Lameness is one of the most important medical issues of horses1 and accounts for annual losses up to $1 billion for the US equine industry.2 Horses with subclinical or mild lameness often have suboptimal performance.3,4 Early detection of mild lameness is important for horses, particularly competition horses, in which suboptimal performance can be career limiting, so that appropriate measures can be taken to alleviate the lameness and improve the performance and quality of life of affected horses.
Lameness in horses is generally detected and monitored by means of a subjective lameness examination.5 The most commonly used lameness scoring systems have grades, or scores, that are defined by specific criteria; however, there can be substantial variability within a grade such that use of that system can be challenging for longitudinal monitoring of lameness in an individual horse, especially when the severity of lameness changes only minimally between examinations.6 Results of multiple studies6–9 suggest that subjective lameness scoring systems are not reliable for clinical use, particularly for horses with mild lameness. Additionally, in 1 study,6 observer bias was detected in the subjective lameness scores assigned to horses following administration of perineural anesthesia. Therefore, an accurate, objective method is needed to supplement the subjective lameness examination for the detection and monitoring of horses with mild lameness as well as to assess the response of those horses to perineural anesthesia.
Several studies5,10–15 have been conducted to investigate the efficacy of kinetics and kinematics for the evaluation of horses with mild lameness. In a study10 in which stationary force platform analysis was used as a kinetic method to detect horses with lameness, peak vertical force and impulse parameters were significantly decreased in horses with mild lameness (ie, grade, < 1.5/5), compared with those for nonlame horses. Unfortunately, the use of stationary force platform analysis for evaluation of lameness in horses is limited because of the lack of availability of equipment and experienced personnel to run the equipment, the increased time required for data collection and analysis, and expense, compared with the time and expense for a subjective lameness examination. In horses, optical methods can be used to detect alterations in distal limb kinematics such as stride length, step length, hoof height, and sagittal-plane joint angles after induction of lameness.11–13 Although alterations in those variables have been detected at both a walk and a trot, the alterations are more pronounced at a trot.11 Because optical kinematics suffer from many of the limitations of stationary force platform analyses, other kinematic analysis systems are currently being investigated to objectively characterize lameness in horses. These kinematic analysis systems use multiple microelectromechanical components, such as accelerometers, gyroscopes, and GPS tracking devices, which have wireless or telemetric components for data transmission.14–16 Results of a study5 indicate that the use of an inertial sensor system that monitors movement of the horse's head or pelvis during a trot detected unilateral forelimb or hind limb lameness earlier (ie, when lameness was less severe) than did 3 experienced equine veterinarians who used a subjective lameness scoring system. However, the use of an inertial sensor system to detect lameness in horses at a walk or for longitudinal assessment of lameness in an individual horse has not been evaluated.17 Because inertial sensors are becoming increasingly small and lightweight, it should be possible to attach them to the distal aspect of a limb of a horse without causing substantial alteration to the movement of that limb. In fact, the rigid attachment of an inertial sensor to the hoof is ideal because motion artifact is eliminated. In horses, the kinematics of the limbs change when 1 limb becomes lame11–13; therefore, measurement of hoof kinematics might be another method to diagnose and monitor lameness. Although hoof displacement or position has been investigated in lame horses,11–13 to our knowledge, no studies have been conducted to evaluate other linear and angular changes in the forelimb hooves of horses following induction of unilateral lameness. Optical methods remain the gold standard for collection of kinematic data, and intra- and interlimb comparisons of kinematic changes might be useful for the identification of horses with mild lameness. Linear and angular limb movement can also be measured by means of an IMU, which could be used in a horse-mounted method to evaluate lameness.
The objective of the study reported here was to use optical methods to characterize kinematic variables of the hoof for horses at a trot before and after induction of unilateral, weight-bearing forelimb lameness and following administration of perineural anesthesia to alleviate that lameness. Following lameness induction, we hypothesized that sagittal-plane kinematic variables for the lame limb would differ significantly from those of that limb prior to lameness induction (baseline) and those of the contralateral nonlame limb, and these differences would be detectable even at the mildest grade of lameness induced. We also hypothesized that following perineural anesthesia of the medial and lateral palmar nerves of the lame limb, the sagittal-plane kinematics of that limb would not differ from those at baseline.
Inertial measurement unit
Equi-Thane SuperFast, Vettec Inc, Oxnard, Calif.
H3-IMU, MemSense LLC, Rapid City, SD.
Vetrap, 3M Co, Saint Paul, Minn.
Volant, Peak Performance Technologies Inc, Centennial, Colo.
Vicon-Motus, version 9.2, Vicon Motion Systems Inc, Centennial, Colo.
MEK 92-PAD photoelectric control, Mekontrol Inc, Northboro, Mass.
STATA, version 11, Stata Corp LP, College Station, Tex.
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