C. W. McILWRAITH

Early events in cartilage repair after subchondral bone microfracture.

The current study investigated healing of large full-thickness articular cartilage defects during the first 8 weeks with and without penetration of the subchondral bone using microfracture in an established equine model of cartilage healing. Chondral defects in the weightbearing portion of the medial femoral condyle were made bilaterally; one defect in each horse was microfractured whereas the contralateral leg served as the control. The expression of cartilage extracellular matrix components (Types I and II collagen and aggrecan) was evaluated using histologic techniques, reverse transcription coupled polymerase chain reaction, in situ hybridization, and immunohistochemistry. This study confirms an increase in Type II collagen mRNA expression in repair tissue as early as 6 weeks after microfracture. Although other matrix mRNA and protein levels changed in concentration and tissue location over the course of the study, no significant differences were seen in microfractured defects. Although the microfracture techniques appear to improve clinical functionality, volume of repair tissue, and augment Type II collagen content, aggrecan content is less than ideal. Therefore, methods to enhance key matrix components such as aggrecan after microfracture may additionally improve repair tissue observed after the procedure.

Changes in synovial fluid and serum biomarkers with exercise and early osteoarthritis in horses

OBJECTIVE To discriminate between changes in biomarkers with exercise compared to changes in biomarkers with osteoarthritis (OA) in exercising horses. METHOD Sixteen, 2-year-old horses were randomly assigned either to an exercise-alone (n=8) or OA-affected (also exercised) (n=8) group. All horses had both mid-carpal joints arthroscoped and OA induced in one mid-carpal joint in the OA-affected joints of OA-affected horses. Two weeks after surgery all horses commenced a strenuous exercise program on a high-speed treadmill. Clinical outcomes and synovial fluid and serum biomarkers, were evaluated weekly. Synovial and serum biomarkers evaluated were epitope CS846 (CS846), epitope CPII (CPII), glycosaminoglycans (GAGs), epitope Col CEQ (Col CEQ) (a marker of type II collagen degradation), type I and II collagen degradation fragments (C1,2C), osteocalcin, C-terminal of bone type I collagen (CTX1), type I collagen (Col I) and (synovial fluid only of cartilage) prostaglandin E2 (PGE2) levels. Horses were euthanized at day 91 and their joints assessed grossly, histopathologically, and histochemically. RESULTS Exercise induced a significant increase in synovial fluid CS846, CPII, GAG, Col CEQ, C1,2C, osteocalcin and Col I concentrations. There was a significant increase in synovial fluid CS846, CPII, Col CEQ, C1,2C, osteocalcin, Col I and PGE2 concentrations in OA-affected joints compared to exercise-alone joints. The concentration of serum CS846, CPII, GAG, osteocalcin, C1,2C and Col I increased with exercise. For each of these biomarkers there was also a statistically significant increase in serum biomarker levels in OA-affected horses compared to exercise-alone horses. CONCLUSIONS Six synovial fluid and serum biomarkers were useful in separating early experimental OA from exercise alone but synovial fluid CTX1 and serum Col CEQ and CTX1 were not.

Radiographic changes in Thoroughbred yearlings. Part 1: Prevalence at the time of the yearling sales.

REASONS FOR PERFORMING STUDY Radiography in presale examinations of TB yearlings has become standard practice in recent years. OBJECTIVES To describe the prevalence and distribution of radiographic changes in the fetlocks, carpi, tarsi, stifles and fore feet of Thoroughbred yearlings in central Kentucky when these joints were examined as part of routine pre- and post sale evaluations. METHODS Horses subjected to radiographs included the fore (n = 1127) and hind (n = 1102) fetlocks, carpi (n = 1130), tarsi (n = 1101), stifles (n = 660) and fore feet (n = 300). Radiographic changes were categorised by location and type of change present (e.g. lucency, fragment) for each series. RESULTS In the fore fetlocks 1.6% had fragmentation of the proximal dorsal first phalanx and 0.5% fragmentation of the proximal palmar aspect. In the hind fetlocks 5.9% had fragmentation at the plantar aspect and 3.3% fragmentation dorsally. Lucencies, fragments or loose bodies were detected at the dorsal aspect of the distal third metacarpus in 2.8% and, at the same location on the third metatarsus, 3.2%. Most yearlings (98%) had vascular channels in the proximal sesamoid bones and irregular vascular channels (> 2 mm wide or with nonparallel sides) were more common (79%) than regular vascular channels (56%). The intermediate ridge of the distal tibia was the most common location for fragmentation in the tarsus (4.4%). CONCLUSIONS While some radiographic changes, e.g. vascular channels in proximal sesamoid bones, are very common in Thoroughbred yearlings, others, e.g. fragmentation or subchondral lucency within joints are quite rare usually affecting less than 5% of the population. POTENTIAL RELEVANCE Veterinarians should expect to find radiographic changes in Thoroughbreds presented for examination prior to the yearling sales. The rarity of some changes thought to affect soundness or racing performance will make further invesigation of these conditions in horses without clinical signs more difficult.

The role of conformation in musculoskeletal problems in the racing Thoroughbred.

REASONS FOR PERFORMING STUDY The relationship of conformation to future potential injury is a standard approach in practise but, at present, is largely based on subjective observations. OBJECTIVE To measure conformation in 3-year-old Thoroughbreds and objectively test its relationship with the occurrence of musculoskeletal problems. METHODS Conformation measurements were taken from photographs using specific reference points marked on the horses and processed on the computer. Clinical observations were recorded for each horse on a regular basis. Stepwise (forward) logistic regression analysis was performed to investigate the relationship between the binary response of the clinical outcomes probability and the conformation variables by the method of maximum likelihood. RESULTS Clinical outcomes significantly (P<0.05) associated with conformational variables included effusion of the front fetlock, effusion of the right carpus, effusion of the carpus, effusion of the hind fetlock, fracture of the left or right carpus, right front fetlock problem and hind fetlock problem. CONCLUSIONS Offset knees (offset ratio) contributed to fetlock problems. Long pasterns increased the odds of a fracture in the front limb. An increase in the carpal angle as viewed from the front (carpal valgus) may serve as a protective mechanism, as the odds for a carpal fracture and carpal effusion decreased with an increase in the carpal angle. POTENTIAL RELEVANCE This study demonstrates relationships between conformation and musculoskeletal disease in the racehorse. The information may be useful in selection and management of the racing Thoroughbred.

Radiographic changes in Thoroughbred yearlings. Part 2: Associations with racing performance

REASONS FOR PERFORMING STUDY Although the radiographic examination of yearlings has become commonplace at some large Thoroughbred sales, there are few data to support the decisions facing veterinarians who are asked to evaluate future racing potential. OBJECTIVES To identify radiographic changes in the fetlocks, proximal sesamoid bones, carpi, tarsi, stifles and fore feet of Thoroughbred yearlings associated with future racing performance during ages 2 and 3 years. METHODS Radiographs from routine pre- and post sale examinations of 1162 yearlings were used to identify individual radiographic changes in sale yearlings. Starting a race, the percent of starts placed, money earned and earnings per start were used to assess racing performanceand examined for associations with the radiographic changes observed. RESULTS Overall 946 (81%) yearlings started at least one race during ages 2 or 3 years. Fourteen of 24 (58%) yearlings with moderate or extreme palmar supracondylar lysis of the third metacarpus, 8 of 14 (57%) of those with enthesophyte formation on the proximal sesamoid bones and 19 of 30 (63%) of those with dorsal medial intercarpal joint disease started a race. The odds of starting a race when age 2 or 3 years were 3 times lower for yearlings with these changes (P < 0.01) compared with yearlings that did not have these changes. Twenty-five of 36 (69%) yearlings with proximal dorsal fragmentation of the first phalanx in the hind fetlock started a race and these yearlings were also less likely (OR = 0.51, P = 0.07) to start a race. Yearlings with enthesophyte formation on hind proximal sesamoid bones placed in a smaller percentage of starts (16%, P = 0.01) earned less money (987 US dollars, P = 0.02) and had lower earnings per start (252 US dollars, P = 0.03) compared to starters without this change. CONCLUSIONS Although many of the changes observed on radiographs of sale yearlings do not appear to influence future racing performance, some are associated with reduced performance. POTENTIAL RELEVANCE The results of this study are best applied in parallel with the clinical impressions of veterinarians experienced in examining radiographs of sale yearlings. Some findings support those established in the literature as incidental findings and others suggest new areas for concern not previously reported as a problem in Thoroughbred sale yearlings.

Longitudinal development of equine conformation from weanling to age 3 years in the Thoroughbred

REASONS FOR PERFORMING STUDY There is little information available to define conformational changes with age using an objective but practical method of recording specific body measurements. OBJECTIVE To analyse conformation objectively in a population of racing Thoroughbreds and describe the changes from weanling to age 3 years. METHODS Annual photographs were taken over 4 years and conformation measurements made from photographs using specific reference points marked on the horses. RESULTS Correlation analysis revealed highly significant, moderate to strong relationships between long bone lengths and wither height for all ages. All long bone lengths showed moderate to strong relationships with each other for all ages. The front and rear pastern angles were significantly correlated with the angle of the dorsal surface of the front and rear hooves, respectively, for all. Wither height, croup height and length of neck topline, neck bottomline, scapula, humerus, radius and femur increased significantly from age 0-1 year and age 1-2 years. Hoof lengths (medial and lateral, right and left) grew significantly between the ages of 0 and 1 and 1 and 2 years, but decreased in length between age 2 and 3 years. Horses became more offset in the right limb between weanling and age 3 years, but the offset ratios did not change with age on the left limb. The angle of the scapula (I), shoulder and radiometacarpus significantly increased between all age groups (became more upright). The angle of the dorsal surface of the hooves (both front and hind) decreased significantly from ages 0 to 1 and 1 to 2 years, but showed no significant difference between ages 2 and 3 years. CONCLUSIONS A strong relationship between long bone lengths and wither height for all ages supports the theory that horses are proportional. Longitudinal bone growth in the distal limb increased only 5-7% from weanling to age 3 years and is presumably completed prior to the yearling year. Several growth measures increased from ages 0 to 1 and 1 to 2 years, but did not increase from age 2-3 years; indicating that growth rate either slowed or reached a plateau at this time. POTENTIAL RELEVANCE This study provides objective information regarding conformation and skeletal growth in the Thoroughbred which can be utilised for selection and recognition of significant conformational abnormalities.

Autologous conditioned serum: the comparative cytokine profiles of two commercial methods (IRAP and IRAP II) using equine blood.

REASONS FOR PERFORMING STUDY Osteoarthritis (OA) is one of the most prevalent and debilitating conditions affecting the horse. Autologous conditioned serum (ACS), commercially available as IRAP and IRAP II, is a recently developed treatment for OA in which plasma is prepared from venous blood by incubation with glass beads for 24 h. This product has been shown to increase anti-inflammatory cytokines and growth factors in human blood. However, data for equine ACS preparations are lacking. OBJECTIVES To characterise the protein profiles produced by commercially available ACS systems in equine blood. METHODS Blood was drawn from 5 horses into 6 groups: red top vacutainer (control), IRAP and IRAP II, with and without heparin. Samples were collected 1 or 24 h post draw and analysed for IL-1ra, IL-10, IGF-1, TGF-β, TNF-α and IL-1β using ELISAs. RESULTS Twenty-four hour IRAP and IRAP II samples contained significantly higher levels of all cytokines relative to 1 h serum controls. At 24 h, IRAP II contained significantly higher levels of IL-1ra and IRAP contained significantly higher levels of TNF-α, compared to 24 h controls. In addition, TGF-β, IL-10 and IL-1β in IRAP and IRAP II sera were similar to 24 h serum controls. The addition of heparin significantly reduced levels of IGF-1, TNF-α and TGF-β, and significantly elevated levels of IL-1ra. CONCLUSIONS The cytokine profile that IRAP II produced is modestly better than IRAP. Incubation of whole blood in glass tubes stimulated cytokine synthesis, although not as efficiently as IRAP II. POTENTIAL RELEVANCE Although high levels of IL-1ra were found in ACS, elevation of other factors suggests these cytokines play a previously understated role in clinical improvements. Because ACS has been shown to alleviate clinical symptoms of OA, the present study suggests that factors other than IL-1ra alone might be involved in its clinical efficacy. Species-dependent elevations of cytokines warrant further investigation and optimisation of the systems appears to be necessary based on the differences between human and equine blood.

Current joint therapy usage in equine practice: a survey of veterinarians 2009.

REASONS FOR PERFORMING STUDY Medications are frequently employed to treat intra-articular (IA) problems in the performance horse. Actual usage of the different IA medications in horses is not available. OBJECTIVES To determine the most common usage of these medications, members of the American Association of Equine Practitioners (AAEP) were surveyed. METHODS An email link to an online survey was electronically sent to 6305 AAEP members and the responses tabulated and analysed with a logistic regression model. RESULTS A total of 831 survey responses were submitted and tabulated. Eighty per cent of the respondents indicated that they see 100% equine cases in their practice. The majority of respondents (77%) use triamcinolone acetonide (TA) to treat high motion joints and 73% use methylprednisolone acetate (MPA) to treat low motion joints. Veterinarians treating the Western performance and Sport horse were significantly more likely to use TA in high motion joints compared to MPA (P = 0.0201 and P<0.0001, respectively). Triamcinolone acetonide use compared to MPA in high motion joints by racehorse veterinarians was significantly lower compared to other veterinarians (P<0.0001). Polysulphated glycosaminoglycan (Adequan) and hyaluronate sodium (Legend) were the most commonly used disease modifying products (63 and 57% of respondents, respectively). Sport horse practitioners were significantly more likely than race or show horse veterinarians to utilise IRAP products (P = 0.0035 and P = 0.04, respectively). Respondents who had been in practice for more than 10 years were significantly less likely to use antimicrobials in their joint injections compared to those in practice for less than 10 years (P<0.0001). CONCLUSIONS Significant differences existed in usage of medications related to primary discipline treated and years practicing. POTENTIAL RELEVANCE The results of this study aid in defining the current usage of different joint therapy medications within equine practice. This knowledge can guide further research as well as education.

Evidence supporting an increased presence of reactive oxygen species in the diseased equine joint

Reactive oxygen species (ROS) are capable of degrading many components of the joint in the presence of insufficient antioxidant defences, and as a result have been implicated in the pathogenesis of joint disease in horses. However, to our knowledge, evidence of ROS occurring in diseased joints of horses has not been reported. The objective of this experiment was to compare differences in synovial fluid protein carbonyl content (as a marker of oxidative modification of synovial fluid proteins by ROS) and the antioxidant status of synovial fluid between clinically normal and diseased equine joints. Synovial fluid was collected from the metacarpophalangeal, metatarsophalangeal, carpal and tarsal joints of 4 horses, age 2-5 years, as controls, and from diseased joints (metacarpophalangeal, metatarsophalangeal, carpal, tarsal and/or femoropatellar) of 61 horses, age 2-5 years. Synovial fluid protein carbonyl content was higher (P<0.01) in diseased joints as compared to controls. Antioxidant status of synovial fluid from diseased joints was higher, but not significantly, than that of controls (P = 0.0595). These findings require further study to determine their contribution to the overall disease process.

Effects of exercise vs experimental osteoarthritis on imaging outcomes

OBJECTIVE To identify changes in imaging outcomes in a controlled model of osteoarthritis (OA) vs exercise. METHOD Sixteen 2-year-old horses were randomly assigned to an exercise control (n=8) or an exercise OA (n=8) group. All horses had middle carpal joints arthroscopically explored and an osteochondral fragment was induced in one middle carpal joint of the OA group. All horses were treadmill exercised for the duration of the study (91 days). Clinical, radiographic, nuclear scintigraphic, computed tomographic and magnetic resonance imaging (MRI) examinations were performed and outcomes of these were compared between groups. Imaging results were correlated to clinical, biomarker and gross pathologic results. RESULTS The OA group had significant increases in clinical outcomes and most imaging parameters. Specifically, the OA group showed significant increases in radiographic lysis and nuclear scintigraphic uptake. There was very little change in subchondral bone density, but a significant change in subchondral bone edema. Radiographic lysis, radial carpal bone edema and nuclear scintigraphy were strongly correlated with clinical changes and radial carpal bone edema was strongly correlated with changes in Type I and Type II collagen found in the synovial fluid. CONCLUSIONS OA induced significant changes in imaging parameters beyond the adaptation seen with exercise. Bone edema detected with MRI was closely correlated with collagen biomarkers detected in the synovial fluid.