Associations of blood pressure and arterial stiffness with knee cartilage volume in patients with knee osteoarthritis.

OBJECTIVE: To describe the associations of blood pressure and arterial stiffness with knee cartilage volume in patients with knee OA. METHODS: A secondary analysis was performed on the data from participants in a randomized controlled trial that identified the effects of vitamin D supplementation on knee structures and symptoms among patients with symptomatic knee OA. Brachial and central blood pressure, arterial stiffness indicators and knee cartilage volume were measured at baseline and the 2 year follow-up. Associations were assessed using generalized estimating equations. RESULTS: Among 231 participants (average age 63.2 years), 48.9% were females. Higher supine systolic and diastolic pressures were significantly associated with lower tibial cartilage volume (systolic: lateral ß -6.23, medial ß -5.14, total ß -11.35 mm3/mmHg; diastolic: lateral ß -10.25, medial ß -11.29, total ß -21.50 mm3/mmHg). Higher supine systolic pressure was associated with lower femoral cartilage volume (lateral ß -17.35, total ß -28.31 mm3/mmHg). Central systolic pressure and arterial stiffness indicators (including pulse wave velocity, central pulse pressure and peripheral pulse pressure) were largely not associated with knee cartilage volume; however, higher augmentation index was associated with lower tibial and femoral cartilage volume (tibial: medial ß -8.24, total ß -19.13 mm3/%; femoral: lateral ß -23.70, medial ß -26.42, total ß -50.12 mm3/%). CONCLUSIONS: Blood pressure and arterial stiffness are associated with knee cartilage volume at several sites in knee OA patients. This supports that blood pressure and arterial stiffness may involve in the progression of knee OA.

Osteochondrosis in the Distal Femoral Physis of Pigs Starts With Vascular Failure.

Articular osteochondrosis (OC) arises due to vascular failure and ischemic chondronecrosis. The aim of the study was to describe the histological and computed tomographic (CT) characteristics of changes in the distal femoral physis of pigs, to determine if they represented OC lesions and if the pathogenesis was the same as for articular OC. The material included 19 male Landrace pigs bred for predisposition to OC. One or 2 pigs were euthanized and CT-scanned at 2-week intervals from 82 to 180 days of age. Material from 10 pigs was available for histological validation. The CT scans revealed 31 lesions confirmed in 3 planes and 1 additional macroscopically visible lesion confirmed in 2 CT planes. Twelve of the lesions were histologically validated. All lesions were compatible with OC. Cartilage canal and eosinophilic streak morphological changes corresponded to failure of end arteries coursing from the epiphysis, toward the metaphysis. The location of lesions was compatible with failure at the point of vessel incorporation into bone. Vascular failure was associated with retention of viable hypertrophic chondrocytes and delayed ossification but not cartilage necrosis. Lesion width ranged from 1.1% to 45.6% of the physis. Several lesions were expected to resolve due to small size and evidence of CT-identifiable, reparative ossification. Angular limb deformity was not detected in any pig. The pathogenesis of physeal OC started with vascular failure that was morphologically identical to articular OC. The heritable predisposition may therefore be the same. The association between lesions and limb deformity should be studied further in older pigs in future.

Mixed cell therapy of bone marrow-derived mesenchymal stem cells and articular cartilage chondrocytes ameliorates osteoarthritis development.

Of the many cell-based treatments that have been tested in an effort to regenerate osteoarthritic articular cartilage, none have ever produced cartilage that compare with native hyaline cartilage. Studies show that different cell types lead to inconsistent results and for cartilage regeneration to be considered successful, there must be an absence of fibrotic tissue. Here we report of a series of experiments in which bone marrow-derived stem cells (BMSCs) and articular cartilage chondrocytes (ACCs) were mixed in a 1:1 ratio and tested for their ability to enhance cartilage regeneration in three different conditions: (1) in an in vitro differentiation model; (2) in an ex vivo cartilage defect model implanted subcutaneously in mice; and (3) as an intra-articular injection in a meniscectomy-induced OA model in rats. The mixed cells were compared with monocultures of BMSCs and ACCs. In all three experimental models there was significantly enhanced cartilage regeneration and decreased fibrosis in the mixed BMSCs+ACCs group compared with the monocultures. Molecular analysis showed a reduction in vascularization and hypertrophy, coupled with higher chondrogenic gene expression resulting from the BMSCs+ACCs treatment. Together, our data suggest that mixed BMSCs+ACCs treatment is highly chondro-protective and is more effective in regenerating damaged cartilage in both the ex vivo cartilage defect and post-trauma OA disease models. The results from this approach could potentially be used for regeneration of cartilage in OA patients.

Juvenile osteochondritis dissecans of the knee is a result of failure of the blood supply to growth cartilage and osteochondrosis.

OBJECTIVE: Juvenile osteochondritis dissecans (JOCD) is similar to osteochondrosis dissecans (OCD) in animals, which is the result of failure of the cartilage canal blood supply, ischemic chondronecrosis and delayed ossification, or osteochondrosis. The aim of the current study was to determine if osteochondrosis lesions occur at predilection sites for JOCD in children. METHOD: Computed tomographic (CT) scans of 23 knees (13 right, 10 left) from 13 children (9 male, 4 female; 1 month to 11 years old) were evaluated for lesions consisting of focal, sharply demarcated, uniformly hypodense defects in the ossification front. Histological validation was performed in 11 lesions from eight femurs. RESULTS: Thirty-two lesions consisting of focal, uniformly hypodense defects in the ossification front were identified in the CT scans of 14 human femurs (7 left, 7 right; male, 7-11 years old). Defects corresponded to areas of ischemic chondronecrosis in sections from all 11 histologically validated lesions. Intra-cartilaginous secondary responses comprising proliferation of adjacent chondrocytes and vessels were detected in six and two lesions, whereas intra-osseous responses including accumulation of chondroclasts and formation of granulation tissue occurred in 10 and six lesions, respectively. One CT cyst-like lesion contained both a pseudocyst and a true cyst in histological sections. CONCLUSION: Changes identical to osteochondrosis in animals were detected at predilection sites for JOCD in children, and confirmed to represent failure of the cartilage canal blood supply and ischemic chondronecrosis in histological sections.

Vessel architecture in human knee cartilage in children: an in vivo susceptibility-weighted imaging study at 7 T.

OBJECTIVES: To evaluate the clinical feasibility of ultrahigh field 7-T SWI to visualize vessels and assess their density in the immature epiphyseal cartilage of human knee joints. METHODS: 7-T SWI of 12 knees (six healthy volunteers, six patients with osteochondral abnormalities; mean age 10.7 years; 3 female, 9 male) were analysed by two readers, classifying intracartilaginous vessel densities (IVD) in three grades (no vessels, low IVD and high IVD) in defined femoral, tibial and patellar zones. Differences between patients and volunteers, IVDs in different anatomic locations, differences between cartilage overlying osteochondral abnormalities and corresponding normal zones, and differences in age groups were analysed. RESULTS: Interrater reliability showed moderate agreement between the two readers (κ = 0.58, p < 0.001). The comparison of IVDs between patients and volunteers revealed no significant difference (p = 0.706). The difference between zones in the cartilage overlying osteochondral abnormalities to corresponding normal zones showed no significant difference (p = 0.564). IVDs were related to anatomic location, with decreased IVDs in loading areas (p = 0.003). IVD was age dependent, with more vessels present in the younger participants (p = 0.001). CONCLUSIONS: The use of SWI in conjunction with ultrahigh field MRI makes the in vivo visualization of vessels in the growing cartilage of humans feasible, providing insights into the role of the vessel network in acquired disturbances. KEY POINTS: • SWI facilitates in vivo visualization of vessels in the growing human cartilage. • Interrater reliability of the intracartilaginous vessel grading was moderate. • Intracartilaginous vessel densities are dependent on anatomical location and age.

Normal sonoanatomy of small joints in healthy children: changes in cartilage and vascularisation according to age and gender.

OBJECTIVES: The metacarpophalangeal (MCP) and metatarsophalangeal (MTP) joints may be involved in juvenile idiopathic arthritis. Our goal was to describe their normal sonoanatomy in healthy children, according to age and gender. METHODS: We studied 41 consecutive healthy children (20 girls, 21 boys; age 2-15 years) divided into four age groups: 2-4 years (n=9), 5-7 years (n=11), 8-12 years (n=12), and 13-15 years (n=9). Longitudinal ultrasound axis of the MCP and MTP joints were obtained. The evolution of the cartilage thickness and vascularisation of these joints were studied according to age and gender. The MCP or MTP joints were the statistical unit. RESULTS: At all sites, on B-mode images, cartilage thickness was associated with age (p<0.0001). Cartilage thickness at different sites was significantly greater in boys than in girls (p≤0.05). Blood vessels were seen within the cartilage, with differences across age groups. CONCLUSIONS: This study provides children's age- and gender-specific sonoanatomy data of MCP and MTP and confirms the importance of using colour Doppler or Power Doppler to study cartilage vascularisation.

Osteochondral Angiogenesis and Promoted Vascularization: New Therapeutic Target.

The control of the different angiogenic process is an important point in osteochondral regeneration. Angiogenesis is a prerequisite for osteogenesis in vivo; insufficient neovascularization of bone constructs after scaffold implantation resulted in hypoxia and cellular necrosis. Otherwise, angiogenesis must be avoided in chondrogenesis; vascularization of the cartilage contributes to structural damage and pain. Finding a balance between these processes is important to design a successful treatment for osteochondral regeneration. This chapter shows the most important advances in the control of angiogenic process for the treatment of osteochondral diseases focused on the administration of pro- or anti-angiogenic factor and the design of the scaffold.

Cartilage MRI T2∗ relaxation time and perfusion changes of the knee in a 5/6 nephrectomy rat model of chronic kidney disease.

OBJECTIVE: Chronic kidney disease (CKD) is characterized by metabolic disturbances in calcium and phosphorus homeostasis as kidney function declines. Alterations in blood perfusion in bone resulting from arteriosclerosis of bone vessels may relate to the progression of CKD. Herein, change in dynamic contrast enhanced (DCE) MRI parameters (A: amplitude, kel: elimination constant, and kep: permeability rate constant) and MRI T2∗ relaxation time of the knee cartilage were measured in a rodent nephrectomy model in order to (1) examine the relationship of peripheral blood perfusion to CKD and (2) demonstrate the feasibility of using DCE-MRI parameters and MRI T2∗ as imaging biomarkers to monitor disease progression. DESIGN: Two groups of male Sprague-Dawley rats received either (1) no intervention or (2) 5/6 nephrectomy. RESULTS: We found that the CKD group (compared with the control group) had lower A and kel values and similar kep value in the lateral and medial articular cartilages beginning at 12 weeks (P < 0.05); statistically significantly higher T2∗ values in the lateral and medial articular cartilages beginning at 18 weeks (P < 0.05); statistically significantly decreased inner luminal diameter of the popliteal artery, and altered structure of the lateral and medial articular cartilages (P < 0.05). CONCLUSION: Perfusion deficiency and CKD may be related. DCE parameters and MRI T2∗ could serve as imaging biomarkers of cartilage degeneration in CKD progression.

Contribution of Circulatory Disturbances in Subchondral Bone to the Pathophysiology of Osteoarthritis.

PURPOSE OF REVIEW: This review describes the contributions of abnormal bone circulation to the pathophysiology of osteoarthritis. Combining dynamic imaging with MRI and PET with previous observations reveals that venous stasis and a venous outlet syndrome is most likely the key circulatory pathology associated with the initiation or progression of osteoarthritis. RECENT FINDINGS: MRI and PET have revealed that venous outflow obstruction results in physicochemical changes in subchondral bone to which osteoblasts are responsive. The osteoblasts express an altered pattern of cytokines, many of which can serve as structural or signaling molecules contributing to both bone remodeling and cartilage degeneration. The patterns of circulatory changes are associated with alterations in the physicochemical environment of subchondral bone, including hypoxia. Osteoblast cytokines can transit the subchondral bone plate and calcified cartilage and communicate with chondrocytes.

Non-linear optical microscopy of cartilage canals in the distal femur of young pigs may reveal the cause of articular osteochondrosis.

BACKGROUND: Articular osteochondrosis is a common cause of leg weakness in pigs and is defined as a focal delay in the endochondral ossification of the epiphysis. The first demonstrated steps in the pathogenesis consist of loss of blood supply and subsequent chondronecrosis in the epiphyseal growth cartilage. Blood vessels in cartilage are located in cartilage canals and become incorporated into the secondary ossification centre during growth. It has been hypothesized that vascular failure occurs during this incorporation process, but it is not known what predisposes a canal to fail. To obtain new information that may reveal the cause of vascular failure, the distal femur of 4 pigs aged 82-140 days was sampled and examined by non-linear optical microscopy. This novel technique was used for its ability to reveal information about collagen by second harmonic generation and cellular morphology by two-photon-excited fluorescence in thick sections without staining. The aims were to identify morphological variations between cartilage canal segments and to examine if failed cartilage canals could be followed back to the location where the blood supply ceased. RESULTS: The cartilage canals were shown to vary in their content of collagen fibres (112/412 segments), and the second harmonic and fluorescence signals indicated a variation in the bundling of collagen fibrils (245/412 segments) and in the calcification (30/412 segments) of the adjacent cartilage matrix. Failed cartilage canals associated with chondronecrosis were shown to enter the epiphyseal growth cartilage from not only the secondary ossification centre, but also the attachment site of the caudal cruciate ligament. CONCLUSION: The variations between cartilage canal segments could potentially explain why the blood supply fails at the osteochondral junction in only a subset of the canals. Proteins linked to these variations should be examined in future genomic studies. Although incorporation can still be a major cause, it could not account for all cases of vascular failure. The role of the caudal cruciate ligament in the cause of osteochondrosis should therefore be investigated further.

The role of the prolactin/vasoinhibin axis in rheumatoid arthritis: an integrative overview.

Rheumatoid arthritis (RA) is a chronic, autoimmune, inflammatory disease destroying articular cartilage and bone. The female preponderance and the influence of reproductive states in RA have long linked this disease to sexually dimorphic, reproductive hormones such as prolactin (PRL). PRL has immune-enhancing properties and increases in the circulation of some patients with RA. However, PRL also suppresses the immune system, stimulates the formation and survival of joint tissues, acquires antiangiogenic properties upon its cleavage to vasoinhibins, and protects against joint destruction and inflammation in the adjuvant-induced model of RA. This review addresses risk factors for RA linked to PRL, the effects of PRL and vasoinhibins on joint tissues, blood vessels, and immune cells, and the clinical and experimental data associating PRL with RA. This information provides important insights into the pathophysiology of RA and highlights protective actions of the PRL/vasoinhibin axis that could lead to therapeutic benefits.

Discontinuities in the endothelium of epiphyseal cartilage canals and relevance to joint disease in foals.

Cartilage canals have been shown to contain discontinuous blood vessels that enable circulating bacteria to bind to cartilage matrix, leading to vascular occlusion and associated pathological changes in pigs and chickens. It is also inconsistently reported that cartilage canals are surrounded by a cellular or acellular wall that may influence whether bacterial binding can occur. It is not known whether equine cartilage canals contain discontinuous endothelium or are surrounded by a wall. This study aimed to examine whether there were discontinuities in the endothelium of cartilage canal vessels, and whether canals had a cellular or acellular wall, in the epiphyseal growth cartilage of foals. Epiphyseal growth cartilage from the proximal third of the medial trochlear ridge of the distal femur from six healthy foals that were 1, 24, 35, 47, 118 and 122 days old and of different breeds and sexes was examined by light microscopy (LM), transmission electron microscopy (TEM) and immunohistochemistry. The majority of patent cartilage canals contained blood vessels that were lined by a thin layer of continuous endothelium. Fenestrations were found in two locations in one venule in a patent cartilage canal located deep in the growth cartilage and close to the ossification front in the 118-day-old foal. Chondrifying cartilage canals in all TEM-examined foals contained degenerated endothelial cells that were detached from the basement membrane, resulting in gap formation. Thirty-three percent of all canals were surrounded by a hypercellular rim that was interpreted as contribution of chondrocytes to growth cartilage. On LM, 69% of all cartilage canals were surrounded by a ring of matrix that stained intensely eosinophilic and consisted of collagen fibres on TEM that were confirmed to be collagen type I by immunohistochemistry. In summary, two types of discontinuity were observed in the endothelium of equine epiphyseal cartilage canal vessels: fenestrations were observed in a patent cartilage canal in the 118-day-old foal; and gaps were observed in chondrifying cartilage canals in all TEM-examined foals. Canals were not surrounded by any cellular wall, but a large proportion was surrounded by an acellular wall consisting of collagen type I. Bacterial binding can therefore probably occur in horses by mechanisms that are similar to those previously demonstrated in pigs and chickens.

[Effect of lumbar (perirenal) procaine blockade on microcirculation and exchange proteoglycans with experimental gonarthrosis].

Experimental studies on guinea pigs of both sexes (n = 30). Experimental animals are awicea into equal groups oJ 10 animals: 1--the control group (intact animals), 2--the comparison group (modelling of gonarthrosis by crossing his own patellar ligament has been made, exposure 6 months), 3--the main group (animals with gonarthrosis treatment was carried out by performing lumbar procaine blockade (LPB) with an interval of 3-5 days three times). We establish that after a course of LPB in gonarthrosis marked increase in the density of the injected channel in the articular and periarticular structures, which reflects a growth in the microcirculation, and more intense accumulation in the basic substance of epiphyseal cartilage PAS (+) indicates the material to increase the level of proteoglycan in articular cartilage.

Quantitative assessment of the subchondral vascularity of the talar dome: a cadaveric study.

BACKGROUND: The arterial supply to the talus has been extensively studied previously but never to specifically examine the subchondral region of the talar dome, a frequent site of localised pathology. This study aims to analyse and quantify the subchondral vascularity of the talar dome. METHODS: We performed cadaveric arterial injection studies. After processing, the vascularity to the subchondral region of the talar dome was visualised and mapped using three-dimensional computer technology, then quantified and reported using a nine-section anatomical grid. RESULTS: The areas of relative poor perfusion across the talar dome are the posterior/medial, posterior/lateral and middle/medial sections of a nine-section grid. The rest of the subchondral region shows more richly vascularised bone. CONCLUSIONS: The vascularity of the subchondral surface of the talar dome is not uniformly distributed. This may be relevant to the aetiology and management of osteochondral lesions and shows some correlation with their more frequent locations.

Effects of hypoxia/ischemia on catabolic mediators of cartilage in a human chondrocyte, SW1353.

Cells from a human chondrocyte cell line were studied in 1% oxygen and/or a lower glucose concentration (5.5 mM), compared to the routine culture conditions of normoxia and high glucose. HIF-1α, IL-1ß, IL-6, IL-8, COX-2, TNFα, LIF, MMP-3, MMP-13, and reactive oxygen species (ROS) were evaluated, respectively. Effects of hypoxia inducing expression of HIF-1α were statistically significant at 72 h (p<0.05). Increased production of ROS by hypoxia was also observed with passage of time (p<0.05). The effects of hypoxia on HIF-1α and IL-1ß were potentiated by 5.5 mM glucose, especially after 48 h (p<0.05). IL-8 production was significantly induced in 1% O(2), with 5.5 mM glucose (p<0.01). IL-8 mRNA expression and production in response to IL-1ß were potentiated by hypoxia/ischemia (p<0.05, p<0.01, respectively). Up-regulation of IL-1ß, ROS, and IL-8 by hypoxia/ischemia in human chondrocytes may occur in correlation with HIF-1α. IL-8 response to IL-1ß may be potentiated synergically by hypoxia/ischemia, as an effector of hypoxia/ischemia. The results may suggest aggressive biology of the ordinary cartilage hypoxia/ischemia in the context of arthro-degeneration.

Cartilage oligomeric matrix protein inhibits vascular smooth muscle calcification by interacting with bone morphogenetic protein-2.

RATIONALE: Vascular calcification is a significant contributor to cardiovascular morbidity and mortality. We recently reported that cartilage oligomeric matrix protein (COMP) is pivotal for maintaining the homeostasis of vascular smooth muscle cells (VSMCs). Whether COMP affects the process of vascular calcification is unknown. OBJECTIVE: We aimed to test whether COMP modulates vascular calcification. METHODS AND RESULTS: VSMC calcification in vitro was induced by calcifying media containing high inorganic phosphate or calcium. In vivo medial vessel calcification was induced in rats by 5/6 nephrectomy with a high-phosphate diet or by periadventitial application of CaCl(2) to the abdominal aorta. COMP protein level was markedly reduced in both calcified VSMCs and arteries. COMP deficiency remarkably exacerbated VSMC calcification, whereas ectopic expression of COMP greatly reduced calcification. Furthermore, COMP knockdown facilitated osteogenic markers expression by VSMCs even in the absence of calcifying media. By contrast, COMP overexpression significantly inhibited high phosphate- or high calcium-induced VSMC osteochondrogenic transition. Induction of osteogenic marker expression by COMP silencing was reversed by a soluble form of bone morphogenetic protein (BMP)-2 receptor IA, which suggests a BMP-2-dependent mechanism. Our data revealed that COMP bound directly to BMP-2 through the C terminus, inhibited BMP-2 receptor binding, and blocked BMP-2 osteogenic signaling, indicating COMP inhibits osteochondrogenic transition of VSMCs at least partially through inhibiting BMP-2. CONCLUSIONS: Our data strongly suggest that COMP is a novel inhibitor of vascular calcification. The imbalance between the effects of COMP and BMP-2 may provide new insights into the pathophysiology of vascular calcification.

Morphological effects of mesenchymal stem cells and pulsed ultrasound on condylar growth in rats: a pilot study.

AIM: The aim of this study was to assess and describe the morphological effects of an intra-articular iniection of Mesenchymal Stem Cells (MSCs) and/or Low Intensity Pulsed Ultrasound (LIPUS) stimulation on the mandibular condyles of growing rats, using cone beam computed tomography (CBCT) and histology. METHODS: Twenty-six young (23-day-old) rats were divided into 5 groups identified as LIPUS-stimulated (20 minutes daily using 50 mW/cm2, 1MHz, 0.2 millisecond pulses), MSCs injected (1 x 10(5) cells/kg), LIPUS + MSCs, medium inlected, and untreated controls. All treatments were performed in the left temporomandibular joint of each rat (TMJs). At day 21, CBCTs were obtained for cephalometric analysis and 3D reconstructions. After animal sacrifice, left and right TMJ sections were histologically prepared and examined. The Wilcoxon sign rank test and the Kruskal-Wallis 2 test were applied for statistical comparison. RESULTS: Imaging results showed that left condyles were wider in all LIPUS-treated groups (p < 0.05), while the LIPUS-only group had a greater left sagittal condylar length. LIPUS-treated groups displayed a lower midline shift to the right (p < 0.02). No significant differences were observed in the MSC group. Bone marrow morphology and vascularity differed between the groups as LIPUS-treated groups exhibited increased vascularity in the erosive cartilage zone. CONCLUSION: It was established that LIPUS and MSC application to the TMJ region of growing rats favoured transverse condylar growth, while LIPUS application alone may enhance sagittal condylar development.The MSC injection model had little effect on sagittal condylar growth.

Angiogenic activity of subchondral bone during the progression of osteoarthritis in a rabbit anterior cruciate ligament transection model.

OBJECTIVE: To investigate the longitudinal angiogenic activity of subchondral bone and cartilage during the progression of osteoarthritis (OA) using a rabbit model of OA. MATERIALS AND METHODS: OA was surgically induced by anterior cruciate ligament transaction (ACLT) in left knee of 12 months old female New Zealand white rabbits (n = 33). Histological examination, immunohistochemistry, and angiogenic activity assay was done at 0, 2, 4, 6, 8, 12 weeks after ACLT. Histologic evaluation was performed with haematoxylin and eosin, safranin-O staining to assess the OA change of medial femoral condyle (MFC) and lateral femoral condyle (LFC). CD31 immunohistochemistry was performed to confirm the vascular invasion at osteochondral junction. A co-cultured tubule formation assay was conducted to evaluate angiogenic activity of the subchondral bone and cartilage of MFC and LFC as well as synovium. Association between histological changes, angiogenic activity, and vascular invasion were evaluated. RESULTS: OA changes increased in a time-dependent manner both in MFC and LFC. Angiogenic activity of subchondral bone showed a monomodal change during the OA progression, achieved a peak in the early to progressive stage and decreased to normal level in the late stage of OA. Surge of vascular invasion was observed following the increase of angiogenic activity in the progressive stage of OA. Angiogenic activity of cartilage did not change during the course of OA progression. CONCLUSION: Angiogenic activity of subchondral bone was elevated in the early to progressive stage of OA and vascular invasion into the osteochondral junction followed.

Vascularity and histology of fetal labrum and chondrolabral junction: its relevance to chondrolabral detachment tears.

PURPOSE: Recently, acetabular labral tears were recognized as a source of hip pain. Most of these tears were found to be localized at the chondrolabral junction. The purpose of this study was to evaluate the chondrolabral junction in reference to its collagen fiber orientation and its vascularity, which might be used to explain the preponderance of labral tears. METHODS: Eighteen formalinized fetuses with a mean gestational age of 17 weeks (range: 11-24 weeks) were examined. The acetabuli were removed en bloc with the proximal femur for ease of orientation. The acetabuli were prepared and examined in four quadrants, namely, anterior, superior, posterior, and inferior. RESULTS: The staining pattern of the posteroinferior labrum was more dense than the anterosuperior labrum, due to its high collagen content. Collagen fibers in the posteroinferior quadrants were oriented perpendicularly to the chondrolabral junction, while those in the anterosuperior quadrants had a parallel oriented. Perpendicular collagen orientation and high collagen content may explain the stronger anchorage of the labrum to the bony acetabulum in posteroinferior quadrants. All of the vessels supplying the labrum originate from the capsular connective tissue and traverse the body of the labrum to reach the articular side. None of these vessels traverse the chondrolabral junction to reach the bony acetabulum. The total number of blood vessels was significantly higher in the capsular zone than in the articular zones. The number of blood vessels did not differ between the acetabular quadrants. CONCLUSIONS: In an effort to understand the chondrolabral junction tears, we can conclude that collagen content and fiber orientation may represent the histological basis for the predominance of tears at the anterosuperior region.

An atypical degenerative osteoarthropathy in Hyp mice is characterized by a loss in the mineralized zone of articular cartilage.

Patients with X-linked hypophosphatemia (XLH) develop enthesophytes and osteophytes secondary to articular cartilage degeneration and together are the primary cause of morbidity in adult patients so afflicted. We have previously characterized the enthesopathy in Hyp mice, a murine model of XLH. We now extend these studies to the synovial joint in order to characterize potential cellular changes in articular cartilage that may predispose patients to the osteoarthropathy of XLH. We report that, despite highly elevated levels of alkaline phosphatase activity throughout articular cartilage, there is a complete loss in the mineralized zone of articular cartilage as assessed by von Kossa staining of mineral and as quantified by EPIC-microCT analysis and evidence of vascular invasion. We also identify the downregulation of extracellular matrix (ECM) factors identified as regulators of terminally differentiated mineralizing articular chondrocytes. There is also a striking increase in the histochemical staining of sulfated proteoglycans, a change that may reflect the loss of a transitional tissue that reduces mechanical stress at the interface between cartilage and subchondral bone. The failure of mineralizing articular chondrocytes to develop in the hypophosphatemic state suggests that phosphate may be a key regulator of chondrocyte mineralization. Accordingly, we find that the appropriate zonal arrangement and phenotypic markers of articular cartilage are significantly reestablished by phosphate-replacement therapy. Given the turnover and maintenance of articular cartilage ECM, the identification of early and abnormal cellular changes unique to XLH will undoubtedly aid in a more effective management of this disease to minimize the onset of degenerative osteoarthropathy.