Early lesions of osteochondrosis in the distal tibia of foals

Osteochondrosis in the central and third tarsal bones of young horses

Recently, the central and third tarsal bones of 23 equine fetuses and foals were examined using micro-computed tomography. Radiological changes, including incomplete ossification and focal ossification defects interpreted as osteochondrosis, were detected in 16 of 23 cases. The geometry of the osteochondrosis defects suggested they were the result of vascular failure, but this requires histological confirmation. The study aim was to examine central and third tarsal bones from the 16 cases and to describe the tissues present, cartilage canals, and lesions, including suspected osteochondrosis lesions. Cases included 9 males and 7 females from 0 to 150 days of age, comprising 11 Icelandic horses, 2 standardbred horses, 2 warmblood riding horses, and 1 coldblooded trotting horse. Until 4 days of age, all aspects of the bones were covered by growth cartilage, but from 105 days, the dorsal and plantar aspects were covered by fibrous tissue undergoing intramembranous ossification. Cartilage canal vessels gradually decreased but were present in most cases up to 122 days and were absent in the next available case at 150 days. Radiological osteochondrosis defects were confirmed in histological sections from 3 cases and consisted of necrotic vessels surrounded by ischemic chondronecrosis (articular osteochondrosis) and areas of retained, morphologically viable hypertrophic chondrocytes (physeal osteochondrosis). The central and third tarsal bones formed by both endochondral and intramembranous ossification. The blood supply to the growth cartilage of the central and third tarsal bones regressed between 122 and 150 days of age. Radiological osteochondrosis defects represented vascular failure, with chondrocyte necrosis and retention, or a combination of articular and physeal osteochondrosis.

Refixation of a Large Osteochondral Fragment with Magnesium Compression Screws-A Case Report

INTRODUCTION

Osteochondrosis dissecans (OCD) is a disease affecting the subchondral bone and the overlying articular cartilage. The etiology is most likely a combination of biological and mechanical factors. The incidence is highest in children >12 years old and it predominantly affects the knee. In high-grade OCD lesions, free osteochondral fragments usually are refixed via titanium screws or biodegradable screws or pins. In this case, headless compression screws made from magnesium were used for refixation.

CASE REPORT

A thirteen-year-old female patient with a two-year history of knee pain was diagnosed with an OCD lesion of the medial femoral condyle. After initial conservative treatment, displacement of the osteochondral fragment occurred. Refixation was performed using two headless magnesium compression screws. At the 6 months follow up, the patient was pain free, and the fragment showed progressive healing while the implants were biodegrading.

DISCUSSION

Existing implants for refixation of OCD lesions either require subsequent removal or show less stability and possible inflammatory reactions. The new generation of magnesium screws used in this case did not lead to a gas release, as described for previous magnesium implants, while maintaining stability during continuous biodegradation.

CONCLUSIONS

The data available to date on magnesium implants for the treatment of OCD are promising. However, the evidence on the magnesium implants in refixation surgery of OCD lesions is still limited. Further research needs to be conducted to provide data on outcomes and possible complications.

Osteochondrosis and other lesions in all intervertebral, articular process and rib joints from occiput to sacrum in pigs with poor back conformation, and relationship to juvenile kyphosis

Background

Computed tomography (CT) is used to evaluate body composition and limb osteochondrosis in selection of breeding boars. Pigs also develop heritably predisposed abnormal curvature of the spine including juvenile kyphosis. It has been suggested that osteochondrosis-like changes cause vertebral wedging and kyphosis, both of which are identifiable by CT. The aim of the current study was to examine the spine from occiput to sacrum to map changes and evaluate relationships, especially whether osteochondrosis caused juvenile kyphosis, in which case CT could be used in selection against it. Whole-body CT scans were collected retrospectively from 37 Landrace or Duroc boars with poor back conformation scores. Spine curvature and vertebral shape were evaluated, and all inter-vertebral, articular process and rib joints from the occiput to the sacrum were assessed for osteochondrosis and other lesions.

Results

Twenty-seven of the 37 (73%) pigs had normal spine curvature, whereas 10/37 (27%) pigs had abnormal curvature and all of them had wedge vertebrae. The 37 pigs had 875 focal lesions in articular process and rib joints, 98.5% of which represented stages of osteochondrosis. Five of the 37 pigs had focal lesions in other parts of vertebrae, mainly consisting of vertebral body osteochondrosis. The 10 pigs with abnormal curvature had 21 wedge vertebrae, comprising 10 vertebrae without focal lesions, six ventral wedge vertebrae with ventral osteochondrosis lesions and five dorsal wedge vertebrae with lesions in the neuro-central synchondrosis, articular process or rib joints.

Conclusions

Computed tomography was suited for identification of wedge vertebrae, and kyphosis was due to ventral wedge vertebrae compatible with heritably predisposed vertebral body osteochondrosis. Articular process and rib joint osteochondrosis may represent incidental findings in wedge vertebrae. The role of the neuro-central synchondrosis in the pathogenesis of vertebral wedging warrants further investigation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-03091-6.

Osteochondritis Dissecans: Current Understanding of Epidemiology, Etiology, Management, and Outcomes

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Osteochondritis dissecans occurs most frequently in the active pediatric and young adult populations, commonly affecting the knee, elbow, or ankle, and may lead to premature osteoarthritis.

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While generally considered an idiopathic phenomenon, various etiopathogenetic theories are being investigated, including local ischemia, aberrant endochondral ossification of the secondary subarticular physis, repetitive microtrauma, and genetic predisposition.

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Diagnosis is based on the history, physical examination, radiography, and advanced imaging, with elbow ultrasonography and novel magnetic resonance imaging protocols potentially enabling early detection and in-depth staging.

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Treatment largely depends on skeletal maturity and lesion stability, defined by the presence or absence of articular cartilage fracture and subchondral bone separation, as determined by imaging and arthroscopy, and is typically nonoperative for stable lesions in skeletally immature patients and operative for those who have had failure of conservative management or have unstable lesions.

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Clinical practice guidelines have been limited by a paucity of high-level evidence, but a multicenter effort is ongoing to develop accurate and reliable classification systems and multimodal decision-making algorithms with prognostic value.

Bone tissue and histological and molecular events during development of the long bones

The bones are of mesenchymal or ectomesenchymal origin, form the skeleton of most vertebrates, and are essential for locomotion and organ protection. As a living tissue they are highly vascularized and remodelled throughout life to maintain intact. Bones consist of osteocytes entrapped in a mineralized extracellular matrix, and via their elaborated network of cytoplasmic processes they do not only communicate with each other but also with the cells on the bone surface (bone lining cells). Bone tissue develops through a series of fine-tuned processes, and there are two modes of bone formation, referred to either as intramembranous or endochondral ossification. In intramembranous ossification, bones develop directly from condensations of mesenchymal cells, and the flat bones of the skull, the clavicles and the perichondral bone cuff develop via this process. The bones of the axial (ribs and vertebrae) and the appendicular skeleton (e.g. upper and lower limbs) form through endochondral ossification where mesenchyme turns into a cartilaginous intermediate with the shape of the future skeletal element that is gradually replaced by bone. Endochondral ossification occurs in all vertebrate taxa and its onset involves differentiation of the chondrocytes, mineralization of the extracellular cartilage matrix and vascularization of the intermediate, followed by disintegration and resorption of the cartilage, bone formation, and finally - after complete ossification of the cartilage model - the establishment of an avascular articular cartilage. The epiphyseal growth plate regulates the longitudinal growth of the bones, achieved by a balanced proliferation and elimination of chondrocytes, and the question whether the late hypertrophic chondrocytes die or transform into osteogenic cells is still being hotly debated. The complex processes leading to endochondral ossification have been studied for over a century, and this review aims to give an overview of the histological and molecular events, arising from the long bones' (e.g. femur, tibia) development. The fate of the hypertrophic chondrocytes will be discussed in the light of new findings obtained from cell tracking studies.

Evaluation of the Suitability of Miniature Pigs as an Animal Model of Juvenile Osteochondritis Dissecans

Juvenile osteochondritis dissecans (JOCD) is a developmental disease characterized by formation of intra-articular (osteo)chondral flaps or fragments. Evidence-based treatment guidelines for JOCD are currently lacking. An animal model would facilitate study of JOCD and evaluation of diagnostic and treatment approaches. The purpose of this study was to assess the suitability of miniature pigs as a model of JOCD at the distal femur. First, stifle (knee) joints harvested from three juvenile miniature pigs underwent magnetic resonance imaging (MRI) to establish the vascular architecture of the distal femoral epiphyseal cartilage. Second, vessels supplying the axial or abaxial aspects of the medial femoral condyle were surgically interrupted in four additional juvenile miniature pigs, and the developing epiphyseal cartilage lesions were monitored using three consecutive MRI examinations over nine weeks. The miniature pigs were then euthanized, and their distal femora were harvested for histological evaluation. Vascular architecture of the distal femoral epiphyseal cartilage in the miniature pigs was found to be nearly identical to that of juvenile human subjects, characterized by separate vascular beds supplying the axial and abaxial aspects of the condyles. Surgical interruption of the vascular supply to the abaxial aspect of the medial femoral condyle resulted in ischemic cartilage necrosis (a precursor lesion of JOCD) in 75% (3/4) of the miniature pigs. Cartilage lesions were identified during the first MRI performed 3 weeks post-operatively. No clinically apparent JOCD-like lesions developed. In conclusion, miniature pigs are suitable for modeling JOCD precursor lesions. Further investigation of the model is warranted to assess induction of clinically apparent JOCD lesions. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2130-2137, 2019.

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.

Prevalence of osteochondral lesions in the fetlock and hock joints of Standardbred horses that survived bacterial infection before 6 months of age

BACKGROUND

Young Standardbred horses frequently develop fragments in joints. Some fragments represent osteochondrosis; others are considered developmental, but it is uncertain whether they result from preceding osteochondrosis. Osteochondrosis occurs as a consequence of failure of the cartilage canal blood supply and ischaemic chondronecrosis. In heritably predisposed foals, failure was associated with incorporation of vessels into bone. However, bacterial vascular failure was also recently documented in foals suffering spontaneous infections, proving that bacteria can cause osteochondral lesions in foals up to 150 days old. The aim was to determine prevalence of fetlock and hock lesions at screening age in Standardbred horses that survived infections before 6 months of age, and compare this to prevalence reported in the literature.

METHODS

The material consisted of 28 Standardbred horses; 17 males and 11 females that presented and were diagnosed clinically with bacterial infections from 1 to 150 days of age (average: 41.3 days). A screening set of 8 radiographic projections was available from all 28 horses at 7-85 months of age (average: 23.6 months). Lesion prevalence was compared to three previously reported Standardbred cohorts.

RESULTS

Osteochondral lesions were detected in one or more joints of 19/28 horses (67.9%); in the fetlock joint of 14/28 horses (50%) and the hock joint of 11/28 horses (39.3%). These prevalences were ≥ 2 x higher than the corresponding prevalences in the comparison cohorts, and statistically significantly so in 5:6 comparisons (p-values from < 0.00001 to 0.01). In the sepsis cohort, there were an average of 2.3 affected joints and 2.5 lesions per affected horse, whereas there in the one comparable literature cohort were an average of 1.5 affected joints and 1.7 lesions per affected horse.

CONCLUSIONS

Standardbred horses that survived bacterial infections before 6 months of age had more osteochondral lesions than literature comparison cohorts at screening age. The implication was that some of the lesions in this group were caused by bacteria. It may become necessary to develop methods for differentiating between acquired, septic and aseptic, heritably predisposed lesions.

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.

Septic Arthritis/Osteomyelitis May Lead to Osteochondrosis-Like Lesions in Foals

Failure of the cartilage canal blood supply leads to ischemic chondronecrosis which causes osteochondrosis, and osteochondral lesions. Osteochondrosis is a disease with a heritable component and usually occurs under aseptic conditions. Because bacteria can bind to growth cartilage and disrupt the blood supply in pigs and chickens, we considered whether this might play a role in development of equine osteochondrosis. The aim of this study was to examine whether bacteria are present in canals in the growth cartilage of foals with septic arthritis/osteomyelitis, and whether this is associated with osteochondrosis. The material consisted of 7 foals aged 9-117 days euthanized because of septic arthritis/osteomyelitis. The 7 cases had 16 lesions in growth cartilage that were evaluated histologically. Bacteria were present in cartilage canals in foals with septic arthritis/osteomyelitis. Portions of necrotic canals adjacent to bacteria frequently contained neutrophils, termed acute septic canals; or granulation tissue with neutrophils, termed chronic septic canals. Acute and chronic septic canals were associated with ischemic chondronecrosis in the articular-epiphyseal cartilage complex (AECC) of 5 cases and in the physis of 2 cases, and ossification was focally delayed in 5 of those 7 cases. Lesions occurred with and without adjacent osteomyelitis. Bacteria were present in cartilage canals and were associated with focal chondronecrosis in both the AECC and the physis. This establishes sepsis as a plausible cause of some osteochondral lesions in horses. It is recommended that horses with sepsis-related osteochondral lesions may be used for breeding without increasing the prevalence of OCD-predisposing genes in the population.

Characterization of cellular and matrix alterations in the early pathogenesis of osteochondritis dissecans in pigs using second harmonic generation and two-photon excitation fluorescence microscopy

Osteochondritis dissecans is a joint disease that is observed in several species. The disease can develop as a cause of ischemic chondronecrosis in the epiphyseal growth cartilage. Some lesions of chondronecrosis undergo spontaneous resolution, but it is not possible to predict whether a lesion will resolve or progress and require intervention. Proliferation of cells into clusters occurs at the lesion margin, but it is unclear if the clusters have a repair function. The aims of the current study were to examine clusters and potential matrix changes in response to ischemic chondronecrosis in the distal femur of 10 pigs aged 70-180 days using advanced microscopy based on two-photon excitation fluorescence and second harmonic generation. These microscopy techniques can perform 3D imaging of cells and collagen without staining. The results indicated a lower collagen density in the chondronecrotic areas compared to the normal growth cartilage, and fissures and breaks in the matrix integrity were demonstrated that potentially can propagate and cause osteochondritis dissecans. A higher number of cells in clusters was correlated with reduction in collagen density in the lesions. Some of the cells in the clusters had a morphology similar to progenitor cells, suggesting a potential repair role of the clusters. The study has shed further light on the secondary responses after initial lesion formation, which information can be of potential use to create models that can predict lesion progression and that may hence avoid unnecessary interventions in the future. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Quantitative and qualitative aspects of standing-up behavior and the prevalence of osteochondrosis in Warmblood foals on different farms: could there be a link?

BACKGROUND

Osteochondrosis (OC) is a common, clinically important joint disorder in which endochondral ossification is focally disturbed. Reduced blood supply to growing cartilage is considered an important cause of the condition, which has both genetic and environmental origins. Housing conditions can influence cartilage injury through peak-pressure changes during limb sliding. Additionally, circulatory perturbation can cause the avascular necrosis of cartilage. In this study, we evaluated the type and frequency of limb sliding during standing up and the occurrence of OC in foals aged up to 12 months on different farms.

METHODS

Standing-up behavior was observed in 50 weaned, group-housed, Dutch Warmblood foals aged 6-9 months at five farms using black-and-white surveillance cameras, and their standing-up behavior was scored using a predetermined ethogram. OC was scored using a categorical scale between 6 and 12 months of age in 50 foals in the weanling period, and in 48 from the weanling to yearling periods because two foals died in this time.

RESULTS

At both 6 and 12 months of age, the total prevalence of OC differed between the farms: the lowest prevalence was observed on a farm with no sliding, and the highest prevalence was evident on a farm with a higher sliding frequency. The mean ratio of sliding versus normal standing-up behavior was 29% (range: 0-50%); i.e., foals experienced limb sliding during around 29% of standing-up maneuvres. The frequency of sliding instead of normal standing-up behavior differed significantly between the farms (range: 0-50%; P < 0.05), but significantly decreased when foals could better prepare themselves to stand, e.g., when there was an obvious provocation such as the announced approach of another foal (P < 0.05).

CONCLUSIONS

Small but significant differences exist between farms in the sliding frequency and total OC incidence in Warmblood foals, but whether environmental factors are causally related to these differences requires further elucidation.

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.

Cartilage canals in the distal intermediate ridge of the tibia of fetuses and foals are surrounded by different types of collagen

Some epiphyseal growth cartilage canals are surrounded by a ring of hypereosinophilic matrix consisting of collagen type I. Absence of the collagen type I ring may predispose canal vessels to failure and osteochondrosis, which can lead to fragments in joints (osteochondrosis dissecans). It is not known whether the ring develops in response to programming or biomechanical force. The distribution that may reveal the function of the ring has only been described in the distal femur of a limited number of foals. It is also not known which cells are responsible for producing the collagen ring. The aims of the current study were to examine fetuses and foals to infer whether the ring forms in response to biomechanical force or programming, to describe distribution and to investigate which cell type produces the ring. The material consisted of 46 fetuses and foals from 293 days of gestation to 142 days old, of both sexes and different breeds, divided into three groups, designated the naïve group up to and including the day of birth, the adapting group from 2 days up to and including 14 days old, and the loaded group from 15 days and older. The distal tibia was sawn into parasagittal slabs and the cranial half of the central slab from the intermediate ridge was examined by light microscopy and immunohistochemical staining for collagen type I. Presence, completeness and location of the collagen ring was compared, as was the quantity of perivascular mesenchymal cells. An eosinophilic ring present on HE-stained sections was seen in every single fetus and foal examined, which corresponded to collagen type I in immunostained sections. A higher proportion of cartilage canals were surrounded by an eosinophilic ring in the naïve and adapting groups at 73 and 76%, respectively, compared with the loaded group at 51%. When considering only patent canals, the proportion of canals with an eosinophilic ring was higher in the adapting and loaded than the naïve group of foals. The ring was present around 90 and 81% of patent canals in the deep and middle layers, respectively, compared with 58% in the superficial layer, and the ring was more often complete around deep compared with superficial canals. The ring was absent or partial around chondrifying canals. When an eosinophilic ring was present around patent canals, it was more common for the canal to contain one or more layers of perivascular mesenchymal cells rather than few to no layers. It was also more common for the collagen ring to be more complete around canals that contained many as opposed to few mesenchymal cells. In conclusion, the proportion of cartilage canals that had an eosinophilic ring was similar in all three groups of fetuses and foals, indicating that the presence of the collagen ring was mostly programmed, although some adaptation was evident. The ring was more often present around deep, compared with superficial canals, indicating a role in preparation for ossification. The collagen ring appeared to be produced by perivascular mesenchymal cells.

In vivo visualization using MRI T2 mapping of induced osteochondrosis and osteochondritis dissecans lesions in goats undergoing controlled exercise

In vivo visualization of subclinical osteochondrosis (OC) lesions, characterized by necrosis of epiphyseal growth cartilage, is necessary to clarify the pathogenesis of this disease. Hence, our objectives were to demonstrate induced necrosis of the epiphyseal cartilage in vivo using MRI and to monitor progression or resolution of resulting lesions. We also aimed to improve the goat model of OC by introducing controlled exercise. Vascular supply to the epiphyseal cartilage was surgically interrupted in four 5-day-old goats to induce ischemic cartilage necrosis in a medial femoral condyle. Starting 3 weeks postoperatively, goats underwent daily controlled exercise until euthanasia at 6, 10, 11 (n = 2) weeks postoperatively. T2 maps of operated and control femora were obtained in vivo at 3 (n = 4), 6 (n = 4), 9 (n = 3), and 11 (n = 2) weeks postoperatively using a 3 T MR scanner. In vivo MRI findings were validated against MRI results obtained ex vivo at 9.4 T in three goats and compared to histological results in all goats. Surgical interruption of the vascular supply caused ischemic cartilage necrosis in three out of four goats. T2 maps obtained in vivo at 3 T identified regions of increased relaxation time consistent with discrete areas of cartilage necrosis 3-11 weeks postoperatively and demonstrated delayed progression of the ossification front at 9 (n = 1) and 11 (n = 2) weeks postoperatively. In vivo MRI findings were confirmed by ex vivo MRI at 9.4 T and by histology. Identification of cartilage necrosis in clinical patients in the early stages of OC using T2 maps may provide valuable insight into the pathogenesis of this condition. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:868-875, 2017.

Vascular Canals in Permanent Hyaline Cartilage: Development, Corrosion of Nonmineralized Cartilage Matrix, and Removal of Matrix Degradation Products

Core areas in voluminous pieces of permanent cartilage are metabolically supplied via vascular canals (VCs). We studied cartilage corrosion and removal of matrix degradation products during the development of VCs in nose and rib cartilage of piglets. Conventional staining methods were used for glycosaminoglycans, immunohistochemistry was performed to demonstrate collagens types I and II, laminin, Ki-67, von Willebrand factor, VEGF, macrophage marker MAC387, S-100 protein, MMPs -2,-9,-13,-14, and their inhibitors TIMP1 and TIMP2. VCs derived from connective tissue buds that bulged into cartilage matrix ("perichondrial papillae", PPs). Matrix was corroded at the tips of PPs or resulting VCs. Connective tissue stromata in PPs and VCs comprised an axial afferent blood vessel, peripherally located wide capillaries, fibroblasts, newly synthesized matrix, and residues of corroded cartilage matrix (collagen type II, acidic proteoglycans). Multinucleated chondroclasts were absent, and monocytes/macrophages were not seen outside the blood vessels. Vanishing acidity characterized areas of extracellular matrix degradation ("preresorptive layers"), from where the dismantled matrix components diffused out. Leached-out material stained in an identical manner to intact cartilage matrix. It was detected in the stroma and inside capillaries and associated downstream veins. We conclude that the delicate VCs are excavated by endothelial sprouts and fibroblasts, whilst chondroclasts are specialized to remove high volumes of mineralized cartilage. VCs leading into permanent cartilage can be formed by corrosion or inclusion, but most VCs comprise segments that have developed in either of these ways. Anat Rec, 300:1067-1082, 2017. © 2016 Wiley Periodicals, Inc.

Femoral epiphyseal cartilage matrix changes at predilection sites of equine osteochondrosis: Quantitative MRI, second-harmonic microscopy, and histological findings

Osteochondrosis is an ischemic chondronecrosis of epiphyseal growth cartilage that results in focal failure of endochondral ossification and osteochondritis dissecans at specific sites in the epiphyses of humans and animals, including horses. The upstream events leading to the focal ischemia remain unknown. The epiphyseal growth cartilage matrix is composed of proteoglycan and collagen macromolecules and encases its vascular tree in canals. The matrix undergoes major dynamic changes in early life that could weaken it biomechanically and predispose it to focal trauma and vascular failure. Subregions in neonatal foal femoral epiphyses (n = 10 osteochondrosis predisposed; n = 6 control) were assessed for proteoglycan and collagen structure/content employing 3T quantitative MRI (3T qMRI: T1ρ and T2 maps). Site-matched validations were made with histology, immunohistochemistry, and second-harmonic microscopy. Growth cartilage T1ρ and T2 relaxation times were significantly increased (p < 0.002) within the proximal third of the trochlea, a site predisposed to osteochondrosis, when compared with other regions. However, this was observed in both control and osteochondrosis predisposed specimens. Microscopic evaluation of this region revealed an expansive area with low proteoglycan content and a hypertrophic-like appearance on second-harmonic microscopy. We speculate that this matrix structure and composition, though physiological, may weaken the epiphyseal growth cartilage biomechanically in focal regions and could enhance the risk of vascular failure with trauma leading to osteochondrosis. However, additional investigations are now required to confirm this. 3T qMRI will be useful for future non-invasive longitudinal studies to track the osteochondrosis disease trajectory in animals and humans. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1743-1752, 2016.

Cartilage canals in newborn dogs: histochemical and immunohistochemical findings

Cartilage canals (CCs) are microscopic structures involved in secondary ossification centers (SOCs) development. The features of CCs were investigated in the humeral and femoral proximal epiphyses of small-sized newborn dogs (from premature to 28 days after birth) with histochemical and immunohistochemical approaches. Masson's Trichrome revealed a ring-shaped area around CCs, which changes in colour from green (immature collagen) to red (mature collagen) as ossification progresses; perichondrium staining always matched the ring colour. Safranin-O was always negative. Immunohistochemical analysis revealed immunopositivity for both collagen type I and V around the CCs; collagen type II was negative. CCs count showed a tendency to be higher in the humerus than in the femur. This work enlightened for the first time changes in composition of CCs surrounding matrix during SOCs development in dogs, paving the way to further investigations.

Heritability and prevalence of selected osteochondrosis lesions in yearling Thoroughbred horses

BACKGROUND

Osteochondrosis is considered multifactorial in origin, with factors such as nutrition, conformation, body size, trauma and genetics thought to contribute to its pathogenesis. Few studies have investigated the effects of genetic variability of osteochondrosis in Thoroughbreds.

OBJECTIVES

To describe the prevalence and genetic variability of a subset of osteochondrosis lesions in a group of Thoroughbred yearlings.

STUDY DESIGN

Retrospective cohort study.

METHODS

Radiographs of 1962 Thoroughbred yearlings were retrieved from clinical records obtained between 2005 and 2013. Pedigree information was obtained from the Australian Stud Book. Osteochondrosis lesions were documented in selected joints and estimates of heritability were obtained by fitting linear mixed models in ASREML software.

RESULTS

The overall prevalence of osteochondrosis was 23%. Osteochondrosis was identified in 10% of stifle joints, 6% of hock joints and 8% of fetlock joints. The heritability estimates ranged from 0 to 0.21. The largest estimates were 0.10, 0.14, 0.16 and 0.21 for lesions of the distal intermediate ridge of the tibia, dorso-proximal proximal phalanx (P1), any stifle osteochondrosis, and lesions of the lateral trochlear ridge of the distal femur, respectively. Although calculated heritability estimates had high standard errors, meta-analyses combining the present results with published estimates were significant at 0.10, 0.17, 0.15 and 0.20 for stifle, tarsal, fetlock and these joints combined, respectively. In addition, there was a permanent environment attributable to the dam effect.

MAIN LIMITATIONS

Inclusion criteria were based on radiographic findings in specific joints at a specific age range in Thoroughbreds.

CONCLUSIONS

The present results indicate that only a proportion of osteochondrosis in Thoroughbreds is heritable. The permanent environment effects of the dam were observed to have effects on some categories of osteochondrosis.

Differences in the vascular tree of the femoral trochlear growth cartilage at osteochondrosis-susceptible sites in foals revealed by SWI 3T MRI

Focal ischemic chondronecrosis of epiphyseal growth cartilage (EGC) during endochondral ossification is believed to be a key early event on the pathway to osteochondrosis (OC) in both animals and humans. The lateral ridge of the equine trochlea is a site where severe osteochondritis dissecans lesions frequently arise and is a model for the study of naturally occurring disease. Non-invasive imaging to investigate EGC vascularity may help elucidate why focal ischemia occurs. 3T MRI susceptibility-weighted imaging (SWI) of femoral trochlea of OC predisposed (n = 10) and control (n = 6) day-old foals, with minimal joint loading after birth, was performed. SWI and 3D images revealed the EGC vascular architecture without a contrast agent, and matched histologic observations. No vascular lesions were identified. There was no difference in the vascular density and architecture between control and OC specimens, but a striking difference in vascular pattern was seen at the OC-predilected site in the lateral ridge of the trochlea in all specimens, when compared to the medial ridge of the trochlea, where OC lesions are rarely observed. This site was less ossified with more perichondrial vessels not yet bridging with the subchondral bone. Furthermore, the mean vascular density of all specimens was significantly higher at this site. We speculate that joint morphology and focal internal trauma on this site with a unique vascular architecture may trigger ischemic events at this site. SWI permitted visualization of EGC in young foals with a clinical 3T MRI and paves the way for non-destructive longitudinal studies to improve understanding of OC in all species. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1539-1546, 2016.

Clinicopathological findings in horses with a bi- or tripartite navicular bone

Background

Navicular bone partition is a rare condition reported in horses, which is during the evaluation of a lameness or prepurchase examination often misinterpreted for a parasagittal fracture. In this report, the clinicopathological findings of three cases of navicular bone partition are evaluated. The possible pathomechanisms underlying the condition are hypothesised, focusing on a potential origin of foetal vascular disturbance. This study is furthermore aiming at a clearer and earlier recognition of navicular bone partition, since this condition would finally predispose for a clinical lameness with a poor prognosis.

Case presentations

Case 1 was a 10-year-old Belgian Warmblood gelding with a Grade 3/5 chronic, recurrent left-forelimb lameness that had persisted for 4 months. Perineural palmar digital nerve block of the distal foot abolished the lameness. Radiographic examination revealed a bipartite navicular bone in the left forelimb. Unfortunately, the animal was lost to follow-up. Case 2 was a 7-year-old Quarter Horse stallion with a Grade 3/5 recurrent right forelimb lameness that had persisted for 2 years. The lameness switched to the contralateral left forelimb with a palmar digital nerve block. Radiographic examination identified a tripartite navicular bone in both forelimbs. Pathological examination additionally revealed chronic degenerative changes of the cartilage and subchondral bone with marked cystic changes. Case 3 was a 5-year-old Dutch Warmblood gelding with a Grade 3/5 recurrent left hindlimb lameness that had persisted for 6 months. Owing to the uncooperative behaviour of the horse, only a combined peroneal and tibial nerve block could be performed, which abolished the lameness. Radiographic examination revealed a bipartite navicular bone in the left hindlimb. Pathological examination showed a navicular bipartition in the left hindlimb, with microscopic changes comparable to those evident in Case 2; additionally, cartilage indentations were also found in the navicular bones of the right front- and hindlimb at a similar location as the partition site in the left hindlimb.

Conclusions

It is speculated that a navicular bone partition has a congenital origin and is caused by vascular disturbance during foetal development. This may lead to aberrant endochondral ossification or the formation of multiple ossification centres resulting in navicular bone partitioning. In the adult horse, chronic repetitive biomechanical challenges at the partition sites may induce local degenerative changes with subchondral cyst formation and thus would cause a gradually developing chronic lameness with a poor prognosis.

Identification of novel osteochondrosis--Associated genes

During the early stages of articular osteochondrosis, cartilage is retained in subchondral bone, but the pathophysiology of this condition of growing humans and domestic animals is poorly understood. A subtractive hybridization study was undertaken to compare gene expression between the cartilage of early experimentally induced equine osteochondrosis lesions and control cartilage. Of the many putative differentially expressed genes identified, eight were confirmed by quantitative PCR analysis as differentially expressed, in addition to those already known to be associated with early lesions. Genes encoding vacuolar H(+)-ATPase V0 subunit d2 (ATP6V0D2), cathepsin K, integrin-binding sialoprotein, integrin αV, low density lipoprotein receptor-related protein 4, lumican, osteopontin, and thymosin β4 (TMSB4) were expressed at higher levels in lesions than in control cartilage. These genes included 34 genes not previously identified in cartilage. Some genes identified as associated with early lesions are known chondrocyte hypertrophy-associated genes, and in transmission electron microscopy studies normal hypertrophic chondrocytes were observed in lesions. Differential expression of ATP6V0D2 and TMSB4 in the cartilage of early naturally occurring osteochondrosis lesions was confirmed by immunohistochemistry. These results identify novel osteochondrosis-associated genes and provide evidence that articular osteochondrosis does not necessarily result from failure of chondrocytes to undergo hypertrophy.

Associations of conformation and locomotive characteristics in growing gilts with osteochondrosis at slaughter

Osteochondrosis (OC) and abnormalities in conformation and locomotive characteristics (CLC) have been associated with premature culling in sows. Several CLC have been suggested to be associated with OC and might help as an in vivo indicator for and increased risk of having OC. The aim of this study was to investigate associations of OC with CLC assessed at several ages in growing gilts from 2 separate experiments over the effects of dietary restriction (Exp. 1) and floor type (Exp. 2) on OC prevalence. In Exp. 1, gilts (n = 211) were subjectively assessed for CLC at, on average, 4, 9, 11, 16, and 24 wk of age. In Exp. 2, gilts (n = 212) were subjectively assessed for CLC at, on average, 4, 9, 11, 16, and 22 wk of age. Assessment was done on 10 conformation and 2 locomotive characteristics using a 9-point grading scale by 2 observers. At, on average, 27 wk of age in Exp. 1 and 24 wk of age in Exp. 2, gilts were slaughtered and the knee, elbow, and hock joints were macroscopically assessed for OC. The CLC most frequently associated with OC were O shape or X shape of the hind legs, straight or bowed hind legs, and straight or sickled hock. X-shaped hind legs were associated with OC at slaughter in the knee joint at 4, 9, and 24 wk of age and at the animal level (all joints taken together) at 4, 9, and 16 wk of age. Straight or bowed hind legs were associated with OC at slaughter in the knee joint at 4 and 11 wk of age; in the hock joint at 11 wk of age; and at the animal level at 4, 9, 11, and 22 wk of age. Straight or sickled hock was associated with OC at slaughter in the knee joint at 4 wk of age, in the hock joint at 9 and 22 wk of age, and at the animal level at 9 and 22 wk of age. Results show that several CLC assessed at several ages were associated with OC, but consistent associations of a type of CLC in every assessment could not be found. The associations of CLC with OC are, therefore, difficult to be used as an in vivo indicator of increased risk for OC.

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.

Novel Application of Magnetic Resonance Imaging Demonstrates Characteristic Differences in Vasculature at Predilection Sites of Osteochondritis Dissecans

BACKGROUND

Understanding the pathogenesis of osteochondrosis/osteochondritis dissecans and other developmental orthopaedic diseases that are thought to occur secondary to defects in vascular supply to growth/epiphyseal cartilage has been hampered by the inability to image the vasculature in this tissue. This is particularly true in human beings due to limitations of current imaging techniques and the lack of availability of appropriate cadaveric samples for histological studies.

HYPOTHESIS

Susceptibility-weighted imaging, an MRI sequence, allows identification of characteristic differences in the vascular architecture in species that are affected by osteochondrosis/osteochondritis dissecans on the femoral condyle (humans and pigs) versus a species that is free of the disease (goat).

STUDY DESIGN

Controlled laboratory study.

MATERIALS

Distal femora from cadavers of juvenile humans (n = 5), pigs (n = 3), and goats (n = 3) were scanned in a 9.4-T MRI scanner using susceptibility-weighted imaging. Three-dimensional reconstructions were created, and minimum intensity projections were calculated in 3 planes to enhance visualization of the vascular architecture.

RESULTS

Susceptibility-weighted imaging allowed clear visualization of the epiphyseal vasculature in all species. Vascular architecture, with vessels primarily arising from the perichondrium, was similar in humans and pigs, which are predisposed to osteochondrosis/osteochondritis dissecans, and was starkly different from that present in goats, a species in which there are no reports of osteochondrosis/osteochondritis dissecans. Furthermore, vessels in the distal femoral predilection site disappeared with age in humans in a pattern similar to that reported previously in pigs.

CONCLUSION

Nearly identical vascular architecture at the shared primary predilection site of osteochondrosis/osteochondritis dissecans in the femoral condyles in human beings and pigs suggests that vascular failure, which is known to be central to the pathogenesis of this disease in pigs, may also play a role in humans.

CLINICAL RELEVANCE

This assumption of a shared pathogenesis is supported by the pattern of disappearance of vessels with age at the primary predilection site of osteochondritis dissecans in humans, which is essentially identical to that which has been reported in pigs. Susceptibility-weighted imaging will likely help further elucidate this potential relationship in the future.

An Update on the Pathogenesis of Osteochondrosis

Osteochondrosis is defined as a focal disturbance in endochondral ossification. The cartilage superficial to an osteochondrosis lesion can fracture, giving rise to fragments in joints known as osteochondrosis dissecans (OCD). In pigs and horses, it has been confirmed that the disturbance in ossification is the result of failure of the blood supply to epiphyseal growth cartilage and associated ischemic chondronecrosis. The earliest lesion following vascular failure is an area of ischemic chondronecrosis at an intermediate depth of the growth cartilage (osteochondrosis latens) that is detectable ex vivo, indirectly using contrast-enhanced micro- and conventional computed tomography (CT) or directly using adiabatic T1ρ magnetic resonance imaging. More chronic lesions of ischemic chondronecrosis within the ossification front (osteochondrosis manifesta) are detectable by the same techniques and have also been followed longitudinally in pigs using plain CT. The results confirm that lesions sometimes undergo spontaneous resolution, and in combination, CT and histology observations indicate that this occurs by filling of radiolucent defects with bone from separate centers of endochondral ossification that form superficial to lesions and by phagocytosis and intramembranous ossification of granulation tissue that forms deep to lesions. Research is currently aimed at discovering the cause of the vascular failure in osteochondrosis, and studies of spontaneous lesions suggest that failure is associated with the process of incorporating blood vessels into the advancing ossification front during growth. Experimental studies also show that bacteremia can lead to vascular occlusion. Future challenges are to differentiate between causes of vascular failure and to discover the nature of the heritable predisposition for osteochondrosis.

Genome-wide association analysis of osteochondrosis of the tibiotarsal joint in Norwegian Standardbred trotters

Osteochondrosis (OC), a disturbance in the process of endochondral ossification, is by far the most important equine developmental orthopaedic disease and is also common in other domestic animals and humans. The purpose of this study was to identify quantitative trait loci (QTL) associated with osteochondrosis dissecans (OCD) at the intermediate ridge of the distal tibia in Norwegian Standardbred (SB) using the Illumina Equine SNP50 BeadChip whole-genome single-nucleotide polymorphism (SNP) assay. Radiographic data and blood samples were obtained from 464 SB yearlings. Based on the radiographic examination, 162 horses were selected for genotyping; 80 of these were cases with an OCD at the intermediate ridge of the distal tibia, and 82 were controls without any developmental lesions in the joints examined. Genotyped horses descended from 22 sires, and the number of horses in each half-sib group ranged from 3 to 14. The population structure necessitated statistical correction for stratification. When conducting a case-control genome-wide association study (GWAS), mixed-model analyses displayed regions on chromosomes (Equus callabus chromosome - ECA) 5, 10, 27 and 28 that showed moderate evidence of association (P ≤ 5 × 10(-5); this P-value is uncorrected i.e. not adjusted for multiple comparisons) with OCD in the tibiotarsal joint. Two SNPs on ECA10 represent the most significant hits (uncorrected P=1.19 × 10(-5) in the mixed-model). In the basic association (chi-square) test, these SNPs achieved statistical significance with the Bonferroni correction (P=0.038) and were close in the permuted logistic regression test (P=0.054). Putative QTL on ECA 5, 10, 27 and 28 represent interesting areas for future research, validation studies and fine mapping of candidate regions. Results presented here represent the first GWAS of OC in horses using the recently released Illumina Equine SNP50 BeadChip.

Development of a Large Animal Model of Osteochondritis Dissecans of the Knee: A Pilot Study

Background:

Treatment of osteochondritis dissecans (OCD) of the knee is challenging, and evidence for stage-dependent treatment options is lacking. Basic science approaches utilizing animal models have provided insight into the etiology of OCD but have yet to produce a reliable and reproducible large animal model of the disease on which to test new surgical strategies.

Purpose/Hypotheses:

The purpose of this study was to develop an animal model featuring an OCD-like lesion in terms of size, location, and International Cartilage Repair Society (ICRS) grading. The hypothesis was that surgical creation of an osteochondral defect followed by placement of a barrier between parent bone and progeny fragment would generate a reproducible OCD-like lesion.

Study Design:

Controlled laboratory study.

Methods:

Bilateral osteochondral lesions were created in the medial femoral condyles of 9 Yucatan minipigs. After lesion creation, a biodegradable membrane was interposed between the progeny and parent bone. Five different treatment groups were evaluated at 2 weeks: a control with no membrane (ctrl group; n = 4), a slowly degrading nanofibrous poly(∊-caprolactone) membrane (PCL group; n = 4), a fenestrated PCL membrane with 1.5-mm holes covering 25% of surface area (fenPCL group; n = 4), a collagen membrane (Bio-Gide) (CM group; n = 3), and a fenestrated CM (fenCM group; n = 3). Five unperturbed lateral condyles (1 from each treatment group) served as sham controls. After euthanasia on day 14, the lesion was evaluated by gross inspection, fluoroscopy, micro–computed tomography (micro-CT), and histology. To quantify changes between groups, a scoring system based on gross appearance (0-2), fluoroscopy (0-2), and micro-CT (0-6) was established. Micro-CT was used to quantify bone volume per total volume (BV/TV) in a defined region surrounding and inclusive of the defect.

Results:

The no scaffold group showed healing of the subchondral bone at 2 weeks, with continuity of subchondral bone elements. Conversely, condyles treated with PCL or CM showed substantial remodeling, with loss of bone in both the progeny fragment and surrounding parent bone. When these membranes were fenestrated (fenPCL and fenCM groups), bone loss was less severe. Histological analysis showed no integration in the cartilage layer in any treatment group, while fibrous tissue formed between the parent and progeny fragments. Micro-CT showed significant differences in mean BV/TV between the PCL (27.4% ± 2.3%) and the sham (47.7% ± 1.4%) or no scaffold (54.9% ± 15.1%) groups (P < .01 and P < .05, respectively). In addition, a significant difference in bone loss was evident between the PCL and fenPCL groups (mean BV/TV, 46.6% ± 15.2%; P < .05), as well as between the PCL and fenCM (mean BV/TV, 50.9% ± 3.5%) and fenPCL groups (P < .01). Grading by 6 blinded reviewers using an OCD scoring system with 3 subcategories showed a significant difference between control and PCL groups.

Conclusion:

This study successfully developed a large animal model of OCD-like lesions in the knee joint of Yucatan minipigs. The lesions generated matched characteristics of an ICRS grade 3 OCD lesion in humans. These findings set the stage for ongoing model refinement as well as exploration of novel interventional therapies to restore function and bone and cartilage patency in individuals affected by this rare but significant disease.

Clinical Relevance:

This developed model will serve as a platform on which to further investigate the natural course as well as emerging treatment options for OCD.

Omics technologies provide new insights into the molecular physiopathology of equine osteochondrosis

Background

Osteochondrosis (OC(D)) is a juvenile osteo-articular disorder affecting several mammalian species. In horses, OC(D) is considered as a multifactorial disease and has been described as a focal disruption of endochondral ossification leading to the development of osteoarticular lesions. Nevertheless, OC(D) physiopathology is poorly understood. Affected horses may present joint swelling, stiffness and lameness. Thus, OC(D) is a major concern for the equine industry. Our study was designed as an integrative approach using omics technologies for the identification of constitutive defects in epiphyseal cartilage and/or subchondral bone associated with the development of primary lesions to further understand OC(D) pathology. This study compared samples from non-affected joints (hence lesion-free) from OC(D)-affected foals (n = 5, considered predisposed samples) with samples from OC-free foals (n = 5) considered as control samples. Consequently, results are not confounded by changes associated with the evolution of the lesion, but focus on altered constitutive molecular mechanisms. Comparative proteomics and micro computed tomography analyses were performed on predisposed and OC-free bone and cartilage samples. Metabolomics was also performed on synovial fluid from OC-free, OC(D)-affected and predisposed joints.

Results

Two lesion subtypes were identified: OCD (lesion with fragment) and OC (osteochondral defects). Modulated proteins were identified using omics technologies (2-DE proteomics) in cartilage and bone from affected foals compare to OC-free foals. These were associated with cellular processes including cell cycle, energy production, cell signaling and adhesion as well as tissue-specific processes such as chondrocyte maturation, extracellular matrix and mineral metabolism. Of these, five had already been identified in synovial fluid of OC-affected foals: ACTG1 (actin, gamma 1), albumin, haptoglobin, FBG (fibrinogen beta chain) and C4BPA (complement component 4 binding protein, alpha).

Conclusion

This study suggests that OCD lesions may result from a cartilage defect whereas OC lesions may be triggered by both bone and cartilage defects, suggesting that different molecular mechanisms responsible for the equine osteochondrosis lesion subtypes and predisposition could be due to a defect in both bone and cartilage. This study will contribute to refining the definition of OC(D) lesions and may improve diagnosis and development of therapies for horses and other species, including humans.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-947) contains supplementary material, which is available to authorized users.

Articular osteochondrosis: a comparison of naturally-occurring human and animal disease

BACKGROUND

Osteochondrosis (OC) is a common developmental orthopedic disease affecting both humans and animals. Despite increasing recognition of this disease among children and adolescents, its pathogenesis is incompletely understood because clinical signs are often not apparent until lesions have progressed to end-stage, and examination of cadaveric early lesions is not feasible. In contrast, both naturally-occurring and surgically-induced animal models of disease have been extensively studied, most notably in horses and swine, species in which OC is recognized to have profound health and economic implications. The potential for a translational model of human OC has not been recognized in the existing human literature.

OBJECTIVE

The purpose of this review is to highlight the similarities in signalment, predilection sites and clinical presentation of naturally-occurring OC in humans and animals and to propose a common pathogenesis for this condition across species.

STUDY DESIGN

Review.

METHODS

The published human and veterinary literature for the various manifestations of OC was reviewed. Peer-reviewed original scientific articles and species-specific review articles accessible in PubMed (US National Library of Medicine) were eligible for inclusion.

RESULTS

A broad range of similarities exists between OC affecting humans and animals, including predilection sites, clinical presentation, radiographic/MRI changes, and histological appearance of the end-stage lesion, suggesting a shared pathogenesis across species.

CONCLUSION

This proposed shared pathogenesis for OC between species implies that naturally-occurring and surgically-induced models of OC in animals may be useful in determining risk factors and for testing new diagnostic and therapeutic interventions that can be used in humans.

Local Morphological Response of the Distal Femoral Articular-Epiphyseal Cartilage Complex of Young Foals to Surgical Stab Incision and Potential Relevance to Cartilage Injury and Repair in Children

OBJECTIVE

Describe the local morphological response of the articular-epiphyseal cartilage complex to surgical stab incision in the distal femur of foals, with emphasis on the relationship between growth cartilage injury, enchondral ossification, and repair.

DESIGN

Nine foals were induced into general anesthesia at the age of 13 to 15 days. Four full-thickness stab incision defects were created in the cartilage on the lateral aspect of the lateral trochlear ridge of the left distal femur. Follow-up examination was carried out from 1 to 49 days postoperatively, including examination of intact bones, sawed slabs, and histological sections.

RESULTS

Incision defects filled with cells displaying fibroblast-, chondrocyte-, and osteoblast-like characteristics, potentially validating the rationale behind the drilling of stable juvenile osteochondritis dissecans lesions in children. Incisions induced necrosis within the cartilage on the margins at all depths of the defects. Sharp dissection may therefore be contraindicated in cartilage repair in young individuals. Incisions caused a focal delay in enchondral ossification in 2 foals, apparently related to the orientation of the incision defect relative to the direction of ossification. Defects became progressively surrounded by subchondral bone, in which granulation tissue containing clasts and foci of osteoblast-like cells was observed. Continued enchondral ossification was therefore likely to result in healing of uncomplicated defects to morphologically normal bone.

CONCLUSIONS

Epiphyseal growth cartilage injury had the potential to exert a negative effect on enchondral ossification. Enchondral ossification exerted a beneficial effect on repair. This relationship warrants consideration in future studies of cartilage injury and repair within the articular-epiphyseal cartilage complex of all species.

Transection of vessels in epiphyseal cartilage canals leads to osteochondrosis and osteochondrosis dissecans in the femoro-patellar joint of foals; a potential model of juvenile osteochondritis dissecans

OBJECTIVE

To transect blood vessels within epiphyseal cartilage canals and observe whether this resulted in ischaemic chondronecrosis, an associated focal delay in enchondral ossification [osteochondrosis (OC)] and pathological cartilage fracture [osteochondrosis dissecans (OCD)] in the distal femur of foals, with potential translational value to the pathogenesis of juvenile osteochondritis dissecans (JOCD) in children.

METHOD

Ten Norwegian Fjord Pony foals were operated at the age of 13-15 days. Two vessels supplying the epiphyseal growth cartilage of the lateral trochlear ridge of the left distal femur were transected in each foal. Follow-up examination was carried out from 1 to 49 days post-operatively and included plain radiography, macroscopic and histological examination.

RESULTS

Transection of blood vessels within epiphyseal cartilage canals resulted in necrosis of vessels and chondrocytes, i.e., ischaemic chondronecrosis, in foals. Areas of ischaemic chondronecrosis were associated with a focal delay in enchondral ossification (OC) in foals examined 21 days or more after transection, and pathological cartilage fracture (OCD) in one foal examined 42 days after transection.

CONCLUSION

The ischaemic hypothesis for the pathogenesis of OC has been reproduced experimentally in foals. There are several similarities between OCD in animals and JOCD in children. It should be investigated whether JOCD also occurs due to a focal failure in the cartilage canal blood supply, followed by ischaemic chondronecrosis.

Early Lesions of Articular Osteochondrosis in the Distal Femur of Foals

Failure of the cartilage canal blood supply to epiphyseal growth cartilage has been implicated in the pathogenesis of articular osteochondrosis in horses and other animal species. In a previous study of the developmental pattern of the blood supply in the tarsus of foals, early lesions of osteochondrosis were consistently found in regions where the cartilage canal vessels traversed the chondro-osseous junction. The developmental pattern of blood vessels has also been described in the distal femoral epiphysis; however, the group of foals examined in that study did not have lesions of osteochondrosis in this location. Therefore, the relationship between the occurrence of early lesions of osteochondrosis and the developmental pattern of the blood supply to epiphyseal growth cartilage in this site in foals has not been examined. Distal femora were collected from 30 fetuses and foals (up to 11 months old) submitted for postmortem examination. Sections from the lateral trochlear ridge and medial femoral condyle of both hind limbs were examined histologically. Sixteen cartilage lesions were found in 7 of the 30 fetuses and foals. All lesions contained evidence of cartilage canal necrosis and ischemic chondronecrosis. The lesions were located in regions where cartilage canal vessels traversed the chondro-osseous junction, as previously observed in the tarsus. The location and morphology of lesions indicated that a subclinical stage of ischemic chondronecrosis existed that preceded and predisposed to the development of osteochondrosis dissecans and subchondral bone cysts.

Assessment of synovial fluid biomarkers in healthy foals and in foals with tarsocrural osteochondrosis

Although alterations in biomarkers of cartilage turnover in synovial fluid (SF) have been demonstrated in horses with osteochondrosis (OC), there have been few investigations of such alterations in animals <1 year old. In this study tarsocrural SF samples from foals aged 18, 22 and 52 weeks of age were assessed for: (1) 'turnover' biomarkers of type II collagen (CPII and C2C) and proteoglycan (CS846 and glycosaminoglycans [GAG]); (2) matrix metalloproteinase (MMP) activity; (3) insulin-like growth factor (IGF)-1; (4) transforming growth factor (TGF)-β1; (5) prostaglandin (PG) E(2); and (6) leukotriene B(4). Using a linear mixed model, the concentration of biomarkers was compared between animals that developed or did not develop radiographic evidence of OC at 24 or 48 weeks of age. The CPII:C2C ratio tended to be higher in OC-affected joints compared to controls at all ages, and this difference was statistically significant at 22 weeks of age. The concentrations of CS846 and IGF-1, and the CS846:GAG ratio were reduced in OC-affected joints relative to controls at 18 weeks of age only. At 52 weeks of age, the PGE(2) concentration was lower in joints with OC. Overall, there appears to be a consistent anabolic shift in type II collagen turnover in juvenile joints affected by OC. Aberrant proteoglycan turnover is not a hallmark of the late repair of this lesion but reduced concentrations of IGF-1 in SF may be associated with early-stage lesions.

Osteochondritis dissecans (OCD), an endoplasmic reticulum storage disease?: a morphological and molecular study of OCD fragments

Osteochondritis dissecans (OCD) fragments, cartilage and blood from four patients were used for morphological and molecular analysis. Controls included articular cartilage and blood samples from healthy individuals. Light microscopy and transmission electron microscopy (TEM) showed abnormalities in chondrocytes and extracellular matrix of cartilage from OCD patients. Abnormal type II collagen heterofibrils in "bundles" and chondrocytes with abnormal accumulation of matrix proteins in distended rough endoplasmic reticulum were typical findings. Further, Von Kossa staining and TEM showed empty lacunae close to mineralized "islands" in the cartilage and hypertrophic chondrocytes containing accumulated matrix proteins. Immunostaining revealed: (1) that types I, II, VI and X collagens and aggrecans were deposited intracellulary and (2) co-localization within the islands of types I, II, X collagens and aggrecan indicating that hypertrophic chondrocytes express a phenotype of bone cells during endochondral ossification. Types I, VI and X collagens were also present across the entire dissecates suggesting that chondrocytes were dedifferentiated. DNA sequencings were non-conclusive, only single nucleotide polymorphism was found within the COL2A1 gene for one patient. We suggest that OCD lesions are caused by an alteration in chondrocyte matrix synthesis causing an endoplasmic reticulum storage disease phenotype, which disturbs or abrupts endochondral ossification.