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Effect of forelimb lameness on hoof kinematics of horses at a walk

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  • 1 Gail Holmes Equine Orthopaedic Research Center, Departments of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523.
  • | 2 Health and Exercise Science, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523.
  • | 3 Department of Mechanical Engineering, College of Engineering, University of Maine, Orono, ME 04469.
  • | 4 Gail Holmes Equine Orthopaedic Research Center, Departments of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523.
  • | 5 Gail Holmes Equine Orthopaedic Research Center, Departments of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523.

Abstract

Objective—To determine kinematic changes to the hoof of horses at a walk after induction of unilateral, weight-bearing forelimb lameness and to determine whether hoof kinematics return to prelameness (baseline) values after perineural anesthesia.

Animals—6 clinically normal Quarter Horses.

Procedures—For each horse, a sole-pressure model was used to induce 3 grades of lameness in the right forelimb, after which perineural anesthesia was administered to eliminate lameness. Optical kinematics were obtained for both forelimbs with the horse walking before (baseline) and after induction of each grade of lameness and after perineural anesthesia. Linear acceleration profiles were used to identify hoof events, and each stride was divided into hoof-contact, break-over, initial-swing, terminal-swing, and total-swing segments. Kinematic variables were compared within and between limbs for each segment by use of mixed repeated-measures ANOVA.

Results—During the hoof-contact and terminal-swing segments, the hoof of the left (nonlame) forelimb had greater sagittal-plane orientation than did the hoof of the right (lame) forelimb. For the lame limb following lameness induction, the break-over duration and maximum cranial acceleration were increased from baseline. After perineural anesthesia, break-over duration for the lame limb returned to a value similar to that at baseline, and orientation of the hoof during the terminal-swing segment did not differ between the lame and nonlame limbs.

Conclusions and Clinical Relevance—Subclinical unilateral forelimb lameness resulted in significant alterations to hoof kinematics in horses that are walking, and the use of hoof kinematics may be beneficial for the detection of subclinical lameness in horses.

Abstract

Objective—To determine kinematic changes to the hoof of horses at a walk after induction of unilateral, weight-bearing forelimb lameness and to determine whether hoof kinematics return to prelameness (baseline) values after perineural anesthesia.

Animals—6 clinically normal Quarter Horses.

Procedures—For each horse, a sole-pressure model was used to induce 3 grades of lameness in the right forelimb, after which perineural anesthesia was administered to eliminate lameness. Optical kinematics were obtained for both forelimbs with the horse walking before (baseline) and after induction of each grade of lameness and after perineural anesthesia. Linear acceleration profiles were used to identify hoof events, and each stride was divided into hoof-contact, break-over, initial-swing, terminal-swing, and total-swing segments. Kinematic variables were compared within and between limbs for each segment by use of mixed repeated-measures ANOVA.

Results—During the hoof-contact and terminal-swing segments, the hoof of the left (nonlame) forelimb had greater sagittal-plane orientation than did the hoof of the right (lame) forelimb. For the lame limb following lameness induction, the break-over duration and maximum cranial acceleration were increased from baseline. After perineural anesthesia, break-over duration for the lame limb returned to a value similar to that at baseline, and orientation of the hoof during the terminal-swing segment did not differ between the lame and nonlame limbs.

Conclusions and Clinical Relevance—Subclinical unilateral forelimb lameness resulted in significant alterations to hoof kinematics in horses that are walking, and the use of hoof kinematics may be beneficial for the detection of subclinical lameness in horses.

Lameness is an important and prevalent medical condition in horses1 and accounts for up to $1 billion in losses for the US equine industry annually.2 Horses with subclinical or mild lameness have suboptimal performance,3,4 and mild lameness is often a precursor to severe or catastrophic musculoskeletal injury. Therefore, detection of horses with subclinical or mild lameness is important so that measures can be taken to correct or alleviate the lameness and thereby improve the welfare of affected horses. Additionally, sensitive methods are needed for assessment of lame horses following treatment to determine when an individual horse can safely return to prelameness activity or exercise without risking reinjury.

In horses, lameness is typically detected and monitored by means of a subjective lameness examination, in which horses are visually assessed at both a walk and a trot before a lameness grade, or score, is assigned.5 Unfortunately, results of multiple studies6–9 suggest that the use of subjective lameness scoring systems is not clinically reliable for identification of lame horses, especially when the lameness is mild. Furthermore, in 1 study,6 investigators identified inherent bias in subjective lameness scores following administration of perineural anesthesia. Thus, adjunct methods that are more sensitive and objective than the subjective lameness examination are necessary for detection and monitoring of horses with mild lameness and assessment of lame horses after administration of perineural anesthesia. Because horses with mild or moderate lameness are frequently not perceptibly lame at a walk,5 they are often not extensively examined at that gait during a subjective lameness examination. However, effective evaluation of lameness in horses at a walk would be beneficial, particularly for those in which observation at a gait faster than a walk might be detrimental.

Multiple studies10–14 have been conducted to evaluate the efficacy of objective methods, such as kinetics and kinematics, for the detection of lameness in horses at both a walk and a trot. Results of studies10–12 suggest that the use of stationary force platform kinetic and optical kinematic systems is just as sensitive as or more sensitive than subjective lameness examination performed by experienced equine veterinarians for diagnosing mild lameness in horses that are trotting. Few studies have been conducted to evaluate the efficacy of kinetic or kinematic methods for detecting subclinical or mild lameness in horses at a walk. In 1 study,13 horses in which mild lameness at a trot but no detectable lameness at a walk was induced had significant changes in hoof kinetics, compared with hoof kinetics obtained prior to lameness induction. Investigators of another study14 reported that optical kinematic values of the hoof were altered from prelameness values for horses in which mild to moderate lameness at a walk was induced. In clinically normal horses with unilateral, weight-bearing forelimb lameness, alterations in hoof kinematics occur in both the lame and nonlame limbs at a trot12; therefore, alterations in hoof kinematics may also occur at a walk, and characterization of those changes might be beneficial for the diagnosis of lameness in horses.

The objectives of the study reported here were to determine kinematic changes to the hoof of horses at a walk after induction of unilateral, weight-bearing forelimb lameness that was perceptible only at a trot and to determine whether hoof kinematics return to prelameness (baseline) values after perineural anesthesia. We hypothesized that after lameness induction, kinematic variables would vary from baseline values and between the lame and nonlame forelimbs for various segments of the stride when horses were walking, and that kinematic variables would return to values similar to those at baseline after perineural anesthesia. Our goal was to identify specific kinematic variables that were substantially altered at a walk by lameness during predefined segments of the stride.

Materials and Methods

Animals—Six Quarter Horses were used for the study reported here as well as a companion study,12 and data for the 2 studies were obtained concurrently. Each horse was determined to be clinically normal and was not perceptibly lame at a walk or a trot. The horses ranged in age from 2 to 9 years and had a mean ± SD weight and wither height of 364 ± 19 kg and 1.46 ± 0.03 m, respectively. Prior to study initiation, horses were acclimated to the laboratory where the gait analysis data were collected. The hooves of each horse were trimmed and balanced, and the hooves of the forelimbs were shod as described.12 Each horse was instrumented with retroreflective markers and an inertial measurement unita for collection of kinematic data as described.12 All study procedures were approved by the Colorado State University Institutional Animal Care and Use Committee.

Study design—For each horse, kinematic data for both forelimbs were obtained before (baseline) and after induction of each of 3 grades (grades 1, 2, and 3) of lameness in the right forelimb as well as after administration of perineural anesthesia to the right forelimb to alleviate the lameness. A 5-point lameness scale, modified from the one developed by the American Association of Equine practitioners,5 was used to define the grades of lameness induced. Grade of lameness was subjectively assessed at a trot. Briefly, grade 1 was defined as intermittent mild lameness, grade 2 was defined as consistent mild lameness, and grade 3 was defined as consistent, moderate lameness; none of the grades resulted in perceptible lameness at a walk. Between data collection periods, horses were allowed to rest for several minutes to minimize the effect of fatigue.

Induction of lameness and perineural anesthesia—For each horse, 3 grades of lameness were induced in the right forelimb in a sequential manner by means of a sole-pressure model as described.12 Briefly, a 6-mm-diameter screw with either a blunt or tapered end was threaded into both the medial and lateral nuts welded to the steel shoe on the hoof of the right forelimb such that the head of the screw was in contact with the ground when the horse was bearing weight on that limb. The horse was trotted briefly to subjectively determine the severity of lameness, and the process was repeated with longer or shorter screws as necessary until the desired severity of lameness was achieved. The screw length (range, 11 to 17 mm) required to induce each grade of lameness was recorded. After induction of each grade of lameness, lameness trials were performed for data collection purposes. Following data collection for grade 3 lameness, perineural anesthesia was administered with a 2% mepivacaine solution to the regions surrounding the medial and lateral palmar nerves of the right forelimb of each horse as described.12

Lameness trial facilities and protocol—All lameness trials were performed in a gait analysis laboratory as described.12 Briefly, each horse was walked or trotted on an asphalt runway (length, 24.8 m; width, 1.2 m) that was covered with a 9.3-mm-thick rubberized mat. The optical capture volume (ie, portion of the runway where kinematic data for the horse were obtained; length, 3.7 m; width, 1.3 m; height, 2.4 m) was located in the central portion of the runway such that the horse could maintain a constant velocity when passing through it. Eight infrared camerasb were used to obtain 3-D optical kinematic data; 4 cameras were suspended from overhead beams on each side of the optical capture volume. The cameras operated at 200 Hz and were connected to an optical kinematic systemc that was calibrated to provide coordinates to within 1.2 mm. Five infrared timing gatesd were spaced 1.5 m apart along the central portion of the runway, which included the entire optical capture volume. During each trial (ie, trip over the runway), the timing gates were triggered by the passing of the horse to send a signal to the optical kinematic system, and the time stamps of those signals were used to calculate the horse's mean velocity.

The mean velocity at a walk and a trot was determined for each horse during collection of baseline data. Subsequently, for each horse after induction of each grade of lameness and perineural anesthesia, 4 to 5 acceptable trials were recorded for the right and left forelimbs at both a walk and trot. An acceptable trial was defined as a trial during which the horse traveled straight through the optical capture volume with a velocity that was ± 10% of its mean baseline velocity for the gait being evaluated.

Data collection—Optical coordinate data were low-pass filtered at 15 Hz with a recursive fourth-order Butterworth filter. Between the cranial and caudal retroreflective markers on the marker triad, a virtual marker was created to serve as a local origin, or reference point, to track the motion of the hoof. Linear movement of the hoof was tracked in the sagittal plane (cranial to caudal [X] and proximal to distal [Z]) as described.12 The X and Z acceleration profiles of the stride were used to identify hoof events. Briefly, hoof-contact was defined as the last peak in the Z acceleration curve before a period of smaller accelerations, and heel-off was defined as the last peak in the Z acceleration curve after the smaller accelerations. Toe-off was defined as the second peak in the Z acceleration curve, which corresponded to an inflection point in the X acceleration curve. These hoof events were used to divide the stride into total-stance (hoof-contact to toe-off), break-over (heel-off to toe-off), total-swing (toe-off to hoof-contact), initial-swing (toe-off to initial 25% of swing), and terminal-swing (75% of swing to hoof-contact) segments.

The global origin for the coordinate system was toe-off, and translations of the hoof at all other events were relative to the location of the virtual marker at toe-off. For each trial, the x-axis was aligned with the virtual marker at the second hoof-contact to ensure that the coordinate system was aligned with the direction of travel for the horse. The x-axis was positive cranially, and the z-axis was positive proximally. Within the sagittal plane about the y-axis (medial to lateral) through the virtual marker, heel-down hoof orientation was positive and toe-down hoof orientation was negative. Because the marker triad was not perfectly parallel to the ground, the hoof orientation during the middle of the total-stance segment (when the metacarpal bone was perpendicular to the ground) was used to adjust the sagittal orientation of the hoof such that 0° was level with the ground.

Data collected for each forelimb during each lameness trial included the instantaneous position, velocity, acceleration and sagittal-plane orientation of the hoof at hoof-contact, heel-off, and toe-off. Also, the total range of motion for the hoof was determined for the initial-swing, terminal-swing, and total-swing segments of the stride.

Statistical analysis—Data were analyzed in a manner similar to that described.12 Briefly, each data collection period was considered a treatment, which was categorized as baseline (prior to induction of lameness), grade 1, grade 2, grade 3, and after block (after administration of perineural anesthesia). For each treatment and forelimb hoof during each segment of the stride (hoof-contact, break-over, initial-swing, terminal-swing, and total-swing segments), descriptive statistics were generated for each kinematic variable or outcome. Mixed ANOVA for repeated measures was used to make comparisons between and within forelimbs for each outcome. For each respective model, treatment and forelimb (lame or nonlame) were included as fixed effects, horse identification was included as a random effect, and horse velocity during the trial was included as a confounding factor. For within-limb comparisons, each respective treatment (grade 1, grade 2, grade 3, or after block) was compared with the baseline treatment. All analyses were performed with a commercially available statistical software program,e and values of P < 0.05 were considered significant.

Results

Animals—Lameness that was subjectively apparent only at a trot was successfully induced in all horses; however, as discussed,12 grade 3 lameness could not be induced in 1 horse. Therefore, analyses for grade 3 and after-block treatments included data from only 5 horses, whereas analyses for baseline, grade 1, and grade 2 treatments included data from all 6 study horses. None of the horses had perceptible lameness when trotting 24 hours after lameness induction.

Intralimb kinematic changes—Select kinematic variables for the right (lame) and left (nonlame) forelimbs during total stance (Table 1) and swing (Table 2) at a walk were summarized. For the lame limb, significant kinematic changes from baseline were detected during both the stance and swing phases of the stride. Maximum and mean X position were increased for grade 1 and grade 2 treatments, duration of break-over was increased after induction of all grades of lameness, maximum X acceleration during break-over and mean hoof orientation during total-swing were increased for grade 2 and after-block treatments, duration of total-stance was increased for grade 3 and after-block treatments, hoof orientation at hoof contact and maximum Z velocity during initial-swing and total-swing were increased, and mean X position during break-over was decreased for the after-block treatment. For the nonlame limb, significant kinematic changes were detected only during the stance phase of the stride. Hoof orientation during hoof-contact was increased for the grade 3 treatment, minimum X position during break-over was decreased for grade 3 and after-block treatments, and mean X position during break-over was decreased for the after-block treatment.

Table 1—

Mean (SD) kinematic variables for the lame (right) and nonlame (left) forelimbs during the total stance (hoof-contact to toe-off) phase of the stride at a walk for 6 clinically normal Quarter Horses before (baseline) and after induction of 3 grades (grades 1, 2, and 3) of increasingly severe lameness in the right forelimb and following perineural anesthesia in the right forelimb to alleviate the lameness (after block).

  Treatment
Stance segmentVariableBaselineGrade 1Grade 2Grade 3After block
Hoof-contactOrientation (°)
  Lame0.70 (3.16)0.61 (2.90)0.58 (2.50)*0.37 (1.96)*1.54 (2.83)
  Nonlame1.20 (2.72)0.81 (2.73)1.41 (2.42)1.84 (2.72)1.19 (2.96)
Break-overDuration (s)
  Lame0.092 (0.013)*0.094 (0.015)0.095 (0.013)0.093 (0.012)0.092 (0.010)
  Nonlame0.096 (0.012)0.091 (0.015)0.094 (0.015)0.094 (0.015)0.091 (0.014)
 X position (m)
  Minimum
   Lame−0.046 (0.008)−0.046 (0.008)*−0.046 (0.007)*−0.044 (0.007)*−0.043 (0.007)*
   Nonlame−0.043 (0.007)−0.042 (0.008)−0.042 (0.007)−0.041 (0.007)−0.039 (0.008)
  Mean
   Lame−0.031 (0.006)−0.031 (0.006)*−0.031 (0.005)*−0.030 (0.005)*−0.029 (0.005)*
   Nonlame−0.029 (0.005)−0.028 (0.005)−0.029 (0.005)−0.027 (0.005)−0.027 (0.006)
 X acceleration (m/s2)
  Maximum
   Lame39.162 (5.242)*41.083 (6.257)*42.564 (7.094)*41.630 (6.408)*44.046 (7.109)*
   Nonlame37.290 (8.409)37.885 (7.821)38.876 (7.446)38.055 (6.447)38.111 (6.890)
 Z velocity (m/s)
  Maximum
   Lame0.697 (0.140)*0.714 (0.173)*0.729 (0.174)*0.774 (0.102)*0.801 (0.101)*
   Nonlame0.625 (0.157)0.615 (0.168)0.659 (0.143)0.620 (0.145)0.645 (0.135)
Total-stanceDuration (s)
   Lame0.804 (0.051)0.786 (0.068)0.799 (0.067)0.831 (0.069)0.840 (0.047)
   Nonlame0.819 (0.046)0.792 (0.065)0.805 (0.064)0.840 (0.065)0.838 (0.050)

Grade of lameness was subjectively determined at a trot. Grade 1 was defined as intermittent lameness; grade 2 was defined as consistent, mild lameness; and grade 3 was defined as consistent, moderate lameness; none of the grades resulted in lameness at a walk. Each stride taken by a horse was divided into segments on the basis of 3 hoof events that were defined by the kinematic data curves. The hoof events included hoof contact, which was defined as the last peak in the Z acceleration curve before a period of smaller accelerations; heel-off, which was defined as the first peak in the Z acceleration curve after the period of smaller accelerations; and toe-off, which was defined as the second peak in the Z acceleration curve and corresponded to an inflection point in the X acceleration curve. The segments of the stride were total-stance, which consisted of hoof-contact and break-over (heel-off to toe-off); initial-swing (toe-off to initial 25% of swing); terminal-swing (75% of swing to hoof contact); and total-swing (toe-off to hoof-contact). The orientation of the hoof during the middle of total-stance (when the metacarpal bone was perpendicular to the ground) was used to adjust the sagittal orientation of the hoof such that 0° was level with the ground. Cranial-to-caudal (X) variables were positive cranially, vertical (Z) variables were positive proximally, and the sagittal-plane orientation was positive in a counterclockwise rotation (ie, heel-down was positive). Range of motion was calculated from the difference in the maximum and minimum orientations for each stride segment. Grade 3 lameness could not be induced in 1 horse; therefore, for grade 3 and after-block treatments, the mean (SD) represents data from only 5 horses, whereas the mean (SD) for the other treatments represents data from all 6 horses.

Within a treatment and variable, the value for the lame forelimb differs significantly (P < 0.05) from that for the nonlame forelimb.

Within a forelimb, value differs significantly (P < 0.05) from that at baseline.

Table 2—

Mean (SD) kinematic variables for the lame and nonlame forelimbs during the swing (toe-off to hoof-contact) phase of the stride at a walk for the horses of Table 1.

  Treatment
Swing segmentVariableBaselineGrade 1Grade 2Grade 3After block
Initial-swingZ velocity (m/s)
  Maximum
   Lame0.817 (0.125)0.823 (0.183)0.858 (0.175)*0.879 (0.124)*0.934 (0.110)*
   Nonlame0.752 (0.174)0.779 (0.135)0.762 (0.119)0.764 (0.154)0.765 (0.137)
Terminal-swingX position (m)
  Maximum
   Lame1.542 (0.091)1.575 (0.079)1.578 (0.082)1.549 (0.079)1.540 (0.106)
   Nonlame1.559 (0.099)1.578 (0.089)1.581 (0.090)1.565 (0.093)1.561 (0.120)
  Mean
   Lame1.455 (0.085)1.487 (0.076)1.485 (0.069)1.457 (0.061)1.443 (0.089)
   Nonlame1.475 (0.094)1.496 (0.072)1.494 (0.077)1.478 (0.081)1.475 (0.104)
 Orientation (°)
  Maximum
   Lame1.81 (3.44)1.28 (3.44)1.39 (3.11)*0.91 (2.17)*2.49 (2.89)
   Nonlame2.65 (4.44)2.57 (4.62)2.85 (3.71)2.79 (3.79)2.08 (4.00)
  Mean
   Lame−14.78 (3.56)−15.31 (4.14)−16.01 (3.97)*−15.40 (3.71)−16.10 (4.06)
   Nonlame−13.08 (3.88)−13.13 (4.60)−13.56 (3.89)−14.15 (5.26)−15.49 (4.99)
Total-swingX position (m)
  Maximum
   Lame1.542 (0.091)1.575 (0.079)1.578 (0.082)1.549 (0.079)1.540 (0.106)
   Nonlame1.551 (0.095)1.571 (0.088)1.568 (0.089)1.551 (0.092)1.534 (0.108)
  Mean
   Lame0.802 (0.046)0.824 (0.045)0.820 (0.038)0.803 (0.031)0.795 (0.047)
   Nonlame0.812 (0.055)0.821 (0.040)0.821 (0.040)0.806 (0.044)0.798 (0.054)
 Z velocity (m/s)
  Maximum
   Lame0.823 (0.128)0.844 (0.165)0.858 (0.175)*0.900 (0.171)*0.958 (0.152)*
   Nonlame0.791 (0.190)0.776 (0.133)0.759 (0.120)0.768 (0.152)0.770 (0.133)
 Orientation (°)
  Maximum
   Lame2.02 (3.56)1.39 (3.54)1.39 (3.11)0.91 (2.17)*2.49 (2.89)
   Nonlame2.02 (3.89)1.81 (4.59)2.09 (3.64)2.83 (3.50)1.63 (3.92)
  Mean
   Lame−64.70 (3.36)−64.78 (3.24)−66.53 (3.29)*−64.9 (2.42)−66.07 (3.27)
   Nonlame−64.57 (3.98)−64.98 (3.93)−64.57 (2.60)−63.99 (3.29)−65.40 (2.80)

See Table 1 for key.

Interlimb kinematic changes—Among the treatments, 38 of 94 (40.4%) kinematic variables varied significantly between the lame and nonlame forelimbs. Of those variables, significant differences were detected for 12 of 36 cranial-to-caudal (X) variables, 20 of 35 vertical (Z) variables, 5 of 17 sagittal-plane orientation variables, and 1 of 6 temporal variables. For all treatments, significant interlimb differences were detected during all segments of the stride.

Discussion

Results of the present study indicated that several sagittal-plane hoof kinematic variables were significantly altered at a walk following induction of mild, unilateral, weight-bearing forelimb lameness (ie, lameness was visually perceptible only at a trot) in clinically normal horses. These kinematic alterations were detected during both the stance and swing phases of the stride, even at the most mild (grade 1) severity of lameness induced. For example, in the lame limb, duration of break-over and mean and maximum cranial (X) position during total-swing (ie, swing length) were significantly increased from baseline following induction of grade 1 lameness. Investigators of other studies15,16 reported that the duration of the stance phase (hoof-contact to toe-off) during a trot increases following induction of unilateral, weight-bearing forelimb lameness, compared with that before lameness induction for both the lame and nonlame limbs, and suggested that this is a compensatory mechanism by the horse to maintain the vertical impulse of the limbs in response to a decrease in peak vertical force. Results of the present study were similar to those of studies15,16 that evaluated forelimb kinematics at a trot and indicated that mild lameness alters the duration of stance at a walk as well. To our knowledge, the present study was the first to evaluate forelimb kinematics during break-over in horses at a walk. In the companion study12 to the one reported here, in which data were obtained concurrently from the same horses, the duration of break-over for the lame limb at a trot was significantly shorter than that at baseline, whereas in the present study, the duration of break-over for the lame limb at a walk was significantly longer than that at baseline. These findings suggested that the mechanism responsible for break-over duration varies and is dependent on the gait of the horse.

In the present study and its companion study,12 maximum cranial acceleration of the lame limb during break-over was significantly increased at both a walk (grade 2 lameness only) and trot (grade 1 and grade 2 lameness). After perineural anesthesia, the maximum cranial acceleration of the lame limb during break-over returned to a value similar to that at baseline when horses were trotted,12 but remained significantly increased from baseline when horses were walked.

For the horses of the present study, the swing length for the lame limb increased significantly from baseline after induction of grade 1 and grade 2 lameness, but returned to a value similar to that at baseline after induction of grade 3 lameness and after perineural anesthesia. Conversely, in another study,17 swing length of the lame forelimb was significantly decreased from its prelameness swing length when horses were trotted; however, the lameness induced in the horses of that study17 was perceptible at a walk and was more severe than the lameness induced in the horses of the present study. The difference in the severity of lameness induced between the present and that other study17 might be responsible for the apparently contradicting findings regarding swing length. Thus, swing length is likely dependent on and will vary with severity of lameness and the gait at which the horse is evaluated.

For the nonlame limb after induction of grade 3 lameness, the hoof orientation at hoof-contact during a walk was significantly increased from that at baseline, which suggested that the hoof of the nonlame limb landed with a more heel-down orientation when the contralateral limb was moderately lame than it did prior to lameness induction. In the companion study,12 the hoof orientation at hoof-contact for the nonlame limb during a trot was significantly increased from baseline following induction of all grades of lameness. Conversely, for the lame limb, the hoof orientation at hoof-contact did not vary significantly from that at baseline following induction of lameness at either a walk or a trot; however, hoof orientation of the lame limb at hoof-contact was increased from baseline after perineural anesthesia when horses were walked. Additionally, at a walk, hoof orientation at hoof-contact varied significantly between the lame and nonlame limbs following induction of grade 2 and grade 3 lameness, whereas at a trot, hoof orientation at hoof-contact varied significantly between the lame and nonlame limbs after all 3 grades of lameness were induced.12 Thus, although hoof orientation at hoof-contact was significantly altered for both forelimbs at a walk and a trot, this alteration was only evident at a walk after induction of more severe (grade 2 or grade 3) lameness.

Following administration of perineural anesthesia in the present study, break-over duration and mean and maximum swing length during terminal- and total-swing segments for the lame limb returned to values that did not differ significantly from those at baseline, and values for mean and maximum hoof orientation during the terminal-swing segment no longer varied significantly between the lame and nonlame limbs. However, following perineural anesthesia, the hoof orientation at hoof-contact for the lame limb was increased significantly from baseline, whereas it did not differ from baseline following induction of all 3 grades of lameness. This finding suggested that hoof orientation of the lame limb at hoof-contact during a walk might be a clinically useful kinematic to assess to determine whether lameness was successfully alleviated by perineural anesthesia.

The sole-pressure model consistently induced lameness that was rapidly reversible in the horses of the present study. Although sole pressure is not a common cause of lameness in clinically lame horses, the kinematic changes that occur with this model are believed to be similar to those associated with lameness induced by other causes.14 Consequently, the sole-pressure model has been used by investigators of multiple studies11–13,17–19 to induce lameness in horses to evaluate objective methods of lameness detection at both a walk and trot. However, most of those studies12,13,17–19 did not investigate kinematic alterations in horses at a walk.

To our knowledge, significant lameness-induced alterations in forelimb kinematics of horses at a walk have been reported by investigators of only 1 other study.14 The lameness induced in the horses of that study14 was perceptible at a walk and was more severe than the lameness induced in the horses of the present study. Nevertheless, results of the present study indicated that horses with unilateral forelimb lameness that was perceptible only at a trot had several kinematic changes in both the lame and nonlame limbs when walking. On the basis of results of the present study and its companion study,12 sagittal-plane orientation of the hoof at hoof-contact and maximum cranial acceleration during break-over were increased from baseline for the lame limb after lameness induction when horses were walked and trotted. Therefore, those variables should be assessed further in a larger number of horses with lameness of varying severity to determine whether they could be clinically useful for identifying and monitoring lame horses. Additionally, because the values for several hoof kinematic variables (eg, mean and maximum X position during terminal- and total-swing segments and break-over duration for the lame limb and hoof orientation at hoof-contact for the nonlame limb) returned to values similar to those at baseline following perineural anesthesia, further research should be conducted to determine whether monitoring those variables can be used to assess whether perineural anesthesia was successful in alleviating lameness at a walk in horses that are subjectively lame only at a trot. Identification of such variables would be clinically valuable, particularly for horses for which a subjective lameness examination conducted at a trot is contraindicated. Horse-mounted kinematic systems are becoming more readily available; thus, use of a hoof-based sensor system may be useful clinically as an objective method for evaluation of lameness in horses. Further research is necessary to determine changes in the hoof kinematics of lame horses in the frontal and transverse planes.

a.

H3-IMU, MEMSense LLC, Rapid City, SD.

b.

Volant, Peak Performance Technologies Inc, Centennial, Colo.

c.

Vicon-Motus, version 9.2, Vicon Motion Systems Inc, Centennial, Colo.

d.

MEK 92-PAD photoelectric control, Mekontrol Inc, Northboro, Mass.

e.

STATA, version 11, StataCorp LP, College Station, Tex.

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Contributor Notes

Supported by the United States Equestrian Federation Equine Health Research Fund.

The authors thank Erin Contino, Dora Ferris, and Jennifer Suddreth for technical assistance and Francisco Olea-Popelka for assistance with statistical analysis.

Address correspondence to Dr. Kawcak (christopher.kawcak@colostate.edu).