Horizontal moment around the hoof's centre of pressure during walking in a straight line

Reasons for performing study: Joint congruity and ligaments restrain the distal limb joints from excessive motion in the transverse and frontal planes, but the magnitudes and direction of the horizontal twisting moments around the hoof's centre of pressure (CoP) that induce these motions are unknown. Objectives: To quantify the horizontal moment around the vertical axis through the hoof's CoP at walk, and to determine whether these are symmetric. Methods: Nine sound Thoroughbred horses (mean age 5.3 years; mean mass 502 kg) were led at walk in a straight line across a Kistler force platform. Five trials were collected for each fore and hindlimb. The resultant moment around the hoof's CoP was calculated from the horizontal moment arms between the calculated CoP and the 4 horizontal forces in the transverse (X) and cranio‐caudal (Y) directions. Results: The calculated moments were consistent within limbs and horses, but variable between horses. Hindlimbs demonstrated a biphasic moment pattern and the largest moments were typically in the first half of stance. Mean ± s.d. peak moments were internal under both hindlimbs (L: Int 14.1 ± 4.6 Nm; R: Int 13.3 ± 5.5 Nm). In the forelimbs, 7/9 horses demonstrated an asymmetric moment pattern, with the left forelimb exerting an internal moment (L: Int 6.9 ± 2.9 Nm) and the right forelimb an external moment (R: Ext 8.4 ± 4.4 Nm), while the remaining 2 horses exerted internal moments in both forelimbs (L: Int 11.7 ± 1.4 Nm; R: Int 6.6 ± 1.9 Nm). Conclusion: In 7/9 horses, the forelimbs exerted asymmetric horizontal moments around the hoof CoP. The hindlimbs appear to behave with mechanical symmetry during stance, exerting an internal moment during retraction. Potential relevance: Extrasagittal joint motions in the forelimb are unlikely to be symmetric and future studies should account for possible bilateral variations.     

The effect of hoof angle variations on dorsal lamellar load in the equine hoof

Reasons for performing study: In the treatment of laminitis it is believed that reducing tension in the deep digital flexor tendon by raising the palmar angle of the hoof can reduce the load on the dorsal lamellae, allowing them to heal or prevent further damage. Objective: To determine the effect of alterations in hoof angle on the load in the dorsal laminar junction. Methods: Biomechanical finite element models of equine hooves were created with palmar angles of the distal phalanx varying from 0–15°. Tissue material relations accounting for anisotropy and the effect of moisture were used. Loading conditions simulating the stages in the stance where the vertical ground reaction force, midstance joint moment and breakover joint moment were maximal, were applied to the models. The loads were adjusted to account for the reduction in joint moment caused by increasing the palmar angle. Models were compared using the stored elastic energy, an indication of load, which was sampled in the dorsal laminar junction. Results: For all loading cases, increasing the palmar angle increased the stored elastic energy in the dorsal laminar junction. The stored elastic energy near the proximal laminar junction border for a palmar angle of 15° was between 1.3 and 3.8 times that for a palmar angle of 0°. Stored elastic energy at the distal laminar junction border was small in all cases. For the breakover case, stored elastic energy at the proximal border also increased with increasing palmar angle. Conclusions and potential relevance: The models in this study predict that raising the palmar angle increases the load on the dorsal laminar junction. Therefore, hoof care interventions that raise the palmar angle in order to reduce the dorsal lamellae load may not achieve this outcome. See also correspondence by Redden See also correspondence by Curtis     

Influence of riders’ skill on plasma cortisol levels of horses walking on forest and field trekking courses

The aim of this study was to evaluate the influence of rider's skill on the plasma cortisol levels of trekking horses on two courses, walking on field and forest courses (about 4.5 to 5.1 km each). Three riders of different skills did horse trekking (HT) in a tandem line under a fixed order: advanced‐leading, beginner‐second and intermediate‐last. A total of six horses were used and they experienced all positions in both courses; a total of 12 experiments were done. Blood samples were obtained before HT, immediately after and 2 h after HT. As a control, additional blood samples were obtained from the same horses on non‐riding days. Irrespective of the course and the rider's skill, the cortisol level before HT was higher than that of control (P < 0.05). In both courses, the cortisol levels immediately after HT ridden by the advanced rider were higher than that of control (P < 0.05). However, in every case, the cortisol level 2 h after HT was closely similar to the level of the control. Thus, we concluded the stress of trekking horse was not sufficient to disturb the circadian rhythm of the cortisol level, irrespective of the course and the rider's skill.     

The difference in kinematics of horses walking, trotting and cantering on a flat and banked 10 m circle

Reasons for performing study: Locomotion adaptation mechanisms have been observed in horses, but little information is available in relation to banked and nonbanked curve locomotion, which might be important to optimise training environments. Objectives: To determine if adaptation mechanisms in horses existed when moving on a banked compared to a flat curve and whether adaptation was similar in different gaits. Methods: Eight infrared cameras were positioned on the outside of a 10 m lungeing circle and calibrated. Retroreflective markers were used to define left and right metacarpus (McIII) and proximal phalanges (P1), metatarsus (MtIII), head and sacrum. Data were recorded at 308 Hz from 6 horses lunged at walk, trot and canter on a flat and 10° banked circle in a crossover design. Measurements extracted were speed, stride length, McIII inclination, MtIII inclination, relative body inclination and duty factor. Data were smoothed with a fourth order Butterworth filter with 30 Hz cut‐off. ANOVA was used to determine differences between conditions and limbs. Results: Adaptation mechanisms were influenced by gait. At canter inside forelimb duty factor was significantly longer (P<0.05) on a flat curve compared to a banked curve; at walk this was reversed. McIII inclination, MtIII inclination and relative body inclination were significantly greater (P<0.05) at trot and canter on a flat curve, so more inward tilt was found relative to the bearing surface. Conclusion: Adaptation to curved motion is gait specific. At faster gaits it appears that horses negotiate a banked curve with limb posture closer to body posture and probably with demands on the musculoskeletal system more similar to straight canter.     

Kinetics and kinematics of the horse comparing left and right rising trot

Reasons for performing study: At rising trot the rider sits alternately down on one diagonal pair of limbs and rises up on the other. The possible effects on asymmetry of locomotion induced by rising trot have rarely been studied. Objectives: To demonstrate whether, and if so to what extent, rising trot causes asymmetrical loading in the vertical ground reaction force (VGRF) and/or asymmetrical effects on the locomotion pattern, comparing left and right side. Methods: Seven elite horses were ridden in left and right rising trot on a treadmill, while VGRF and kinematics were measured, with the horses' neck raised, the poll high and the bridge of the nose slightly in front of the vertical. Results: Force loading was generally increased in the limbs of the sitting diagonal. The lumbar back was lower between mid‐stances of the sitting and nonsitting stance, pelvic roll was limited and the tuber coxae heights were lower on the sitting side. Maximal hindlimb protraction was decreased. Forelimb retraction was increased and the T6 height decreased. Conclusion: The rider movement induces an uneven biphasic load that affects the back, pelvis and limb kinematics and VGRF. Potential relevance: The generally advocated technique of alternating limbs when riding in rising trot is supported. The VGRF changes between rising on the left or right diagonal were distinct, but minor in absolute terms and therefore unlikely to have direct impact on the occurrence of locomotor injuries. Knowledge of an increase of asymmetry in rising trot is potentially useful for riders/trainers.     

An investigation of the shape of the hoof capsule in hindlimbs,its relationship with the orientation of the distal phalanx and comparison with forelimb hoof capsule conformation

There is limited information documenting hind foot conformation. The objectives of the study were to describe the shape of the hoof capsule of hindlimbs from the lateral aspect in horses of variable breeds, and, within horses, to compare the conformation of the hoof capsule of forelimbs and hindlimbs and determine the orientation of the distal phalanx within the hoof capsule in hindlimbs. Lateral photographs of the fore and hind feet (n = 225) and lateromedial radiographs of the hind feet (n = 29) were obtained. Differences among breed and shoeing status groups were assessed using multivariable mixed-effects linear regression models. Angular parameters and ratios of linear measurements were compared between fore and hind feet; angular radiological variables and photographic parameters of the hind feet were compared. The mean dorsal hoof wall angle for hind feet (50.9°±3.7°) was smaller than forefeet (51.8°±3.9°) (P = 0.04). The mean heel angles for hind feet (36.4°±9.6°) were smaller than forefeet (40.1°±9.3°; P < 0.001). Dorsal hoof wall (P < 0.001) and heel (P = 0.002) angles were larger in unshod than shod feet. In the hind feet, the dorsal hoof wall was parallel to the dorsal aspect of the distal phalanx. The median angle of the distal phalanx to the horizontal (angle S) was 0.6° (interquartile range: −1.4, 2.3°). There was a positive relationship between angle S and the hoof wall angle (W); each 1° increase in angle S was associated with 0.6° increase in angle W (P < 0.001). Angle S was also positively associated with photographic heel angle; each degree increase in the angle S was associated with 1.8° increase in the heel angle (P < 0.001). It was concluded that the angle of the distal phalanx to the horizontal in hindlimbs is smaller than published values for forelimbs. The orientation of the distal phalanx in hindlimbs is correlated with external characteristics of the hoof capsule.     

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.     

Evaluation of discriminant analysis based on dorsoventral symmetry indices to quantify hindlimb lameness during over ground locomotion in the horse

Reasons for performing study: Advances in gait analysis techniques have led to assessment tools that can aid in detecting and quantifying lameness; here, bilateral tuberà coxae and pelvic movement during over ground locomotion are compared in order to investigate a practical method to assess hindlimb lameness in the horse. Objectives: To evaluate which parameters from anatomical landmarks on trunk and proximal hindlimbs are the best indicators of degree and side of hindlimb lameness. Methods: Fifteen horses (age 11–23 years, 6 nonlame and 9 unilaterally hindlimb lame horses 1/10 to 2/10 lame) were fitted with 4 inertial sensors: tuber sacrale, left and right tubera coxae and withers; 889 strides were collected from 6 trot trials per horse. Horses were assessed for lameness by a qualified equine orthopaedic surgeon from videos. Vertical displacement data for each sensor were used to calculate symmetry indices as well as published Fourier analysis based parameters. Linear discriminant analysis was used to determine the most discriminative parameters for 2 scenarios: grading of severity of lameness and identification of the affected limb. Results: Pelvic energy ratio gave the best indication for the degree of lameness. Directional symmetry index of the tubera coxae sensors yielded the highest discriminative power for identification of the lame limb. Conclusions and potential relevance: A good indication of the degree of hindlimb lameness can be obtained from vertical displacement data of the pelvic midline, collected from inertial sensors during over ground locomotion. The trunk mounted inertial sensor system allows for a time efficient collection of a representative database from horses with differing grade and site of lameness in a clinical setting. This is crucial for future work on a robust definition of the best parameters for lameness classification under practical conditions.     

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.     

The effects of limb posture on relationships between in vitro radial hoof strain,load and joint angles

Reasons for performing study: Radial strain in normal hooves has been found to vary with strain gauge location, limb posture and sample limb but reported magnitudes were considered to be low. More accurate measurement of radial strain may enhance the understanding of hoof function. Objectives: To explore in vitro radial hoof strain in relation other kinetic and kinematic variables that may be related. Methods: Five normal forelimbs were removed at the proximal articular surface of the third metacarpal bone (McIII). The limbs were loaded using a modified Instron test machine. Six calibrated infrared cameras captured movement from markers on the hoof and bone fixed markers on the second and first phalanxes and McIII, whilst radial hoof strain was measured using a calibrated instrumented plug. Change in strain, joint angle and load were found at simulated walking postures and bivariate correlations were used to compare the relationships between them. Results: Radial strain was moderately correlated with proximal interphalangeal joint (PIPJ) rotation (r =?0.519). Large reductions in radial strain were found in loading and midstance with 10° of heel lift postures. Conclusions and potential relevance: PIPJ rotation has previously been linked to the magnitude of deep digital flexor tendon (DDFT) loads and it is therefore suspected that these loads may have the greatest influence on radial strain magnitudes. Further investigation of radial strain is needed to describe the patterns fully during the stance phase in vivo.     

Skeletal forelimb measurements and hoof spread in relation to asymmetry in the bilateral forelimb of horses

Reasons for performing study: Research has highlighted a high frequency of skeletal asymmetries in horses. In addition, research into hoof asymmetries has shown that within a bilateral pair, the hoof with the smaller angle is often subjected to greater loading. There has been limited attention paid to understanding compensatory mechanisms for skeletal asymmetries in the horse; the dynamic structure of the hoof could potentially be acting in a compensatory capacity. Objectives: To investigate the relationship between morphometry of forelimb segments and hoof spread and their incidence of asymmetry. Methods: Ten bilateral measurements of the hoof and forelimb were taken from 34 leisure horses. The relationship between hoof spread and forelimb segment measurements were analysed using a generalised linear model (GLM). Results: In relation to left hoof spread, the GLM identified significant negative relationships with left side measurements (third metacarpal length, elbow height), and significant positive relationships with right side measurements (fetlock height, third metacarpal length, elbow height). In relation to right hoof spread, the GLM identified significant negative relationship with left elbow height, and significant positive relationships with right side measurements (fetlock height, point of shoulder). The difference between the number of horses larger to the left or to the right was found to be significant for point of shoulder height (X²= 4.8, P<0.05), and highly significant for heel height (X²= 9.53, P<0.01) and the third metacarpal length (X²= 7.26, P<0.01). Conclusions and clinical relevance: The study demonstrated considerable asymmetry in left‐right morphometry of the equine limb. The fact that measurements of hoof spread were significantly associated with limb segment measurements could possibly indicate that an interaction exists. Any asymmetry in hoof spread measurements may suggest unequal loading of the limbs, which in turn may contribute to injuries and reduced performance.