Etiology and Pathogenesis of Osteochondrosis

Osteochondrosis is a common and clinically important joint disorder that occurs in human beings and in multiple animal species, most commonly pigs, horses, and dogs. This disorder is defined as a focal disturbance of enchondral ossification and is regarded as having a multifactorial etiology, with no single factor accounting for all aspects of the disease. The most commonly cited etiologic factors are heredity, rapid growth, anatomic conformation, trauma, and dietary imbalances; however, only heredity and anatomic conformation are well supported by the scientific literature. The way in which the disease is initiated has been debated. Although formation of a fragile cartilage, failure of chondrocyte differentiation, subchondral bone necrosis, and failure of blood supply to the growth cartilage all have been proposed as the initial step in the pathogenesis, the recent literature strongly supports failure of blood supply to growth cartilage as being the most likely. The term osteochondrosis has been used to describe a wide range of different lesions among different species. We suggest a refinement of this terminology to include the modifiers latens (lesion confined to epiphyseal cartilage), manifesta (lesion accompanied by delay in endochondral ossification), and dissecans (cleft formation through articular cartilage). The purpose of this review is to provide an overview of the disease, focusing on the most commonly cited theories, recent research findings, and our own views regarding the etiology and pathogenesis of osteochondrosis, in order to provide a better understanding of this apparently complex disease.

Relationship between serum biomarkers of cartilage and bone metabolism and joint injury in young Thoroughbred racehorses in training

OBJECTIVE

To compare serum concentrations of biomarkers of cartilage and bone metabolism between racehorses with a carpal or metacarpophalangeal or metatarsophalangeal (ie, fetlock) joint injury and matched uninjured control horses, determine changes in biomarker concentrations following joint injury, and establish the biomarkers' diagnostic test performance.

ANIMALS

50 Thoroughbred racehorses with a carpal or fetlock joint injury and 50 matched uninjured horses (control horses).

PROCEDURES

Serum concentrations of 2 cartilage synthesis biomarkers (carboxy-terminal propeptide of type II collagen [CPII] and chondroitin sulfate epitope 846 [CS846]), 2 cartilage degradation biomarkers (neoepitope generated by collagenase cleavage of type II collagen [C2C] and cross-linked carboxy-terminal telopeptide fragments of type II collagen [CTX-II]), and serum activity of a bone formation marker (bone-specific alkaline phosphatase [BAP]) were measured around the time of injury diagnosis and monthly thereafter for as long as possible.

RESULTS

Injured horses as a group and horses specifically with fetlock joint injuries had significantly lower serum CPII concentrations and significantly higher serum BAP activities than matched control horses. Concentrations of CTX-II were decreased between 2 and 4 months following joint injury. Measurement of CPII concentration at baseline could distinguish between injured horses and control horses with a sensitivity of 82% and specificity of 50%.

CONCLUSIONS AND CLINICAL RELEVANCE

Although significant differences in specific biomarker concentrations between horses with carpal and fetlock joint injuries and matched control horses were identified, there was no convincing evidence of the suitability of these biomarkers as diagnostic or prognostic tools in a clinical setting.

Cartilage matrix changes in the developing epiphysis: early events on the pathway to equine osteochondrosis?

REASONS FOR PERFORMING STUDY

The earliest osteochondrosis (OC) microscopic lesion reported in the literature was present in the femorotibial joint of a 2-day-old foal suggesting that OC lesions and factors initiating them may arise prior to birth.

OBJECTIVE

To examine the developing equine epiphysis to detect histological changes that could be precursors to OC lesions.

METHODS

Osteochondral samples from 21 equine fetuses and 13 foals were harvested from selected sites in the scapulohumeral, humeroradial, metacarpophalangeal, femoropatellar, femorotibial, tarsocrural and metatarsophalangeal joints. Sections were stained with safranin O and picrosiruis red to assess cartilage changes and structural arrangement of the collagen matrix.

RESULTS

Extracellular matrix changes observed included perivascular areas of paleness of the proteoglycan matrix associated with hypocellularity and, sometimes, necrotic chondrocytes. These changes were most abundant in the youngest fetuses and in the femoropatellar/femorotibial (FP/FT) joints. Indentations of the ossification front were also observed in most specimens, but, most frequently, in scapulohumeral and FP/FT joints. A cartilage canal was almost always present in these indentations. The vascular density of the cartilage was higher in the youngest fetuses. In these fetuses, the most vascularised joints were the metacarpo- and metatarsophalangeal joints but their cartilage canals regressed quickly. After birth, the most vascularised cartilage was present in the FP/FT joint. Articular cartilage differentiated into 4 zones early in fetal life and the epiphyseal cartilage also had a distinct zonal cartilage structure. A striking difference was observed in the collagen structure at the junction of the proliferative and hypertrophic zones where OCD lesions occur.

CONCLUSION

Matrix and ossification front changes were frequently observed and significantly associated with cartilage canals suggesting that they may be physiological changes associated with matrix remodelling and development. The collagen structure was variable through the growing epiphysis and a differential in biomechanical properties at focal sites may predispose them to injury.

Micro-computed tomography of early lesions of osteochondrosis in the tarsus of foals

INTRODUCTION

Osteochondrosis (OC) is an important developmental orthopedic disease of human and equine patients. The disease is defined as a focal disturbance in enchondral ossification. In horses, the disturbance can occur secondary to failure of the blood supply to growth cartilage. Diagnosis of the early, subclinical stages that can clarify the etiology is currently confined to cross-sectional histological examination. The potential for micro-computed tomography (micro-CT) with angiography to detect early lesions of OC has not yet been investigated.

MATERIALS AND METHODS

Nine Standardbred foals bred from parents with OC of the tarso-crural joint were sacrificed at weekly intervals from birth to 7 weeks of age. Permanent barium angiograms were created within one hind limb post mortem, and samples collected from two predilection sites for OC within the tarso-crural joint of the perfused hind limb. The resulting 18 sample blocks were scanned with a custom-built micro-CT equipment set-up, and analyzed as 2D slices and 3D volume rendered models before sectioning for conventional histological examination.

RESULTS

Histological examination identified eight early lesions in seven locations within six joints from the nine foals. Micro-CT with angiography was able to detect seven lesions in the same sites as histological examination. Lesions consisted of non-perfused foci within growth cartilage. No perfused vessels exited from subchondral bone deep to any lesion. Six of the seven lesions were associated with focal defects in the subchondral bone plate. Evidence of ongoing ossification was seen in three out of the seven lesions and included one separate center of ossification.

CONCLUSION

Micro-CT was a useful technique for examination of early lesions of OC. The results of micro-CT were compatible with failure of cartilage canal vessels at the point where they cross the ossification front. Resultant areas of ischemic chondronecrosis were associated with focal delay in enchondral ossification as visualized in 3D volume rendered models. Micro-CT combined with histology clarified the role of different forms of ossification in the secondary repair responses to lesions.

Hypertrophy and physiological death of equine chondrocytes in vitro

REASON FOR PERFORMING STUDY

Equine osteochondrosis results from a failure of endochondral ossification during skeletal growth. Endochondral ossification involves chondrocyte proliferation, hypertrophy and death. Until recently no culture system was available to study these processes in equine chondrocytes.

OBJECTIVE

To optimise an in vitro model in which equine chondrocytes can be induced to undergo hypertrophy and physiological death as seen in vivo.

METHODS

Chondrocytes isolated from fetal or older (neonatal, growing and mature) horses were cultured as pellets in 10% fetal calf serum (FCS) or 10% horse serum (HS). The pellets were examined by light and electron microscopy. Total RNA was extracted from the pellets, and quantitative PCR carried out to investigate changes in expression of a number of genes regulating endochondral ossification.

RESULTS

Chondrocytes from fetal foals, grown as pellets, underwent hypertrophy and died by a process morphologically similar to that seen in vivo. Chondrocytes from horses age >5 months did not undergo hypertrophy in pellet culture. They formed intramembranous inclusion bodies and the cultures included cells of osteoblastic appearance. Pellets from neonatal foals cultured in FCS resembled pellets from older horses, however pellets grown in HS underwent hypertrophy but contained inclusion bodies. Chondrocytes from fetal foals formed a typical cartilage-like tissue grossly and histologically, and expressed the cartilage markers collagen type II and aggrecan mRNA. Expression of Sox9, collagen type II, Runx2, matrix metalloproteinase-13 and connective tissue growth factor mRNA increased at different times in culture. Expression of fibroblast growth factor receptor-3 and vascular endothelial growth factor mRNA decreased with time in culture.

CONCLUSIONS

Freshly isolated cells from fetal growth cartilage cultured as pellets provide optimal conditions for studying hypertrophy and death of equine chondrocytes.

POTENTIAL RELEVANCE

This culture system should greatly assist laboratory studies aimed at elucidating the pathogenesis of osteochondrosis.

Genetic parameters for the prevalence of osteochondrosis in the limb joints of South German Coldblood horses

Heritabilities were estimated for osteochondrosis (OC) in fetlock and hock joints and palmar/plantar osseous fragments in fetlock joints of South German Coldblood (SGC) horses using Residual Maximum Likelihood (REML) under a linear animal model. The analyses were based on the results of a standardized radiographic examination of 167 SGC horses with a mean age of 14 months. The heritabilities linearly estimated and transformed onto the liability scale were for OC in fetlock joints 0.16 and for OC in hock joints 0.04. Considering fetlock and hock OC together, results in a heritability of 0.17. Palmar/plantar osseus fragments of the fetlock joints showed a heritability of 0.48. We concluded that there is most likely a genetic component in the variation of the development of osteochondrosis in fetlock and hock joints as well as for palmar/plantar osseus fragments of fetlock joints of the investigated population of SGC horses.

Genome-wide search for markers associated with osteochondrosis in Hanoverian warmblood horses

A genome-wide scan was performed to detect quantitative trait loci (QTLs) for osteochondrosis (OC) and osteochondrosis dissecans (OCD) in horses. The marker set comprised 260 microsatellites. We collected data from 211 Hanoverian warmblood horses consisting of 14 paternal half-sib families. Traits used were OC (fetlock and/or hock joints affected), OCD (fetlock and/or hock joints affected), fetlock OC, fetlock OCD, hock OC, and hock OCD. The first genome scan included 172 microsatellite markers. In a second step 88 additional markers were chosen to refine putative QTLs found in the first scan. Genome-wide significant QTLs were located on equine chromosomes 2, 4, 5, and 16. QTLs for fetlock OC and hock OC partly overlapped on the same chromosomes, indicating that these traits may be genetically related. QTLs reached the chromosome-wide significance level on eight different equine chromosomes: 2, 3, 4, 5, 15, 16, 19, and 21. This whole-genome scan was a first step toward the identification of candidate genome regions harboring genes responsible for equine OC. Further investigations are necessary to refine the map positions of the QTLs already identified for OC.

Mapping quantitative trait loci for osteochondrosis in fetlock and hock joints and palmar/plantar osseus fragments in fetlock joints of South German Coldblood horses

The aim of this study was to identify quantitative trait loci (QTL) for osteochondrosis (OC) and palmar/plantar osseous fragments (POF) in fetlock joints in a whole-genome scan of 219 South German Coldblood horses. Symptoms of OC and POF were checked by radiography in 117 South German Coldblood horses at a mean age of 17 months. The radiographic examination comprised the fetlock and hock joints of all limbs. The genome scan included 157 polymorphic microsatellite markers. All microsatellite markers were equally spaced over the 31 autosomes and the X chromosome, with an average distance of 17.7 cM and a mean polymorphism information content (PIC) of 63%. Sixteen chromosomes harbouring putative QTL regions were further investigated by genotyping the animals with 93 additional markers. QTL that had chromosome-wide significance by non-parametric Z-means and LOD scores were found on 10 chromosomes. This included seven QTL for fetlock OC and one QTL on ECA18 associated with hock OC and fetlock OC. Significant QTL for POF in fetlock joints were located on equine chromosomes 1, 4, 8, 12 and 18. This genome scan is an important step towards the identification of genes responsible for OC in horses.

Early lesions of osteochondrosis in the distal tibia of foals

Material available for research into osteochondrosis (OC) in humans tends to represent chronic lesions. Comparative studies of early lesions in young animals are, therefore, important in clarifying the pathogenesis of OC in humans. Recent studies in pigs provide strong evidence that lesions of articular OC are associated with a focal failure in the cartilage canal vascular supply to epiphyseal growth cartilage (articular-epiphyseal cartilage complex excluding the articular cartilage). The purpose of the present study was to examine histological sections from a specific predilection site for articular OC in the distal tibia of a large number of young foals to determine if the same is true in horses. Material from the distal tibiae of 100 foals aged from 191 days of gestation to 153 days old was collected from routine submissions of fetuses and foals for post mortem examination. The tibiae were band-sawed into slabs, and selected slabs were processed for histology, stained with hematoxylin and eosin, and examined using light microscopy. Early subclinical developmental stages of OC were found in the most common site for clinical OC lesions of horses in nine of 100 foals aged 12 to 122 days old. All lesions contained areas of chondrocyte necrosis that were associated with cartilage canal necrosis in five of nine foals. Five of these foals also had focal disruption of enchondral ossification at the chondro-osseous junction in the same site. Early lesions purported to play a role in the initial stages of articular OC in the distal tibia of horses were characterized by chondrocyte necrosis and likely occurred secondary to a failure of cartilage canal vascular supply to epiphyseal growth cartilage. The similarities in appearance between early lesions of piglets and foals suggest that information gained in one species may be transferable to others, including humans.

Identification of infrared absorption spectral characteristics of synovial fluid of horses with osteochondrosis of the tarsocrural joint

OBJECTIVE

To determine the feasibility of the use of Fourier-transform infrared (FTIR) spectroscopy within the midinfrared range to differentiate synovial fluid samples of joints with osteochondrosis from those of control samples.

ANIMALS

33 horses with osteochondrosis of the tarsocrural joint and 31 horses free of tarsocrural joint disease.

PROCEDURES

FTIR spectroscopy of synovial fluid was used. Sixty-four synovial fluid samples from the tarsocrural joint were collected. Of these, 33 samples were from horses with radiographic evidence of osteochondrosis of the tarsocrural joint and 31 from control joints. Disease-associated features within infrared spectra of synovial fluid were statistically selected for spectral classification, and the variables identified were used in a classification model. Linear discriminant analysis and leave-one-out cross-validation were used to develop a classifier to identify joints with osteochondrosis.

RESULTS

12 significant subregions were identified that met the selection criteria. The stepwise discriminant procedure resulted in the final selection of 6 optimal regions that most contributed to the discriminatory power of the classification algorithm. Infrared spectra derived from synovial fluid of joints with osteochondrosis were differentiated from the control samples with accuracy of 77% (81% specificity and 73% sensitivity).

CONCLUSIONS AND CLINICAL RELEVANCE

The disease-associated characteristics of infrared spectra of synovial fluid from joints with osteochondrosis may be exploited via appropriate feature selection and classification algorithms to differentiate joints with osteochondrosis from those of control joints. Further study with larger sample size including age-, breed-, and sex-matched control horses would further validate the clinical value of infrared spectroscopy for the diagnosis of osteochondrosis in horses.

[Prevalence of hereditary diseases in three-year-old Swiss Warmblood horses]

The objective of this study was to investigate clinical signs indicating hereditary diseases like equine sarcoid, osteochondrosis (OC) and the idiopathic laryngeal hemiplegia (ILH), and to demonstrate relationships between environment, feeding habits and conformation ("exterieur" evaluation) of the horses. For this purpose, we analyzed veterinary examinations of 403 stallions at the approvals since 1994 examined 493 three-year-old Swiss Warmblood horses, which were shown at the Swiss-Field-Tests in 2005. With the help of the owners a questionnaire on health, environment and feeding habits of the animals was completed. At the same time, the horses were assessed and graded for their "exterieur" (type, conformation, gaits) by judges of the Swiss Sporthorse breeding association. In 11.5% of horses sarcoids were found, 8.7% showed one and 2.8% several tumors. The prevalence of sarcoids in offspring of sires with known sarcoids was not significantly higher than in descendants from stallions without a known history of sarcoids. We found distended joints as a possible symptom of OC in 11.4% of the horses, 3.9% (n = 19) in both tarsal joints. We did not find a relationship between enlarged joints in the offspring and the presence of OC in the sires. Abnormal respiratory noise at work, as a possible sign for ILH, was heard only in 1.2% (n = 6). It is important to note that while we found a high number of sarcoid affected horses compared to other studies, presence of enlarged joints was not very frequent and very few horses showed abnormal respiratory noise. Additionally, we found no correlation between "exterieur" marks and the horse's general health.

Osteochondral fragments involving the dorsomedial aspect of the proximal interphalangeal joint in young horses: 6 cases (1997–2006)

OBJECTIVE

To determine clinical and diagnostic imaging findings in young horses with osteochondral fragments involving the dorsomedial aspect of the proximal interphalangeal (PIP) joint.

DESIGN

Retrospective case series.

ANIMALS

6 horses.

PROCEDURES

Medical records were reviewed. Follow-up information was obtained through telephone conversations with owners or trainers or by examining race records.

RESULTS

Horses were between 1 and 4 years old. Three had bilateral osteochondral fragments in the forelimbs (n = 2 horses) or hind limbs (1). Radiographically, all but 1 fragment seemed to originate from the dorsomedial aspect of the distal end of the first phalanx. Fragment size ranged from 6 x 9 mm to 11 x 21 mm. Three horses had lameness referable to the region of the affected joint; the other 3 horses did not have clinical signs referable to affected PIP joints. Two horses were euthanized shortly after diagnosis at the owners' request because of concerns that the horses would be unsuited for their intended athletic use. Two of the 3 horses in which fragments were incidental findings were able to race successfully, although 1 received intra-articular corticosteroid treatments; the third was retired because of unrelated orthopedic problems.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that osteochondral fragments involving the dorsomedial aspect of the PIP joint may be an incidental finding in young horses. Given the absence of clinical signs in 5 of 9 affected joints and the fact that 3 of 6 horses were affected bilaterally, a developmental origin of the fragments was suspected.

Osteochondrosis and copper: Histology of articular cartilage from foals out of copper supplemented and non-supplemented dams

Copper (Cu) supplementation of dams in late gestation may be protective against articular cartilage abnormalities in foals. Articular cartilage was harvested from 22 Thoroughbred foals at 160 days of age, at sites predisposed to osteochondrosis (OC), and examined for evidence of early cartilage abnormalities and established dyschondroplastic (DCP) lesions to determine if there were any significant differences due to mare Cu supplementation by injection during late gestation, or foal liver Cu concentration. Cu supplemented mares received calcium Cu edetate injections in late gestation (250 mg at around 220, 248, 276 and 304 days gestation, then every two weeks until foaling). Foals were euthanased at 160 days of age and articular cartilage was harvested from four defined sites. Samples were examined for histological appearance of chondrocytes after staining with haematoxylin and eosin, and were also stained with toluidine blue to indicate proteoglycan content. Alkaline phosphatase (ALP) activity was detected by histochemistry, and histocytochemical techniques were used to determine the expression of cathepsin B. Cu supplementation of the dam, or liver Cu concentration of the foal at birth or 160 days of age had no statistically significant effect on the frequency of cartilage irregularities observed grossly, or abnormalities detected histologically at four defined sites. ALP expression was similar in all samples. Cathepsin B expression varied between sites, and was seen in chondrocyte clusters. The intensity of toludine blue staining varied between sites. Minor histological cartilage abnormalities were observed in cartilage from clinically normal animals. These abnormalities might be 'early' dyschondroplastic lesions, which could resolve or progress. The role of Cu in the development, resolution or progression of dyschondroplastic lesions is poorly understood.

Application of osteochondral autografts and allografts in the treatment of articular cartilage lesions in animals

The paper describes current views on the use of osteochondral autografts and allografts in the treatment of articular cartilage lesions in animals. It presents surgical techniques of grafting and the biological features of osteochondral auto- and allografts, and their effect on the recipient's cartilage.

Effects of Atelocollagen Gel Containing Bone Marrow-Derived Stromal Cells on Repair of Osteochondral Defect in a Dog

To clarify the contribution of autologous transplantation of mesenchymal stromal cells (MSCs), an atelocollagen gel containing or not containing fluorescently-labeled canine MSCs was transplanted into an osteochondral defect which did not repair spontaneously and the histological repair of the defect was compared. Although an early repair of the cartilage was not observed in either defect, the reproduction of subchondral bone was remarkable in the MSCs-implanted defect. Moreover, in 2 weeks after operation, the implanted MSCs were located in the deeper regions of the defect, suggesting the differentiation of osteoblasts. There was a possibility that the movement of the implanted MSCs was due to an increase in intra-articular pressure from postoperative inflammation.

A high-resolution comparative radiation hybrid map of equine chromosome 4q12-q22

In this study, we present a comprehensive 5000-rad radiation hybrid map of a 40-cM region on equine chromosome 4 (ECA4) that contains quantitative trait loci for equine osteochondrosis. We mapped 29 gene-associated sequence tagged site markers using primers designed from equine expressed sequence tags or BAC clones in the ECA4q12-q22 region. Three blocks of conserved synteny, showing two chromosomal breakpoints, were identified in the segment of ECA4q12-q22. Markers from other segments of HSA7q mapped to ECA13p and ECA4p, and a region of HSA7p was homologous to ECA13p. Therefore, we have improved the resolution of the human-equine comparative map, which allows the identification of candidate genes underlying traits of interest.

Molecular characterization of the equine collagen, type IX, alpha 2 (COL9A2) gene on horse chromosome 2p16-->p15

The mammalian collagen, type IX, alpha 2 gene (COL9A2) encodes the alpha-2 chain of type IX collagen and is located on horse chromosome 2p16-->p14 harbouring a quantitative trait locus for osteochondrosis. We isolated a bacterial artificial chromosome (BAC) clone containing the equine COL9A2 gene and determined the complete genomic sequence of this gene. Cloning and characterization of equine COL9A2 revealed that the equine gene consists of 32 exons spanning approximately 15 kb. The COL9A2 transcript encodes a single protein of 688 amino acids. Thirty two single nucleotide polymorphisms (SNPs) equally distributed in the gene were detected in a mutation scan of eight unrelated Hanoverian warmblood stallions, including one SNP that affects the amino acid sequence of COL9A2. Comparative analyses between horse, human, mouse and rat indicate that the chromosomal location of equine COL9A2 is in agreement with known chromosomal synteny relationships. The comparison of the gene structure and transcript revealed a high degree of conservation towards the other mammalian COL9A2 genes. We chose three informative SNPs for association and linkage disequilibrium tests in three to five paternal half-sib families of Hanoverian warmblood horses consisting of 44 to 75 genotyped animals. The test statistics did not reach the significance threshold of 5% and so we could not show an association of COL9A2 with equine osteochondrosis.

Prevalence of Osteochondrosis in the Limb Joints of South German Coldblood Horses

This study aimed to quantify the factors associated with the prevalence of the radiological signs of osteochondrosis (OC) and osteochondrosis dissecans (OCD) in South German Coldblood (SGC) horses. The prevalence of OC and OCD in fetlock and hock joints was analysed in 167 young coldblood horses with a mean age of 14 months. The presence of at least one osteochondrotic lesion (OC) in fetlock or hock joints was documented for 61.7% of the horses and 26.9% of the horses had osseus fragments. Osteochondrotic findings at the dorsal aspect of the sagittal ridge of the third metacarpal/metatarsal bone were seen in 53.9% of the horses and palmar/plantar osseous fragments in fetlock joints in 16.2% of the horses. Hock joint OC was found in 40.1% of the horses and hock OCD in 0.6%. Osteochondrotic findings in the distal part of the tibia were prevalent in 28.1% and in the lateral trochlea tali in 17.4% of the horses. The sex of the investigated horses significantly influenced the prevalence of OC in fetlock and hock joints, as well as the findings in the distal part of the tibia and lateral trochlea tali. Age at radiological examination was significant for the prevalence of OC in hock joints, palmar/plantar osseous fragments in fetlock joints and osteochondrotic findings in the distal part of the tibia. Female horses showed a 2-fold higher risk for OC in fetlock and hock joints than male horses. The distribution of the affected horses by age classes showed that radiographic signs of OC in fetlock and hock joints significantly increased at an age of about 1 year. We can conclude from our study that fetlock and hock OC is a prevalent radiographic finding in more than 1-year-old female and male SGC horses.

Lameness and fertility of sows and gilts in randomly selected loose-housed herds in Finland

The prevalence of lameness among 646 sows and gilts in 21 selected herds was determined; 8.8 per cent of the animals were lame and the most common clinical diagnoses were osteochondrosis, infected skin lesions and claw lesions. The lame animals had higher serum concentrations of haptoglobin and C-reactive protein than the sound animals. Animals housed on slatted floors had twice the odds of being lame and 3.7 times the odds of being severely lame than animals housed on solid floors. Yorkshire pigs had 2.7 times the odds of being lame than Landrace or crossbred animals. Higher parity and the use of roughage decreased the odds of the sows not becoming pregnant; however, lameness was not a risk factor for non-pregnancy.

Genetics of osteochondral disease and its relationship with meat quality and quantity, growth, and feed conversion traits in pigs

The main objective of this research was to estimate heritabilities of seven osteochondrosis (OC) lesions in station-tested pigs and their genetic and phenotypic correlations with four meat quality (MQ) traits, the percentage of premium cuts (PPC), daily weight gain (DWG), and feed conversion ratio (FCR). Observed OC lesions were on the head of humerus (HK), condylus medialis humeri (CMH), condylus lateralis humeri (CLH), radius and ulna proximal (RUP), distal epiphyseal cartilage of ulna (DEU), head of femur (FK), and condylus medialis femoris (CMF). Meat quality traits were i.m. fat (IMF), muscle pH at 1 h after slaughter (pH1), muscle pH at 30 h after slaughter (pH30), and light reflectance on muscle (H30). The data set comprised 2,710 animals, of which 1,291 animals had OC records. All traits were analyzed by multiple-trait linear mixed model, with the animal's genetic and common litter effects as random. Fixed effects in the model varied between traits. Each OC lesion was further analyzed by a univariate generalized linear mixed model or, equivalently, "threshold models," assuming logistic, probit (normal), and Poisson distributions of the underlying "liability" to the disease. For OC lesions, estimates of heritability were low on the original "incidence" scale (0.06 for HK to 0.16 for CLH) and moderate to high on the liability scale (0.08 to 0.42). Genetic correlations (r(g)) between OC lesions and most MQ traits and PPC were generally unfavorable. Significant r(g) were -0.44 for DWG-CMH, 0.31 for DWG-CMF, 0.40 for FCR-HK, 0.21 for PPC-CLH, 0.32 for PPC-RUP, 0.30 for PPC-CMF, -0.54 for pH1-CLH, 0.47 for pH1-DEU, -0.34 for pH30-CMH, 0.58 for pH30-DEU, -0.50 for H30-HK, -0.31 for H30-DEU, and 0.31 for H30-CMF. Genetic susceptibilities to some OC lesions within the front leg were positively related to each other (r(g) range = 0.57 to 0.69), but r(g) between front and hind leg OC lesions were mostly negative (range = -0.21 to -0.40). Estimated h2 was 0.60 for PPC, and ranged from 0.12 to 0.66 for MQ traits, 0.28 for DWG, and 0.42 for FCR. Genetic correlations among meat quality and quantity traits ranged from -0.66 to 0.37. This is the first study to report genetic and phenotypic correlations between OC lesions and several meat quality and quantity traits in pigs. These findings will be useful to pig industry, especially in designing breeding programs for robust pigs.

COMPARISON OF THE ULTRASONOGRAPHIC APPEARANCE OF OSTEOCHONDROSIS LESIONS IN THE CANINE SHOULDER WITH RADIOGRAPHY, ARTHROGRAPHY, AND ARTHROSCOPY

Osteochondrosis lesions in 29 shoulder joints (from 20 dogs) were evaluated with ultrasound (US) and the results were compared with survey radiography, arthrography, and arthroscopy. US was performed with a 7-12 MHz linear matrix transducer which was placed in cranio-caudal direction just distally to the acromion while the joint was adducted and maximally endorotated to visualize the caudal aspect of the humeral head. With US, the subchondral defect was completely visible in 21 joints and partially visible in 8 joints. The length of the subchondral defect measured on US was comparable with the length measured on survey radiographs. In two joints, the cartilage flap was mineralized and thus already visible on survey radiographs. The mineralized flap was visible on US as a straight hyperechoic line above the subchondral defect. In the other joints, survey radiographs could not assess the status of the articular cartilage. In 17 joints, the presence of a cartilage flap or cartilage fissuring was suspected based on the presence of a second hyperechoic line at the base of the subchondral defect, and this suspicion was confirmed by arthroscopic examination in 16 joints and also by arthrographic examination in 15 joints. One joint that was suspected of having a cartilage flap on US was normal on arthroscopy and arthrography. When US revealed only focal thickening of the anechoic cartilage layer (5 joints), the joints appeared normal on arthroscopic and arthrographic examination. Of the four joints where the subchondral defect was irregular and covered by heteroechogeneous material on US, arthroseopy revealed the presence of a lesion resembling chondromalacia in two joints, the presence of a small cartilage flap in one joint and the presence of scar tissue underneath the flap at the level of the subchondral defect in one joint. In conclusion, US is a helpful imaging modality in the identification of osteochondritic lesions in the canine shoulder joint. US also appears to be a satisfactory imaging tool for identifying lesions such as joint mice, joint effusion, and distinct new bone formation.

Comparison of proteoglycan and collagen in articular cartilage of horses with naturally developing osteochondrosis and healing osteochondral fragments of experimentally induced fractures

OBJECTIVE

To compare articular cartilage from horses with naturally developing osteochondrosis (OC) with normal articular cartilage and healing cartilage obtained from horses with experimentally induced osteochondral fractures.

SAMPLE POPULATION

109 specimens of articular cartilage from 78 horses.

PROCEDURE

Morphologic characteristics, proteoglycan (PG), and type II collagen were analyzed in articular cartilage of OC specimens (group 1), matched healing cartilage obtained 40 days after experimentally induced osteochondral fractures (group 2), and matched normal cartilage from the same sites (group 3).

RESULTS

79 specimens of OC cartilage were obtained from horses. Ex vivo PG synthesis was significantly greater in the femoral cartilage, compared with synthesis in the tibial cartilage, and significantly greater for groups 1 and 2, compared with group 3. For groups 1 and 2, femoral fragments had significantly greater PG content, compared with PG content in tibial fragments. Keratan sulfate content was significantly less in group 3, compared with groups 1 and 2. Cartilage from the OC specimens had loss of structural architecture. The OC tissue bed stained positive for chondroitin sulfate and type II collagen, but the fracture bed did not.

CONCLUSIONS AND CLINICAL RELEVANCE

Our analyses could not distinguish articular cartilage from horses with OC and a healing fracture. Both resembled an anabolic, reparative process. Immunohistochemical analysis suggested a chondromyxoid tissue in the OC bed that was morphologically similar to fibrous tissue but phenotypically resembled hyaline cartilage. Thus, tissue in the OC bed may be degenerative cartilage, whereas tissue in the fracture bed may be reparative fibrous callus.

Articular/epiphyseal osteochondrosis in Thoroughbred foals at 5 months of age: Influences of growth of the foal and prenatal copper supplementation of the dam

AIMS

To determine the influence of copper (Cu) supplementation by injection of mares in late gestation on the frequency and severity of osteochondrosis (OC) lesions in their foals at around 160 days of age. To determine if there was any influence of the concentration of Cu in the liver, growth rate, birthweight, weight at 160 days of age, fatness, sex, or year of birth of the foal on the frequency and severity of OC lesions. To determine the influence of dam's age, and sex and birthweight of the foal on the growth rate from birth to 160 days of age, and weight at 160 days of age.

METHODS

Thirty-three Thoroughbred foals, born in two consecutive years, were weighed every 2 weeks from birth. The dams had been supplemented with parenteral Cu or saline during late gestation, and the supplementation regimens were different in each year. Foals had liver biopsies harvested at birth for determination of Cu concentration. Pasture samples were collected every 4-8 weeks for analysis of concentration of Cu and zinc (Zn). At 160 days of age, articular cartilage of long bones was examined. Gross lesions were counted and scored, then sawn and radiographed, and processed for histopathology. Lesions were given radiographic scores and histopathological scores. Maximum scores for each lesion were combined to give a total OC score for each joint and each foal. The fatness of 20 foals (10 each from Years 1 and 2) at 160 days of age was determined chemically.

RESULTS

Supplementation of dams with Cu had no significant effect on the concentration of Cu in the liver of foals at birth, or on the frequency or severity of lesions in articular cartilage at 160 days of age. The Cu and Zn concentrations of pasture were similar in Years 1 and 2, and were lower than current recommendations. All foals in Year 2, and 9/10 foals in Year 1 had irregularities in cartilage that was confirmed histologically to be indicative of OC. The average number of lesions per foal was 4.7 (SD 1.1) and 5.7 (SD 1.1) in Years 1 and 2, respectively. However, the severity of the lesions was considered mild, and no foals showed any clinical evidence of OC while alive. The number of lesions in the tarsocrural (TC) joint and the TC OC score at 160 days were positively associated with average daily weight gain (ADG) in the previous 4 weeks (p=0.005 and p=0.001, respectively). There was no significant effect of sex, fatness, birthweight, weight at 160 days of age, or year of birth of the foal on the frequency and severity of OC lesions.

CONCLUSIONS

Many of the lesions classified as OC, using classification systems described by other authors, were likely to be normal variations of the process of endochondral ossification. Despite the high frequency of such lesions, they were considered to be of minor significance and none were clinically evident. The distribution of lesions was not typical, and most probably reflected the subtlety of the lesions. These results support the hypothesis that Cu is an over-emphasised factor in the aetiopathogenesis of OC. The relationship between subtle macroscopic lesions and lesions resulting in clinical signs of disease requires further investigation.

Microcomputed tomography and histology of a fragmented medial coronoid process in a 20-week-old golden retriever

A 20-week-old male golden retriever, which was not lame and showed no clinical signs of a fragmented medial coronoid process (FCP), was euthanased for another study and perfused intravenously with formaldehyde. Gross dissection revealed no abnormalities within the right elbow joint. The medial coronoid process was excised, embedded in methylmethacrylate, scanned in a microcomputed tomography (microCT) scanner and sectioned for histology. The microCT scans revealed a dense trabecular bone structure, much denser than in other dogs of similar age, which was considered to be responsible for the sclerosis visible at the base of the coronoid process in radiographs. Three-dimensional reconstructions indicated that there was a small step within the subchondral bone, extending from the apex towards the radial notch. Histology revealed a necrotic lesion between locally thickened articular cartilage and the subchondral bone, characteristic of osteochondrosis.

Characterizing osteochondrosis in the dog: potential roles for matrix metalloproteinases and mechanical load in pathogenesis and disease progression

OBJECTIVE

To address possible roles of matrix metalloproteinases (MMPs) and mechanical stress in the pathogenesis of osteochondrosis (OC).

METHODS

Naturally-occurring canine OC lesions (n=50) were immunohistochemically analyzed for MMP-1, -3, and -13, and normal canine articular cartilage explants (n=6) cultured under 0-, 2-, or 4-MPa compressive loads (0.1 Hz, 20 min every 8 h up to 12 days) were compared to OC samples (n=4) biochemically and molecularly.

RESULTS

MMP-1 and -3 immunoreactivities were readily detected in both OC samples and control tissues obtained from age-matched dogs (n=11) whereas MMP-13 was only detectable in OC samples. MMP-13 gene expression as determined by real-time reverse transcription polymerase chain reaction was elevated in OC samples and cartilage explants cultured without mechanical stimuli (0 MPa groups) compared to normal cartilage (day 0 controls). Glycosaminoglycan content (per weight) in cartilage explants cultured under no load was significantly (P<0.05) lower on day 12 than in the day 0 controls. Gene expression levels of aggrecan and type II collagen in OC samples were lower than those in the day 0 controls. High levels of aggrecan and collagen II expression were seen in the 2 MPa groups.

CONCLUSIONS

These findings imply that impaired biochemical characteristics in OC-affected cartilage may be attributable to decreased extracellular matrix production that may stem from disruption of normal weight bearing forces.

Extracellular matrix changes in early osteochondrotic defects in foals: a key role for collagen?

Osteochondrosis (OC) is the most important developmental orthopaedic disease in the horse. Despite some decades of research, much of the pathogenesis of the disorder remains obscure. Increasing knowledge of articular cartilage development in juvenile animals led to the presumption that the role of collagen in OC might be more important than previously thought. To study collagen characteristics of both cartilage and subchondral bone in young (5 and 11 months of age) horses, samples were taken of subchondral bone and articular cartilage from a group of 43 Dutch Warmblood foals and yearlings that suffered from varying degrees of OC. Based on a histological classification, lesions were graded as early, middle and end stage. Collagen content and some posttranslational modifications (lysyl hydroxylation, hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP) cross-links) were determined, as was proteoglycan content. Data were compensated for site effects and analysed for differences due to the stage of the lesion. In early lesions total collagen was significantly decreased in both cartilage and subchondral bone of 5- and 11-month-old foals. Also in cartilage, HP cross-linking was reduced in the early lesions of 5- and 11-month-old foals, while LP cross-linking was decreased in subchondral bone of the end-stage lesions of both 5- and 11-month-old foals. Hydroxylysine content was unaffected. Collagen content remained reduced in cartilage from middle- and end-stage lesions, but returned to normal in subchondral bone. In cartilage there was a decrease in proteoglycan content in the end-stage lesions of both age groups. Thus, alterations of the collagen component, but not of the proteoglycan component, of the extracellular matrix might play a role in early OC. More severe lesions show a more general picture of an unspecific repair reaction. Biomarkers of collagen metabolism can be expected to be good candidates for early detection of OC.

Magnetic resonance imaging in the diagnosis and surgical management of sacral osteochondrosis in a mastiff dog

The clinical, radiographic, magnetic resonance imaging (MRI), surgical and pathological findings related to an osteochondral lesion of the sacrum in a mastiff dog are described. The dog showed chronic signs of pain in its pelvic limbs. Radiography revealed a triangular mineralised opacity at the craniodorsal aspect of the sacrum consistent with sacral osteochondrosis. A T2-weighted spin-echo MRI revealed dorsal and lateral compression of the cauda equina. The osteochondral fragment was removed via a dorsal laminectomy, and the clinical signs resolved. Histological abnormalities in the fragment were consistent with a diagnosis of osteochondrosis.

Arthroscopic Removal of Axial Osteochondral Fragments of the Proximoplantar Aspect of the Proximal Phalanx Using Electrocautery Probes in 23 Standardbred Racehorses

OBJECTIVES

To describe the outcome after arthroscopic electrosurgical excision of axial osteochondral (OC) fragments of the proximal plantar aspect of the 1st phalanx (P1) in horses.

STUDY DESIGN

Retrospective study.

POPULATION

Twenty-three Standardbred racehorses.

METHODS

Medical records of Standardbred racehorses that had arthroscopic dissection of axial OC fragments of the proximal plantar aspect of P1 with electrocautery probes were reviewed. Horses were positioned in dorsal recumbency; a 1.5% glycine solution was used to maintain joint distension. The arthroscope portal was in the proximal plantar joint pouch and OC fragments were approached using either an ipsilateral or a contralateral triangulation technique. Dissection of the fibrous attachments was performed using loop and hook electrocautery probes. Follow-up was obtained by telephone questionnaire of owners or trainers and examination of race summary records.

RESULTS

Thirty-three axial OC fragments were removed from 28 metatarsophalangeal joints (left, 14; right, 14). No major operative or postoperative complications occurred. Seven of 8 (79%) of horses that raced before surgery raced after surgery. Thirty-six percent (n=4) of horses that had not raced before surgery raced after surgery.

CONCLUSION

Intra-articular electrosurgery is a safe, easy alternative to conventional excision of axial OC fragments of the proximal plantar aspect of P1.

CLINICAL RELEVANCE

Arthroscopic excision using electrocautery probes is a valid alternate method for removal of axial OC fragments of the proximal plantar aspect of P1. In addition, the dorsal recumbency position facilitates removal of several fragments and multiple joint surgery.

Arthroscopic findings in horses with subtle radiographic evidence of osteochondral lesions of the medial femoral condyle: 15 cases (1995–2002)

OBJECTIVE

To determine arthroscopic findings in lame horses with subtle radiographic lesions of the medial femoral condyle.

DESIGN

Retrospective study.

ANIMALS

15 horses examined because of lameness that had subtle radiographic evidence of osteochondral lesions involving the medial femoral condyle in at least 1 joint.

PROCEDURE

Medical records were reviewed, and results of physical examination, radiography, and arthroscopy were recorded. Follow-up information was obtained through reexamination of the horses or telephone conversations with the referring veterinarians, owners, or trainers.

RESULTS

Lameness severity ranged from grade 1 to 3 on a scale from 0 to 5. Radiography and arthroscopy were performed on 28 stifle joints. The 4 unaffected joints in 4 horses with unilateral hind limb lameness that underwent bilateral arthroscopy had no radiographic lesions, but 2 of the 4 had arthroscopic lesions. Of the remaining 24 joints, 20 had radiographic evidence of flattening of the apex of the medial femoral condyle and 4 had minimal subchondral lucency. Lesions were identified arthroscopically in 18 of the 20 joints with flattening of the condyle and in all 4 joints with subchondral lucency. Treatment consisted of abrasion arthroplasty or microfracture. Seven of the 9 horses with focal cartilage lesions and 2 of the 6 horses with generalized cartilage lesions were reportedly sound without any evidence of joint effusion at the time of final follow-up.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that horses with hind limb lameness and subtle radiographic lesions of the medial femoral condyle are likely to have arthroscopically apparent cartilage lesions and subchondral bone defects.

The Effect of Parentage on the Prevalence, Severity and Location of Lesions of Osteochondrosis in Swine

The aims of this study were to determine the effects of parentage and gender on the prevalence, severity and location of lesions of osteochondrosis manifesta (OCM) and osteochondrosis dissecans (OCD) in offspring from different Norwegian Landrace boars and to examine the relationships between lesion characteristics and selected growth parameters. Fifteen sires were selected based on their high breeding value for osteochondrosis. Seven locations in the distal humerus and the distal femur from 1680 offspring of these animals were evaluated for severity of OCM and presence of OCD by gross examination of serially sectioned humeri and femora. Osteochondrosis manifesta was most prevalent in the trochlea of humerus, the sagittal ridge of humerus, the medial condyle of femur and the medial sulcus obliquus of femur. The severity of the lesions and the prevalence of OCD were highest in the trochlea and the sagittal ridge of humerus. Castrates had significantly higher OCM scores than sows. There were significant effects of both sire and dam on the OCM scores of the offspring in most locations; however, growth rate and weight at slaughter did not influence the OCM score.

Expression of bone morphogenetic protein-6 and -2 and a bone morphogenetic protein antagonist in horses with naturally acquired osteochondrosis

OBJECTIVE

To determine the mRNA expression of bone morphogenetic protein (BMP)-6 and -2 and a BMP antagonist (Noggin) in horses with osteochondrosis.

SAMPLE POPULATION

Samples of articular cartilage from affected stifle or shoulder joints of 10 immature horses with naturally acquired osteochondrosis and corresponding joints of 9 clinically normal horses of similar age; additionally, samples of distal femoral growth plate cartilage and distal femoral articular cartilage were obtained from a normal equine fetus.

PROCEDURE

Cartilage specimens were snap-frozen in liquid nitrogen, and total RNA was isolated. Adjacent specimens were fixed in 4% paraformaldehyde for histologic examination. Expression of BMP-6, BMP-2, and Noggin mRNA was evaluated by real-time quantitative polymerase chain reaction (PCR) assays. Spatial tissue mRNA expression of BMP-6 was determined by in situ hybridization.

RESULTS

Nucleotide sequences were obtained for portions of the BMP-6 propeptide and mature peptide region, as well as the signal and mature peptide region of Noggin. Expression of BMP-6, BMP-2, and Noggin mRNA was found to be similar in cartilage from normal and osteochondrosis-affected horses. Spatial expression of BMP-6 correlated with the middle and deep layers of articular cartilage; no differences were observed in overall expression between cartilage specimens from the 2 groups of horses. No expression of BMP-6 was found in the superficial layer, subchondral bone, or osteochondrosis-affected cleft fibrous tissue.

CONCLUSIONS AND CLINICAL RELEVANCE

Although these signaling peptides may play important roles in cartilage differentiation, results did not provide evidence to suggest that they are involved in the disease process of osteochondrosis.

Evaluation of serum concentrations of biomarkers of skeletal metabolism and results of radiography as indicators of severity of osteochondrosis in foals

OBJECTIVE

To determine whether serum concentrations of biomarkers of skeletal metabolism can, in conjunction with radiographic evaluation, indicate severity of osteochondrosis in developing horses.

ANIMALS

43 Dutch Warmblood foals with varying severity of osteochondrosis.

PROCEDURE

24 foals were monitored for 5 months and 19 foals were monitored for 11 months. Monthly radiographs of femoropatellar-femorotibial and tibio-tarsal joints were graded for osteochondral abnormalities. Serial blood samples were assayed for 8 cartilage and bone biomarkers. At the end of the monitoring period, foals were examined for macroscopic osteochondrosis lesions.

RESULTS

Temporal relationships were evident between certain serum biomarkers and osteochondrosis severity in foals during their first year. Biomarkers of collagen degradation (collagenase-generated neoepitopes of type-II collagen fragments, type-I and -II collagen fragments [COL2-3/4C(short)], and cross-linked telopeptide fragments of type-I collagen) and bone mineralization (osteocalcin) were positive indicators of osteochondrosis severity at 5 months of age. In foals with lesions at 11 months of age, osteochondrosis severity correlated negatively with COL2-3/4C(short) and osteocalcin and positively with C-propeptide of type-II procollagen (CPII), a collagen synthesis marker. Radiographic grading of osteochondrosis lesions significantly correlated with macroscopic osteochondrosis severity score at both ages and was strongest when combined with osteocalcin at 5 months and CPII at 11 months.

CONCLUSIONS AND CLINICAL RELEVANCE

The ability of serum biomarkers to indicate osteochondrosis severity appears to depend on stage of disease and is strengthened with radiography. In older foals with more permanent lesions, osteochondrosis severity is significantly related to biomarker concentrations of decreased bone formation and increased cartilage synthesis.

Osteochondrosis of the occipital condyles and atlanto-occipital dysplasia in a Belgian horse

A lesion in the cervical region of a 14-month-old Belgian gelding with severe ataxia was suspected. Necropsy revealed symmetric focal cartilage defects compatible with osteochondrosis of the occipital condyles and atlanto-occipital dysplasia. To our knowledge this is the first equine report of symmetrical osteochondrosis of the occipital condyles causing neurologic signs.

[Bilateral avulsion fracture (apophyseolysis) of the calcaneal tuber in a heifer]

This case report describes the clinical, radiographic, ultrasonographic and histopathological findings of a six-month-old heifer, suffering from bilateral fracture of the calcaneal tuber caused by osteochondrosis. The young cattle was admitted to the clinic for the evaluation of a left hindlimb lameness, having persisted for several weeks. Orthopaedic examination revealed a highly stilted gait with a lameness of the left hind limb, so severe that the heifer was only able to put some weight on the tip of the toe. The calcaneal region on both hindlimbs showed a diffuse swelling, palpation being very painful. The radiological examination revealed a fracture of the calcaneal tuber (apophyseolysis) of both hindlimbs.

Influence of liver copper status of mare and newborn foal on the development of osteochondrotic lesions

REASON FOR PERFORMING STUDY

To elucidate the highly contentious role of copper in the pathogenesis of osteochondrosis.

HYPOTHESIS

There would be no relationship between liver copper concentration of mares and foals and incidence of radiographically detectable osteochondrotic lesions in foals and yearlings was tested.

METHODS

Liver copper concentration was assessed in biopsies taken within 4 days after birth from both mares and foals and from the same foals at age 5 months. Biopsies were taken in the standing, sedated animal under ultrasonographic guidance. Radiographs were taken of both hocks (lateromedial, dorsoplantar and dorsomedial-plantarolateral oblique views) and stifles (lateromedial and caudolateral-craniomedial oblique views) at ages 5 and 11 months and scored for the presence and severity of osteochondrotic lesions.

RESULTS

Copper concentrations in newborn foals were high with a large variation (351 +/- 201 mg/kg DM). They declined until reaching values comparable to those in mature animals at 5 months (20 +/- 8 mg/kg DM; mares: 19 +/- 20 mg/kg DM). Radiographic osteochondrotic lesions decreased in number and severity from 5 to 11 months. This pattern was more predominant in the stifle than in the hock, as has been described previously.

CONCLUSIONS

There was no relationship between foal or mare liver copper concentration and osteochondrosis status at either 5 or 11 months. However, osteochondrotic lesions in foals with low-level copper status at birth decreased significantly less in number and severity than those in foals with high-level copper status at birth.

POTENTIAL RELEVANCE

It is concluded that copper is not likely to be an important factor in the aetiopathogenesis of osteochondrosis, but this study indicates that there may be a significant effect of high copper status on the natural process of repair of early lesions.

Excessive degradation of type II collagen in articular cartilage in equine osteochondrosis

Articular osteochondrosis (OCD) occurs in both man and animals. The etiology remains to be determined. Studies of OCD lesions in animals may provide clues as to its pathogenesis. The aim of our study was to determine whether there was evidence for increased degradation namely proteoglycan (PG) release and type II collagen cleavage in articular cartilage harvested from OCD lesions. We examined ex vivo explants at post-mortem from equine OCD lesions and macroscopically normal site and age matched cartilage. These were cultured over a 10 day period in serum-free medium. Type II collagen cleavage was measured in articular cartilage and media using an Elisa assay to detect the COL2-3/4C(short) epitope, which is generated on cleavage of the triple helix of type II collagen by collagenases. PG release was measured by a dye-binding assay. Cumulative release of PG and COL2-3/4C(short) and their contents in cartilage at the end of the culture period were determined. In OCD lesions there was a significant increase in type II collagen cleavage by collagenase but no evidence for increase of PG degradation. These findings point to a selective increase in type II collagen cleavage by collagenases, in OCD lesions of the kind observed in osteoarthritis. Further work is needed to determine whether changes represent primary or secondary events in the pathogenesis of OCD.

Differences in metabolic parameters and gene expression related to osteochondrosis/osteoarthrosis in pigs fed 25-hydroxyvitamin D3

Osteochondrosis/osteoarthrosis (OC/OA) are common terms for various joint pathologies that occur in pigs. Pathologies that may contribute to these disorders have been described, but the primary cause(s) remain unknown. We hypothesised that as OC has some similarities to dyschondroplasia, which involves a failure of growth plate chondrocytes to fully differentiate and hypertrophy, treatment with 25-hydroxyvitamin D3 (25-D) might reduce the incidence and/or severity of lesions in pigs, as it does in chickens with dyschondroplasia. Control pigs were fed a commercial diet ad libitum. In the treated group this diet was supplemented with 25-D at 0.1 mg/kg. Ten pigs from each of the control and treated groups were sampled at 7, 12, 16 and 21 weeks. Treatment with 25-D had no effect on the incidence or severity of OC/OA lesions. Cartilage dry weight, total collagen content and proteoglycan content, and plasma levels oftotal calcium, inorganic phosphorous, vitamin C, insuline-like growth factor-I, parathyroid hormone and tumour necrosis factor alpha were unaffected by treatment. In addition, none of these parameters were correlated with the incidence or severity of OC/OA lesions. The mRNA expression levels of 21 out of 23 genes assayed by RT-PCR were unaltered in articular cartilage from OA lesion samples as compared to normal articular cartilage. However, collagen type II was reduced and collagen type X increased in OA lesion and near lesion samples. These results suggest that OA in pigs may share some features of osteoarthritis in other mammalian species.

Radiographic, computed tomographic and arthroscopic findings in 23 dogs with osteochondrosis of the tarsocrural joint

Twenty-three dogs with osteochondrosis of the tarsocrural joint were evaluated by radiography, computed tomography (CT) and arthroscopy. The radiographic examination included an extended and flexed mediolateral, a plantarodorsal, a flexed dorsoplantar skyline view, and a plantaromedial-dorsolateral and a plantarolateral-dorsomedial view (two oblique views). The CT examination was carried out in ventral recumbency and 1 mm slices were taken with a bone window setting; 31 lesions were identified in the 46 joints examined. The arthroscopic exploration used either a plantar or a dorsal puncture, depending on the site of the lesion. In six cases the lateral, and in 17 cases the medial trochlear ridge was involved. Although the survey radiographs were sufficient to make a diagnosis, the CT examination helped to determine the exact site, and the number and size of the fragments of bone. A four-stage classification system comparable to the one used in man was established. Arthroscopy provided information about synovial inflammation and damage to the joint cartilage, and made it possible to remove fragments of bone from one-third of the cases.

In vitro characterization of chondrocytes isolated from naturally occurring osteochondrosis lesions of the humeral head of dogs

OBJECTIVE

To characterize chondrocytes from naturally occurring osteochondrosis (OC) lesions of the humeral head of dogs.

SAMPLE POPULATION

15 cartilage specimens from 13 client-owned dogs with humeral head OC and 10 specimens from the humeral head of healthy dogs (controls).

PROCEDURE

Chondrocytes were isolated and cultured in a 3-dimensional system. On days 7, 10, 15, 20, and 25, glycosaminoglycan and hydroxyproline content and cytologic characteristics were evaluated. Expression of collagen types I, II, and X was assessed by use of immunohistochemistry.

RESULTS

Chondrocytes from OC lesions were less viable, compared with control chondrocytes. Glycosaminoglycan content in the OC group was significantly less than in the control group on all days except day 20. Hydroxyproline content was also significantly less in the OC group on days 10, 20, and 25. Expression of collagen type II was significantly less in the OC group, compared with the control group on all days, whereas expression of collagen type I was significantly greater in the OC group on days 20 and 25. Expression of collagen type X was significantly less in the OC group on all days except day 25.

CONCLUSIONS AND CLINICAL RELEVANCE

Chondrocytes from naturally occurring OC lesions of the humeral head of dogs cultured in a 3-dimensional system were less viable and less capable of producing appropriate extracellular matrix molecules than chondrocytes from unaffected dogs. Alterations in the synthetic capabilities of chondrocytes from OC-affected cartilage may be a cause or an effect of the disease process.

Unusual osteochondral lesions of the talus in a horse

A 2-year-old Thoroughbred gelding was evaluated for a grade 3 out of 5 unilateral hind limb lameness. Flexion of the right hock and stifle joints (spavin test) exacerbated the lameness. Response to intra-articular and perineural anaesthesia isolated the source of lameness to the tarsocrural area, despite an absence of tarsocrural joint effusion. Routine radiographic examination of the hock did not reveal any significant abnormalities. Skeletal nuclear scintigraphic evaluation revealed a focal region of increased bone activity in the proximal medial trochlear ridge of the talus. Flexed lateromedial radiographic views identified three discrete semicircular lytic lesions at the proximal articular margin of the medial trochlear ridge of the talus. Conservative management of the lesions was associated with a successful return to racing. The location and appearance of the osteochondral lesions of this report have not been previously reported and may be a manifestation of developmental orthopaedic disease and abnormal endochondral ossification. Nuclear scintigraphy and flexed lateromedial radiographic views facilitated identification of the lesions. This radiographic view is recommended when lameness is isolated to the tarsocrural joint and standard radio-graphic projections fail to identify a cause.

Changes in molecular expression of aggrecan and collagen types I, II, and X, insulin-like growth factor-I, and transforming growth factor-beta1 in articular cartilage obtained from horses with naturally acquired osteochondrosis

OBJECTIVE

To determine molecular changes in the expression of insulin-like growth factor-I (IGF-I) and transforming growth factor-beta1 (TGF-beta1) in horses with osteochondrosis, and to characterize expression of matrix aggrecan and collagen types I, II, and X in articular cartilage of affected joints.

SAMPLE POPULATION

Articular cartilage from affected stifle or shoulder joints of 11 horses with naturally acquired osteochondrosis and corresponding joints of 11 clinically normal horses.

PROCEDURE

Harvested specimens were snap frozen in liquid nitrogen, and total RNA was isolated. Specimens were fixed in 4% paraformaldehyde for histologic examinations. Expression of matrix molecules was assessed by analysis of northern blots and in situ hybridization, using equine-specific cDNA probes and riboprobes, respectively. Expression of IGF-I and TGF-beta1 was assessed by use of noncompetitive quantitative polymerase chain reaction, in situ hybridization, and immunohistochemical analysis.

RESULTS

Cartilage obtained from osteochondrosis lesions had significantly greater expression of IGF-I, compared with normal cartilage. Expression of TGF-beta1 and collagen type I were higher, but not significantly so, in affected tissues. Expression of aggrecan or collagen types II and X did not differ between affected and clinically normal cartilage.

CONCLUSIONS AND CLINICAL RELEVANCE

Increased expression of growth factors and collagen type I was found in cartilage from osteochondrosis lesions. However, this probably reflects a healing response to injured tissue rather than a primary alteration. Therefore, methods aimed at altering concentrations of growth factors in cartilage of growing horses would be unlikely to alter the incidence or progress of the disease.

Lumbosacral osteochondrosis: radiological features and surgical management in 34 dogs

Lumbosacral osteochondrosis has been diagnosed with increasing frequency over the past few years. Nevertheless, poor recognition of the condition continues to lead to frequent misdiagnosis. A study was therefore undertaken over a 12-year period (1986 to 1998) to describe the use of a variety of radiological studies to define the syndrome and the use of different surgical techniques for optimal treatment of the condition. Dogs with clinical signs of cauda equina neuropathy and radiological signs of lumbosacral osteochondrosis were older than 14 months (mean age 6.3 years). German shepherd dogs, boxers and rottweilers were heavily represented. Of the 34 dogs with osteochondrosis in this study, the lesion appeared to be related to the sacrum in 31 dogs (91 per cent) and the seventh lumbar vertebra in the remaining three dogs (9 per cent). Twenty-seven male and seven female dogs were affected (4:1). Out of the 34 dogs, six (18 per cent) were treated conservatively and the remaining 28 (82 per cent) were treated surgically. The outcome of surgical treatment was considered to be satisfactory in 24 (86 per cent) of these latter dogs.