Cinematographic analysis of the gait of lame horses V: Fibrotic myopathy

A horse with fibrotic myopathy of the semitendinosus muscle of the right hind limb was studied. Observation of the horse in movement showed that protraction of the affected limb terminated abruptly and the hoof was slapped down on the ground. High speed cinematography with computer-aided analysis of the film was used to analyze the gait in greater detail. The results showed that the right hind limb approached the ground almost vertically making impact toe-first, whereas the left hind limb was moving forward relative to the ground when it made heel-first impact. Significant differences were recorded in the sequence and placement of the limbs on the 2 diagonals. The hind limb preceded the forelimb at impact on both diagonals, but at lift-off the lame right hind limb preceded the left forelimb, whereas the sound left hind limb lifted off later than the right forelimb. The distance between the diagonal limb pair during the stance phase was shorter for the left diagonal (left fore-right hind limb pair) than for the right diagonal (right fore-left hind limb pair) (P<0.01). The suspension following the left diagonal was longer than that following the right diagonal (P<0.01).     

Cinematographic analysis of the gait of lame horses II: Chronic sesamoiditis

The gait characteristics of a horse with chronic sesamoiditis of the left forelimb are described. On physical examination the affected metacarpophalangeal joint was foundto be enlarged. Extensive fibrosis on the palmar surface of the proximal sesamoid bones and in the suspensory ligament resulted in a reduced range of movement in the joint At rest the horsepointed the left toe and was reluctant to bear weight on that limb. Observation at the trot revealed an obvious head nod on the sound right diagonal. During the left diagonal stance phasethe head and neck were raised, the LF fetlock was held in a rigid upright position, and hyperextension of the joint was restricted.

Cinematographic analysis showed that the LF had a longer stance phase than the RF, due to anincreased anterior phase combined with a slower breakover (p<0.01). At the end of its stance phase the LF overlapped with both the RF and LH, so there was no left suspension. The rightdiagonal stance phase was followed by a short suspension before impact of the LF. With regard to linear measurements the horse took a longer step from the RF to LF and from the RH to LHthan for the contralateral pairs (p<0.01). As a result the distance between the RF and LH inthe right diagonal stance phase was significantly less than that between the LF and RH in the left diagonal stance phase (p<0.01).

Kinematic analysis showed that the sound RF made flat foot impact with the ground, whereas, at the end of the swing phase, the LF toe flipped up and impact was heel first The neck was elevated during the early part of the LF stance phase, until the limb had passed the midstance position when the poll fell, reaching its lowest level at the RF midstance position. Author's address: Department of Veterinary Anatomy, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan.     

Distribution of ground reaction forces of the concurrently loaded limbs of the Dutch Warmblood horse at the normal walk

The distribution of the ground reaction forces (GRF) over the concurrently loaded limbs of the normally walking horse was determined from 'representative' GRF patterns of all limbs, which were plotted in correct time order after analysis of simultaneously taken high-speed film. This procedure visualises the GRF patterns of each of the four limbs in relation to the GRF pattern(s) of the one or two concurrently loaded limb(s) during a complete stride. In 15 clinically sound horses the mean averaged GRF data and temporal stride parameters showed an almost complete symmetry between both the forelimbs and both the hindlimbs and resulted in a load distribution during the first half of the stride being almost identical to those in the second half of the stride. The transverse horizontal force (Fx) was maximum during the unilateral support phase. No more than one limb at a time contributed to either the deceleration or acceleration longitudinal horizontal (Fy) force. The total vertical (Fz) force of the concurrently loaded limbs during a complete stride fluctuated between 7 to 12 N/kg body weight. In a left forelimb lame horse, the decreased GRF amplitudes were compensated by increased GRF amplitudes in the three other limbs during both the swing phase and stance phase of the lame limb. Due to alterations of both GRF data and temporal stride parameters of the lame limb, as well as the three other limbs, the distribution of the GRF during the complete stride was changed dramatically.     

Standardised terminology for the description and analysis of equine locomotion

Terminology for the analysis of equine locomotion is reviewed and the most appropriate terms selected for use by research workers in this field. Each cycle of limb movement comprises a stance phase, when the hoof is in contact with the ground, alternating with a swing phase. The stance phase is subdivided at the mid-stance position into an initial decelerative phase followed by a propulsive phase. When the stance phases of different limbs occur concurrently, the term overlap refers to the duration of simultaneous ground contact. Single support is the term used to describe the phase when the limb is in its stance phase unaided by any other limb. A gait consists of a limb coordination pattern repeated at each stride. The start and finish of the stride must be designated as a prerequisite to the determination of stride length, stride duration and stride frequency. In asymmetrical gaits, such as the gallop, the stride as a whole will have a stride stance phase, when one or more limbs are in contact with the ground, and a suspension phase. In symmetrical gaits, such as the trot and pace, the stride consists of left and right stance phases and suspension phases. Advanced placement and advanced lift off measure the time between ground placement and lift off respectively of consecutive limbs. The line of motion indicates the progressive movement of the centre of gravity in the X-Y plane. Measurements in th Y-Z plane, such as line gait and overcrossing, describe the ground placement of the hooves relative to the line of motion. Diagonal width is the distance between diagonal limb pairs in this plane.     

The forelimb in walking horses: 1. Kinematics and ground reaction forces

Video (60 Hz) and force (2000 Hz) data were collected from 5 sound horses during walking. Forelimb data were analysed for 8 strides (4 left, 4 right) per horse to determine sagittal plane kinematics and ground reaction forces (GRFs). The results suggested that brachial rotation was responsible for protraction and retraction of the limb as a whole, while rotations of the scapula and antebrachium elevated the distal limb during breakover and early swing then lowered it in preparation for ground contact. The coffin joint was flexed maximally at the time of peak longitudinal braking force, which occurred during breakover of the contralateral forelimb. The metacarpus was vertical at 28% stride. This was considerably earlier than the change from a braking to a propulsive longitudinal force (34% stride), which coincided with maximal extension of the fetlock joint. The longitudinal propulsive force peaked just after contact of the contralateral forelimb. During the swing phase the joints distal to the shoulder showed a single flexion cycle that peaked at 76% stride at the carpus, 81% stride at the fetlock and 84% stride at the elbow and coffin joints. The coffin and shoulder joints began to extend in the terminal swing phase and continued to extend through ground contact and early stance. The results provide normative data that will be applied in detecting changes in kinematics and ground reaction forces that are associated with specific lamenesses.     

Effect of induced unilateral synovitis of distal intertarsal and tarsometatarsal joints on sagittal plane kinematics and kinetics of trotting horses

OBJECTIVE: To study the effect of unilateral synovitis in the distal intertarsal and tarsometatarsal joints on locomotion, including the compensating effects within and between limbs. ANIMALS: 4 clinically normal horses. PROCEDURE: Gait analyses including kinematics, force plate, and inverse dynamic analysis were performed at the trot before lameness, after which synovitis was induced by injecting endotoxin into the right distal intertarsal and tarsometatarsal joints. Gait analyses were repeated 24 to 30 hours later during lameness. Differences between the stride variables during the 2 conditions (lame and sound) were identified. RESULTS: Tarsal joint range of motion, peak vertical force, and vertical impulse were decreased during lameness. Mechanical deficits included a decrease in negative work performed by the tarsal extensors during the early stance phase and a decrease in positive work by the tarsal extensors during push off. No compensatory changes in work were performed by other joints within the lame hind limb during the stance phase. Vertical impulse in the diagonal forelimb decreased, but there were no significant changes in forces or impulses in the ipsilateral forelimb or contralateral hind limb. CONCLUSION AND CLINICAL RELEVANCE: Results indicate that horses are able to manage mild, unilateral hind limb lameness by reducing the airborne phase of the stride rather than by increased loading of the compensating limbs.     

Effects of balancing and shoeing of the forelimb feet on kinematic gait analysis in five horses with navicular disease

The effects of balancing the foot and shoeing (B&S) on the kinematics of five Quarter Horses with navicular disease were evaluated using computerized gait analysis. Kinematic measurements of the right forelimb and head were made before and after palmar digital nerve block (PDNB) and before and after B&S of the forelimb feet. Carpal and fetlock joint angle, foot displacement, and temporal gait measurements were made for at least five strides in each horse trotting on a treadmill. Kinematic measurements were compared before and after PDNB and before and after B&S by analysis of variance with an α=0.05. The most significant kinematic changes seen after PDNB were in the vertical head movement parameters studied. Total vertical head excursion and measures of head height asymmetry between right and left forelimb stance phases decreased after PDNB. After B&S mean carpal flexion and maximum hoof height during the swing phase of the stride increased, but none of the head movement parameters significantly changed. Results of this study indicate that the ability of treadmill kinematic gait analysis to evaluate for improvement in lameness by monitoring vertical head movement parameters is not significantly affected in horses with navicular disease three weeks after balancing and shoeing the forelimb feet.     

Compensatory load redistribution of horses with induced weightbearing hindlimb lameness trotting on a treadmill

REASONS FOR PERFORMING STUDY: The compensatory mechanisms of horses with weightbearing hindlimb lameness are still not fully understood. HYPOTHESIS: That weightbearing, unilateral hindlimb lameness would not only alter stride characteristics to diminish structural stress in the affected limb but also induce compensatory load adjustments in the other supporting limbs. OBJECTIVE: To document the load and time shifting mechanisms of horses with unilateral weightbearing hindlimb lameness. METHODS: Reversible lameness was induced in 8 clinically sound horses by applying a solar pressure model. Three degrees of lameness (subtle, mild and moderate) were induced and compared with the nonlame (sound) control measurement. Vertical ground reaction forces were recorded for all 4 limbs simultaneously on an instrumented treadmill. RESULTS: Compared to the sound situation, moderate hindlimb hoof lameness induced a decrease in stride duration (-3.3%) and stride impulse (-3.1%). Diagonal impulse decreased selectively in the lame diagonal stance (-7.7%). Within the diagonal limb pair, vertical impulse was shifted to the forelimb during the lame diagonal stance (+6.5%) and to the hindlimb during the sound diagonal stance (+3.2%). Peak vertical force and vertical impulse decreased in the lame limb (-15%), but only vertical impulse increased in the contralateral hindlimb (+5.7%). Stance duration was prolonged in both hindlimbs (+2.5%). Suspension duration was reduced to a greater extent after push-off of the lame diagonal limb pair (-21%) than after the sound diagonal limb pair (-9.2%). CONCLUSIONS: Four compensatory mechanisms could be identified that served to reduce structural stress, i.e. peak vertical force on the affected limb: 1) reduction of the total vertical impulse per stride; 2) diagonal impulse decreased selectively in the lame diagonal; 3) impulse was shifted within the lame diagonal to the forelimb and in the sound diagonal to the hindlimb; and 4) the rate of loading and peak forces were reduced by prolonging the stance duration. POTENTIAL RELEVANCE: Load shifting mechanisms are not only effective in diminishing peak forces in the affected limb, but also suppress compensatory overload in other limbs. Selected force and time parameters allow the unequivocal identification of the lame limb. Future studies have to examine how far these compensatory mechanisms may be generalised for other defined orthopaedic problems in the hindlimb.     

Impact of walking surface on the range of motion of equine distal limb joints for rehabilitation purposes

The aim of this study was to evaluate the effect of three footing surfaces on the flexion/extension, and range of motion (ROM) of the carpus, tarsus and fetlocks in the horse. The percentage of stride spent in the stance phase of sound horses at the walk was also measured. Nine sound horses were walked on hard ground (HD), soft ground (SF) and a land treadmill (LT), and five complete gait cycles were recorded by a digital video camera. Retro-reflective markers were placed on the skin at four anatomical locations on the left fore and hind limbs, and data were analyzed using two-dimensional (2D) motion-analysis software. Maximal flexion/extension angles and range of motion were calculated for each joint, and the percentage of the stride spent in stance phase was determined for each stride.Maximal flexion of the tarsus and hind fetlock was greater on LT and SF compared to HD, while maximal flexion of the carpus was greater on LT compared to HD and SF. Maximal extension of the carpus was greater on HD compared to SF and LT, maximal extension of the tarsus was greater on HD and SF compared to LT, and maximal extension of the forelimb and hind limb fetlocks was greater on LT compared to HD and SF. The greatest overall ROM of the carpus and fetlocks was achieved on LT, while the greatest overall ROM of the tarsus was achieved on SF. The stance percentage of the stride for the hind limb was significantly different between all surfaces. In conclusion, walking surface influences flexion/extension of the carpus, tarsus and fetlocks in healthy horses, which should be considered when walking equine rehabilitation cases.     

Objective determination of pelvic movement during hind limb lameness by use of a signal decomposition method and pelvic height differences

OBJECTIVE: To evaluate pelvic movement over a large number of strides in sound horses and in horses with induced hind limb lameness by applying methods to the pelvis that have been described for evaluating vertical head movement in horses with induced forelimb lameness. ANIMALS: 17 adult horses. PROCEDURE: Horses were filmed while trotting on a treadmill before and after induction of transient mild and moderate hind limb lamenesses. Vertical pelvic movement was measured by a signal decomposition method. The vertical pelvic signal was decomposed into a periodic component (A1) that occurred at half the stride frequency (representing vertical pelvic movement caused by lameness) and another periodic component (A2) that occurred at stride frequency (representing normal vertical pelvic movement of a trotting horse). Vertical pelvic and foot positions were correlated for each stride to compare the difference between the minimum and maximum heights of the pelvis during and after stance of the right hind limb to the minimum and maximum heights of the pelvis during and after stance of the left hind limb. RESULTS: Maximum pelvic height difference and lameness amplitude (A1) differed significantly between sound and mild or moderate hind limb lameness conditions. Mean A1 value for vertical pelvic movement in sound horses was less than that previously reported for vertical head movement. CONCLUSION AND CLINICAL RELEVANCE: Pelvic height differences and signal decomposition of pelvic movement can be used to objectively evaluate hind limb lameness in horses over a large number of strides in clinical and research settings.     

Evaluation of a Commercial Activity Monitor for Determining Step Counts in Horses

Monitoring activity level has become popular in people and animals. In the horse, these monitors may be helpful for the detection of disease, monitor limb loading after surgery, and assist in rehabilitation. The objective of this study was to evaluate the accuracy of a commercial activity monitor (AM) (FitBit Zip) in horses. In Part 1, four stalled horses had five AMs placed (head, chest, withers, and left forelimb and hindlimbs) with stride length setting of 60.96 cm and were monitored for 24 hours with AM and video. In Part 2, four stalled horses had two AMs placed (left forelimb and hindlimbs) with stride length setting of 30.48 cm and were monitored for 24 hours with AM and video. In Part 3, three horses with two AMs (left forelimb and hindlimbs) had step data collected at the walk and trot in hand by AM and video. AM and video data were compared using Pearson’s correlation coefficients and by calculating AM to video step count ratios. In Part 1, there was considerable movement of AMs at the chest and withers, but head and limb mounted AMs were more secure. In Part 2, video and AM activity counts were moderate to high for forelimb and hindlimbs with R² values of 0.82 and 0.74, respectively. From Part 3, AMs mounted on either forelimb or hindlimbs approximately doubled the step counts compared to the video. While this AM did not accurately count steps, it may be able to provide general information on activity level in the stalled horses.     

The effect of induced forelimb lameness on thoracolumbar kinematics during treadmill locomotion

REASONS FOR PERFORMING STUDY: Lameness has often been suggested to result in altered movement of the back, but there are no detailed studies describing such a relationship in quantitative terms. OBJECTIVES: To quantify the effect of induced subtle forelimb lameness on thoracolumbar kinematics in the horse. METHODS: Kinematics of 6 riding horses was measured at walk and at trot on a treadmill before and after the induction of reversible forelimb lameness grade 2 (AAEP scale 1-5). Ground reaction forces (GRF) for individual limbs were calculated from kinematics. RESULTS: The horses significantly unloaded the painful limb by 11.5% at trot, while unloading at walk was not significant. The overall flexion-extension range of back motion decreased on average by 0.2 degrees at walk and increased by 3.3 degrees at trot (P<0.05). Changes in angular motion patterns of vertebral joints were noted only at trot, with an increase in flexion of 0.9 degrees at T10 (i.e. angle between T6, T10 and T13) during the stance phase of the sound diagonal and an increase in extension of the thoracolumbar area during stance of the lame diagonal (0.7degrees at T13, 0.8 degres at T17, 0.5 degres at L1, 0.4 degrees at L3 and 0.3 degrees at L5) (P<0.05). Lameness further caused a lateral bending of the cranial thoracic vertebral column towards the lame side (1.3 degrees at T10 and 0.9 degrees at T13) (P<0.05) during stance of the lame diagonal. CONCLUSIONS: Both range of motion and vertebral angular motion patterns are affected by subtle forelimb lameness. At walk, the effect is minimal, at trot the horses increased the vertebral range of motion and changed the pattern of thoracolumbar motion in the sagittal and horizontal planes, presumably in an attempt to move the centre of gravity away from the lame side and reduce the force on the affected limb. POTENTIAL RELEVANCE: Subtle forelimb lameness affects thoracolumbar kinematics. Future studies should aim at elucidating whether the altered movement patterns lead to back and/or neck dysfunction in the case of chronic lameness.     

Quantitative analysis of computer-averaged electromyographic profiles of intrinsic limb muscles in ponies at the walk.

The function of several intrinsic muscles of the fore-and hind limbs of 5 ponies walking normally was evaluated via surface electromyography. Electromyographic signals were band-pass filtered, rectified, linear enveloped, and standardized to the stride duration. Mean data from the muscles of the left and right limbs that were obtained from at least 30 strides in 2 recording sessions were recorded as electromyographic signals-time curves. The timing of muscle activity was determined from these graphs. On the basis of the major peaks in the electromyographic signal, muscle functions were identified. In the forelimb, the extensor carpi radialis muscle was involved in extension of the carpus at the end of the swing phase of the stride, and it provided support to flexion of the cubital joint at the beginning of the swing phase. The common digital extensor muscle extended the distal joints of the forelimb at the end of the swing phase. The ulnaris lateralis muscle provided support to extension of the cubital joint at the beginning of the stance phase, and the flexor carpi radialis muscle flexed the carpus at the beginning of the swing phase. The flexor carpi ulnaris muscle extended the cubital joint at the end of the swing phase. In the hind limb, the long digital extensor muscle flexed the tarsus at the beginning of the swing phase and extended the digital joints preceding the stance phase. The deep digital flexor muscle prevented overextension of the distal interphalangeal joint during the stance phase and flexion of the digital joints during the swing phase.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparative biokinematic study of young and adult Andalusian horses at the trot

The purpose of this study was to determine basic kinematic parameters (linear, temporal and angular) in young and adult Andalusian horses (P.R.E.) at the trot, using a normal computer-aided videography system. The trotting gaits of 16 horses were analysed: seven young horses (3.7 +/- 0.2 years old, height at withers 167.1 +/- 4.1 cm) and nine adult stallions (12.3 +/- 2.9 years old, height at withers 162.9 +/- 3.6 cm) were recorded at least 6 times at the trot using a 25-Hz video-camera filming from the side. Video images were processed with a real-time digital system (SMVD). Speeds averaged 3.84 and 3.75 m/s for young and adult horses, respectively. Differences between age groups for speed and linear and temporal parameters of the stride were not significant. However, variations in angular parameters were detected: adults showed a greater ARM than younger horses for most forelimb joints. In the hind limb, hip, stifle, and, to a lesser degree, the tarsal joint, a smaller degree of extension during the stance phase was observed in adult horses.     

A laboratory system for production of flexion rates and forces in the forelimb of the horse

The distal portion of the forelimb of the horse is provided with a stay apparatus composed of tendons, ligaments, and fascia. This stay apparatus provides the major resistance to joint flexion during the support phase of the stride. The laboratory test system described was shown to be able to reproduce in vitro limb motions and hoof forces measured with a running horse. These results indicated the stay apparatus operates in a largely passive mode, active muscle contraction apparently serving to provide rigidity only early in the support phase of the stride. The testing system described was designed to take advantage of the passive nature of the stay apparatus in order to study in vitro the forces, accelerations, and deformations encountered by the limb of the galloping horse in vivo.     

Vertical head and trunk movement adaptations of sound horses trotting in a circle on a hard surface

Trotting a horse in circles is a standard and important part of the subjective equine lameness examination, yet objective data on this form of locomotion are sparse. The aim of this study was to investigate the effect of trotting in a circle on head and trunk movement symmetry. Vertical movements of the head, withers, os sacrum and left and right tuber coxae were measured using inertial sensors as 12 sound horses were trotted on a hard surface in a straight line and in a circle on both reins. Seven asymmetry measures and hip hike were calculated for each horse for at least nine strides of comparable stride duration across the three conditions (deviation on horse level ≤3.7% stride duration). Trotting in a circle introduced systematic changes to the movement pattern of all five body landmarks, affecting most asymmetry measures. On average the asymmetry magnitude was comparable for midline locations between reins and for the tuber coxae on opposite reins with few exceptions, although individual horses showed unsystematic differences between the two reins. The results from this study showed that the thresholds for objective discrimination between lame and non-lame horses will need adjustment on the circle due to the observed asymmetry bias.     

Relationship Between Magnitude and Direction of Asymmetries in Facial and Limb Traits in Horses and Ponies

Directionality of limb and facial asymmetries in nonelite equine populations has been previously reported with results indicating strong similarities to those reported in racehorses. This investigation aimed to consider the relationship between the magnitude of the asymmetries presented within the general equine population, and their previously reported directionality. Direct measurements of 15 bilateral traits (four facial and 11 limb) were captured from a mixed population of 100 horses and ponies. The pooled (whole) population was considered further as horse (withers height >148 cm) and pony (withers height ≤148 cm) groupings. Each of the three groups was further subdivided for each trait, into individuals presenting with larger left or larger right sides. Asymmetries were compared as mean asymmetries and as percentages of the trait size at each grouping level. Asymmetry magnitudes were largely reflective of the directional asymmetries previously recorded. Both the horse and pony groups presented with significantly longer right side third metacarpal (P ≤ .001) and third metatarsal (P ≤ .05 and P ≤ .001) bones, whereas in the horse group, the left fore proximal phalanx was both longer and wider than the right (P ≤ .001 and P ≤ .05). This pattern is reflective of the biomechanical preference for left lead anticlockwise canter, previously only observed in racehorses. The proximal phalanx of the forelimb potentially compensates for the higher loading forces associated with the lead forelimb. When scaled as percentages of trait size, the asymmetry magnitudes largely reflected those reported in humans, suggesting similar measurement criteria could be applied when considering stock selection and controlling for injury predisposition in horses.     

Compensatory load redistribution of horses with induced weight-bearing forelimb lameness trotting on a treadmill

The study was performed to obtain a detailed insight into the load and time shifting mechanisms of horses with unilateral weight-bearing forelimb lameness. Reversible lameness was induced in 11 clinically sound horses by applying a solar pressure model. Three degrees of lameness (subtle, mild and moderate) were induced and compared with sound control measurements. Vertical ground reaction force-time histories of all four limbs were recorded simultaneously on an instrumented treadmill. Four compensatory mechanisms could be identified that served to reduce structural stress, i.e. peak vertical force on the affected limb: (1) with increasing lameness, horses reduced the total vertical impulse per stride; (2) the diagonal impulse decreased selectively in the lame diagonal; (3) the impulse was shifted within the lame diagonal to the hindlimb and in the sound diagonal to the forelimb; (4) the rate of loading and the peak forces were reduced by prolonging the stance duration. Except in the diagonal hindlimb, where peak vertical forces increased slightly in the moderate lameness condition, no equivalent compensatory overload situation was observed in the other limbs. Specific force and time information of all four limbs allow the unequivocal identification of the affected limb.     

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.     

A subjective descriptive study of the warm‐up and turn to a fence,approach, take‐off,suspension, landing and move‐off in 10 showjumpers

There is limited knowledge about causes of musculoskeletal injury in showjumpers. The objectives were to describe features of the turn, approach and jump in a group of experienced showjumpers believed by their riders to be sound, to relate these findings to clinical findings, and to identify features that may predispose to injury. Ten experienced showjumpers in normal competition training jumped an upright and a parallel fence four times off the left and right reins respectively, after a rider‐defined period of warm‐up. Real‐time and high‐speed motion capture was undertaken. Detailed subjective assessment of the gait was performed during the warm‐up, on the turn and approach to the jump and all phases of the jump. Six horses had thoracolumbar pain or epaxial muscle tension. Six horses exhibited a poor‐quality canter. The mean duration of warm‐up was 7 min (range 5–10 min). All horses had lean of the trunk and hindlimbs >45° on the turn. The inside hindlimb was placed in front of the outside hindlimb in 75% of the turns. Sideways oscillations of the hocks during stance were seen in all horses on the turn and on the straight approach in five horses. The inside hindlimb had greater magnitude of oscillation than the outside hindlimb on the turns. Repeated asynchronous push‐off with the hindlimbs at take‐off was seen in three horses. The hindlimbs drifted to the left or right during the ascent‐phase of suspension in four horses, reflecting asymmetrical push‐off. Only two horses landed consistently with the correct forelimb leading relative to the direction in which the horse had to turn after the fence. Four horses landed seven (n = 2) or eight (n = 2) times each with the left (n = 2) and right (n = 2) forelimbs respectively. Repetitive overload through asymmetrical use of the left and right canter leads, inadequate warm‐up, and limb instability could potentially predispose to injury.