A horse's locomotor signature: COP path determined by the individual limb

Evaluation of the hoof centre-of-pressure path in horses affected by chronic osteoarthritic pain

INTRODUCTION

The Centre of Pressure (COP) is the single point summarising all forces transferred to the hoof during the stance phase of a stride. COP path (COPp) is the trajectory that COP follows from footstrike to lift-off. Aim of the present study was to characterize the COP and COPp in horses affected by osteoarthritis and chronic lameness.

MATERIALS AND METHODS

Seventeen adult horses with a diagnosis of osteoarthritis and single limb chronic lameness were recruited. The COP was recorded using a wireless pressure measuring system (TekScan®) with sensors taped to the hooves (either fore- or hind limb, depending on lameness location). The COPp coordinates were further processed. Procrustes analysis was performed to assess the variability of single strides COPp and average COPp among strides, gaits, and limbs by calculating Procrustes distances (D-values). A linear mixed-effects model was run to analyse D-values differences for lame and sound limbs. Additionally, average COPp D-values and COPp hoofprint shape indices were compared for lame and sound limbs with the Signed Rank Test.

RESULTS

At walk and trot the single-stride COPp D-values were significantly lower in lame than in sound limbs (marginal effects p<0.001). Analysis of the average COPp D-values confirmed that each hoof COPp is highly consistent with itself over subsequent trials but is different from the contralateral. COPp and hoofprint shape indices did not differ between sound and lame limbs. Footstrike and lift-off within the hoofprint showed that most horses had lateral footstrike and lift-off, independently of the lameness location.

CONCLUSION

Our findings are in line with previous observations that COPp are highly repetitive and characteristic for each horse and limb. There seems to be a further decrease in COPp variability in the presence of a painful limb pathology.

Characteristics of Hoof Landing in Sound Horses and the Influence of Trimming and Shoeing Examined With Hoof-Mounted Inertial Sensors

The aim of the current in vivo, observational study was to investigate the effects of different hoof manipulations on landing duration (LandD), location (ICloc) and angle of initial contact (ICangle) in the front feet of horses. A novel, hoof-mounted, inertial measurement unit sensor system (IMU) was used. Ten sound, crossbred horses were fitted with an IMU sensor at the dorsal hoof wall and examined barefoot and after trimming. Additionally, the application of 120 g lateral weights and 5° medial side wedges as well as steel, aluminium, egg bar, and lateral extension shoes were tested. Horses were guided in a straight line on firm ground. The use of steel shoes increased LandD compared to barefoot and enhanced the individual ICloc in trot. Application of rolled toe shoes caused a longer LandD than use of plain shoes. None of the other modifications significantly influenced the timing or spatial variables of hoof landing. Trimming and shoeing have less impact on the landing pattern of horses than assumed in practice. Still, the use of steel shoes changes sliding properties of the hooves on firm ground and increases weight causing a longer LandD and reinforcement of the individual ICloc.

The influence of equine hoof conformation on the initiation and progression of laminitis

BACKGROUND

The health and performance of horses are significantly affected by diseases associated with the hoof. Laminitis is a critical hoof disease that causes pain and, potentially, severe hoof and bone pathology.

OBJECTIVE

To generate an equine hoof finite element (FE) model to investigate the impact of normal and toe-in hoof conformations on the degeneration (decrease in elastic modulus) of the laminar junction (LJ), as occurs in chronic laminitis.

STUDY DESIGN

Computer software modelling.

METHODS

A hoof FE model was generated to investigate the biomechanics of hoof laminitis. A 3D model, consisting of nine components, was constructed from computed tomography scans of an equine left forelimb hoof. The model was loaded with 100 cycles of trotting. Two different centres of pressure (COP) paths representing normal and toe-in conformations were assigned to the model. LJ injury was modelled by degenerating the tissue's elastic modulus in the presence of excessive maximum principal stresses.

RESULTS

FE models successfully showed findings similar to clinical observations, confirming third phalanx (P3) dorsal rotation, a symmetric distal displacement of the P3 (2 mm at the lateral and medial sides) in the normal model, and an asymmetric distal displacement of the P3 (4 mm at the lateral and 1.5 mm at the medial side) in the toe-in model. The proximal distance between P3 and the ground after LJ degeneration in the current model was significantly different from experimental measurements from healthy hooves (P < 0.01).

MAIN LIMITATIONS

The inability to account for variations in population geometry and approximation of boundary conditions and system relations were the limitations of the current study.

CONCLUSIONS

The distribution of LJ tissue degeneration was symmetric at the quarters in the normal hoof and in comparison, there was a lateral concentration of degeneration in the toe-in model.

Gait Analysis in Walking and Trotting Dairy Cows on Different Flooring Types with Novel Mobile Pressure Sensors and Inertial Sensors

Mechanical overburdening is a major risk factor that provokes non-infectious claw diseases. Moreover, lameness-causing lesions often remain undetected and untreated. Therefore, prevention of claw tissue overburdening is of interest, especially by analyzing harmful effects within dairy cows’ housing environment. However, objective “on-cow” methods for bovine gait analysis are underdeveloped. The purpose of the study was to apply an innovative mobile pressure sensor system attached at the claws to perform pedobarometric gait analysis. A further goal was the supplementation with accelerative data, generated simultaneously by use of two inertial measurement units (IMUs), attached at metatarsal level. IMU data were analyzed with an automatic step detection algorithm. Gait analysis was performed in ten dairy cows, walking and trotting on concrete flooring and rubber mats. In addition to the basic applicability of the sensor systems and with the aid of the automatic step detection algorithm for gait analysis in cows, we were able to determine the impact of the gait and flooring type on kinematic and kinetic parameters. For pressure sensor output, concrete was associated with significantly (p < 0.001) higher maximum and average pressure values and a significantly smaller contact area, compared to rubber mats. In contrast to walking, trotting led to a significantly higher force, especially under the medial claw. Further, IMU-derived parameters were significantly influenced by the gait. The described sensor systems are useful tools for detailed gait analysis in dairy cows. They allow the investigation of factors which may affect claw health negatively.

Preliminary Study on the Connection Between the Mineral Profile of Horse Hooves and Tensile Strength Based on Body Weight, Sex, Age, Sampling Location, and Riding Disciplines

Hoof mineral profile is important as it could affect locomotion. Factors such as body weight, sex, age, and riding disciplines affect hoof mineral profile. In Mexico and globally, studies are needed on the characterization of mineral profile of hooves and tensile strength, as this could help to prevent overgrowth or microfractures. Therefore, in the present survey, 165 samples of equine hoof cuttings from different sex, ages, breeds, and riding disciplines from different regions of Mexico were analyzed for their mineral composition, and a universal testing machine was used to measure tensile strength. More than half of the samples were from males (63%) and aged 3 to 5 years (52%). Most samples were obtained from horses used for reproduction (36%) and working (29%) purposes. The most preponderant minerals were K (3,416 μg/g), Na (2,242 μg/g), and Ca (631 μg/g). Tensile strength ranged from 1.2 to 45 N. Females had higher (P < 0.05) amounts of Zn than males. Animals younger than 3 years old have lower (P < 0.05) levels of Na than those between 3 and 5 years old. Horses used for reproduction had lower (P < 0.05) Mg concentrations than animals used for running and working. Tensile strength was similar between demographic characteristics. Horses from Santa Gertrudis military ranch had higher (P < 0.05) levels of Ca, Se, and Na compared with horses from other sampling location. Copper was higher (P < 0.05) in horses from racecourse. Potassium was higher (P < 0.05) in horses from the Presidential General Staff. Overall, there was no evident connection between sex, ages, breeds, and riding disciplines from different regions of Mexico and the mineral composition of the hoof or its tensile strength. Further research should focus on the relation on specific feeding regimes, horse individual characteristic, hoof mineral contents, and tensile strength.

The influence of equine limb conformation on the biomechanical responses of the hoof: An in vivo and finite element study

Hoof conformation plays a key role in equine locomotion. Toe-in conformation is an abnormal condition characterized by inward deviation of the limb from its frontal axis. Several studies have documented differences in hoof deformation and hoof kinematics in horses with toe-in and normal hoof conformations. However, the reason behind this has yet to be understood. The present study hypothesizes that a different center of pressure (COP) path underneath the hoof is the cause of different deformation patterns and hoof kinematics in toe-in hooves. In vivo measurements and finite element (FE) analysis were conducted to test the hypothesis. A normal and a toe-in limb were considered for in vivo strain measurements. Strains were measured at three different sites on the hoof wall, and the stride characteristics were investigated using video recording. The magnitude of the minimum principal strain measured at the medial aspect of the toe-in hoof was much lower relative to the normal hoof. Furthermore, the toe-in hoof had a different movement pattern (plaiting) compared to the normal hoof. In the second study, an entire hoof model was simulated from computed tomography (CT) scans of an equine left forelimb. The Neo-Hookean hyperelastic material model was used, and the hoof was under dynamic loading over a complete stride at the trot. Two different COP paths associated with normal and toe-in conformations were assigned to the model. The FE model produced the same in vivo minimum principal strain distributions and successfully showed the different kinematics of the toe-in and normal hooves.

Linear elastic and hyperelastic studies of equine hoof mechanical response at different hydration levels

Most simulation studies on equine hoof biomechanics employed linear elastic (LE) material models. However, the equine hoof wall's stress-strain relationship is nonlinear and varies with hydration level. Therefore, it is essential to investigate the accuracy of the LE model compared to more advanced material models, such as hyperelastic (HE) or viscoelastic models. The current research investigated performances of LE and three HE models (Mooney-Rivlin, Neo-Hookean, and Marlow) in describing equine hoof's mechanical behavior using finite element (FE) analysis. In the first attempt, a rectangular tissue specimen was simulated using the previously published experimental data. The Marlow HE model predicted the hoof wall stress-strain curve more accurately than the LE, Mooney-Rivlin, and Neo-Hookean models. The LE model accuracy, compared with the experimental results, varied within the reported range of the strain. However, the Marlow HE model perfectly matched the experimental data for a wide range of strains. In the second attempt, the entire hoof, including nine associated tissues, was modeled from computed tomography (CT) scans of an equine forelimb, and analyzed at trotting and standing modes of locomotion. The effect of environmental humidity on the hoof wall material properties was incorporated at four hydration levels; 0%, 53%, 75%, and 100%. The simulation results of the LE and HE models indicated that the minimum principal strain distribution on the hoof wall remained under 2% for various hydration levels and gait conditions. The numerical results of the Marlow HE model demonstrated better agreement with published experimental data compared to the LE, Mooney-Rivlin, and Neo-Hookean models. Higher hydration levels significantly increased the strains - a potential explanation could be the fact that the higher hydration levels decreased stiffness of the hoof wall tissues and ultimately increased strains. Higher ground reaction forces increased the von Mises stress at various points in the hoof wall, especially in the quarter regions and close to the coronet, where cracks and fractures are found more often in the physiological conditions.

Detection of Equine Hoof Motion by Using a Hoof-Mounted Inertial Measurement Unit Sensor in Comparison to Examinations with an Optoelectronic Technique - A Pilot Study

This study aimed to determine whether a hoof-mounted inertial measurement unit (IMU) system would provide similar timing characteristics and step lengths, in walk and trot on different grounds, compared to those of an established optoelectronic motion system. The right hoof of one horse was equipped with an IMU sensor with an optical reference marker on top. Fifteen steps on firm ground, and five on penetrable ground, were performed at walk and trot. Level of agreement between the two measurement systems was determined by assessing the concordance correlation coefficients, accuracy, and precision of the duration of different gait events and step length. Timing characteristics and step length were in strong agreement between the two techniques for the majority of assessed parameters in walk and trot on both grounds. The agreement between techniques decreased for breakover and landing duration at trot on penetrable ground. Disparity between the measurement techniques was related to difficulties in accurately defining single parts of the stance phase with marker-based optoelectronic analysis on penetrable ground. Detailed examinations of different parts of the stance phase are more accurately performed using hoof-mounted IMU sensors. Results emphasise the great potential of IMU sensors for equine motion analysis in daily practice.

Effect of Perineural Anesthesia on the Centre of Pressure (COP) Path During Stance Phase at Trot in Sound Horses

This study aimed to examine how short-term loss of proprioception in the equine foot influences the individual COP path during the stance phase of the trot in sound horses. Ten horses were evaluated to be objectively non-lame using the 'Equinosis Q System and subsequently examined using a portable pressure measuring system with pressure foils fixed directly underneath both front hooves prior to and after perineural anesthesia of the palmar digital nerves. The individual COP paths of both forelimbs was assessed prior to and after unilateral and bilateral abaxial sesamoid nerve blocks. COP from initial contact to mid stance and breakover as well as the inter-stride variability were descriptively evaluated for each horse and limb. The individual COP path for each horse and limb during stance was shown to be highly repeatable without significant inter-stride variability. Location of initial contact, COP during midstance and breakover are not affected by unilateral or bilateral short-term loss of sensory feedback from the foot after perineural anesthesia. Anesthesia of the foot with an abaxial sesamoid nerve block does not affect the foot's COP during stance at a trot, therefore, sudden changes in gait pattern after perineural anesthesia should be interpreted with caution and warrant further clinical investigation.

Development of a Novel Gait Analysis Tool Measuring Center of Pressure for Evaluation of Canine Chronic Thoracolumbar Spinal Cord Injury

Gait evaluation after spinal cord injury (SCI) is an important component of determining functional status. Analysis of center of pressure (COP) provides a dynamic reflection of global locomotion and postural control and has been used to quantify various gait abnormalities. We hypothesized that COP variability would be greater for SCI versus normal dogs and that COP would be able to differentiate varying injury severity. Our objective was to investigate COP, COP variability, and body weight support percentage in dogs with chronic SCI. Eleven chronically non-ambulatory dogs after acute severe thoracolumbar SCI were enrolled. COP measurements in x (right-to-left, COPx) and y (craniocaudal, COPy) directions were captured while dogs walked on a pressure-sensitive treadmill with pelvic limb sling support. Root mean square values (RMS_COPx and RMS_COPy) were calculated to assess variability in COP. Body weight support percentage was measured using a load cell. Gait also was quantified using an open field scale (OFS) and treadmill-based stepping and coordination scores (SS, RI). Mean COPx, COPy, RMS_COPx, and RMS_COPy were compared between dogs with SCI and previously evaluated healthy controls. RMS measurements and support percentage were compared with standard gait scales (OFS, SS, RI). Mean COPy was more cranial and RMS_COPx and RMS_COPy were greater in SCI versus normal dogs (p < 0.001). Support percentage moderately correlated with SS (p = 0.019; R² = 0.47). COP analysis and body weight support measurements offer information about post-injury locomotion. Further development is needed before consideration as an outcome measure to complement validated gait analysis methods in dogs with SCI.

Center of pressure limb path differences for the detection of lameness in dogs: a preliminary study

Background

The limb center of pressure (COP) path measures and quantifies the load distribution within a limb in a still or moving subject. Under this premise, the aim of this study was to test whether data derived from this parameter could detect the differences between sound and lame limbs in unilaterally lame dogs with elbow dysplasia.

To accomplish this purpose, ten unilaterally lame dogs of similar conformation were walked over a pressure platform. Next, the COP path, in relation to the position of sound and lame limbs, was measured in a coordinate system over a standard paw template obtained by pedobarography during the whole support phase. To compare variables, force platform data (peak vertical force and vertical impulse) from the same animals were obtained. Sound and lame limb statokinesiograms were also obtained while the animals stood still.

Results

The statistical analysis clearly showed that COP in lame limbs start cranially and were shorter than sound limbs. In addition, the value of the COP excursion index was lower in lame limbs. Finally, the area of statokinesiograms was greater in lame limbs.

Conclusion

This methodology based in limb COP characteristics serves to discriminate between sound and lame limbs in dogs with elbow dysplasia.

Electronic supplementary material

The online version of this article (10.1186/s12917-019-1881-1) contains supplementary material, which is available to authorized users.

Ground Reaction Forces: The Sine Qua Non of Legged Locomotion

Legged locomotion results from the feet pressing against the ground to generate ground reaction forces (GRFs) that are responsible for moving the body. By changing limb coordination patterns and muscle forces, the GRFs are adjusted to allow the horse to move in different gaits, speeds, and directions with appropriate balance and self-carriage. This article describes the typical GRF patterns in each gait, the adaptations that produce turning, and the GRF patterns used to unload the painful limb when the horse is lame. The intent is to provide information that is of practical interest and value to equine scientists rather than being a comprehensive review of the topic.

Changes in hoof kinetics and kinematics at walk in response to hoof trimming: pressure plate assessment

Appropriate hoof preparation and symmetry are linked to the well-being of the horse. Previous studies have shown the efficacy of pressure plates (PPs) in delivering objective biomechanical analysis. We aimed to assess the effect of hoof trimming on hoof biomechanics using a PP. Nine clinically sound Arabian horses were walked across a PP while foot strike was recorded by a digital camera. Kinetic and kinematic parameters were recorded before and after trimming. Changes were considered significant when p < 0.05. Vertical force (p = 0.026) and contact pressure (p = 0.006) increased after trimming. Stance-phase duration (p = 0.006), swing-phase duration (p = 0.023), and gait-cycle duration (p = 0.007) decreased significantly post-trimming. The observed changes in kinetic and kinematic parameters were related to hoof trimming. The reported results underline the importance of farriery practice and its effect on hoof biomechanics, which should be considered by both farriers and veterinarians.

Sagittal plane fore hoof unevenness is associated with fore and hindlimb asymmetrical force vectors in the sagittal and frontal planes

Asymmetry in forelimb dorsal hoof wall angles, termed unevenness, is associated with forelimb gait asymmetries, but compensatory mechanisms and out of plane ground reaction forces (GRFs) due to unevenness have yet to be documented. The aim of this study was therefore to investigate the effects of fore hoof unevenness on contralateral fore and hind limb force vectors patterns, in both sagittal and frontal planes. A group of n = 34 riding horses were classified into four groups: hoof angle difference of more than 1.5 degrees (UNEVEN; n = 27), including higher left fore (HIGH-LF; n = 12), higher right fore (HIGH-RF; n = 15), and hoof angle difference of less than 1.5 degrees (EVEN; n = 7). Three dimensional ground reaction forces GRFs were collected during trotting. GRF summary vectors representing the magnitude (VecMag) and angular direction (VecAng) of the entire stance phase in the sagittal and the frontal plane were calculated. The effects of unevenness on GRF production were explored using linear regression, repeated measures ANOVA and statistical parametric mapping (SPM) with significance at (P<0.05). In all uneven groups, increasing unevenness affected sagittal VecAng values in the forelimbs, with more propulsive GRF in the high hoof. In the HIGH-RF group, medial GRFs were also found in the high RF hoof compared to lateral GRFs in the low LF hoof (RF VecAng: 0.97±1.64 (deg); LF VecAng: -0.64±1.19 (deg); P<0.05). In both HIGH groups, compensatory associations to increasing unevenness were only found in the RH, but also a significantly greater lateral VecAng was found in the LH (P<0.05) compared to the RH limb. No significant differences (P>0.05) were found between hindlimb pairs in the EVEN group. Unbalanced sagittal and increased frontal plane GRFs in uneven horses suggest that they have greater locomotory challenges, as the equine musculoskeletal system is not constructed to withstand movement and loading in the frontal plane as effectively as it is in the sagittal plane.

The development of hoof balance and landing preference in the post-natal period

Background

Foals can follow the herd within hours of birth, but it has been shown that kinetic gait parameters and static balance still have to mature. However, development of dynamic balance has not been investigated.

Objectives

To objectively quantify landing and pressure pattern dynamics under the hoof during the first half year of life.

Study design

Prospective, cohort study performed at a single stud farm.

Methods

Pressure plate measurements at walk and trot from ten Dutch warmblood foals during the first 24 weeks of life were used to quantify toe‐heel and medial‐lateral hoof balance asymmetry indexes and to determine preferred landing strategy. Concurrently, radiographs of the tarsocrural and femoropatellar joints were taken at 4–6 weeks and after 6 months to check for osteochondrosis. A linear mixed model was used to determine the effects of time point, limb pair (front/hind), side (left/right) and osteochondrosis status of every foal.

Results

At 25% of stance duration at walk, front limbs were more loaded in the heel region in weeks 6–20 (P≤0.04), the medial‐lateral balance was more to the lateral side from week 6 onwards at both walk and trot (P≤0.04). Landing preference gradually changed in the same directions. Variability in pressure distribution decreased over time. (Subclinical) osteochondrosis did not influence any of the measured parameters.

Main limitations

This study is limited by the relatively small sample size only containing one breed from a single stud farm.

Conclusions

Dynamic hoof balance in new‐born foals is more variable and less oriented towards the lateral side of the hoof and to the heel than in mature horses. This pattern changes gradually during the first weeks of life. Knowledge of this process is essential for the clinician when considering interventions in this area in early life.

A simple method of equine limb force vector analysis and its potential applications

BACKGROUND

Ground reaction forces (GRF) measured during equine gait analysis are typically evaluated by analyzing discrete values obtained from continuous force-time data for the vertical, longitudinal and transverse GRF components. This paper describes a simple, temporo-spatial method of displaying and analyzing sagittal plane GRF vectors. In addition, the application of statistical parametric mapping (SPM) is introduced to analyse differences between contra-lateral fore and hindlimb force-time curves throughout the stance phase. The overall aim of the study was to demonstrate alternative methods of evaluating functional (a)symmetry within horses.

METHODS

GRF and kinematic data were collected from 10 horses trotting over a series of four force plates (120 Hz). The kinematic data were used to determine clean hoof contacts. The stance phase of each hoof was determined using a 50 N threshold. Vertical and longitudinal GRF for each stance phase were plotted both as force-time curves and as force vector diagrams in which vectors originating at the centre of pressure on the force plate were drawn at intervals of 8.3 ms for the duration of stance. Visual evaluation was facilitated by overlay of the vector diagrams for different limbs. Summary vectors representing the magnitude (VecMag) and direction (VecAng) of the mean force over the entire stance phase were superimposed on the force vector diagram. Typical measurements extracted from the force-time curves (peak forces, impulses) were compared with VecMag and VecAng using partial correlation (controlling for speed). Paired samples t-tests (left v. right diagonal pair comparison and high v. low vertical force diagonal pair comparison) were performed on discrete and vector variables using traditional methods and Hotelling's T2 tests on normalized stance phase data using SPM.

RESULTS

Evidence from traditional statistical tests suggested that VecMag is more influenced by the vertical force and impulse, whereas VecAng is more influenced by the longitudinal force and impulse. When used to evaluate mean data from the group of ten sound horses, SPM did not identify differences between the left and right contralateral limb pairs or between limb pairs classified according to directional asymmetry. When evaluating a single horse, three periods were identified during which differences in the forces between the left and right forelimbs exceeded the critical threshold (p < .01).

DISCUSSION

Traditional statistical analysis of 2D GRF peak values, summary vector variables and visual evaluation of force vector diagrams gave harmonious results and both methods identified the same inter-limb asymmetries. As alpha was more tightly controlled using SPM, significance was only found in the individual horse although T2 plots followed the same trends as discrete analysis for the group.

CONCLUSIONS

The techniques of force vector analysis and SPM hold promise for investigations of sidedness and asymmetry in horses.