Veterinary Science - Theses
Now showing items 1-12 of 328
Clinical use of plasma lactate concentration and evaluation of the analytical performance of two benchtop analyzers for the measurement of L-lactate in canine plasma
Lactate has been used in small animal veterinary medicine since the 1990’s. Ongoing reviews of the literature had revealed that an up to date, comprehensive review of the use of lactate in small animal clinical practice was overdue. Consequently, this became the first objective of this thesis (Chapters 1 and 2). Through this review process, a surprising gap was identified in the veterinary literature. Despite widespread integration into clinical practice and validation of hand-held lactate analyzers against benchtop methods, there was no actual published evidence validating these benchtop methods for use in dogs (Chapter 3). Accordingly, this became the objective of the experimental component of this thesis (Chapter 4). A partial method validation study was designed to satisfy requirements outlined by the American Society of Veterinary Clinical Pathologists (ASVCP). The objective was to evaluate the analytical performance and equivalency of two commercially available benchtop lactate analyzers: a high-end point-of-care analyzer, the Radiometer ABL 800 (ABL800), and a clinical laboratory analyzer, the Cobas Integra 400 (Cobas400). As a gold-standard, definitive method for lactate measurement is poorly defined, we elected to use canine plasma manually spiked with reference standard sodium lactate as our test medium. After a preliminary assessment of linearity, intra-assay precision, and inter-assay precision using manufacturer controls, we used the spiked plasma to assess linearity, intra-assay precision, accuracy, range and equivalency of the two analyzers. Both analyzers demonstrated excellent precision. The Cobas400 was accurate over a wider range than the ABL800, however the ABL800 was more accurate within the most clinically relevant range. Method comparison was performed using the Cobas400 as the nominated reference method. Passing-Bablok linear regression and Bland-Altman analysis revealed that although the methods were in agreement, with ≈ 95% of measured differences falling within ± 1.96 standard deviations of the mean difference, they cannot be considered equivalent due to the presence of a small but clinically significant amount of constant and proportional bias. In conclusion, both analyzers demonstrated adequate analytical performance for use in clinical practice and future validation studies. However, they cannot be considered equivalent due to the presence of both constant and proportional bias and should not be used interchangeably. Consequently, analyzer specific reference intervals should be applied, and the same analyzer should be used when serially trending lactate concentrations in an individual patient.
Genomic resources and genetic studies of parasitic flukes, with an emphasis on Clonorchis sinensis
Clonorchiasis is a complex hepatobiliary disease caused by the foodborne parasite, Clonorchis sinensis (family Opisthorchiidae). This disease can induce cholangiocarcinoma (CCA), a malignant cancer of the bile ducts, and has a major socioeconomic impact on ~ 35 million people predominantly in East Asia. Currently, no vaccine is available to prevent clonorchiasis, and repeated use of the only recommended drug, praziquantel (PZQ) increases the risk of developing drug resistance. Further understanding of the disease epidemiology relies on the knowledge of genetic variation of C. sinensis in endemic areas. Moreover, evidence of karyotypic variation within C. sinensis highlights the importance of comparing the genomes of geographically distinct isolates of this parasite. The two predominant research aims of this thesis were to decode the mitochondrial (mt) and nuclear genomes of a Korean isolate of C. sinensis and assess genetic variation, using high-throughput sequencing technologies and advanced bioinformatic workflows. The mt and nuclear genomes for a C. sinensis isolate from Korea (Cs-k2) were sequenced, assembled, characterised and compared with one or more isolates. In addition, a refined bioinformatic workflow was designed to infer high quality syntenic blocks between the nuclear genome and a previously published draft genome of another isolate from China. The results not only reveal a high level of nucleotide similarity within the syntenic regions, but also pinpoint variable genes that might be central to infection and/or adaptive process. The mt and nuclear genomes and the syntenic blocks now serve as a solid foundation for a future genetic analysis of C. sinensis. The mt genome, on one hand, confirmed the specific identity of the specimen, on the other hand, highlighted potential challenges with using mtDNA markers for genetic analyses. In contrast to the mt genome, the syntenic blocks of the nuclear genome exhibit major potential for future genetic studies due to a vast extent of nucleotide differences in coding regions. These blocks also contain a substantial number of genetic loci that might enhance knowledge of host- parasite relationships in an evolutionary context. Compared with coding regions, the genetic variation in the intronic regions showed an improved phylogenetic signal at both the whole genome and individual gene levels. In future, improved quality of the assembly and annotation of nuclear genomes should be achieved using long read data, allowing a broader range of genetic and structural variation to be identified using whole genomic data of representative individuals. Furthermore, a systematic bioinformatic framework is required to discover individual variants, infer population structure and identify adaptive selection, with the consideration of parasitic life cycle and demographic history. Although the present thesis focused predominantly on C. sinensis, the work extended logically to another trematode. A third research aim was addressed to explore the population genetic structure of a related trematode parasite, Schistosoma japonicum in China and to identify genes under positive selection in particular geographical locations. Clearly, the findings of this thesis and the approaches established should have important and broad implications for studies of a range of flatworm parasites.
Chronic enteropathy in dogs: the role of macrophages and preliminary results in inflammatory cytokines
Chronic enteropathy (CE) is an umbrella term used in dogs to describe a group of diseases with different aetiologies, characterised by chronic gastrointestinal signs. These diseases are clinically classified according to treatment response as food-responsive (FRE), antibiotic-responsive (ARE), and immunosuppressant-responsive enteropathies (IRE). The first part of this PhD thesis prospectively describes the features of CE that are commonly seen in dogs presenting to a referral centre in Australia; information that has not been available previously. We found that similar to other countries, most dogs with CE are food-responsive, followed by antibiotic-responsive with a minority of immunosuppressant-responsive. Furthermore, our study raised concerns about prolonged antibiotic treatment for dogs with ARE. Firstly, most of these dogs do not respond to treatment completely for prolonged periods (as opposed to dogs with FRE that do), raising the question about the real benefit of antibiotic treatment. Secondly, half of the dogs with ARE required long-term or pulse treatment with antibiotics, which raises concerns about development of bacterial resistance. Our findings highlight the need to find alternative treatment for dogs with ARE in view of the poor long-term outcome. Although most dogs with FRE had long-term remission, adequate dietary trials were not performed until reaching the referral setting. This indicates that better education of general veterinary practitioners about the importance of performing adequate diet trial is needed to improve early disease remission in these dogs. The next focus of the research was to evaluate the role of macrophages in CE; this was achieved by using two macrophage markers: calprotectin and cluster of differentiation 163 (CD163) in immunohistochemical examination. Both immunohistochemical markers highlighted two different populations of macrophages in our intestinal biopsy specimens. Overall the number of CD163 positive cells was higher than calprotectin positive cells both in crypts and villi. Dogs with FRE and IRE had a decreased CD163:calprotectin ratio compared to healthy dogs with an increase in the ratio after treatment. Our results suggest that there is an imbalance in macrophage populations in dogs with FRE and IRE, with partial resolution following clinical response characterised by an increase in the ratio CD163:calprotectin. Interestingly, dogs with ARE not only have a poor long-term response, but also have different macrophage populations from dogs with FRE and IRE; and in fact, are very similar to healthy dogs without change in their macrophage populations with treatment response. These results suggest that macrophages play a role in the pathogenesis of FRE and IRE dogs with normalisation of macrophage populations with treatment response. The CD163 receptor is cleaved during macrophage activation and is released into the circulation as a soluble form. In view of the decreased number of CD163 cells in the intestine of dogs with FRE and IRE at diagnosis (and subsequent increase with clinical remission), we wanted to determine if soluble CD163 could be detected in dog serum, and therefore potentially serve as a biomarker. Two different ELISAs were tested and although one of them showed some signal, further testing of the antibodies used in the assay did not support that the signal was specific for CD163. With this experiment, we were not able to quantify soluble CD163 in dogs, but this molecule retains potential as a biomarker for diagnostic and monitoring purposes in CE as well as in other diseases characterised by macrophage activation. Biomarkers of systemic inflammation were also assessed in the same cohort of dogs and we showed that serum IL-6 decreased in dogs with CE after resolution of clinical signs. Similarly to soluble CD163, cytokines might play a role in further differentiating between the different causes of CE for prognostic and therapeutic purposes. Future studies are needed to assess these cytokines in a larger cohort of dogs to be able to study differences between FRE, ARE, and IRE, and further assess their role as biomarkers. Finally, we studied cytokine production by lymphocytes or monocytes in the peripheral blood of healthy dogs, and the effect of different immunosuppressive treatments on cytokine production. Differential activation of lymphocytes or monocytes can easily be achieved by using specific activators in whole blood. The advantage of this technique is that there is minimal handling of the cells with less risk of iatrogenic activation. Cytokine production was affected by cyclosporine and prednisolone, but not by mycophenolate, leflunomide, or azathioprine. Cyclosporine inhibited production of tumour necrosis factor (TNF), interferon gamma and IL-10 by lymphocytes whereas prednisolone inhibited TNF production by both lymphocytes and monocytes. Our findings suggest that this methodology can be used to monitor dogs treated with both drugs concurrently – although this needs to be further assessed with future studies. Future studies highlighted by our research suggest more in-depth assessment of serum cytokines as biomarkers for dogs with CE not only for monitoring purposes, but to determine if different patterns of cytokines can be useful to refine the classification of CE. Similarly, whole blood stimulation can be used to better assess underlying priming of the immune system and to monitor treatment response. Finally, our findings suggest that macrophages play a significant role in the pathophysiology of CE in dogs, particularly in FRE and IRE, but additional work is required to better understand their function in CE.
Inflammation and endothelial perturbation in canine abdominal surgery: the potential modulatory effect of lidocaine
Complication rates following emergency laparotomy surgery are high, with organ dysfunction being a commonly encountered post-operative complication. Given the endothelium acts as the interface between the systemic circulation and the organs, its function is vital to maintaining organ health. The endothelium is in a constant state of flux, impacted largely by the local environment of which it is a part. In the presence of wide-spread systemic inflammation, inflammatory mediators precipitate change to the structure of the endothelial glycocalyx. These changes result in shedding of the endothelial glycocalyx and alteration of the endothelial phenotype. The endothelium may, as a result, lose the capacity to regulate vasomotor tone, and shift toward a pro-inflammatory and pro-coagulant state. This predisposes to reduced tissue oxygen delivery, and organ dysfunction may ensue. This thesis aimed to answer two key questions: does surgical trauma induced in canine patients undergoing emergent abdominal surgery invoke a systemic inflammatory response and subsequent endothelial activation? And if so, does lidocaine, a proposed immunomodulatory drug, mitigate this effect when given in the post-operative period? Chapter two provides a detailed review of endothelial structure and function, and current literature pertaining to systemic inflammation and endothelial activation in the context of abdominal surgery. Chapter two also examines the literature regarding the proposed mechanisms through which lidocaine acts as an immunomodulatory drug, and reviews publications that investigate the use of lidocaine as an anti-inflammatory drug in human patients after abdominal surgery. Chapter three is a randomized, blinded clinical trial quantifying the effect of emergency abdominal surgery on the concentration of markers of systemic inflammation and endothelial perturbation in canine patients in the post-operative period. The trial also assessed the potential use of lidocaine as a post-operative immunomodulatory therapy in dogs having undergone laparotomy. Fifty canine patients undergoing abdominal surgery were enrolled in the study. Patients were randomized into two separate groups: a study group receiving lidocaine intravenously, and a control group receiving 0.9% NaCl intravenously for a twelve-hour period following abdominal surgery. Blood samples were gathered prior to surgery, followed by six and twelve hours post-operatively. Concentrations of markers of systemic inflammation (IL-6) and markers of endothelial perturbation (VEGF and HA) were quantified via means of ELISA at each time point. Results revealed a significant increase in the concentration of markers of systemic inflammation and endothelial perturbation in post-operative blood samples. No immunomodulatory or endothelial preserving effect of lidocaine was appreciated.
Select bacterial and viral pathogens of potential zoonotic or biosecurity importance in Australian brushtail (Trichosurus spp.) and ringtail (Pseudocheirus peregrinus) possums
Possums and gliders represent a diverse group of marsupial mammals native to Australia, including multiple vulnerable and endangered species. Common brushtail (Trichosurus vulpecula) and common ringtail (Pseudocheirus peregrinus) possums are two urban adapted species frequently found in gardens and parks throughout eastern Australia. Their presence in urban areas provides opportunities for transfer of zoonotic pathogens through both direct and indirect contact with humans. Diseases affecting possums are relatively poorly understood, as is the role of possums in the maintenance and transmission of zoonotic pathogens. This study aimed to investigate the significance of these possums as host species for a select range of pathogens, particularly in Victoria. Opportunistically collected serum samples from common ringtail, common brushtail and mountain brushtail possums (Trichosurus cunninghami) from Victoria and South Australia were tested for antibodies against Ross River virus (RRV) and flaviviruses. Cloacal swabs from common brushtail and ringtail possums from Victoria and New South Wales were screened for the presence of Mycobacterium ulcerans (the cause of Buruli ulcer), Campylobacter spp. and Salmonella spp. Spleen samples were screened for Francisella tularensis (the cause of tularaemia) and Coxiella burnetii (the cause of Q fever) by PCR. Antibodies to RRV were detected in 6.2% (16/259) of all possum samples, which were sampled during a concurrent epidemic of RRV in humans. Geographical areas with a moderate to high human case rate were associated with a higher seroprevalence rate in sampled possums. There was a significantly lower rate of detection in possums from urban environments compared to rural and mountainous environments. Seroconversion to an unspecified flavivirus was also present in 5.2% (5/97) of common ringtail possums and 6.5% (2/31) of mountain brushtail possums, but not in common brushtail possums (0/137). Two of the seropositive animals displayed clinical signs of encephalitis. Salmonella spp. was detected in 3.1% (7/229) of possums, while Campylobacter spp. Was found in 27.7% (41/229), with a significant predilection for common brushtail possums (38/106). The exact Campylobacter species was not identified, however, the main human pathogens C. jejuni and C. coli were excluded. No samples were positive for F. tularensis (n = 187), C. burnetii (n = 184) or M. ulcerans (n = 229). These findings indicate that, while urban-adapted possums may potentially carry zoonotic pathogens, they are unlikely to represent a high risk to public health, at least in regards to the infectious agents that were the focus of this study in the areas that were investigated. Finally, serum samples from all three possum species were screened for antibodies to Wobbly Possum Disease virus (WPDV), a recently identified virulent nidovirus in common brushtail possums in New Zealand. Although thought to be absent from Australia, antibodies to WPDV, or an antigenically similar nidovirus, were detected in all three species of possum, originating from both Victoria and South Australia. Overall, 16% (30/188) of samples were positive and 11.7% (22/188) were equivocal, with the two brushtail species most commonly affected. This is the first published report of serological evidence of WPDV, or an antigenically similar nidovirus, in Australian possums. However, attempts to detect viral RNA in spleen samples by PCR were unsuccessful.
Update on clinicopathological assessment of renal health in non-racing greyhounds
Background: Serum creatinine concentrations differ in greyhounds compared with non-sighthounds, but it is not known whether urine creatinine concentrations also differ and whether any difference would influence the interpretation of the urine protein to creatinine ratio (UPC). Additionally, there is some evidence for greyhounds having higher serum symmetric dimethylarginine (SDMA) than non-sighthounds, but this has yet to be confirmed in healthy non-racing greyhounds. Objectives: The objectives of this study were fourfold: (1) to compare the urine creatinine concentrations in healthy greyhounds and a control group of healthy non-sighthounds, (2) to determine the UPC reference interval in healthy greyhounds and to compare this with the UPC reference interval in a control group of healthy non-sighthounds, (3) to determine the serum SDMA concentration reference interval in healthy greyhounds and to compare this with the serum SDMA concentration reference interval in a control group of healthy non-sighthounds and with a previously established canine serum SDMA concentration reference interval, and (4) to establish whether lean body mass is correlated with serum creatinine and urine creatinine concentrations in greyhounds. Methods: The study used an observational cross-sectional design and included 98 clinically healthy non-racing greyhounds and 24 non-sighthound dogs with similar weight, age and sex distributions, as determined by t-test and chi-squared tests. SDMA, urine creatinine concentration and UPC values were measured from blood and urine samples. Linear regression was used to compare the greyhound and non-sighthound groups. Greyhound reference intervals were determined for SDMA and UPC using non-parametric methods. These were compared with the reference intervals for the non-sighthound group and with current International Renal Interest Society guidelines. In the greyhound sample, the association of urine creatinine with thigh circumference, height and weight was estimated using Pearson correlation. Statistical significance was set at P < 0.05 for all analyses. Results: Mean urine creatinine was approximately 22% higher in greyhounds than non-sighthounds after adjusting for urine concentration (P < 0.05). The upper limit of the greyhound UPC reference interval was 0.20 or 0.42, depending on whether strict or moderate exclusion criteria, respectively, were applied. The mean UPC was 29% lower in greyhounds than non-sighthounds, but this difference was not statistically significant (P = 0.1). The serum SDMA reference interval for greyhounds was 6.3–19.7 µg/dL (0.31–0.98 µmol/L). The upper end of this interval was higher than the upper limit of the published canine reference interval (6–13 µg/dL), and the mean concentration was statistically significantly higher in greyhounds (13.0 µg/dL) than non-sighthounds (10.2 µg/dL, P < 0.001). In greyhounds, there were weak correlations between the three morphometric measurements and both serum creatinine and urine creatinine after adjusting for urine concentration. Conclusions and clinical importance: These findings provide further evidence that greyhounds require several breed-specific reference intervals when evaluating renal function. Apart from having higher serum creatinine, greyhounds also have higher SDMA and higher urine creatinine when compared to non-sighthounds. Although UPC trended slightly lower in greyhounds, this finding was not significant, and therefore the threshold for non-proteinuria set by IRIS guidelines appears to be appropriate for greyhounds based on the calculated reference interval.
Investigating the inflammatory pathways involved in placental detachment in the mare
The mechanism of placental detachment in the mare has not been investigated in detail and as such remains poorly understood. Research in other species provides strong evidence that parturition and fetal membrane detachment from the endometrium requires involvement of the immune response. Research in horses has also suggested that movement of leukocytes in the umbilical vessels, and their attraction to fetal membranes at parturition, contribute to placental detachment. The aims of this study were to 1) confirm whether a leukocyte “concentration gradient” exists between the equine neonatal umbilical artery and vein, and whether this gradient was associated with fetal membrane retention time 2) to investigate the expression of pro-inflammatory cytokines in the equine endometrium and fetal membranes at parturition using quantitative real time polymerase chain reaction (RT-qPCR) and 3) to localise pro-inflammatory cytokine proteins within the equine endometrial and fetal membrane tissues using immunohistochemistry to correlate with gene expression. Data was collected from 33 spontaneously foaling mares and their foals on a single Thoroughbred stud farm in New Zealand. Umbilical artery and vein blood, fetal membrane and endometrial biopsy tissue samples were obtained. The average fetal membrane retention time was 92 (+/-130) minutes. The median fatal membrane retention time was 47 minutes (IQR 30). There was a significantly higher number of total leukocytes, lymphocytes and neutrophils in the equine neonatal umbilical artery than the umbilical vein at parturition (p <0.001). Fetal membrane retention time tended to decrease with an increase in umbilical leukocyte concentration gradient but did not reach statistical significance (p = 0.098). The mRNA expression of IL-1, IL-6 and IL-8 was significantly greater in the endometrium of foaling mares compared to control mares (p < 0.001). The mRNA expression of IL-8 was significantly higher in the fetal membranes of foaling compared to control mares (p < 0.001) whereas mRNA expression of IL-6 in fetal membranes was significantly lower between the two groups (p< 0.001). Whilst mRNA expression for IL-1 was lower in the fetal membranes of foaling mares compared to controls, the difference was not significant (p = 0.16). This study has demonstrated the presence of an innate inflammatory immune response in the placenta of spontaneously foaling mares, suggesting the role of inflammation in the detachment of the fetal membranes from the endometrium. The results from this study have highlighted the need to further investigate the mechanism of placental detachment in the mare and also understand the pathophysiology behind abnormal fetal membrane retention.
Recombination of infectious laryngotracheitis virus (ILTV) and the role of vaccination
Infectious laryngotracheitis virus (ILTV; Gallid alphaherpesvirus-1) is an alphaherpesvirus that causes respiratory disease in chickens, resulting in significant production losses in poultry industries worldwide. Recombination between different ILTV strains has recently been identified. Recombination in alphaherpesviruses was first described more than sixty years ago and since then, different techniques have been used to detect recombination in both natural (field) and experimental settings. In the past, natural recombination events between ILTV strains has resulted in the emergence of virulent recombinant viruses that have caused severe disease outbreaks in Australia. In this work, a single nucleotide polymorphism (SNP) genotyping assay was developed to study ILTV recombination in vivo. This assay was used to study recombination in a large number of viruses retrieved from chickens co-inoculated with two Australian ILTV field strains. Further application of this SNP genotyping assay helped unveil other aspects of ILTV recombination such as viral diversity over time and dominant recombination patterns in the recombinant progeny. Whole genome sequencing (WGS) of dominant viruses was performed in order to analyse their recombination breakpoint locations. This latter analysis revealed the presence of recombination hot-spots. The location of these hotspots were consistent with those found after the analysis of publicly available whole genome sequences of ILTV from different geographical regions, such as Australia and the United States (US). Additionally, the recombination output was determined in chickens after vaccination with three commercially available Australian ILTV vaccines (SA2, A20 and Serva), or two vaccines from the US (CEO-Tachivax and HVT-LT). For this later analysis a second SNP genotyping assay was develop to detect recombination between the USA field strains of ILTV used in that study. Results from these analyses indicated that vaccination can limit the number and diversity of recombinant progeny viruses and introduced new research questions about the role of the immune system in limiting recombination. The studies reported in this thesis have provided new insights into recombination in alphaherpesviruses that will be useful for future studies regarding vaccine development and use in both Australia and elsewhere.
Endothelial activation in dogs with severe sepsis
Two components of endothelial biology – endothelial glycocalyx, endothelial activation – have been explored this two-part, in-depth research project. An extensive literature review discusses the endothelial glycocalyx in health and critical illness. A prospective observational clinical research study then measures the concentration of soluble biomarkers of endothelial activation in severely septic dogs. The study found a significant difference in the concentration of biomarkers between the septic dogs and controls, a result consistent with the presence of endothelial activation in dogs with severe sepsis.
The role of the intestinal microbiota in the pathogenesis of chronic enteropathies and their interplay with the immune system
The intestinal microbiota and its associated genome is collectively called the gastrointestinal (GI) microbiome, and is composed of crucial components that help not only to determine host biology but also to maintain host physiology. Dysregulation of the gastrointestinal microbiome has been associated with a range of diseases in people such as inflammatory bowel disease (IBD), diabetes and obesity. Previous studies have found dysbiosis and a reduced bacterial diversity in dogs with chronic enteropathies (CE). However, the precise nature of the intestinal microbiota dysfunction and whether the microbiota has a causative role or is secondarily affected remain to be elucidated. The first step in understanding the relationship between the gut microbiota and disease is the characterisation of the normal gut microbiota, how it is established and how stable it is during different periods of life. In this work, we assessed the dynamics and stability of faecal microbiota over time in healthy dogs of different age groups, and the development of the microbiota from birth in puppies, and the association with the maternal microbiome. Next, we characterised highly immunoglobulin A and G coated bacteria in faecal samples from dogs with chronic enteropathies using flow cytometry and 16S rRNA sequencing and assessed their correlation with disease stage and resolution of the clinical signs. Finally, we characterised the expression of thymic stromal lymphopoetin (TSLP), a cytokine that is produced in response to bacterial contact, in the intestine of healthy dogs and its correlation with disease activity in dogs with chronic enteropathies. The results reported here, help to understand the assembly of the gut microbiota, its interaction with the immune system and emphasise on the importance of longitudinal studies and personalised approach in order to understand the pathogenesis and the role of the microbiota in intestinal diseases in dogs.
Radiographic assessment of bone morphometry, alignment and loading stability of the equine carpal joint in racehorses
The carpus is the most complex joint of the equine forelimb and lameness secondary to carpal injuries accounts for up to 41% of forelimb lameness in racehorses. However, despite suggestions that carpal conformation is a contributory factor to the orthopedic health, performance and forelimb lameness, few attempts have been made to objectively measure radiographic variations of carpal bone morphometry and alignment in horses due to insufficient measurable carpal parameters. Furthermore, non-physiologic loading of carpal bones is believed to result in osteochondral fractures, ligament ruptures and axial instability of the equine forelimb; however, the mechanism of carpal damage due to non-physiologic loading of the carpus is largely unknown. The aims of this thesis were: 1. To investigate the radiographic anatomy of the equine carpus and develop reliable measurable parameters that can be used to consistently and objectively measure carpal conformation in horses 2. To provide baseline data for the developed parameters from radiographs of a group of racing thoroughbred horses. 3. To use some of the developed parameters to assess the stability of the equine carpal joint under incremental load. 4. To observe the roles of the equine carpal ligaments to the load redistribution within the carpus and stability of the carpal joint during axial compressional loads. A pilot study on 6 cadaveric equine forelimbs from 3 adult horses (5.67±2.08 years), was used to investigate the radiographic anatomy of the carpus in “Zero Lateromedial” (ZLM) and “Zero Dorsopalmar” (ZDP) views and 17 measurable parameters with validated anatomical landmarks were developed. Six parameters were developed from the ZLM view and 11 parameters from the ZDP views consisting of angles, ratios and linear measurements. Subsequent studies established: i.) baseline data of these parameters from carpal radiographs of a group of 20 two-year old thoroughbred racehorses in training; ii.) effects of limb postural changes, vertical rotations of radiographic plate, vertical and horizontal rotations of projection angles of primary X-ray beam on the quality of radiographs and carpal measurements; iii.) changes in positions of carpal bones during flexion, extension and incremental load and iv.) a 3-D finite element model of the bony components of the equine carpus. The proximo-distal gliding movement within the carpus enabled transverse movement of the proximal carpal row which in turn allowed the proximal and distal articular surfaces of the radial (Cr), intermediate (Ci) and ulna (Cu) carpal bones to slide into and out of congruity with the distal articular surfaces of the radius and the proximal articular surfaces of the distal carpal row during extension (loading) and flexion. Increased load on the carpus produced carpal hyperextension with measurable radiographic changes in the position and alignment of the carpal bones. A relaxed intercarpal ligament between Cr and Ci (Cr-Ci ICL) during loading, as indicated by decrease in the width of the groove diameter of Cr-Ci ICL (GD.Cr-Ci ICL), signifies minimal or no stretch (strain) on Cr-Ci ICL. This would facilitate absorption and redistribution of concussion forces within the carpal joint during loading, thereby providing a useful mechanism to minimize carpal damage. In conclusion, the carpal bone geomorphometric and loading data, along with information generated on the ligaments of the proximal carpal row in this study, will allow reliable quantitative assessment of carpal conformation and eliminate judgmental errors or variation between observers using subjective visual assessment for the carpus. This data will improve our understanding of carpal biomechanics and pathogenesis of injury. The measurement protocols will require further investigation on large groups of different breeds of horses for wider acceptance, adaptability and validation.
Biomechanical testing of the calcified metacarpal articular surface and its association with subchondral bone microstructure in Thoroughbred racehorses
Subchondral bone adaptation and fatigue likely alter joint surface mechanical properties. The aim of this study was to evaluate the relationship of calcified articular surface biomechanical properties in the distal palmar metacarpal condyle of Thoroughbred racehorses with subchondral bone microstructure and training history. Subchondral bone microstructure was evaluated using both micro- and clinical-computed tomography. Biomechanical properties of the calcified articular surface were tested with reference point indentation at the micron level. Articular surface toughness increased with commencement of race training, and was lower in horses that died as a result of musculoskeletal fatigue injury, had evidence of palmar osteochondral disease, had higher subchondral bone connectivity with more concave surfaces, and higher subchondral bone volume fraction. Further investigation of bone microstructural properties is warranted based on bone connectivity and surface shape findings. At clinically applicable imaging resolution, evidence of subchondral bone modelling may be an important indicator of articular surface biomechanical properties.