age or OA severity. In summary, compositional analysis of the mineralized plate beneath the articular cartilage in OA is characterized by thickened, overmineralized calcified cartilage or subchondral bone, which likely puts added mechanical stress on the joint, contributing to the progression of OA.

Chondrocyte viability in press-fit cryopreserved osteochondral allografts

The viability of chondrocytes in press-fit glycerol-preserved osteochondral allografts was compared to that in fresh autografts, after transplantation into load-bearing and non-load-bearing sites in mature sheep stifle joints. We used macroscopic grading, tonometer pen indentation testing, histology, sulfate uptake and viability as determined by confocal-microscopy to assess cartilage condition. Despite there being no statistical differences between macroscopic appearance and tonometer testing of all grafts, confocal microscopy and histology demonstrated a positive effect of load-bearing placement on cryopreserved osteochondral allografts. Allografts transplanted into load-bearing sites demonstrated superior confocal microscopy-measured chondrocyte viability (77%+/-17%SD) than those transplanted into non-load-bearing sites (25%+/-2%). Load-bearing effect was not seen in autografts (78%+/-15%), and was comparable in adjacent cartilage (83%+/-9%). Similarly, load-bearing allografts demonstrated histological scoring closer to that of autografts and adjacent cartilage, all of which fared significantly better than non-load-bearing allografts. Load-bearing allografts had a greater amount of fibrocartilage than autografts or adjacent cartilage but less fibrocartilage than non-load-bearing allografts. Both autografts and allografts had non-significant increases in metabolism compared to adjacent cartilage as measured by sulfate-uptake. Load-bearing placement improved chondrocyte viability of glycerol cryopreserved osteochondral allograft following a press-fit implantation.

Treatment with licofelone prevents abnormal subchondral bone cell metabolism in experimental dog osteoarthritis

OBJECTIVES

To determine if treatment with licofelone, a combined 5-lipoxygenase and cyclo-oxygenase inhibitor, in vivo in experimental dog osteoarthritis can modify bone cell metabolism in long term in vitro subchondral osteoblast cell cultures (Ob).

METHODS

Group 1 received sectioning of the anterior cruciate ligament (ACL) of the right knee with no active treatment (placebo group). Groups 2 and 3 received sectioning of the ACL of the right knee, and were given licofelone (2.5 or 5.0 mg/kg daily by mouth, respectively) for eight weeks beginning the day after surgery. Primary Ob were prepared from the subchondral bone plate. Levels of phenotypic markers (alkaline phosphatase activity, osteocalcin release), and urokinase plasminogen activator (uPA) and insulin-like growth factor-1 (IGF-I) levels, were evaluated in each group. Lastly, prostaglandin E(2) (PGE(2)) and leucotriene B(4) levels were evaluated.

RESULTS

No significant differences in alkaline phosphatase activity or osteocalcin release from Ob between the three groups, under either basal or 1,25(OH)(2)D(3) induction were seen. In contrast, treatment with licofelone reduced uPA and IGF-I levels in Ob. PGE(2) levels, which were still raised in the placebo group, were decreased sharply by licofelone. A relationship was found between licofelone treatment and either the reduction in the size of lesions on tibial plateaus or the levels of uPA, IGF-I, or PGE(2).

CONCLUSIONS

Licofelone treatment prevents and/or delays the abnormal metabolism of subchondral osteoblasts in this model. Licofelone reduced PGE(2) levels after long term Ob, suggesting that the reduction in uPA and IGF-I levels is linked, at least in part, to this reduction.

Value of micro-CT as an investigative tool for osteochondritis dissecans

PURPOSE

To evaluate micro computed tomography (micro-CT) for the assessment of osteochondritis dissecans in comparison with histology.

MATERIAL AND METHODS

Osteochondritis dissecans lesions of 3 patients were evaluated using micro-CT (0.125 mA, 40 keV, 60 microm slice thickness, 60 microm isotropic resolution, entire sample) and light microscopy (toluidine blue, 3-5 microm slice thickness). The methods were compared regarding preparation time, detectability of tissue types and morphologic features of bone and cartilage.

RESULTS

Non-destructive micro-CT imaging of the entire sample was faster than histologic preparation of a single slice for light microscopy. Morphologic features of bone and cartilage could be imaged in a comparable way to histology. It was not possible to image cells or different tissue types of bone and cartilage with micro-CT.

CONCLUSION

Micro-CT is a fast, non-destructive tool that may be a supplement or, if detailed histologic information is not necessary, an alternative to light microscopy for the investigation of osteochondritis dissecans.

Role of eicosanoids in structural degradation in osteoarthritis

PURPOSE OF REVIEW

Osteoarthritis is characterized mainly by degenerative changes in joint cartilage, ultimately resulting in loss of cartilage, and alterations in the subchondral bone. Osteoarthritis osteoblasts show a number of metabolic alterations that may interfere with normal cell metabolism and signaling, possibly leading to altered extracellular matrix composition. This review examines the role of eicosanoids in this structural degradation.

RECENT FINDINGS

Prostaglandins exert diverse modulatory roles in osteoarthritis, with prostaglandin E2 known to play an important role in inflammation. Prostaglandins and leukotriene B4 have been shown to regulate proinflammatory cytokine and interstitial collagenase synthesis in human osteoarthritis synovial membrane explants. Human osteoarthritis osteoblasts produce variable levels of prostaglandin E2 and leukotriene B4 compared with normal osteoblasts. Prostaglandin E2 levels can distinguish two types of patients with osteoarthritis: osteoblasts from one group produce low levels of prostaglandin E2 and interleukin-6, and the other shows an increase in production. In contrast, osteoarthritis osteoblasts that produce high levels of prostaglandin E2 produce low levels of leukotriene B4 and vice versa. This observation could be explained by the selective metabolism of arachidonic acid via the 5-lipoxygenase or cyclooxygenase pathways in osteoarthritis osteoblasts.

SUMMARY

Prostaglandins play a significant role not only in joint physiology, but also in the pathogenesis of joint disorders. In addition, it has been identified that osteoarthritis subchondral osteoblasts can synthesize leukotriene B4, indicating a role of leukotrienes in bone remodeling associated with osteoarthritis. A therapeutic intervention that blocks lipoxygenase/cyclooxygenase pathways, thereby inhibiting production of prostaglandins and leukotrienes, may therefore be very attractive for the treatment of osteoarthritis patients.

Subchondral bone in osteoarthritis: a biologic link with articular cartilage leading to abnormal remodeling

PURPOSE OF REVIEW

This review deals with new findings highlighting the concept of cross-talk between subchondral bone tissue and articular cartilage that may be crucial for the initiation and/or progression of osteoarthritis. In this review, new factors either produced by subchondral bone tissue or modifying osteoblast metabolism, yet implicated in osteoarthritis, are discussed.

RECENT FINDINGS

The development of cartilage degeneration is concomitant with subchondral bone thickness in osteoarthritis, whereas it is related to higher subchondral bone activity and dysregulation in the synthesis of bone proteins. As an immediate consequence, homotrimers of type 1 collagen are formed that could lead to undermineralization of this tissue. This dysregulation also leads to abnormal production of different factors by osteoblasts such as prostaglandins, leukotrienes, and growth factors. Because microcracks or neovascularization provide a link between the subchondral bone tissue and articular cartilage, these factors could contribute to the abnormal remodeling of osteoarthritic cartilage.

SUMMARY

These findings have an immediate implication for research because new tools need to be developed to study the subchondral bone-cartilage functional unit. Moreover, it could lead to a possible cure for osteoarthritis because this pathology should be considered both a bone and cartilage disease.

Percutaneous arthrodesis

It has been generally accepted that residual cartilage and subchondral bone has to be removed in order to get bony fusion in arthrodeses. In 1998 we reported successful fusion of 11 rheumatoid ankles, all treated with percutaneous fixation only. In at least one of these ankle joint there was cartilage left. This was confirmed by arthrotomy in order to remove an osteophyte, which hindered dorsiflexion. More than 25 rheumatoid patients with functional alignment in the ankle joint have subsequently been operated on with the percutaneous technique, and so far we have had only one failure. Patients with rheumatoid arthritis are known to sometimes fuse at least their subtalar joints spontaneously, and the destructive effect of the synovitis on the cartilage could contribute to fusion when using the percutaneous technique. In a rabbit study we therefore tested the hypothesis that even a normal joint can fuse merely by percutaneous fixation. The patella was fixated to the femur with lag screw technique without removal of cartilage, and in 5 of 6 arthrodeses with stable fixation bony fusion followed. Depletion of synovial fluid seemed to be the mechanism behind cartilage disappearance. The stability of the fixation achieved at arthrodesis surgery is an important factor in determining success or failure. Dowel arthrodesis without additional fixation proved to be deleterious. A good fit of the bone surfaces appears necessary. In the ankle joint, it would be technically demanding to retain the arch-shaped geometry of the joint after resection of the cartilage. Normally the joint surfaces are resected to produce flat osteotomy surfaces that are thus easier to fit together, encouraging healing to occur. On the other hand it is considered an advantage to preserve as much subchondral bone as possible, as the strong subchondral bone plate can contribute to the stability of the arthrodesis. Ankle arthrodesis can be successfully performed in patients with rheumatoid arthritis by percutaneous screw fixation without resection of the joint surfaces. This procedure has two advantages: first, it is less surgically traumatic, second, both the arch-shaped geometry and the subchondral bone are preserved, and thus both could contribute to the postoperative stability of the construct. Intuitively, preservation of the arch-shape should increase rotational stability. The results of our experimental sawbone study indicate that the arch shape and the subchondral bone should be preserved when ankle arthrodesis is performed. The importance of this is likely to increase in weak rheumatoid bone. In a finite element study the initial stability provided by two different methods of joint preparation and different screw configurations in ankle arthrodesis, was compared. Better initial stability is predicted for ankle arthrodesis when joint contours are preserved rather than resected. Overall, inserting the two screws at a 30-degree angle with respect to the long axis of the tibia and crossing them above the fusion site improved stability for both joint preparation techniques. The question rose as to whether patients with osteoarthritis could also be operated on solely by percutaneous fixation technique. The first metatarsophalangeal joint in patients with hallux rigidus was chosen as an appropriate joint to test the percutaneous technique. In this small series we have shown that it is possible to achieve bony fusion with a percutaneous technique in an osteoarthrotic joint in humans, but failed to say anything about the fusion rate.

Can altered production of interleukin-1beta, interleukin-6, transforming growth factor-beta and prostaglandin E(2) by isolated human subchondral osteoblasts identify two subgroups of osteoarthritic patients

OBJECTIVE

To determine the capacity of human subchondral osteoarthritic osteoblasts (Ob) to produce interleukin (IL)-1beta, IL-6, transforming growth factor-beta (TGF-beta) and prostaglandin E(2) (PGE(2)), and determine if a relationship exists between IL-1beta, TGF-beta, PGE(2) and IL-6 production.

METHODS

We measured the abundance of IL-1beta, IL-6, TGF-beta and PGE(2) using very sensitive ELISA in conditioned-media of human primary subchondral Ob from normal individuals and osteoarthritic patients. Selective inhibition of IL-6 or IL-6 receptor signaling was performed to determine its effect on PGE(2) production whereas the inhibiton of PGE(2) production was performed to determine its effect on IL-6 production. The expression of bone cell markers and urokinase plasminogen activator (uPA) activity was also determined.

RESULTS

Osteoarthritic Ob produced all these factors with greater variability than normal cells. Interestingly, the production of IL-6 and PGE(2) by osteoarthritic Ob separated patients into two subgroups, those whose Ob produced levels comparable to normal (low producers) and those whose Ob produced higher levels (high producers). In those cells classified as high osteoarthritic Ob, PGE(2) and IL-6 levels were increased two- to three-fold and five- to six-fold, respectively, compared with normal. In contrast, while using their IL-6 and PGE(2) production to separate osteoarthritic Ob into low and high producers, we found that IL-1beta levels were similar in normal and all osteoarthritic Ob. Using the same criteria, TGF-beta levels were increased in all osteoarthritic Ob compared with normal. Reducing PGE(2) synthesis by Indomethacin [a cyclo-oxygenase (COX) -1 and -2 inhibitor] reduced IL-6 levels in all osteoarthritic Ob, whereas Naproxen (a more selective COX-2 inhbitor) reduced PGE(2) and IL-6 levels only in the high osteoarthritic group. Conversely, PGE(2) addition to osteoarthritic Ob enhanced IL-6 production in both groups. Moreover, the addition of parathyroid hormone also stimulated IL-6 production to similar normal levels in both osteoarthritic groups. In contrast, using an antibody against IL-6 or IL-6 receptors did not reduce PGE(2) levels in either group. The evaluation of alkaline phosphatase activity, osteocalcin release, collagen type I and uPA activity in osteoarthritic Ob failed to show any differences between these cells regardless to which subgroup they were assigned.

CONCLUSIONS

These results indicate that IL-6 and PGE(2) production by subchondral Ob can discriminate two subgroups of osteoarthritic patients that cannot otherwise be separated by their expression of cell markers, and that endogenous PGE(2) levels influence IL-6 synthesis in osteoarthritic Ob.

A study on the influence of calcified intervertebral disk and aorta in determining bone mineral density

This study utilized dual-energy X-ray absorptiometry (DXA) to determine the association that age-related calcinosis of the aorta and intervertebral disks have in determining bone mineral density (BMD). Eight cadavers were chosen at random and were scanned with DXA before and after the removal of the aorta and intervertebral disks. Our results showed that the removal of sclerotic aortas decreased the vertebral BMD an average of 4.64% and the removal of two lumbar intervertebral disks further decreased BMD an average of 11.93%. These results were deemed significant at the 0.01 level using a Friedman two-way analysis of variance by ranks. It can be concluded that the presence of aortic arteriosclerotic lesions and intervertebral disk chondrocalcinosis add a significant contribution to BMD.

Quantitative in situ correlation between microscopic MRI and polarized light microscopy studies of articular cartilage

OBJECTIVE

To establish the correlation between the non-invasive imaging by magnetic resonance microscopy (microMRI) and the histological imaging by polarized light microscopy (PLM) accurately, quantitatively, at the highest possible MRI resolution (13.7 microm), and based on the same piece of tissue (articular cartilage from canine shoulder joint).

DESIGN

In microMRI experiments, the laminar appearance (the magic angle effect) of the proton intensity images and the anisotropic characteristics of the T(2)relaxation images were analysed. In PLM experiments, the images of the optical retardation and collagen-fibre orientation in cartilage were constructed in two dimensions.

RESULTS

The T(2)profile has a distinctly asymmetric bell-shaped curve and three featured zones. The retardation profile has a non-zero minimum at the middle of the transitional zone of the tissue. The angle profile has a smooth variation across the transitional zone. These facts suggest that the collagen fibres in the transitional zone are not entirely random but have a residual order. In addition, the peak of the T(2)profile coincides with the minimum of the retardation profile, both represent the most isotropic region of the tissue. A hyperbolic tangent function was found to best describe the transition of the collagen fibres in cartilage. A set of criteria was developed for each technique to define the features in the quantitative measurements.

CONCLUSIONS

The criteria offer, for the first time, a set of quantitative and objective means to subdivide the tissue thickness into the zones in histology and in MRI. It is shown that the microMRI zones based on the T(2)characteristics are statistically equivalent to the histological zones based on the collagen fibre orientation (t-probabilities of 0.730, 0.973, 0.647, 0.850 for the superficial, transitional, radial zones and the total thickness).

MRI techniques in early stages of cartilage disease

Cartilage degenerative diseases affect millions of people. Our understanding of these diseases and our ability to establish efficacious treatment strategies have been confounded by the difficulty of nondestructively evaluating the state of cartilage. Imaging strategies that allow visualization of cartilage integrity would revolutionize the field by allowing us to visualize early stages of degeneration and thus to evaluate predisposing factors for cartilage disease and changes resulting from interventions (eg, therapies) in culture studies, tissue-engineered systems, animal models, and in vivo in humans. Here we briefly review current state-of-the-art MRI strategies relevant to understanding and following treatment in early cartilage degeneration. We review MRI as applied to the assessment of the whole joint, of cartilage as a whole (as an organ), of cartilage tissue, and of cartilage molecular composition and structure. Each of these levels is amenable to assessment by MRI and offers different information that, in the long run, will serve as an important element of cartilage imaging.

Subchondral bone and cartilage disease: a rediscovered functional unit

The role of subchondral bone in the pathogenesis of cartilage damage has likely been underestimated. Subchondral bone is not only an important shock absorber, but it may also be important for cartilage metabolism. Contrary to many drawings and published reports, the subchondral region is highly vascularized and vulnerable. Its terminal vessels have, in part, direct contact with the deepest hyaline cartilage layer. The perfusion of these vessels accounts for more than 50% of the glucose, oxygen, and water requirements of cartilage. Bony structure, local metabolism, hemodynamics, and vascularization of the subchondral region differ within a single joint and from one joint to another. Owing to these differences, repetitive, chronic overloading or perfusion abnormalities may result in no pathological reaction at all in one joint, while in another joint, these same conditions may lead to osteonecrosis, osteochondritis dissecans, or degenerative changes. According to this common etiological root, similar pathological reactions beginning with marrow edema and necrosis and followed by bone and cartilage fractures, joint deformity, and insufficient healing processes are found in osteonecrosis, osteochondritis dissecans, and degenerative disease as well.