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.

Changes in synovial fluid biomarker concentrations following arthroscopic surgery in horses with osteochondritis dissecans of the distal intermediate ridge of the tibia.

OBJECTIVE: To quantify concentrations of cartilage oligomeric matrix protein (COMP) and fibromodulin in synovial fluid from the tarsocrural joints (TCJs) of horses with osteochondritis dissecans (OCD) of the distal intermediate ridge of the tibia and determine whether concentrations would change following arthroscopic removal of osteochondral fragments. ANIMALS: 115 client-owned horses with OCD of the TCJ and 29 control horses euthanized for unrelated reasons. PROCEDURES: COMP and fibromodulin concentrations were measured in synovial fluid from the TCJs of the affected horses before and after osteochondral fragments were removed arthroscopically and in synovial fluid from the TCJs of the control horses after euthanasia. Synovial biopsy specimens from the TCJs of affected and control horses were examined histologically for evidence of inflammation. RESULTS: Synovial fluid COMP and fibromodulin concentrations prior to surgery in horses with OCD were not significantly different from concentrations in control horses. Fibromodulin, but not COMP, concentration in horses with OCD was significantly decreased after surgery, compared with the concentration before surgery. Fibromodulin concentration was significantly correlated with joint effusion score but not with lameness score or results of a flexion test and was correlated with histologic score for number of synoviocytes on the surface of the synovium but not with score for degree of infiltration of inflammatory cells in the synovium. Synovial fluid COMP concentration was not significantly correlated with clinical or histologic findings. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that fibromodulin, but not COMP, could potentially be a biomarker of joint inflammation in horses with OCD of the TCJ.

Consequences of the natural course of articular osteochondrosis in pigs for the suitability of computed tomography as a screening tool.

BACKGROUND: A significant heritability has been documented for articular osteochondrosis. Selection against osteochondrosis has historically been based on macroscopic evaluation, but as computed tomography (CT) now is used to select boars with optimal body composition it can potentially also be used to screen for osteochondrosis. False negative diagnosis will occur if defects have not developed or have resolved prior to screening at a single time point. The aim of the current study was to assess the suitability of the use of CT at a single point in time as a screening tool in piglets for articular osteochondrosis, which is known to be a highly dynamic condition in which lesions develop and resolve over time. METHODS: Male Landrace piglets (n = 18) were serial CT scanned from 2-8 times at biweekly intervals from 70-180 days of age. At each interval, 1-2 piglets were euthanased and the left distal femur processed for histological validation. RESULTS: A total of 795 defects were identified in the 112 available CT scans. Within the hind and fore limbs, the incidence of defects was highest in the stifle (n = 321) and elbow joints (n = 110), respectively. Ninety-eight per cent of the defects in the stifle and elbow joints had developed by the 7th examination interval when the piglets were a mean age of 159 days old. The proportion of defects that resolved was lowest in the stifle joint at 51% and highest in the elbow joint at 69%. CONCLUSIONS: Scanning of the current piglets at an age of 159 days resulted in detection of 98% of the total number of defects that developed up to the maximum age of 180 days. The proportion of defects that resolved ranged from 51-69% for different joints, but may not adversely affect prevalence as this category of false negative diagnosis will result in selection of pigs that are disposed for healing. Optimally timed CT is a powerful screening tool for osteochondrosis.

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.

Identification of differentially expressed genes associated with osteochondrosis in standardbred horses using RNA arbitrarily primed PCR.

The aim of this study was to investigate genes for differential expression in cartilage of foals predisposed to osteochondrosis (OC). Tissue was sampled from the cranial part of the distal intermediate ridge of the tibia in the tarso-crural joint. Foals were considered predisposed to OC when parents had OC at the distal intermediate ridge of the tibia. RNA was isolated and subjected to arbitrarily primed PCR (RAP-PCR) followed by fingerprinting to screen for differentially expressed genes. By verification of results from the RAP-PCR fingerprint screening using real-time RT-PCR, we identified two genes not previously correlated with OC as differentially expressed. The two genes, which were identical to TLK2 and an equine EST, are good targets for future research on OC.

Association between clinical signs and histopathologic changes in the synovium of the tarsocrural joint of horses with osteochondritis dissecans of the tibia.

OBJECTIVE: To develop a scoring system for histopathologic changes in the synovium of tarsocrural joints (TCJs) of horses with osteochondritis dissecans (OCD) and to test for association between histopathologic changes and joint effusion or lameness. ANIMALS: 93 horses with OCD of the intermediate ridge of the tibia of 1 or both TCJs (134 joints) and 38 control horses without disease of TCJs (38 joints). PROCEDURES: For OCD-affected horses, pretreatment lameness, TCJ effusion, and results of pelvic limb flexion test were scored. Synovial biopsy specimens were obtained from TCJs of OCD-affected horses during arthroscopy, and similar postmortem tissue specimens were obtained from control horses through a small arthrotomy. Histologic signs of synovitis in 172 biopsy specimens were scored by 2 pathologists (A and B) by use of 2 criteria: synoviocyte proliferation and cellular infiltration. RESULTS: Analysis of scoring revealed good to very good intraobserver agreement within pathologist A (weighted kappa [WK], 0.76 to 0.81), and moderate to good agreement within pathologist B (WK, 0.56 to 0.63). Interobserver agreement for synoviocyte proliferation (WK, 0.34 to 0.52) and cellular infiltration (WK, 0.38 to 0.48) scores was fair to moderate. Joint effusion and synoviocyte proliferation were significantly associated, as were joint effusion and cellular infiltration. There was no association between histopathologic changes and the other clinical signs evaluated. CONCLUSIONS AND CLINICAL RELEVANCE: The scoring system was helpful for evaluating synovial inflammation caused by OCD of the intermediate ridge of the tibia in horses. Histopathologic signs of synovial inflammation were associated with effusion but not with lameness.

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.

Electroencephalographic and cardiovascular variables as nociceptive indicators in isoflurane-anaesthetized horses.

OBJECTIVE: To evaluate Fourier-transformed electroencephalographic (EEG) variables, mean arterial blood pressure (MAP) and pulse rate as nociceptive indicators in isoflurane-anaesthetized horses. ANIMALS: Five standardbred and three Norwegian cold-blooded trotter stallions undergoing castration, aged 2-4 years, mass 378-538 kg. MATERIALS AND METHODS: All horses received intravenous (IV) detomidine (10 microg kg(-1) IV) and butorphanol (0.01 mg kg(-1) IV). Additional detomidine (4 microg kg(-1) IV) was administered in the induction area. Anaesthesia was induced with ketamine (2.5 mg kg(-1) IV) and diazepam (40 microg kg(-1) IV), and maintained for 30 minutes with isoflurane (end-tidal concentration of 1.4%) vaporized in oxygen. The electroencephalogram, MAP and pulse rate were recorded for 15 minutes, beginning 5 minutes before skin incision. Differences between the mean values of recordings taken before, and during surgery were calculated and tested for significant differences using a two-sided Student's t-test. RESULTS: A significant rise in MAP and a fall in pulse rate were found. No significant change was found in any EEG variable. CONCLUSION/CLINICAL relevance Of the variables evaluated, MAP seems to be the most sensitive and reliable indicator of nociception in isoflurane-anaesthetized horses.

Evaluation of the bispectral index as an indicator of degree of central nervous system depression in isoflurane-anesthetized horses.

OBJECTIVE: To determine whether the bispectral index (BIS) can be used as an indicator of degree of CNS depression in isoflurane-anesthetized horses. ANIMALS: 10 Standardbred and 6 Norwegian cold-blooded trotter stallions admitted for routine castration. PROCEDURE: A 2-channel referential electrode configuration was used to record EEG for calculation of BIS by the EEG monitor. The BIS was calculated before (awake) and after (sedated) administration of detomidine (0.01 mg/kg of body weight, IV) and butorphanol (0.01 mg/kg, IV). Anesthesia was induced with ketamine hydrochloride (2.5 mg/kg, IV) and diazepam (0.04 mg/kg, IV) and maintained with isoflurane delivered in oxygen. The BIS was calculated after 30 minutes of equilibration at an end-tidal isoflurane concentration of 1.4% (n = 8) or 1.9% (8) and recorded continuously during surgery. RESULTS: Bispectral index was significantly less in sedated and anesthetized horses, compared with awake horses. However, BIS was not significantly different between sedated and anesthetized horses. Mean BIS in horses anesthetized at 1.9% isoflurane was significantly greater, compared with horses anesthetized at an end-tidal concentration of 1.4%. Four horses in the 1.4% group moved during surgery, and BIS increased immediately prior to movement in 2 of these horses. CONCLUSIONS AND CLINICAL RELEVANCE: BIS is not a precise indicator of degree of CNS depression in isoflurane-anesthetized horses. Thus, determination of BIS may not be a useful technique for monitoring anesthetic depth in isoflurane-anesthetized horses.