Limb loading activity of adult horses confined to box stalls in an equine hospital barn

OBJECTIVE: To determine a range of limb loading activity for healthy adult horses confined to box stalls in an equine veterinary teaching hospital and determine the effects of hospital environmental factors on load rates and daily limb loading patterns. ANIMALS: 6 mature healthy horses of various ages, breeds, and sexes, and 1 horse with a repaired metatarsal fracture. PROCEDURE: Step monitors were placed on 2 limbs of adult horses confined to box stalls. Relocation steps and weight shifts were recorded, as loading events, for 24 hours. Influence of forelimb versus hind limb and environmental factors on load rate (loading events per hour) were assessed with repeated-measures ANOVA. RESULTS: Loading activity was greater for the forelimb than the hind limb and was greater during the day than the night. Loading activity differences were not associated with daytime environmental factors. CONCLUSIONS AND CLINICAL RELEVANCE: Horses with normal locomotor activity appear to have higher load rates for forelimbs compared with hind limbs and higher load rates during the day compared with night. Knowledge of influence of environmental factors and mechanical restraint on limb loading activity may be useful in management of horses with musculoskeletal disorders. This information may also be used for in vitro simulation of in vivo loading of limbs during cyclic biomechanical investigations.     

Voluntary limb-load distribution in horses with acute and chronic laminitis

OBJECTIVES: To compare limb-load distribution between horses with and without acute or chronic laminitis. ANIMALS: 10 horses with carbohydrate-induced acute laminitis, 20 horses with naturally occurring chronic laminitis, and 20 horses without foot abnormalities (controls). PROCEDURES: Limb-load distribution was determined, using a custom-designed system that allowed simultaneous quantification of the mean percentage of body weight voluntarily placed on each limb (ie, mean limb load) and the SD of the mean load over a 5-minute period (ie, load distribution profile [LDP]). Load distribution profile was used as an index of frequency of load redistribution. RESULTS: Mean loads on fore- and hind limbs in control horses were 58 and 42%, respectively, and loads were equally and normally distributed between left and right limbs. In addition, forelimb LDP was greater, compared with hind limbs, and was affected by head and neck movement. In comparison, limb-load distribution in horses with chronic laminitis was characterized by an increase in the preferential loading of a forelimb, a decrease in total forelimb load, and an increase in LDP that was correlated with severity of lameness. In horses with carbohydrate-induced acute laminitis, mean limb loads after onset of lameness were not different from those prior to lameness; however, LDP was significantly decreased after onset of lameness. CONCLUSION AND CLINICAL RELEVANCE: Quantification of limb-load distribution may be an applicable screening method for detecting acute laminitis, grading severity of lameness, and monitoring rehabilitation of horses with chronic laminitis.     

Kinematics and ground reaction forces in horses with superficial digital flexor tendinitis

OBJECTIVE: To measure and correlate kinematic and ground reaction force (GRF) data in horses with superficial digital flexor tendinitis. ANIMALS: 6 sound horses. PROCEDURE: Horses were evaluated before (sound evaluation) and after (lame evaluation) induction of superficial digital flexor tendinitis in 1 forelimb (randomized) by injection of collagenase. As each horse trotted, kinematic data were collected by use of an optoelectronic system, and GRF data were measured by use of a force plate. Three-dimensional kinematic and GRF data were projected onto a 2-dimensional sagittal plane. RESULTS: Lame limbs had significantly lower peak vertical GRF, less flexion of the distal interphalangeal joint, and less extension of the metacarpophalangeal joint, compared with compensating limbs. Carpal joint kinematics did not change. Compensating limbs had a more protracted orientation throughout the stance phase and higher braking longitudinal force and impulse; however, total range of rotation from ground contact to lift off did not change. Transfer of body weight from lame to compensating limbs was smooth, without elevation of the body mass into a suspension phase. Propulsive components of longitudinal GRF did not differ between limbs. CONCLUSIONS AND CLINICAL RELEVANCE: In horses with experimentally induced superficial digital flexor tendinitis, changes in vertical GRF were reflected in angular excursions of the distal interphalangeal and metacarpophalangeal joints, whereas changes in longitudinal GRF were associated with alterations in the protraction-retraction angle of the entire limb.     

Developmental aspects of distal limb conformation in the horse: the potential consequences of uneven feet in foals

REASONS FOR PERFORMING STUDY: Distal limb conformation is generally accepted to be an important item with respect to performance and soundness in mature horses, but little is known about the developmental aspects. OBJECTIVES: To gain insight into the development of distal limb conformation and to assess the possible consequences of uneven feet in foals. METHODS: Conformation of the distal front limbs of 23 Warmblood foals was scored visually and measured using radiographs, at ages 27 and 55 weeks. At the same ages, pressure measurements were made under both front feet. RESULTS: At both ages the hoof-pastern axis was broken-backwards on radiographs, but only occasionally recognised as such, when scored by eye. Over time, the hoof angle decreased, while both the angles of the dorsal and solar surfaces of the distal phalanx (P3) increased and the parallelism between hoof wall and P3 improved. The foals with uneven feet at age 27 weeks showed a significant difference in distal limb loading that persisted until age 55 weeks. CONCLUSIONS: The alignment of the distal limb in the sagittal plane increased in a 6 month period. Visual assessment was not sensitive enough to appreciate this. The growth processes in the distal limb could not compensate for existing unevenness and ensuing asymmetrical limb loading. POTENTIAL RELEVANCE: Foals have a different conformation of the distal limb from mature horses, which should be taken into account when interpreting radiographs. Unevenness of the feet resulted in asymmetrical loading of the proximal and distal interphalangeal joint, which might lead to increased susceptibility to overload injuries and decreased performance at mature age.     

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.     

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

REASON FOR PERFORMING STUDY: There are no detailed studies describing a relationship between hindlimb lameness and altered motion of the back. OBJECTIVES: To quantify the effect of induced subtle hindlimb lameness on thoracolumbar kinematics in the horse. METHODS: Kinematics of 6 riding horses were measured during walk and trot on a treadmill before and during application of pressure on the sole of the left hindlimb using a well-established sole pressure model. Reflective markers were located at anatomical landmarks on the limbs, back, head and neck for kinematic recordings. Ground reaction forces (GRF) in individual limbs were calculated from kinematics to detect changes in loading of the limbs. RESULTS: When pressure on the sole of the hindlimb was present, horses were judged as lame (grade 2 on the AAEP scale 1-5) by an experienced clinician. No significant unloading of this limb was found in the group of horses (unloading was observed in 4 animals, but was not detectable in the other 2), but statistically significant effects on back kinematics were detected. The overall flexion-extension (FE) range of motion (ROM) of the vertebral column was increased at walk, especially in the thoracic segments. Axial rotation (AR) ROM of the pelvis was also increased. At trot, the FE ROM was decreased only in the segment L3-L5-S3. During the stance phase of the lame limb, the segment T6-T10-T13 was more flexed and the neck was lowered at both gaits; the thoracolumbar segments were more extended at walk and trot. There were no significant changes in the stride length or protraction-retraction angles in any of the limbs. CONCLUSIONS: Subtle hindlimb lameness provoked slight but detectable changes in thoracolumbar kinematics. The subtle lameness induced in this study resulted in hyperextension and increased ROM of the thoracolumbar back, but also in decreased ROM of the lumbosacral segment and rotational motion changes of the pelvis. POTENTIAL RELEVANCE: Even subtle lameness can result in changes in back kinematics, which emphasises the intricate link between limb function and thoracolumbar motion. It may be surmised that, when chronically present, subtle lameness induces back dysfunction.     

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.     

Evaluation of displacement of the digital cushion in response to vertical loading in equine forelimbs

OBJECTIVE: To evaluate patterns of digital cushion (DC) displacement that occur in response to vertical loading of the distal portion of the forelimb in horses. Sample Population-Forelimbs from 10 horses with normal feet. PROCEDURE: Patterns of DC displacement induced by in vitro vertical limb loading were determined. Load-induced displacement of the DC was defined as the magnitude and direction of displacement of 6 radio-dense, percutaneously implanted markers in specific regions of the DC. The effects of solar support and nonsupport on displacement of the DC were compared. RESULTS: Regional displacement of the DC occurred principally along distal and palmar vectors in response to vertical loading. Medial or lateral abaxial displacements were variable and appeared to be dependent on response of the limb to the applied load. Displacement of the DC was not affected by the degree of solar support. CONCLUSIONS AND CLINICAL RELEVANCE: Data indicated that the biomechanical function of the DC is to act as a restraint to the displacement of the second phalanx or as a passive structure that allows flexibility of the caudal two thirds of the foot. Results did not indicate that the DC provides a force that induces displacement of or an active restraint against outward displacement of the hoof wall capsule.     

MRI FINDINGS IN 232 HORSES WITH LAMENESS LOCALIZED TO THE METACARPO(TARSO)PHALANGEAL REGION AND WITHOUT A RADIOGRAPHIC DIAGNOSIS

Two hundred and thirty‐two horses with lameness localized to the metacarpo(tarso)phalangeal (MCP/MTP) region without a radiographic diagnosis were evaluated. All horses had high‐field magnetic resonance (MR) imaging of the MCP/MTP region performed for the lame limb and the contralateral limb for comparison. There were 46 horses that had bilateral abnormalities in the forelimbs; 27 of these horses were not lame in the contralateral limb at the time of examination. Bilateral hind limb abnormalities were observed in 37 horses; 22 horses were not lame in the contralateral limb. Soft tissue abnormalities alone were observed in 218 limbs (162 horses). Subchondral bone and articular cartilage abnormalities alone were observed in 43 limbs (34 horses). A combination of soft tissue, subchondral bone, and cartilage abnormalities were observed in 64 limbs (36 horses). The distribution of primary abnormalities was as follows; oblique distal sesamoidean ligament desmitis (73 limbs in 56 horses), straight distal sesamoidean ligament desmitis (44 limbs in 38 horses), chronic subchondral bone injuries (15 limbs in 12 horses), suspensory ligament branch desmitis (14 limbs in 12 horses), collateral ligament desmitis (12 limbs in 12 horses), tendonitis of the superficial and deep digital flexor tendons (10 limbs in 10 horses), osteochondral defects greater than 1 cm (nine limbs in six horses), osteochondral defects less than 1 cm (eight limbs in seven horses), bone marrow lesions (six limbs in five horses), intersesamoidean ligament desmitis (five limbs in four horses). MR imaging is useful in diagnosing bone and soft tissue injuries when radiographs and ultrasound fail to yield a diagnosis.     

SCINTIGRAPHIC EVALUATION OF THE DISTAL TARSAL REGION IN HORSES WITH DISTAL TARSAL PAIN

Distal tarsal pain is a common reason for hind limb lameness, but diagnosis cannot always be made on radiographic examination. Scintigraphy may allow detection of subtle changes undetected by other diagnostic methods. We hypothesized that (1) distal tarsal pain would be associated with a loss of the expected pattern of radiopharmaceutical uptake (RU) detected in normal horses, (2) distal tarsal RU would be greater in limbs with tarsal pain than without pain, (3) RU in painful tarsi with radiographic evidence of osteoarthritis (OA) would be greater than in distal tarsal pain with no radiographic evidence of OA. The study aimed to describe radiopharmaceutical distribution in the distal tarsal region of horses with distal tarsal pain, and to compare this with the contralateral limb and results from horses without tarsal pain. Retrospective evaluation of scintigraphic images of the distal tarsal region was performed for 52 horses with distal tarsal pain: 15 with no radiographic evidence of OA (Group 1) and 37 with radiographic evidence (Group 2). The images were assessed using vertical and horizontal profile analysis across the distal tarsal region and regions of interest comparisons between the distal tarsal region and tibia within each horse (RU ratio). Painful limbs in unilaterally lame horses from Groups 1 and 2 had a significantly greater RU ratio than the respective contralateral limbs, and were significantly greater than the RU ratio in normal horses. On plantar images, mean region of interest counts were greater in the lame than the contralateral limb in Group 2 but not in Group 1. Although there was a positive correlation between lame and contralateral limb RU ratio in group 1, this was lost in group 2 horses. In lame limbs, the normal vertical activity profile was lost in 85% of group 1 and all of group 2, and the normal horizontal activity profile was lost in all of group 1 and 96% of group 2. There was a significant effect of lameness, but not of group on sites of peak activity on all profiles. The results of this study indicate that distal tarsal pain is associated with loss of the expected pattern of RU detected in normal horses. The findings also suggest that distal tarsal RU in lame limbs is greater than in limbs without pain, and that painful limbs with radiographic evidence of OA have a greater RU than painful limbs without radiographic evidence of OA.     

Kinetics and kinematics of the passage

Reasons for performing study: The load acting on the limbs and the load distribution between fore‐ and hindlimbs while performing specific dressage exercises lack objective assessment. Hypothesis: The greater a horse's level of collection, the more load is shifted to the rear and that during the passage the vertical load on the limbs increases in relation to the accentuated vertical movement of the centre of mass. Methods: Back and limb kinematics, vertical ground reaction force and time parameters of each limb were measured in 6 Grand Prix dressage horses performing on an instrumented treadmill at the trot and the passage. Horses were ridden by their own professional rider. Results: At the passage, horses moved at a slower speed (?43.2%), with a lower stride frequency (?23.6%) and, therefore, higher stride impulses (+31.0%). Relative stance duration of fore‐ and hindlimbs and suspension duration remained unchanged. While at the trot the diagonal limbs impacted almost simultaneously, the hindlimbs always impacted first at the passage; the time dissociation between landing and lift‐off remained unchanged. Because of the prolonged stride duration, stride impulse and consequently limb impulses were higher at the passage in the fore‐ as well as in the hindlimbs (+24.8% and +39.9%, respectively). Within the diagonal limb pair, load was shifted from the forehand to the hindquarters (percentage stride impulse carried by the forehand ?4.8%). Despite the higher impulses, peak vertical forces in the fore‐ and hindlimbs remained unchanged because of the prolonged absolute stance durations in fore‐ and hindlimbs (+28.1% and +32.2%, respectively). Conclusions: Based on the intralimb timing, the passage closely resembles the trot. Compared to other head‐neck positions, the higher degree of collection resulted in a pronounced shift in impulse towards the hindquarters. Despite the higher limb impulses, peak forces acting on the limbs were similar to those observed at the trot. Potential clinical relevance: An understanding of load distribution between fore‐ and hindlimbs in relation to different riding techniques is crucial to prevent wear‐and‐tear on the locomotor apparatus.     

Calculated forelimb flexor tendon forces in horses with experimentally induced superficial digital flexor tendinitis and the effects of application of heel wedges

OBJECTIVE: To calculate forces in the flexor tendons and the influence of heel wedges in affected and contralateral (compensating) forelimbs of horses with experimentally induced unilateral tendinitis of the superficial digital flexor (SDF) tendon. ANIMALS: 5 Warmblood horses. Procedure-Ground reaction force and kinematic data were obtained during a previous study while horses were trotting before and after induction of tendinitis in 1 forelimb SDF and after application of 6 degrees heel wedges to both forehooves. Forces in the SDF, deep digital flexor (DDF), and the suspensory ligament (SL) and strain in the accessory ligament (AL) of the DDF were calculated, using an in vitro model of the distal region of the forelimb. RESULTS: After induction of tendinitis, trotting speed slowed, and forces decreased in most tendons. In the affected limb, SL force decreased more than SDF and DDF forces. In the compensating limb, SDF force increased, and the other forces decreased. After application of heel wedges, SDF force in both limbs increased but not significantly. Furthermore, there was a decrease in DDF force and AL strain. CONCLUSIONS AND CLINICAL RELEVANCE: The increase in SDF force in the compensating forelimb of horses with unilateral SDF tendinitis may explain the high secondary injury rate in this tendon. The lack of decrease of SDF force in either limb after application of heel wedges suggests that heel wedges are not beneficial in horses with SDF tendinitis. Instead, heel wedges may exacerbate the existing lesion.     

The effect of different head and neck positions on the caudal back and hindlimb kinematics in the elite dressage horse at trot

Reasons for performing study: Dressage involves training of the horse with the head and neck placed in a position defined by the rider. The best position for dressage training is currently under debate among riders and trainers, but there are few scientific data available to confirm or disprove the different views. Objective: To evaluate the kinematic effects of different head and neck positions (HNPs) in elite dressage horses ridden at trot. Methods: Seven high‐level dressage horses were subjected to kinetic and kinematic measurements when ridden on a treadmill with the head and neck in 5 different positions. Results: Compared to free trot on loose reins the HNP desired for collected trot at dressage competitions increased T6 vertical excursion, increased sacral flexion and decreased limb retraction after lift‐off. Further increasing head or head and neck flexion caused few additional changes while an extremely elevated neck position increased hindlimb flexion and lumbar back extension during stance, increased hindlimb flexion during swing and further increased trunk vertical excursion. Conclusions: The movements of the horse are significantly different when ridden on loose reins compared to the position used in collected trot. The exact degree of neck flexion is, however, not consistently correlated to the movements of the horse's limbs and trunk at collected trot. An extremely elevated neck position can produce some effects commonly associated with increased degree of collection, but the increased back extension observed with this position may place the horse at risk of injury if ridden in this position for a prolonged period. Potential relevance: Head and neck positions influence significantly the kinematics of the ridden horse. It is important for riders and trainers to be aware of these effects in dressage training.     

In vitro biomechanical properties of 2 compression fixation methods for midbody proximal sesamoid bone fractures in horses

OBJECTIVE: To evaluate 2 methods of midbody proximal sesamoid bone repair--fixation by a screw placed in lag fashion and circumferential wire fixation--by comparing yield load and the adjacent soft-tissue strain during monotonic loading. STUDY DESIGN: Experimental study. SAMPLE POPULATION: 10 paired equine cadaver forelimbs from race-trained horses. METHODS: A transverse midbody osteotomy of the medial proximal sesamoid bone (PSB) was created. The osteotomy was repaired with a 4.5-mm cortex bone screw placed in lag fashion or a 1.25-mm circumferential wire. The limbs were instrumented with differential variable reluctance transducers placed in the suspensory apparatus and distal sesamoidean ligaments. The limbs were tested in axial compression in a single cycle until failure. RESULTS: The cortex bone screw repairs had a mean yield load of 2,908.2 N; 1 limb did not fail when tested to 5,000 N. All circumferential wire repairs failed with a mean yield load of 3,406.3 N. There was no statistical difference in mean yield load between the 2 repair methods. The maximum strain generated in the soft tissues attached to the proximal sesamoid bones was not significantly different between repair groups. CONCLUSIONS: All repaired limbs were able to withstand loads equal to those reportedly applied to the suspensory apparatus in vivo during walking. CLINICAL RELEVANCE: Each repair technique should have adequate yield strength for repair of midbody fractures of the PSB immediately after surgery.     

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.     

Superficial digital flexor tendon lesions in racehorses as a sequela to muscle fatigue: a preliminary study

REASON FOR PERFORMING STUDY: Racing and training related lesions of the forelimb superficial digital flexor tendon are a common career ending injury to racehorses but aetiology and/or predisposing causes of the injury are not completely understood. OBJECTIVES: Although the injury takes place within the tendon, the lesion must be considered within the context of the function of the complete suspensory system of the distal limb, including the associated muscles. METHODS: Both muscle and tendon function were investigated in vivo using implanted strain gauges in 3 Thoroughbred horses walking, trotting and cantering on a motorised treadmill. These data were combined with assessments of muscle architecture and fibre composition to arrive at an overview of the contribution of each muscle-tendon unit during locomotion. RESULTS: The superficial digital flexor muscle has fatigue-resistant and high force production properties that allow its tendon to store and return elastic energy, predominantly at the trot. As running speed increases, deep digital flexor tendon force increases and it stabilises hyperextension of the fetlock, thus reinforcing the superficial digital flexor in limb load support. The deep digital flexor muscle has fast contracting properties that render it susceptible to fatigue. CONCLUSION: Based on these measurements and supporting evidence from the literature, it is proposed that overloading of the superficial digital flexor tendon results from fatigue of the synergistic, faster contracting deep digital flexor muscle. POTENTIAL RELEVANCE: Future research investigating distal limb system function as a whole should help refine clinical diagnostic procedures and exercise training approaches that will lead to more effective prevention and treatment of digital flexor tendon injuries in equine athletes.     

Body centre of mass movement in the sound horse

The body centre of mass (BCM) is a key factor in the analysis of equine locomotion, as its position and movement determines the distribution and magnitude of loads on the limbs. In this study, the three-dimensional (3D) movement of the BCM in walking and trotting horses was assessed using a kinematic, segmental method. Thirty markers representing 20 body segments were recorded in 12 sound horses while standing, walking and trotting on a treadmill using a high-speed video system. Based on segmental inertial data, 3D positions of the segmental centres of mass as well as the total BCM were calculated. The position within the trunk during square standing and the movements of the BCM were determined for the three planes.The position of the BCM in the standing horse is presented relative to external reference points. At the trot, vertical displacement amplitude of the BCM amounted to 53 (6) mm as mean (sd), which was 27% smaller than external trunk movement. Medio-lateral displacement amplitude of the BCM was 19 (4) mm, 34% less than trunk amplitude. Sagittal forward-backward oscillations of the BCM independent from general forward movement were 13 (3) mm, being 24% less than trunk movements. At the walk, vertical, medio-lateral and sagittal BCM movements were smaller than trunk movements by 43, 65 and 65% respectively.The results show reduced and efficient BCM movements compared to the trunk and form a basis for the assessment of various clinical conditions such as lameness, the influence of a rider and various dressage performances.     

Shoeing sound warmblood horses with a rolled toe optimises hoof-unrollment and lowers peak loading during breakover

REASONS FOR PERFORMING STUDY: Overload injuries in sport horses commonly occur; shoeing techniques are believed to be important in prevention of these injuries, but there is a paucity of scientific information identifying the potential connection. OBJECTIVES: To test a horseshoe with a modified rolled toe designed to ease the process of breakover and decrease loading of lesion-prone structures of the distal limb. METHODS: Twenty clinically sound Warmblood horses trotted over a track containing a pressure/force measuring system and 6 infrared cameras. The horses were measured with 2 types of shoes, standard flat shoes and shoes with a rolled toe. The shoeing procedure was randomised and horses had 2 days between measurements to adapt to the shoes. RESULTS: Limb placement and timing characteristics, e.g. breakover duration, did not change significantly. There was an improvement in the ease of movement to roll over the toe in the shoes with a rolled toe, due mainly to a smoother hoof-unrollment pattern. The peak indicative moment decreased substantially at the onset of breakover in the shoe with the rolled toe. CONCLUSIONS: With a rolled toe the process of hoof-unrollment is smoother, which improves the coordination of this process, and lowers peak loading of the distal limb during breakover. POTENTIAL RELEVANCE: This study stresses the importance of proper shoeing in sound horses, showing that shoe modifications can optimise the loading characteristics of the distal limb and therefore might be a means to prevent sport horses from overload injuries.     

A Quantitative Review of the Equinalysis System for Equine Locomotion Analysis

Movement analysis techniques allow objective and quantitative assessment of kinematic gait analysis. Consistent repeatability of the kinematic data is essential for such assessments. This study investigated whether the repeatability of a standardized Equinalysis Elite gait analysis system is sufficient to allow its use in clinical evaluation of equine lameness with reliable documentation of individual locomotion patterns. The extent to which examinations on different days affected the results when a standardized protocol was used was investigated. The repeatability of distal limb kinematics in nine sound horses over three successive days at one location was investigated. Measurements were performed at the examination area, for three motion cycles at the walk and trot, in each direction per day. Skin markers were placed on the lateral aspect of the coffin joint, forelimb fetlock joint, hindlimb fetlock joint, carpus, tarsus, elbow, and stifle, at clipped sites marked with a permanent marker. The inter-day repeatability of angular measurements of the carpus, tarsus, forelimb fetlock, and hindlimb fetlock joints was determined. A low degree of inter-day repeatability was found with statistically significant (P ≤ .05) differences between findings on different days, observed in the time-angle diagrams of left and right carpus, tarsus, forelimb fetlock, and hindlimb fetlock joints of all horses, at both walk and trot. The standardized Equinalysis Elite system for gait analysis of distal limb kinematics in the horse did not provide highly repeatable data in this setting.