The suspensory apparatus of the distal phalanx in normal horses.

REASONS FOR PERFORMING STUDY: The suspensory apparatus of the distal phalanx (SADP) is functionally and clinically important. OBJECTIVES: To investigate SADP form and function and the microanatomy of its insertion zone. STUDY DESIGN: Descriptive gross and microanatomy. METHODS: The feet of 6 normal Standardbred horses were sectioned into blocks along the traditional perpendicular transverse axis and along functional axes of the SADP, decalcified and processed for staining with haematoxylin and eosin, Jones' periodic acid silver methenamine or Masson's trichrome stains. RESULTS: In traditional midline toe transverse plane sections SADP collagen bundles were irregular with an unstructured appearance. In sections made transversely along planes (70° and 30°) aligned with the long axis of the SADP, collagen bundles were arranged in linear rows. The linear bundles were continuous from their origin on parietal ridges of the distal phalanx through to the secondary epidermal lamellar basement membrane. At the parietal ridge interface the collagen bundles coalesced into smaller, strongly silver staining, linear structures that penetrated the cortical bone and merged with adjacent osteons. In proximal sagittal sections collagen bundles were also linear, angled at 70° to the ground surface. In distal sagittal sections collagen bundles were also arranged linearly but in a multi-angled, 'spokes of a wheel' arrangement, centred on the distal phalanx apex. CONCLUSIONS: Sectioning along functional axes demonstrated the true suspensory nature of the SADP connecting the parietal surface to the lamellar hoof wall. SADP/distal phalanx insertions showed penetrating fibres extending through the chondral-apophyseal interface up to and between distal phalanx osteons. Lamellar measurements made from sections perpendicular to the dorsal aspect of the distal phalanx are underestimations but if made along the longer, functional midline 70° transverse plane would accurately reflect the suspensory function of the lamellae. Laminitis pathophysiology correctly viewed as SADP degradation should inform logical, future therapeutic strategies.

Regional intravenous limb perfusion compared to systemic intravenous administration for marimastat delivery to equine lamellar tissue.

Pharmaceutical agents with potential for laminitis prevention have been identified. Many of these, including the MMP inhibitor marimastat, are impractical for systemic administration. This study compared local delivery of marimastat by regional limb perfusion (RLP) to systemic intravenous bolus dosing (SIVB), and established whether RLP results in local lamellar drug delivery. Six adult horses received 0.23 mg/kg of marimastat by RLP followed by 0.23 mg/kg marimastat by SIVB, with a 24-h washout period. Lamellar ultrafiltration probes sampled lamellar interstitial fluid as lamellar ultrafiltrate (LUF). LUF and plasma marimastat concentrations (LUF[M] and P[M] respectively) were measured for 24 h after each treatment. Regional pharmacokinetic parameters were calculated using noncompartmental analyses. The LUF C(max) following RLP was 232 [34-457] times that following SIVB. LUF[M] after RLP were higher than those obtained after SIVB for 18 h (P < 0.03). Median LUF[M] were > IC(90) of equine lamellar MMP-2 and MMP-9 for 9 h after tourniquet removal. RLP appeared superior to SIVB for lamellar marimastat delivery (higher LUF C(max),, AUC and T > IC(90) of lamellar MMPs). However, frequent dosing is necessary to achieve therapeutic lamellar concentrations. RLP could be used to investigate whether marimastat prevents experimentally induced laminitis. Further refinement of the technique and dosing interval is necessary before clinical application.

Prevalence of and risk factors for equine obesity in Great Britain based on owner-reported body condition scores.

REASONS FOR PERFORMING THE STUDY: Few data are available on the prevalence of obesity in the general equine population of Great Britain (GB), and its associated risk factors. OBJECTIVES: To estimate the prevalence of owner-reported obesity in veterinary-registered horses and ponies in GB, and identify factors associated with obesity. STUDY DESIGN: A cross-sectional survey of horse/pony owners in GB was undertaken using a postal questionnaire. METHODS: Thirty veterinary practices randomly selected horse/pony owners to complete a self-administered postal questionnaire. Owners estimated body condition score using a modified Carroll and Huntington method (1-6 scale), and animals were classified as obese if they were scored as either 5 (fat) or 6 (very fat). Factors associated with obesity were assessed using logistic regression analysis. RESULTS: Prevalence of obesity was 31.2% (n = 247/792; 95% confidence interval [CI] 27.9-34.2%). Factors associated with increased odds of obesity were breed (P<0.001), ease of maintaining weight (P<0.001) and primary use (P = 0.002). Compared to Thoroughbreds, draught-type (odds ratio [OR] 7.3; 95% CI 3.1-17.1), cob-type (OR 5.6; 95% CI 2.5-12.5), native (OR 3.2; 95% CI 1.8-5.78) and Welsh breeds (OR 3.5; 95% CI 1.9-6.2) were more likely to be obese. Animals described as 'good doers' were more likely to be obese than those described as readily maintaining normal weight (OR 3.7; 95% CI 2.6-5.3). Compared to competition animals, animals used for pleasure riding (OR 2.5; 95% CI 1.4-4.4) and nonridden animals (OR 2.9; 95% CI 1.5-5.5) were more likely to be obese. CONCLUSIONS: Identification of at-risk breeds and other horse- and management-level risk factors for obesity will enable optimal targeting of owner education regarding management strategies to reduce the frequency of equine obesity.

Equine lamellar energy metabolism studied using tissue microdialysis.

Failure of lamellar energy metabolism may contribute to the pathophysiology of equine laminitis. Tissue microdialysis has the potential to dynamically monitor lamellar energy balance over time. The objectives of this study were to develop a minimally invasive lamellar microdialysis technique and use it to measure normal lamellar energy metabolite concentrations over 24 h. Microdialysis probes were placed (through the white line) into either the lamellar dermis (LAM) (n = 6) or the sublamellar dermis (SUBLAM) (n = 6) and perfused continuously over a 24 h study period. Probes were placed in the skin dermis (SKIN) for simultaneous comparison to LAM (n = 6). Samples were collected every 2 h and analysed for glucose, lactate, pyruvate, urea and glycerol concentrations. LAM was further compared with SUBLAM by simultaneous placement and sampling in four feet from two horses over 4 h. Horses were monitored for lameness, and either clinically evaluated for 1 month after probe removal (n = 4) or subjected to histological evaluation of the probe site (n = 10). There were no deleterious clinical effects of probe placement and the histological response was mild. Sample fluid recovery and metabolite concentrations were stable for 24 h. Glucose was lower (and lactate:glucose ratio higher) in LAM compared with SUBLAM and SKIN (P < 0.05). Pyruvate was lower in SUBLAM than SKIN and urea was lower in LAM than SKIN (P < 0.05). These differences suggest lower perfusion and increased glucose consumption in LAM compared with SUBLAM and SKIN. In conclusion, lamellar tissue microdialysis was well tolerated and may be useful for determining the contribution of energy failure in laminitis pathogenesis.

Demographics and management practices of horses and ponies in Great Britain: a cross-sectional study.

The objectives of this study were to describe the demographic characteristics and management practices undertaken by owners of horses/ponies within GB and assess seasonal and geographical variations in management practices. A cross-sectional study was conducted, surveying a random sample of veterinary-registered owners in GB, using a self-administered postal questionnaire. A total of 797 useable responses were received. Only 4.0% of animals were stabled 24h/day, this proportion being greater in winter compared to other seasons (p<0.001). Shavings (45.7%) and straw (35.3%) were the most frequently used bedding. Ninety-two percent of animals had access to pasture (median 91 h/week). The majority of animals received forage (82.6%) and concentrate/supplementary feeding (86.1%). Retired/companion animals and ponies received supplementary feed less frequently and most animals were used for pleasure riding (60.6%). Seasonal and regional differences in management practices were identified, of relevance to practitioners and researchers in the investigation and management of disease conditions.

Preventive health care and owner-reported disease prevalence of horses and ponies in Great Britain.

This study aimed to describe the provision of preventive health care and owner-reported disease prevalence in horses and ponies within Great Britain (GB), and to assess geographical variations in health care provision. A cross-sectional survey was conducted, using a postal questionnaire administered to a random sample of veterinary-registered owners of horses and ponies in GB (n=797). The majority of animals received regular preventive health care: 95.6% had regular hoof care; 71.3% were vaccinated for both influenza and tetanus and median time since last anthelmintic administration was 8.7 weeks. Thirty-one percent of owners indicated their animal was overweight/obese. A new health problem within the previous 7 days was reported for 7.4% of animals, 59.3% of which were veterinary-diagnosed. Thirty-two percent of animals were reported to have a long-term/recurrent condition, of which osteoarthritis (13.9%) was the most prevalent. Obesity, musculoskeletal disorders, and dermatological conditions were the most prevalent conditions affecting veterinary-registered horses/ponies.

A cohort study of equine laminitis in Great Britain 2009-2011: estimation of disease frequency and description of clinical signs in 577 cases.

REASONS FOR PERFORMING STUDY: A previous systematic review highlighted a lack of good evidence regarding the frequency of equine laminitis in Great Britain. OBJECTIVES: To estimate the frequency of veterinary-diagnosed active laminitis in the general horse population of Great Britain and to describe the clinical signs present in cases. STUDY DESIGN: Prospective cohort study. METHODS: Data on active episodes of equine laminitis were collected from veterinary practitioners. RESULTS: The prevalence of veterinary-diagnosed active laminitis was 0.47% (95% confidence interval [CI] 0.42-0.52%) for the veterinary-attended population and 0.49% (95% CI 0.43-0.55%) for the veterinary-registered population, suggesting that active episodes of laminitis accounted for nearly one in 200 equine visits and occurred in nearly one in 200 horses registered with veterinary practices. The incidence of veterinary-diagnosed active laminitis was 0.5 cases per 100 horse-years at risk (95% CI 0.44-0.57). Laminitis occurred in all limbs, but most commonly affected the forelimbs bilaterally (53.5%, 95% CI 49.4-57.7%) and was most severe in the front feet. The most common clinical signs were increased digital pulses, difficulty turning and a short, stilted gait at walk. CONCLUSIONS AND POTENTIAL RELEVANCE: The frequency of veterinary-diagnosed active laminitis was considerably lower than previously published estimates, which is probably due to differences in geographical setting, study period, case definition, study design and study populations.

Radiological anatomy of the donkey's foot: objective characterisation of the normal and laminitic donkey foot.

REASONS FOR PERFORMING STUDY: Anatomical change within a laminitic foot is of diagnostic and prognostic importance. A lateromedial radiograph represents the current 'gold standard' by which these changes are identified. Detection of anatomical change is dependent upon a priori knowledge of normality and subjective assessment alone may not identify modest change. Normal baseline data is, therefore, needed against which objective comparisons can be made. There is little information regarding the radiological anatomy of the donkey foot, hence an equine model has been widely adopted. However, descriptive accounts suggest fundamental anatomical differences between these 2 species. OBJECTIVES: To characterise objectively the radiological anatomy of normal donkey feet and define the nature and extent of anatomical change associated with laminitis. METHODS: The anatomy of the forefoot was quantified from lateromedial radiographs of 83 normal and 74 laminitic donkeys, using a computer based imaging system. Data were analysed using univariate and bivariate statistical methods. RESULTS: Baseline data were established that define the radiological characteristics of the anatomy of normal donkey feet. The key hoof, bone and weightbearing stance parameters of lateromedial radiographs have been evaluated. Laminitis was associated with significant rotation and distal displacement of the distal phalanx, increases in integument depth and morphometric change to the distal phalanx (P<0.05). CONCLUSIONS: This study challenges the validity of applying an equine model to the radiological anatomy of donkey feet. Hence, the diagnosis of anatomical change cannot be based on baseline data previously given for the horse and guidelines should be revised accordingly for the donkey. POTENTIAL RELEVANCE: This study provides an objective basis for the identification of anatomical change associated with laminitis in donkey feet.

An investigation of the relationships between angles and shapes of the hoof capsule and the distal phalanx.

REASONS FOR PERFORMING STUDY: There is little scientific evidence to support the premise that poor foot conformation predisposes to foot pain and lameness. OBJECTIVES: To determine relationships between external characteristics of the hoof capsule and angles of the distal phalanx; to determine variability in shape of the distal phalanx; and to investigate association between distal phalanx angles and the injury causing lameness. MATERIALS AND METHODS: Feet were documented photographically and radiographically. Linear and angle measurements were obtained for the hoof capsule and distal phalanx and compared statistically. Horses were categorised according to injury group, and angles and linear ratios were compared between groups. RESULTS: There was modest correlation between hoof wall and heel angles and angles of the distal phalanx. There was variation in shape of the distal phalanx. There was no significant association between injury type and angles of the distal phalanx, although there was a trend for the angle of the dorsal aspect of the distal phalanx with the horizontal to be smaller in horses with injuries of the podotrochlear apparatus or deep digital flexor tendon compared with other groups. CONCLUSIONS: There are variations in shape of the distal phalanx largely due to differences in orientation of the concave solar border and the solar border to the horizontal. Variations in shape of the distal phalanx were not accurately correlated with external characteristics of the hoof capsule. There were weak associations between injury groups and angles of the distal phalanx. CLINICAL RELEVANCE: Further work is required to elucidate risk factors for foot-related lameness.

Influence of cup orientation on the wear performance of metal-on-metal hip replacements.

There are a number of factors that determine the overall outcome of total hip replacement (THR) surgery, some of which appear to be related to the surgical procedure. In particular, the inclination angle at which the acetabular component is placed has been reported to influence the long-term successful performance of THR. The present study assessed the influence of cup orientation on the wear of 40 mm diameter metal-on-metal (MoM) hip bearings tested in a hip simulator. The bearings had a mean radial clearance of 150 microm; the cups oriented at 35 degrees, 50 degrees, and 60 degrees to the horizontal were loaded for up to 6 x 10(6) cycles. In each test the wear rates during the run-in phase were higher than in the steady state phase; the wear rates during the run-in phase were not significantly different for each cup orientation. However, at cup angles of 50 degrees and 60 degrees, the steady state wear rates were 0.69 mm3/ 10(6) cycles and 1.7 mm3/10(6) cycles respectively, significantly higher than at 35 degrees (0.24 mm3/10(6) cycles). The results indicated that larger cup inclination angles not only move the position of the wear scar but also, more significantly in MoM bearings, increase the wear rates and total wear volume generated.

Thirty-two component finite element models of a horse and donkey digit.

REASONS FOR PERFORMING STUDY: The finite element (FE) method is the most powerful modelling technique available to explicate the biomechanics of the digit. It has already proved to be of high value in human podiatry. However, accurate models of the complex anatomy of the horse and donkey digit are currently lacking. OBJECTIVES: To develop FE models of the horse and donkey digit from computed tomography data, including all functionally relevant anatomy, and to perform simulations to replicate prestrain in the flexor tendons and quasistatic weightbearing. METHODS: Computed tomography data of the front right digits were obtained under general anaesthesia. The anatomy was rationalised into 32 functional components. The FE models were generated using a forward engineering technique. Linear or nonlinear material properties were applied according to published data. Prestraining of the flexor tendons was achieved by z-direction displacement, and loading by the application of 1 x body mass. RESULTS: The resultant FE models comprised over 10(6) elements. Z-direction displacement of the digital flexor tendons to compensate for general anaesthesia relaxation gave von Mises stress levels up to 134 MPa for the deep and 0.56 MPa for the superficial in the horse and 0.78 MPa and 0.27 MPa in the donkey, respectively. Weightbearing resulted in capsular deformation patterns consistent with in vivo observations, and maximum stress levels of 1.46 MPa for the horse and 0.89 MPa for the donkey. CONCLUSION: These high resolution FE models could give new insight into the biomechanics of the equid digit and provide new data regarding stress and strain levels within the tissues of the digit that are unobtainable by other means. POTENTIAL RELEVANCE: Application of the FE modelling technique could enable investigation of the biomechanics of orthopaedic problems and may provide a mechanistic basis for enhanced preventative and remedial management and treatment.

Development of a twenty-one-component finite element distal hind limb model: stress and strain in bovine digit structures as a result of loading on different floorings.

Finite element modeling is a unique way of introducing technical and material research into medical science. A bovine distal hind limb was scanned using computed tomography for geometric image capture and the data were subsequently divided (segmented) into 4 tissue types: bone, bone marrow, soft tissue, and the horn capsule. Material data from previous studies were integrated into the model. Flexor tendons were assembled as longitudinal structures starting at their cross-sectional areas at the height of the metatarsophalangeal joint, proceeding in the plantaro-distal direction and meeting the distal phalanx at the tuberculum flexorium. Three different flooring situations (full support floor, bearing weight in the abaxial half of the lateral claw and in the dorsal halves of both claws, respectively) were created to evaluate the effects of loading. Full support resulted in von Mises stress levels between 3.5 and 1.5 MPa for the osseous structures and some regions of the segmented soft tissue; stress patterns in the bulb and sole of the claw capsule (1.5 MPa) and in the floor (0.5 MPa) were similar to pressure plate data in vivo and in vitro, with corresponding strain values of 2.4%. Reduced support resulted in higher stresses (up to approximately 8 MPa) in bones, claw capsules, and tendons; high strains ( approximately 11%) were found in the soft tissue, depending on how the floor was constructed. Although the models may still be anatomically improved, stress and strain calculations are possible with results comparable to related research, and the model shows interaction between the 2 digits. This possibly will help with further understanding of the biomechanical function of this 2-digit structure. With respect to clinical interpretation, reduced support to the bovine hind limb increases focal stress peaks in the different tissues, which may indicate a location of potential injury.

Tubule density of the stratum medium of horse hoof.

The number of tubules/mm2 (tubule density) of horse hoof horn was quantified in samples taken from the left forefeet of 8 randomly selected slaughterhouse horses in order to establish the normal tubule density characteristics at the midline dead centre (MDC) for the stratum medium of horse hoof. In the past the measurement of tubule distribution within the hoof has lacked objectivity. The horse hoof tubule density results are compared to a recent objective study carried out on pony hoof. A similar 4 zone pattern of tubule density was observed, although the precise zonal boundaries and tubule density values differed to those found for pony hoof. There were significant differences in tubule density between zones. Comparison with pony hoof revealed significant tubule density differences in zones 1, 2 and 4; however, there was no significant difference in zone 3. The existence of a 4 zoned pattern of tubule density for horse hoof, as for pony hoof, has been confirmed.

Finite element analysis of static loading in donkey hoof wall.

A finite element model of donkey hoof wall was constructed from measurements taken directly from the hoof capsule of the left forefoot. The model was created with a 2 mm mesh and consisted of 11,608 nodes. A linear elastic analysis was conducted assuming isotropic material properties in response to a 375 newton (N) load, to simulate static loading. The load was applied to the wall via 400 laminae in order to simulate the way in which the pedal bone is suspended within the donkey hoof capsule. Displacement, stress concentration, principal strain, and force distribution across the hoof wall were evaluated. The hoof wall model revealed loading responses that were in broad agreement with previously reported in vivo and modelled observations of the equid hoof. Finite element analysis offers the potential to model hoof wall function at the macroscopic and microscopic level. In this way, it could help to develop further our understanding of the functional relationship between the structural organisation and material properties of the hoof wall.

Prospective clinical and joint simulator studies of a new total hip arthroplasty using alumina ceramic heads and cross-linked polyethylene cups.

We report the findings from independent prospective clinical and laboratory-based joint-simulator studies of the performance of ceramic femoral heads of 22.225 mm diameter in cross-linked polyethylene (XLP) acetabular cups. We found remarkable qualitative and quantitative agreement between the clinical and simulator results for the wear characteristics with time, and confirmed that ceramic femoral heads penetrate the XLP cups at only about half the rate of otherwise comparable metal heads. In the clinical study, 19 hips in 17 patients were followed for an average of 77 months. In the hip-joint simulator a similar prosthesis was tested for 7.3 million cycles. Both clinical and simulator results showed relatively high rates of penetration over the first 18 months or 1.5 million cycles, followed by a very much lower wear thereafter. Once an initial bedding-in of 0.2 mm to 0.4 mm had taken place the subsequent rates of penetration were very small. The initial clinical wear during bedding-in averaged 0.29 mm/year; subsequent progression was an order of magnitude lower at about 0.022 mm/year, lower than the 0.07 mm/year in metal-to-UHMWP Charnley LFAs. Our results show the excellent tribological features of alumina-ceramic-to-XLP implants, and also confirm the value of well-designed joint simulators for the evaluation of total joint replacements.