Review of the clinical diagnosis of sacroiliac dysfunction in horses - Challenges and limitations.

Sacroiliac dysfunction (SID) is a condition seen in horses associated with poor performance that affects hind limb gait and impulsion. The condition comprises pain and dysfunction but there lacks clarity around the aetiopathogenesis and whether SID encompasses abnormal joint pathology, abnormal joint movement, abnormal regional biomechanical function, joint laxity and pain, or various combinations of these that may vary over time. Clinical assessment remains challenging for equine clinicians due to the deep location of the sacroiliac joint (SIJ) and surrounding structures which limits access for palpation, diagnostic imaging and joint-specific injection. There is no recognised single reference standard diagnostic test for SID. Clinical diagnosis has been based on ruling out other causes of hind limb lameness, along with combinations of ultrasonography, scintigraphy and periarticular anaesthesia of the SIJ. Recent studies have highlighted the lack of specificity of injections targeting the SIJ, with significant dispersal of injectate into surrounding structures including around the lumbosacral joint (LSJ). Advanced imaging modalities such as computed tomography offers promise for assessment of the structure and pathology of the SIJ and surrounding bony structures. However, there is a need to improve the understanding of the significance of anatomic variation of the sacroiliac region structures, with recent studies reporting detailed anatomic variation in groups of horses with and without SID. There are also limitations around functional assessment of the joint which is still largely reliant on a thorough clinical examination. This review aims to present an update on clinical approaches to the diagnosis of horses with SID, and to consider the challenges and limitations.

Hoof conformation and performance in the racing Thoroughbred in Macau.

OBJECTIVES: To investigate associations between race performance and hoof-ground angle (HG), pastern-hoof angle (PH) and mediolateral hoof angle (ML) of the left forelimb. METHODS: A total of 1570 starts were recorded from 636 horses, and meetings were equally divided between sand and turf tracks. HG, PH and ML were measured on each starter in a race, over a 3-month period, using a Finnegan hoof gauge (Tallahesse Asia Holdings Ltd, Hong Kong) and digital photographic images. Race performance was recorded as win or place (1st-3rd). RESULTS: There was no association between the probability of winning or placing and gauge HG, photographic HG or photographic ML. There was a significant negative association between PH and the probability of winning on the turf track. On the turf surface, the odds ratio of winning for each 1° decrease in PH was 1.06 (95% confidence interval 1.01-1. 12). There was no association between the probability of winning or placing on the sand track and PH. CONCLUSIONS AND CLINICAL RELEVANCE: Direct measures of hoof conformation (HG and ML) were not related to racehorse performance in Macau. Lower PH was associated with better performance on a turf track. Further investigation into factors affecting PH and why it is related to performance are warranted. This study demonstrated that PH was associated with performance on a turf track. This information may be useful in the management and selection of Thoroughbred racehorses.

Morphometrical study of bony elements of the forelimb fetlock joints in horses.

There are many reports describing fractures in the bony elements of the equine fetlock joint and a few of these discuss possible relationships of these fractures to the mechanical loading of these bones. The likelihood of fracture must be related to the size and shape of bones involved, but information concerning the normal range in size and shape of these bones in horses is lacking. This study aimed to identify morphometrical variations of these bones within different groups of horses. Right and left metacarpal, proximal phalangeal and proximal sesamoid bones were collected from 10 Thoroughbreds (TB), five Standardbreds (SB) and eight Ponies (P) euthanized for non-orthopaedic reasons. All bones were boiled, cleaned and dried. Dimensional parameters were measured using a custom-built apparatus, calliper and plastic tape. The width and depth of the medial condyles of Mc3 were greater than the lateral condyles in all groups. The length to the lateral condyle was greater than the length to the medial condyle of Mc3, and the lengths of the lateral sides of the Mc3 and P1 bones were greater than the lengths of the medial sides in both forelimbs of all groups. The lateral sesamoids were similar to, or larger than, the medial sesamoids in all dimensions. There were some morphometrical variations in the bony elements of the equine fetlock joints in all groups.

Morphometrical variations of the carpal bones in thoroughbreds and ponies.

There is scant morphological data for equine carpal bones despite the frequent pathology in Thoroughbreds (TB). This study aimed to identify morphological and morphometrical variations and similarities in carpal bones between and within TB and Ponies (Po). Carpal bones from nine TB and 13 Po were prepared by boiling and drying. Lateromedial width, dorsopalmar depth, proximodistal height, relative density and volume of each bone were measured. Normalized measurements of the radial (Cr) and third (C3) carpal bones were significantly different in all dimensions, and there were significant variations in relative sizes of articular facets of the ulnar (Cu), C3 and fourth (C4) carpal bones between the groups. Bilaterally, the proportionate volume of the intermediate carpal bone (Ci) was significantly greater in Po while that of Cu and C4 were significantly greater in TB. Relative density of most bones was greater in Po. The palmar tuberosity of the proximal surface of Ci and palmar tubercle on the palmar surface of Cu were more prominent and relatively larger in TB. In the second carpal bone (C2), the distal extent of the proximal articular surface on the palmar surface was greater in Po. The inconsistent first carpal bone (C1) was relatively larger in Po. Morphometrical similarities and differences in carpal bones between TB and Po indicate potential effects of selection for body size or fast exercise.

Metacarpal geometry changes during Thoroughbred race training are compatible with sagittal-plane cantilever bending.

REASONS FOR PERFORMING STUDY: Bending of the equine metacarpal bones during locomotion is poorly understood. Cantilever bending, in particular, may influence the loading of the metacarpal bones and surrounding structures in unique ways. HYPOTHESIS: We hypothesised that increased amounts of sagittal-plane cantilever bending may govern changes to the shape of the metacarpal bones of Thoroughbred racehorses during training. We hypothesised that this type of bending would require a linear change to occur in the combined second moment of area of the bones for sagittal-plane bending (I) during race training. METHODS: Six Thoroughbred racehorses were used, who had all completed at least 4 years of race training at a commercial stable. The approximate change in I that had occurred during race training was computed from radiographic measurements at the start and end of training using a simple model of bone shape. RESULTS: A significant (P < 0.001), approximately linear pattern of change in I was observed in each horse, with the maximum change occurring proximally and the minimum change occurring distally. CONCLUSIONS: The pattern of change in I was compatible with the hypothesis that sagittal-plane cantilever bending governed changes to the shape of the metacarpal bones during race training.

Ex vivo calibration and validation of in vivo equine bone strain measures.

REASONS FOR PERFORMING STUDY: Data are required to confirm that strain gauges recording high bone strains in Thoroughbred racehorses provide an accurate record of bone strain. OBJECTIVE: To test the accuracy and reliability of very high in vivo strain recordings made during fast exercise in Thoroughbred racehorses. METHODS: Strains were recorded during exercise from rosette gauges implanted onto the mid-shaft dorsal cortex of each third metacarpal bone (MC3) in 6 yearling and 6 mature Thoroughbreds in a previous experiment. Bulk elastic modulus (E(US)) was calculated from ultrasound speed and single photon absorptiometry measures. Each cleaned MC3 with the original gauge in situ and new gauges placed in a region of strain similarity (as shown by photoelastic coating) was loaded in a materials testing system (MTS) and strains recorded during loading. Elastic moduli were calculated from strain measures from new rosette gauges on the medial, dorsal, lateral and palmar surfaces (E(m); E(d); E(El); E(p), and bulk moduli calculated from the displacement of the MTS machine heads during loading (Ebt). Peak loads were increased incrementally to failure. RESULTS: Of 14 original gauges tested against new gauges, 11 recorded strains from 80-115% of the new gauges and 3 showed reduced function (31-40%). Ebt were similar to E(m), and E(US) were similar to E(l) and not significantly different from Ed. Maximum strains at yield were recorded by the medial gauges and ranged from -7500 to -16,000 microepsilon. CONCLUSIONS AND CLINICAL RELEVANCE: Similarities between recordings from gauges used in vivo and new gauges confirmed the reliability and likely accuracy (or possible underestimate) of very high strains (exceeding -6000 microepsilon) recorded in exercising Thoroughbred racehorses. The similarity between E(bt) and E(m) confirms that the gauges measured the true distortion of the bone in the MTS. These results confirm that mammalian bone may withstand much greater compressive loads than -4000 microepsilon under some conditions at least.

Influence of different exercise regimes on the proximal hoof circumference in young Thoroughbred horses.

REASONS FOR PERFORMING STUDY: Most lameness in horses relates to foot problems and may be associated with changes in hoof shape, but there is a lack of information on the influence of normal exercise on hoof shape. OBJECTIVES: To investigate the effect of training on proximal hoof circumference in young Thoroughbred racehorses being prepared for racing. METHODS: Thirty-seven young Thoroughbred racehorses were included in this study. Front hoof circumference immediately below the coronary band was measured weekly with a measuring tape in all horses present at the stable. Most horses accomplished a minimum of 2 training periods at the stable separated by periods of rest on a paddock. One sample t tests were used to evaluate if the mean change per week differed from zero. To estimate the repeatability coefficient, the left proximal hoof circumference of 25 horses was measured 3 times in a random order on one day. RESULTS: Most horses showed a similar pattern of change. The proximal hoof circumference decreased during the training periods (P < 0.0001) and increased when the horse was rested (P < 0.0001). The decrease of the circumference during the first training period was -0.66 mm/week on the left and -0.64 mm/week on the right. During the second training period, this was -0.58 mm/week on the left and -0.57 mm/ week on the right. During the rest period, the circumference increased by 1.03 mm/week on the left and 1.12 mm/week on the right. The repeatability coefficient for the left circumference was 1.8 mm. CONCLUSIONS: Horses showed a decrease in circumference during race training that reversed when they were rested. POTENTIAL RELEVANCE: Measurement of front hoof circumference is a simple method to assess change in hoof shape. It provides an opportunity to investigate the relationships between specific training, hoof shape and soundness.

Physiological death of hypertrophic chondrocytes.

OBJECTIVE: Post-proliferative chondrocytes in growth cartilage are present in two forms, light and dark cells. These cells undergo hypertrophy and die by a mechanism that is morphologically distinct from apoptosis, but has not been characterized. The aims of the current study were to document the ultrastructural appearance of dying hypertrophic chondrocytes, and to establish a culture system in which the mechanism of their death can be examined. DESIGN: Growth cartilage from fetal and growing postnatal horses was examined by electron microscopy. Chondrocytes were isolated from epiphyseal cartilage from fetal horses and grown in pellet culture, then examined by light and electron microscopy, and quantitative polymerase chain reaction. RESULTS: In tissue specimens, it was observed that dying dark chondrocytes underwent progressive extrusion of cytoplasm into the extracellular space, whereas light chondrocytes appeared to disintegrate within the cellular membrane. Pellets cultured in 0.1% fetal calf serum (FCS) contained dying light and dark chondrocytes similar to those seen in vivo. Transforming growth factor-beta1 or 10% FCS increased the proportion of dark cells and induced cell death. Triiodothyronine increased the differentiation of dark and light cells and induced their death. Dark cells were associated with higher levels of matrix metalloproteinase-13 expression than light cells, and light cells were associated with higher levels of type II collagen expression. CONCLUSIONS: Light and dark hypertrophic chondrocytes each undergo a distinctive series of non-apoptotic morphological changes as they die. Pellet culture can be used as a model of the two forms of physiological death of hypertrophic chondrocytes.

Estimating peak strains associated with fast exercise in thoroughbred racehorses.

REASONS FOR PERFORMING STUDY: The third metacarpal bones (MC3) of racing Thoroughbreds are a common site for bone damage. The midshaft dorsal cortex (DC) of MC3 thickens in response to fast exercise. It is not clear if it changes to a shape and size that limits the peak bone strains to a range associated with normal loading in other species. OBJECTIVES: To relate the proportionate size of the DC cortex in racehorses exercising at racing speed to surface strains, and test whether the DC reached a plateau that was sustained through subsequent exposures to racing speed exercise. METHODS: Standardised lateral MC3 radiographs were taken weekly for 2-5 years in 40 racehorses in race training (16-19 m/sec). DC, medulla (M), and palmar cortex (PC) thickness were measured. at 2.5 cm distal to the nutrient foramen. An index (RI) of the relative thickness of the DC was calculated for each radiograph (RI = [DC+PC]/ M multiplied by [DC/ PC]) and used to calculate strains at 12 m/sec from an equation published previously. RESULTS: Mean time to plateau in DC thickness was 501 days, mean increase in DC was 3.9 mm on the left and 3.7 mm on the right. Rate of change was 8.8 microm/day on the left, and 8.4 microm/day on the right during this time. In most horses the medulla width did not change between the first and last measurements so these bone growth rates reflect periosteal bone growth on the DC surface. No further significant change in DC or RI was found, once they had reached a plateau. Mean DC thickness at the plateau was 14.7 mm on the left and 14.9 mm on the right. Mean RI at the plateau was 3.7. This equated to peak microstrains at 12 m/sec of -2492 and suggests that strains much greater than 3000 microstrains occur at racing speed in most horses. CONCLUSIONS: Experienced racehorses are likely to be exposed to peak strains beyond the normal limit for adult mammalian bone to resist without damage and strains associated with very fast exercise may not be sufficient stimulus to induce further bone modelling in these horses. POTENTIAL RELEVANCE: Strains occur in the bones of experienced racehorses at a higher level than normal for other mammalian bones. Hence there may be other mechanisms operating in this particular bone in racehorses that protects the bone from failure when exposed to the high strains associated with fast exercise speeds. Investigation of such mechanisms may provide an insight on how to reduce the likelihood of damage to this bone during very fast exercise.

The effect of gallop training on hoof angle in thoroughbred racehorses.

REASONS FOR PERFORMING STUDY: The economic impact of soundness problems in racehorses is very high and low hoof angle at the toe has been associated with a lack of soundness. However, it is not clear what environmental and management factors might contribute to a low hoof angle. OBJECTIVES: To investigate the hypothesis that the hooves of racehorses become flatter when in gallop training, as well as to determine factors contributing to this trend. METHODS: Weekly hoof measurements were taken with a hoof gauge from 45 Thoroughbred racehorses; 4 Thoroughbred show horses kept in consistent conditions and shod by the same farrier as some of the racehorses; and 6 unshod free-ranging horses. A further 15 horses were measured twice in one day to determine the repeatability of the method. RESULTS: Repeatability coefficients were 0.31 degrees for the left hoof and 0.37 degrees for the right. Racehorses in training showed a significant decrease in hoof angle over time while free ranging horses and show horses did not. Free-ranging horses had a significantly lower angle in winter (wet) compared with summer (dry) in both left (P = 0.040) and right (P = 0.017). Show horses had no significant change in hoof angle. Racehorses that had a period of rest during the experiment (n = 11) showed a decrease in hoof angle during training and an increase over their rest period for both hooves (P = 0.005 for the left hoof, P = 0.0009 for the right). CONCLUSIONS: Training for fast exercise in Thoroughbred racehorses is associated with a reduction in hoof angle and wet pasture conditions may also be associated with a reduced hoof angle in free-ranging horses. POTENTIAL RELEVANCE: Gallop exercise has a potentially large effect on hoof angle and therefore, a change in angle should be expected to occur in racehorses starting fast exercise work. Hence management of horses with abnormally low hoof angles may require an adaptation to their training regime in order to minimise this effect.

Determination of mechanical loading components of the equine metacarpus from measurements of strain during walking.

REASONS FOR PERFORMING STUDY: The mechanical environment of the distal limb is thought to be involved in the pathogenesis of many injuries, but has not yet been thoroughly described. OBJECTIVES: To determine the forces and moments experienced by the metacarpus in vivo during walking and also to assess the effect of some simplifying assumptions used in analysis. METHODS: Strains from 8 gauges adhered to the left metacarpus of one horse were recorded in vivo during walking. Two different models - one based upon the mechanical theory of beams and shafts and, the other, based upon a finite element analysis (FEA) - were used to determine the external loads applied at the ends of the bone. RESULTS: Five orthogonal force and moment components were resolved by the analysis. In addition, 2 orthogonal bending moments were calculated near mid-shaft. Axial force was found to be the major loading component and displayed a bi-modal pattern during the stance phase of the stride. The shaft model of the bone showed good agreement with the FEA model, despite making many simplifying assumptions. CONCLUSIONS: A 3-dimensional loading scenario was observed in the metacarpus, with axial force being the major component. POTENTIAL RELEVANCE: These results provide an opportunity to validate mathematical (computer) models of the limb. The data may also assist in the formulation of hypotheses regarding the pathogenesis of injuries to the distal limb.

Third metacarpal bone laterality asymmetry and midshaft dimensions in Thoroughbred racehorses.

OBJECTIVE: The aims of this study were to test whether longer third metacarpal (MC3) bones had thicker dorsal cortices in a group of racehorses that were exercising at similar maximum speeds, and to establish if horses with larger differences in length between their right and left MC3 bones showed larger differences in the dorsal cortical thickness between the two limbs. DESIGN: An observational study. PROCEDURE: Forty Thoroughbred racehorses aged between 2 and 6 years and in training at racing speed at two racing stables were used. Two sets of radiographs of each left and right metacarpus of each horse were measured for bone length and dorsal cortical width according to standardised methods. RESULTS: The dorsal cortex thickness showed a linear relationship with bone length for the range of lengths between 25 and 30 cm for both the right MC3 (R2 = 0.30, P = 0.0003) and the left (R2 = 0.23, P = 0.002). The longer bones had thicker dorsal cortices. When results from the two limbs were combined to test if the difference in length between the right and left MC3 in an individual horse was associated with a thicker dorsal cortex in the longer MC3 there was no consistent relationship (R2 = 0.008, P = 0.58). CONCLUSION: In this sample of racehorses longer MC3 bones were likely to have been exposed to a greater dorsopalmar bending moment at the mid shaft that was reflected in a thicker dorsal cortex. The lack of a relationship between midshaft thickness and bone length within individual horses suggests that direct mechanical effects of conformation and environment were less important than the individual's level of skill (or the degree of laterality in their movements) developed before their exposure to fast exercise. It is likely that racehorses with longer right MC3 bones were more able to control the loading of the right MC3 than the left during fast exercise.

The timing and distribution of strains around the surface of the midshaft of the third metacarpal bone during treadmill exercise in one Thoroughbred racehorse.

OBJECTIVE: To confirm that the midshaft dorsal cortex of the third metacarpal bone experienced higher compressive strains during fast exercise than the medial or lateral cortices, and that the strain peak occurred earlier in the hoof-down phase of the stride on the dorsal cortex than the medial or lateral cortices. DESIGN: Observations of a single horse. PROCEDURE: Strains were collected from a single, sound, 3-year-old Thoroughbred mare during treadmill exercise from rosette strain gauges implanted onto the medial, lateral and dorsal surfaces of the midshaft of the right cannon bone, simultaneously with data from a hoof switch that showed when the hoof was in the stance phase. RESULTS: Peak compressive strains on the dorsal surface of the third metacarpal bone were proportional to exercise speed and occurred at about 30% of stance. Peak compressive strains on the medial surface of the non-lead limb reached a maximum at a speed around 10 m/s and occurred at mid-stance. Peak compressive strains on the lateral surface varied in timing and size between strides at all exercise speeds, but remained less than -2000 microstrains. CONCLUSIONS: The timing of peak compressive strains on the dorsal cortex suggests a relationship to deceleration of the limb following hoof impact, so the main determinants of their size would be exercise speed and turning (as shown in previous experiments). This experiment confirms data from other laboratories that were published but not discussed, that peak compressive strains on the medial surface occur at mid-stance. This suggests that they are related to the support of body weight. The strains on the lateral cortex occurred at variable times so may be associated with the maintenance of balance as well as the support of body weight. Understanding the loading of the third metacarpal bone will help to determine causes of damage to it and ways in which the bone might be conditioned to prevent such damage.

Surface strains around the midshaft of the third metacarpal bone during turning.

REASONS FOR PERFORMING STUDY: Bone strains quantify skeletal effects of specific exercise and hence assist in designing training programmes to avoid bone injury. OBJECTIVE: To test whether compressive strains increase on the lateral surface of the inside third metacarpal bone (McIII) and the medial surface of the outside McIII in a turn. METHODS: Rosette strain gauges on dorsal, medial and lateral surfaces of the midshaft of the left McIII in 2 Thoroughbred geldings were recorded simultaneously during turning at the walk on a bitumen surface. RESULTS: Medial surface: Compression peaks were larger in the outside limb. Tension peaks were larger in the inside limb and in a tighter turn. On the lateral surface compression and tension peaks were larger on the inside limb, which showed the largest recorded strains (compression of -1400 microstrains). Dorsal compression strains were larger on the outside limb and on a larger circle. Tensile strains were similar in both directions and larger on a larger circle. CONCLUSIONS: Compressive strains increased on the lateral surface of the inside McIII and medial surface of the outside McIII in a turn. POTENTIAL RELEVANCE: Slow-speed turning exercise may be sufficient to maintain bone mechanical characteristics in the inside limb lateral McIII cortex. Further work is needed to confirm these findings and to determine whether faster gaits and/or tighter turns are sufficient to cause bone modelling levels of strain in the medial and lateral McIII cortex.

Dorsal metacarpal cortex ultrasound speed and bone size and shape.

In Thoroughbred racehorses, the dorsal cortex (DC) of the third metacarpal bone (MC3) enlarges when horses are first exposed to fast exercise speeds. It is now possible to measure ultrasound speed through 3 to 5 mm depths of bone around the bone shaft using Sunlight Medical's 'Omnisense' machine. The aim of this experiment was to determine whether the ultrasound speed measured in the surface 3-5 mm of the midshaft dorsal cortex of MC3 could be related directly to the midshaft shape and size of the MC3s of young Thoroughbred racehorses at the same stage of training. Sixteen 2-year-old and sixteen 3 to 6-year-old racehorses, exercising at racing speed at the same training stable, had their ultrasound speed measured and were radiographed to measure their MC3 midshaft size (width of DC) and shape ([DC/palmar cortex] x [[DC+palmar cortex]/medulla widths]). There were significant linear relationships between ultrasound speed and radiographic bone size and shape measurements. The faster ultrasound speeds were associated with bones that were both absolutely and proportionately thinner in the dorsal cortex in both groups of racehorses. The measurement of ultrasound speed with the Sunlight Omnisense machine should allow more detailed and accurate predictions to be made for responses of the bone to exercise in the midshaft of MC3 than is possible using radiographic size and shape measurements alone. This should make it possible to predict, for example, how soon after a change in bone shape a specific horse can race with minimal risk of damage to the newly-forming bone surface.

A radiographic technique to assess the longitudinal balance in front hooves.

The aim of this study was to validate a radiographic technique to measure objectively the longitudinal hoof balance in the horse. Ten left third phalanges (P3) obtained from front hooves and 19 left front hooves were used in order to assess the reliability of the radiographic technique and to identify any effect of rotation or alignment of specimens or distance between the X-ray machine and the radiographic cassette, in measuring P3s structures and balance related parameters. A rotational support was made to hold specimens in order to standardise some of the conditions of X-raying. The main axis of the frog was used as a marker for the sagittal plane of P3. Results showed that single radiographic measurements could have wide limits of agreement with actual measurements of the hoof (gold standard values). In order to limit errors we suggest the use of a combination instead of single parameters to assess balance. Rotation of the hoof is also to be controlled when a measurement of angles is needed. The radiographic technique used in this study can be used to objecticely measure balance parameters considered important in order to assess hoof balance.