Pathology of Natural Cases of Equine Endocrinopathic Laminitis Associated With Hyperinsulinemia.

Laminitis in equids is a clinical syndrome usually associated with systemic disease. Endocrinopathies recently have been recognized as the most common cause of laminitis, with hyperinsulinemia playing a key role. Descriptions of laminitis-associated lesions have been confusing due to the wide range of experimental models used, failure of adequate clinical documentation for naturally occurring cases, lack of separate analysis of inflammatory and endocrinopathic laminitis, and uncertainty regarding normal morphological variation of lamellae. In this study, lamellar morphology and pathology were described in 14 laminitic horses and ponies that had hyperinsulinemia (>20 mIU/l), with reference to 25 age- and breed-matched controls. The type and severity of lesions noted had no correlation with reported clinical duration and in at least some cases must have preceded it. Lesions were largely localized abaxially within the lamellar tissue and included apoptotic cell death, as well as lamellar fusion, hyperplasia, and partial replacement with aberrant keratin containing nucleated debris and proteinaceous lakes. The lesions resulted in irregular margins between the inner horn and the lamellar tissue. Acute separation originated from the abaxial region, with minimal associated inflammation. Axially, epidermal lamellar tapering was the most frequent morphological observation. The lesions in these chronic cases of laminitis were similar to those described in some inflammatory laminitis models and contained features seen in developmental phases of hyperinsulinemic models. These findings support the theory that repeated episodes of subclinical laminitis occur prior to clinical presentation. In addition, the pathology does not include extensive basement membrane failure seen in some inflammatory models.

Catastrophic biaxial proximal sesamoid bone fractures in UK Thoroughbred races (1999-2004): horse characteristics and racing history.

REASON FOR PERFORMING STUDY: Catastrophic biaxial proximal sesamoid bone fractures (PSBF) have not yet been described in detail in the UK racing population. OBJECTIVES: To determine the incidence and relative risk (RR) of PSBF in different types of racing in the UK; and to describe horse-level characteristics and racing histories of horses sustaining these injuries. METHODS: Distal limbs were collected from all racehorses suffering catastrophic fractures during racing at all 59 racecourses in the UK, in a prospective study from February 1999 to December 2004. Post mortem investigation identified the anatomical location and type of fracture. Horse, racing history, race and racecourse details were obtained. Characteristics of the horses that sustained PSBF were described. The incidence and RR of PSBF in the different types of racing in the UK were calculated. RESULTS: Thirty-one horses suffered PSBF during the study period. The incidence of PSBF in all types of race was 0.63 per 10,000 starts (31/494,744). The incidence was highest in flat races on all weather surfaces (1.63 per 10,000 starts: 12/73,467; RR = 4.4 when compared to turf flat racing). Affected horses had an average age of 5.6 years and had started a mean of 28 races at the time of fracture. CONCLUSION AND POTENTIAL RELEVANCE: There is a strong association between type of racing surface and PSBF. Horses competing in flat races on all weather surfaces have an increased risk of PSBF. These fractures appear to happen in experienced horses with several starts, with few fractures occurring within the first season of racing. Further research should focus on identification of underlying pathology of these fractures. Epidemiological studies aimed at the identification of risk factors for PSBF in the UK racing population would require a large number of cases acquired over many years given the relatively low incidence of PSBF.

Are bi-axial proximal sesamoid bone fractures in the British Thoroughbred racehorse a bone fatigue related fracture? A histological study.

OBJECTIVES: To investigate whether microfractures and alterations in the trabecular bone area are associated with catastrophic bi-axial proximal sesamoid bone fractures (PSBF). METHODS: Proximal sesamoid bones (PSB) from 10 racehorses with PSBF and from 10 control racehorses without musculoskeletal injury were examined using the bulk basic fuchsin method. Bone histomorphometric and microfracture analysis was performed, and cases and controls compared using two-sample t-test, paired t-test, and Mann-Whitney U test. RESULTS: There was no significant difference in the microfracture density and the trabecular bone area between bones from case and control horses, and between fractured and non-fractured bones in case horses. CLINICAL RELEVANCE: Microfracture density was low in the areas of the PSB examined. Microfracture density was not significantly different between groups, indicating that propagation of micro-cracks is an unlikely predisposing pathologic alteration in PSBF in British racehorses. There was no significant difference in the bone surface area between groups, which one would expect if modelling, adaptation and an increase in bone density were associated with PSBF fracture in the case horses. Therefore, PSBF in the British racehorse does not appear to be associated with microfractures of the trabecular bone of the PSB. The PSB fractures might represent an acute monotonic fracture; however, the aetiology of the fractures remains unknown with additional research required.

A multi-centre cohort study investigating the outcome of synovial contamination or sepsis of the calcaneal bursae in horses treated by endoscopic lavage and debridement.

BACKGROUND: Previous studies investigating factors associated with survival following endoscopic treatment of contamination/sepsis of the calcaneal bursa are limited. OBJECTIVES: To investigate the factors associated with survival in horses with contamination/sepsis of the calcaneal bursae treated endoscopically and to describe the bacterial isolates involved in the synovial infections. STUDY DESIGN: Retrospective analysis of clinical records. METHODS: Medical records from 128 horses with contamination/sepsis of the calcaneal bursae treated by endoscopic lavage at seven equine hospitals were reviewed. A follow-up questionnaire was used to determine survival and return to athletic performance. Descriptive statistics and Cox proportional hazards survival models were used to determine factors associated with survival. RESULTS: Horses underwent one (n = 107), two (n = 19), or three (n = 2) surgeries. Survival to hospital discharge was 84.4%. Univariable survival analysis revealed that administration of systemic antimicrobials prior to referral was associated with reduced mortality (hazard ratio, [HR] 0.41, 95% CI 0.18-0.91, P = 0.03). Increased mortality was associated with bone fracture/osteomyelitis (HR 2.43, 95% CI 1.12-5.26, P = 0.03), tendon involvement (≥30% cross sectional area) (HR 3.78 95% CI 1.78-8.04, P = 0.001), duration of general anaesthesia (HR 1.01, 95% CI 1.00-1.02, P = 0.04), post-operative synoviocentesis (HR 3.18, 95% CI 1.36-7.43, P = 0.006) and post-operative wound dehiscence (HR 2.5, 95% CI 1.08-5.65, P = 0.04). Multivariable Cox proportional hazards model revealed reduced mortality after systemic antimicrobial administration prior to referral (HR 0.25, 95% CI 0.11-0.60, P = 0.002) and increased mortality with tendinous involvement (≥30% cross-sectional area) (HR 7.92, 95% CI 3.31-19.92, P<0.001). At follow-up (median 30 months, range 0.25-13 years, n = 70) 87.1% horses were alive, 7.1% had been euthanised due to the calcaneal injury and 5.7% had been euthanised for unrelated reasons. From 57 horses with athletic performance follow-up, 91.2% returned to the same/higher level of exercise, 5.3% to a lower level and 3.5% were retired due to persistent lameness of the affected limb. MAIN LIMITATIONS: Retrospective study and incomplete follow-up. CONCLUSION: Endoscopic treatment of contamination/sepsis of the calcaneal bursae has an 84% survival rate to hospital discharge. Tendinous involvement reduced survival whilst systemic antimicrobials administration prior to referral improved survival.

Is there a relationship between clinical presentation, diagnostic and radiographic findings and outcome in horses with osteoarthritis of the small tarsal joints?

REASONS FOR PERFORMING STUDY: Despite the possibility that sound horses may have radiographic signs consistent with osteoarthritis of the small tarsal joints (OA-STJ), a diagnosis of 'bone spavin' as a cause of lameness is often made based only on radiographic examination. OBJECTIVES: To determine whether severity of radiographic change and response to treatment are correlated with the duration and degree of lameness and the response to intraarticular anaesthesia in horses with OA-STJ. METHODS: A retrospective study of all horses that showed a positive response to intra-articular anaesthesia of the STJ was performed. Details of history, clinical presentation and diagnostic findings were recorded. Radiographs of affected tarsi were evaluated and scored independently by 2 observers. Follow-up was via a telephone questionnaire with the owner. Statistical analysis was used to assess the association between the duration and degree of lameness, the response to intra-articular anaesthesia and radiographic findings. Response to treatment was compared with the findings from the diagnostic work-up. RESULTS: Ninety-one horses were included (61 unilateral and 30 bilateral lameness). Fifty-nine percent of horses had been lame for over 2 months. There was no association between the duration and degree of lameness, or between duration or degree of lameness, intra-articular anaesthesia and radiographic findings. Response to treatment showed a significant positive association with less severe radiographic changes within the tarsometatarsal (TMT) joint. Follow-up was available for 48% of cases, with 52% horses returning to the same level of exercise. CONCLUSIONS: There is no association between the duration and degree of lameness, the response to intra-articular anaesthesia and radiographic findings in horses with OA-STJ. However, horses that improved following treatment tended to have less marked TMT joint pathology. POTENTIAL RELEVANCE: Response to intra-articular anaesthesia should remain the gold standard for diagnosis of OA-STJ. Predicting which cases are likely to improve following treatment remains difficult.

Histological examination of the interspinous ligament in horses with overriding spinous processes.

The equine interspinous ligament (ISL) consists of an oblique crossing arrangement of collagenous bundles which are thought to counteract the tensile and rotational forces of distraction between the spinous processes (SPs) in the caudal thoracic and cranial lumbar spine. The aim of this controlled histological study was to assess the structural anatomy and innervation of the ISL in horses with clinically significant overriding (dorsal) SPs (ORSPs) and to compare the findings with the ISL of normal horses. Samples of the ISL were obtained from 10 horses that underwent subtotal ostectomy for treatment of ORSPs. Control samples were obtained from horses without spinal pathology. Histological staining of ISL sections with haematoxylin and eosin was performed to assess the morphology of the ligaments and with Alcian blue-periodic acid-Schiff to determine the proteoglycan and glycosaminoglycan content. Immunohistochemistry for S100 was performed for quantitative evaluation of nerves within the ISL. The ISL in horses with ORSPs had an altered collagen fibre alignment and arrangement of the ligamentous layers when compared to healthy controls. A significant increase in fibrocartilaginous tissue with evidence of fibrocartilaginous metaplasia was detected (P=0.001). The number of nerves in the ISL samples was significantly higher in horses with ORSPs than in controls (P=0.017). Structural alterations of the ISL, including loss of fibre alignment and fibrocartilaginous metaplasia, are associated with ORSPs in the equine thoracolumbar spine. In addition, an increase in innervation of the ISL in horses with ORSPs, compared to normal, may explain the thoracolumbar pain experienced by some horses with ORSPs.

Retrospective study of palmar/plantar annular ligament injury in 71 horses: 2001-2006.

REASON FOR PERFORMING STUDY: Constriction of the digital flexor tendon sheath (DFTS) and its contents by the palmar/plantar annular ligament (PAL) is well recognised. However, primary injury of the PAL has not been well documented. OBJECTIVES: To describe the clinical features of PAL injury, determine its prevalence with or without subcutaneous fibrosis and/or concurrent injury within the DFTS, and assess response to treatment. METHODS: Horses were selected for inclusion based upon clinical features consistent with PAL injury and the presence of a thickened PAL (> or =2 mm) verified ultrasonographically. A retrospective analysis of case records from 3 clinics was performed. Details of breed, age and use, and results of clinical and ultrasonographic assessments and response to treatment were recorded. Horses were treated conservatively or surgically by desmotomy of the PAL, with or without tenoscopic evaluation of the DFTS. A telephone questionnaire was performed to assess response to treatment. RESULTS: Seventy-one horses were included in the study and middle aged or older general purpose riding horses predominated. PAL desmopathy occurred more frequently in hind- than in forelimbs. The method of treatment, thickness of the PAL or presence of subcutaneous fibrosis did not significantly affect prognosis; however, <50% of horses were able to return to athletic function. There was a trend for horses with PAL desmopathy alone to have the best outcome. Bilateral thickening of the PAL or concurrent fore- and hindlimb injuries had a negative effect on prognosis, as did the simultaneous presence of subcutaneous fibrosis and lesions within the DFTS. CONCLUSIONS AND CLINICAL RELEVANCE: PAL injury is characterised by a convex contour of the palmar/plantar aspect of the fetlock, associated with thickening of the ligament with or without subcutaneous fibrosis. Bilateral PAL thickening is common in older horses, ponies and cobs; however, bilateral PAL enlargement is often present with only unilateral lameness. Treatment methods used in this study did not appear to influence outcome significantly.

Structure and Innervation of the Equine Supraspinous and Interspinous Ligaments.

Pain related to the osseous thoracolumbar spine is common in the equine athlete, with minimal information available regarding soft tissue pathology. The aims of this study were to describe the anatomy of the equine SSL and ISL (supraspinous and interspinous ligaments) in detail and to assess the innervation of the ligaments and their myofascial attachments including the thoracolumbar fascia. Ten equine thoracolumbar spines (T15-L1) were dissected to define structure and anatomy of the SSL, ISL and adjacent myofascial attachments. Morphological evaluation included histology, electron microscopy and immunohistochemistry (S100 and Substance P) of the SSL, ISL, adjacent fascial attachments, connective tissue and musculature. The anatomical study demonstrated that the SSL and ISL tissues merge with the adjacent myofascia. The ISL has a crossing fibre arrangement consisting of four ligamentous layers with adipose tissue axially. A high proportion of single nerve fibres were detected in the SSL (mean = 2.08 fibres/mm2 ) and ISL (mean = 0.75 fibres/mm2 ), with the larger nerves located between the ligamentous and muscular tissue. The oblique crossing arrangement of the fibres of the ISL likely functions to resist distractive and rotational forces, therefore stabilizing the equine thoracolumbar spine. The dense sensory innervation within the SSL and ISL could explain the severe pain experienced by some horses with impinging dorsal spinous processes. Documentation of the nervous supply of the soft tissues associated with the dorsal spinous processes is a key step towards improving our understanding of equine back pain.

Analysis of horse race videos to identify intra-race risk factors for fatal distal limb fracture.

The objective of this study was to identify risk factors, during racing, associated with imminent fatal distal limb fracture in Thoroughbreds. One hundred and nine cases of fatal distal limb fracture were identified from all 59 UK racecourses over a 2-year period (February 1999-January 2001). Three uninjured control horses were randomly selected from the same race as the case horse. Videos of races in which fractures occurred were viewed using a defined protocol. Fractures in flat races occurred at any time during the race, whereas 74% (45/61) of cases in national hunt type races occurred in the second half of races. More than 75% (79/103) of cases were spontaneous, i.e. there was no obvious external influence such as a fall at a fence or collision with another horse. Sixty-six percent (44/67) of horses, sustaining a forelimb fracture, fractured the forelimb they were using as lead leg at the time of fracture. When case and control horses were compared, horses that were: (a) making good progress through the race, (b) reluctant to start and (c) received encouragement in the final 10s before the time of fracture, were more likely to sustain a fracture.

Complete and partial hoof wall resection for keratoma removal: post operative complications and final outcome in 26 horses (1994-2004).

REASONS FOR PERFORMING STUDY: There are no data on the frequency of post operative complications following keratoma removal, such as recurrence, hoof wall instability and excessive granulation tissue formation, or their relation to the method of surgical removal. OBJECTIVE: To identify important factors in the outcome for horses undergoing surgical removal of a keratoma and compare the post operative complications encountered following keratoma removal by complete hoof wall resection (CR) and partial hoof wall resection (PR). HYPOTHESIS: Horses undergoing PR would have fewer post operative complications and would return to work more quickly than those undergoing CR. METHODS: A retrospective review of medical records from one equine hospital identified 26 horses that underwent removal of a keratoma by CR or PR. Clinical, radiological and surgical findings and outcome were analysed. RESULTS: Common clinical signs included lameness and the presence of a subsolar abscess. Fourteen horses underwent CR and 12 PR. The complication rate following CR (71%) was significantly lower than that following PR (25%) (P<0.01). Complications encountered included excess granulation tissue formation, hoof crack formation and keratoma recurrence at the surgical site. The time taken to return to full work post operatively was significantly shorter in horses undergoing PR compared to CR (P<0.01). All horses, except one, returned to their previous exercise level. CONCLUSIONS: PR resulted in fewer post operative complications and a more rapid return to athletic activity than CR. POTENTIAL RELEVANCE: Although the overall complication rate for CR was higher than for PR, the overall prognosis for return to soundness and the previous performance level is very good.

The risk of a horse-and-rider partnership falling on the cross-country phase of eventing competitions.

REASONS FOR PERFORMING STUDY: Fatalities resulting from horse falls occurring during the cross-country phase of eventing competitions initiated epidemiological investigation of the risk factors associated with horse falls. OBJECTIVES: To identify variables that increased or decreased the risk of a horse fall during the cross-country phase of an eventing competition. METHODS: Data were collected from randomly selected British Eventing competitions held in Great Britain during 2001 and 2002. Data were obtained for 173 cases (jumping efforts resulting in a fall of the horse-and-rider partnership) and 503 matched controls (jumping efforts not resulting in a fall). The risk of falling was modelled using conditional logistic regression. RESULTS: An increased risk of a horse fall was associated with jumping into or out of water; taking off from good-to-soft, soft or heavy ground; fences with a drop landing; nonangled fences with a spread > or =2 m; and angled fences. Other risk factors included riders who knew that they were in the lead within the competition before the cross-country phase; an inappropriate speed of approach to the fence (too fast or too slow); horse-and-rider partnerships that had not incurred refusals at earlier fences; and riders who received cross-country tuition. CONCLUSIONS: This study has identified modifiable course- and fence-level risk factors for horse falls during the cross-country phase of eventing competitions. The risk of horse and rider injury at eventing competitions should be reduced by 3 simple measures; maintaining good to firm take-off surfaces at fences, reducing the base spread of fences to <2 m and reducing the use of fences at which horses are required to jump into or out of water. Risk reduction arising from course and fence modification needs to be confirmed by intervention studies. POTENTIAL RELEVANCE: Knowledge of factors that increase or decrease the risk of a horse fall can be used by UK governing bodies of the sport to reduce the risk of horse falls on the cross-country phase of eventing competitions, and reduce the risk of horse and rider injuries and fatalities. As one in 3 horses that fall injure themselves and one in 100 horse falls results in fatality to the horse, we suggest that immediate consideration is given to these recommendations.

Catastrophic fracture of the lateral condyle of the third metacarpus/metatarsus in UK racehorses - fracture descriptions and pre-existing pathology.

The characteristics of, and pre-existing pathology associated with 75 cases of fatal lateral condylar fracture sustained by Thoroughbreds while racing in the UK were described. Cases were identified from 220 cases of fatal distal limb fracture submitted as part of studies designed to identify risk factors for all fatal distal limb fractures. Fractures were most common in hurdle races and affected the right forelimb twice as often as the left forelimb. Fracture dimensions were similar to previous reports, however there was a much greater prevalence of articular and diaphyseal comminution and of concurrent fractures in the current report. Pre-existing pathology was particularly common in the medial and lateral parasagittal grooves of the distal articular surfaces of the third metacarpus/metatarsus. The degree of this pathology was not associated with horse age, length of career or number of career starts.

Lamellar pathology in horses with pituitary pars intermedia dysfunction.

REASONS FOR PERFORMING STUDY: Hoof lamellar pathology in horses with pituitary pars intermedia dysfunction (PPID) has not been described previously. OBJECTIVES: To describe the histomorphometry and pathological lesions in hoof lamellar tissue of animals that had PPID with or without concurrent laminitis, with reference to age-matched controls. We hypothesised that lamellar lesions consistent with laminitis would be associated with PPID, even in animals without current or historical laminitis. STUDY DESIGN: Prospective case-control study. METHODS: Mid-dorsal hoof histological sections were obtained post mortem from the forelimbs of 16 PPID-affected animals either with (n = 6) or without laminitis (n = 10) and 10 age- and breed-matched controls. Sections were examined by a blinded veterinary pathologist. The length and width of 10 primary epidermal lamellae were measured using image analysis software. The morphology and pathology of primary and secondary epidermal lamellae were then typed or graded in axial, middle and abaxial regions. Fasting serum insulin, plasma adrenocorticotropin and blood glucose concentration were measured from blood samples taken prior to euthanasia. RESULTS: All animals with PPID and laminitis had fasting hyperinsulinaemia (median 74.1 miu/l, interquartile range 49.9-349.5 miu/l) whereas PPID animals without laminitis had serum insulin concentrations below the upper limit of the reference range (<20 miu/l). Lamellar pathology in PPID animals with laminitis was variable in severity and unrelated to the reported duration of laminitis (range 2 months-5 years). Most lesions were located abaxially within the lamellar tissue and included increased length and width of the lamellae, chronic abnormal keratinisation, interlamellar epidermal bridging and cell death with more acute lamellar tearing in some cases. The lamellae of PPID animals without laminitis were normal referent to the relevant control group. CONCLUSIONS: Whether PPID and hyperinsulinaemia have a causal inter-relationship or not, it may only be the hyperinsulinaemia that is associated with lamellar morphological alteration and pathology consistent with laminitis.

Prevalence and antimicrobial susceptibility of bacterial isolates from horses with synovial sepsis: A cross-sectional study of 95 cases.

Bacterial culture and antimicrobial susceptibility testing of septic synovial samples allows instigation of targeted antimicrobial therapy; however, bacterial culture takes more than 24 h and has low sensitivity. This study aimed to identify the most frequently cultured bacteria and their antimicrobial susceptibility profile from septic synovial samples in our referral equine hospital, to allow recommendations regarding appropriate initial antimicrobial therapy prior to culture results. Hospital records for all horses with synovial sepsis and a synovial sample submitted to the microbiology laboratory between 2004 and 2013 were retrieved (n= 379 samples). One horse had positive cultures from more than one synovial structure, and two horses had positive cultures obtained from repeat samples. Overall, 114 bacterial isolates were obtained. Gram-positive bacteria were isolated in 75% of cases, of which 22% were haemolytic Staphylococcus spp., and 52% were Staphylococcus aureus including two multidrug-resistant isolates. Gram-negative bacteria were isolated from 25% of cases. Anaerobic Clostridium spp. was isolated in 3% of cases. Of the first line antimicrobials, oxytetracycline and doxycycline were effective against 70-100% of the Gram-positive bacteria and 20-100% of the Gram-negative organisms, whilst trimethoprim-sulphamethoxazole and gentamicin efficacy ranged between 50% and 88% for both Gram-positive and Gram-negative bacteria. Of the equine protected antimicrobials, ceftiofur was effective against 70-90% of all bacterial isolates whilst 80% of isolates were susceptible to enrofloxacin. These results indicate that tetracyclines, trimethoprim-sulphamethoxazole or gentamicin may be suitable first-line antimicrobials for treatment of synovial sepsis cases while awaiting laboratory results, findings which support current recommendations for antimicrobial stewardship in equine medicine.

Risk factors for cross-country horse falls at one-day events and at two-/three-day events.

The cross-country phase of eventing competitions has been associated with injuries and fatalities to horses and riders. A case-control study was carried out to identify variables that were associated with increased or decreased risk of a horse fall on the cross-country phase at event competitions. After initial analysis, the dataset was split according to the categories of one-day events as compared to two- or three-day events to establish whether significant risk factors varied between the different types of eventing competitions. Data were collected for 121 cases (horse falls) at one-day events, 59 cases at two- or three-day events and for their 540 matched controls. The data were analysed using conditional logistic regression. The variables of no previous refusals on the course, fences with a landing in water and the combined variable of the angle and the spread of the fence were significantly associated with the risk of a horse fall in both datasets. Additional risk factors for one-day event falls were: fences requiring a take-off from water, a drop landing, the rider's knowledge of their position before the cross-country phase and if the rider received cross-country tuition. Three-day event risk factors in the multivariable model included: the camber of the fence and participation in non-equestrian sports by the rider. This study identified variables that were significantly associated with an increase or a decrease in the risk of a horse fall during the cross-country phase of different types of eventing competitions. Some of these variables are modifiable and the results of this study have been reported to the governing body of the sport of eventing in the UK so that possible interventions might be considered.

Two clinical manifestations of desmopathy of the accessory ligament of the deep digital flexor tendon in the hindlimb of 23 horses.

REASONS FOR PERFORMING STUDY: Desmopathy of the accessory ligament of the deep digital flexor tendon (ALDDFT) in the hindlimb is an unusual cause of lameness in horses, and reports of the condition are sparse. OBJECTIVES: To describe the clinical and ultrasonographic findings, therapy and outcome of 23 horses treated for desmopathy of the ALDDFT in the hindlimb. METHODS: Records of 23 horses with ultrasonographic evidence of desmopathy of the ALDDFT in one or both hindlimbs from 3 referral centres were reviewed retrospectively. Age, breed, sex, duration and nature of clinical signs, results of clinical and lameness examinations, treatment and outcome were recorded. RESULTS: In 13 horses (Group A), there was an acute onset of unilateral lameness. Ten horses (Group B) had an insidious or sudden onset of postural abnormality. There were 10 cobs, 5 British native-breed ponies and 8 horses of various larger breeds. Twenty horses were used for general purposes, and mean age was 12 years. Enlargement of the ALDDFT in the affected hindlimb(s) was identified in all horses. In 44% of horses, ultrasonographic abnormalities were localised to part of the ALDDFT. Treatment included box-rest and controlled exercise, and 10 horses were subjected to desmotomy or desmectomy of the ALDDFT. Seventy-three percent of horses in Group A returned to full function, while 90% of those in Group B remained lame. CONCLUSIONS: Two distinct clinical conditions are associated with the ALDDFT of the hindlimb. Traumatically induced injury resulting in acute onset lameness appears to have a favourable prognosis, with most horses returning to previous work. However, postural changes, once present, are irreversible and indicate a poor prognosis. POTENTIAL RELEVANCE: Desmopathy of the ALDDFT should be recognised as a potential cause of hindlimb lameness and this study provides clinical and prognostic information. Knuckling and/or semiflexion of the metatarsophalangeal joint may accompany the condition; therefore, if a horse is presented with a flexural deformity of this joint, desmopathy of the ALDDFT should be considered as a primary differential diagnosis.

Risk factors for fatal lateral condylar fracture of the third metacarpus/metatarsus in UK racing.

REASONS FOR PERFORMING STUDY: Lateral condylar fractures of the third metacarpus/metatarsus are the most common cause of equine fatality on UK racecourses. Identification of risk factors for such injuries and the subsequent implementation of intervention strategies could significantly reduce the total number of racecourse fatalities. OBJECTIVES: To identify horse-, race- and course-level risk factors for fatal lateral condylar fracture in Thoroughbreds on UK racecourses. METHODS: Case-control study designs were used. Case horses were defined as those that were subjected to euthanasia having sustained an irreparable lateral condylar fracture while racing at any of the 59 UK racecourses. Case races were defined as those in which one or more horses sustained a fatal lateral condylar fracture. Three controls for each case horse were selected at random from the race in which the case was running. Three controls for each case race were selected at random from all races of the same type held in the same year. Ninety-eight cases were included in the study. Conditional logistic regression was used to identify the relationship between a number of independent variables and the likelihood of fracture. RESULTS: Horses doing no gallop work during training and those in their first year of racing were at significantly increased risk of fracture on the racecourse. Case horses were also more likely to have started racing as 3- or 4-year-olds. Fractures were found to be more likely in longer races with a larger number of runners, races in which professional jockeys were not permitted to ride and races in which the going was described as firm or hard. CONCLUSIONS AND POTENTIAL RELEVANCE: Modifications to training schedules, specifically within the first year of racing, may have a large impact on the risk of fatal lateral condylar fracture on the racecourse. Horses should do some gallop work in training and our results suggest that the minimum distance galloped should be between 201 m (1 furlong) and 1609 m (8 furlongs) per week. The association with age at first race requires further investigation for flat and National Hunt racing separately. A reduction in the number of races taking place on very firm going could have an impact on the number of lateral condylar fractures.

Effect of age at presentation on outcome following arthroscopic debridement of subchondral cystic lesions of the medial femoral condyle: 85 horses (1993--2003).

REASONS FOR PERFORMING STUDY: Subchondral cystic lesions of the medial femoral condyle (SCMFC) are well documented in horses < or =3 years; arthroscopic debridement or enucleation of the cyst is currently the surgical treatment of choice. However, studies of occurence and outcome following surgery in older horses are lacking. OBJECTIVE: To identify factors important in outcome for horses with SCMFC treated by arthroscopic debridement. HYPOTHESIS: Age of horse at presentation has a significant influence on return to work following arthroscopic treatment for SCMFC. Clinical and diagnostic findings are also significant with respect to prognosis. METHODS: A retrospective review of medical records from 6 equine referral centres identified 85 horses that underwent arthroscopic debridement of SCMFC. Clinical examination, radiographic and arthroscopic findings were analysed together with follow-up data. Univariable analysis and multivariable logistic regression models were used to determine factors affecting return to soundness. Event-time analysis was performed to evaluate return to work. RESULTS: Older horses (>3 years) were less likely to return to soundness (P = 0.02) or to work (P = 0.04) than younger horses (< or = 3 years). Of 39 horses age 0-3 years, 25 (64%, 95% CI 49-79%) returned to soundness. Of 46 horses age >3 years, 16 (35%,95% CI 21-49%) returned to soundness. In addition, cartilage damage at sites other than the SCMFC negatively affected prognosis (P = 0.05). The hospital where treatment was performed had no influence on return to soundness. CONCLUSIONS: Older horses carry a worse prognosis for both return to soundness and return to work. POTENTIAL RELEVANCE: It is important for clients to be made aware of the difference in outcome between age groups.

Memory decay and performance-related information bias in the reporting of scores by event riders.

We used data from a case-control study investigating risk factors for horse falls in the cross-country phase of eventing in Great Britain (GB) to examine evidence for memory decay and information bias. Responses to two questions obtained by telephone for 173 cases and 521 controls were examined for evidence of differential reporting according to the respondent's case-control status and performance in the dressage and cross-country phases of competitions. Information bias was found in the accuracy of reporting dressage penalty scores when analysed as a function of performance level (good/poor). Poor dressage performers were less likely to report accurate dressage scores than good performers. The accuracy of reporting dressage scores decreased as the time between the event and questionnaire completion increased, with no case-control interaction. Competitors who incurred cross-country jumping penalties at the event preceding the selected event reported their cross-country scores with less accuracy when compared with competitors who incurred no penalties. No information bias was found when the reporting of dressage and cross-country scores were analysed as a function of respondent category (case/control).