Force platform evaluation of lameness severity following extracorporeal shock wave therapy in horses with unilateral forelimb lameness

Jessica A. Dahlberg Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011.

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Scott R. McClure Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011.

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Richard B. Evans Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA 50011.

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Eric L. Reinertson Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011.

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Abstract

Objective—To measure alterations in lameness severity that occur following use of extracorporeal shock wave therapy (ESWT) in horses with naturally occurring unilateral forelimb lameness.

Design—Nonrandomized clinical trial.

Animals—9 horses with unilateral forelimb lameness.

Procedures—Force platform gait analysis was performed prior to administration of any treatments (baseline) and after use of local anesthesia to eliminate the lameness. Extracorporeal shock wave therapy was then administered, and gait analysis was repeated 8 hours later and then daily for 7 days.

Results—Compared with the baseline value, peak vertical force was significantly increased 8 hours and 2 days after ESWT, and peak vertical force on day 2 was not significantly different from force measured after use of local anesthesia to eliminate the lameness. Similarly, vertical impulse was significantly increased, compared with the baseline value, 8 hours and 2 days after ESWT, but at all times, it was significantly lower than vertical impulse measured after use of local anesthesia.

Conclusions and Clinical Relevance—Results suggest that in horses with naturally occurring lameness, use of ESWT results in a period of acute improvement in lameness severity that typically persists for 2 days. Thus, in horses undergoing ESWT, exercise should be controlled for a minimum of 2 days after treatment to prevent further injury.

Abstract

Objective—To measure alterations in lameness severity that occur following use of extracorporeal shock wave therapy (ESWT) in horses with naturally occurring unilateral forelimb lameness.

Design—Nonrandomized clinical trial.

Animals—9 horses with unilateral forelimb lameness.

Procedures—Force platform gait analysis was performed prior to administration of any treatments (baseline) and after use of local anesthesia to eliminate the lameness. Extracorporeal shock wave therapy was then administered, and gait analysis was repeated 8 hours later and then daily for 7 days.

Results—Compared with the baseline value, peak vertical force was significantly increased 8 hours and 2 days after ESWT, and peak vertical force on day 2 was not significantly different from force measured after use of local anesthesia to eliminate the lameness. Similarly, vertical impulse was significantly increased, compared with the baseline value, 8 hours and 2 days after ESWT, but at all times, it was significantly lower than vertical impulse measured after use of local anesthesia.

Conclusions and Clinical Relevance—Results suggest that in horses with naturally occurring lameness, use of ESWT results in a period of acute improvement in lameness severity that typically persists for 2 days. Thus, in horses undergoing ESWT, exercise should be controlled for a minimum of 2 days after treatment to prevent further injury.

Use of focused ESWT to treat musculoskeletal disorders in horses has been an area of clinical and research interest in recent years, and several studies1–6 evaluating the effects of ESWT in horses with various musculoskeletal disorders have been published. In people, ESWT has been reported to result in analgesia of the treated area,7,8,a although the mechanism of action by which analgesia is induced is currently not understood.7,9,10 Use of ESWT to treat heel spurs in people, for instance, reportedly results in a bimodal analgesic effect,a with a decrease in pain for the initial 3 to 4 days after treatment, followed by a gradual return of pain and a subsequent decrease again as healing progresses. Similarly, use of ESWT to treat painful diseases of bone, ligament, or tendon in humans will result in a rapid decrease in pain without radiographic changes.11 In many instances, the analgesic effect appears to be independent of the healing process.11

There is also some evidence that ESWT may result in analgesia in horses. In 1 study,12 for instance, local cutaneous analgesia was identified for 72 hours following ESWT administered with an electrical stimulus. Not surprisingly, this has raised concerns that use of ESWT to treat musculoskeletal injuries in horses may, because of the analgesic effects, result in overuse of the injured limb, causing further injury to the affected part and posing a risk to treated horses and their riders. For this reason, racing jurisdictions in the United States and the Federation Equestre Internationale have adopted regulations that require a 5- to 7-day period after treatment before the horse is allowed to perform.

Evaluation of skin analgesia following ESWT can provide some information as to the duration of treatment effects. However, pain associated with musculoskeletal disease involves deeper tissues that cannot be evaluated by measuring skin sensation. Therefore, the objective of this study was to evaluate the duration of effect of ESWT in horses with naturally occurring lameness. Specifically, the purpose of the study reported here was to determine whether 1-time use of ESWT would result in a significant decrease in severity of lameness, as determined by means of force platform gait analysis, in horses with chronic unilateral forelimb lameness and, if so, how long this effect would last.

Materials and Methods

Horses—Nine horses (5 geldings and 4 females) with chronic unilateral forelimb lameness were included in the study. Median age was 9 years (range, 6 to 28 years), and mean body weight was 524 kg (1,153 lb; range, 442 to 640 kg [972 to 1,408 lb]). There were 2 American Paint Horses, 3 Thoroughbreds, and 4 Quarter Horses. All horses were in good health other than the forelimb lameness and had been lame for at least 6 months. In all horses, severity of lameness was graded as 2 or 3 on a scale from 1 to 5.13 Horses were excluded if they had received any injections in the affected joint within 90 days prior to the start of the study; had undergone surgery on the affected joint within 180 days prior to the start of the study; or had been treated orally, topically, or systemically with any products meant to alleviate lameness, including nonsteroidal anti-inflammatory drugs and glucosamine, within 14 days prior to the start of the study. In all horses, the source of the forelimb lameness had been localized by means perineural or intra-articular anesthesia and had been confirmed radiographically. The study protocol was approved by the Iowa State University Animal Care and Use Committee.

Experimental protocol—Two veterinarians not otherwise associated with the study independently examined horses prior to the start of the study and on day 7 and assigned a lameness score from 1 to 5 with increments of 0.5. The average of the 2 grades was used for analysis.

Force platform gait analysis was performed daily for 3 consecutive days prior to administration of any treatments to obtain baseline data. In addition, on the first of these 3 days, local anesthesia was used to eliminate the lameness and gait analysis was repeated. Following collection of baseline data, ESWT was performed and gait analysis was performed 7 to 8 hours later and then daily for 7 days.

Force platform gait analysis—Force platform gait analysis was performed with a biomechanical platformb embedded in a 30-m walkway. Three sets of retroreflective photocell receptorsc embedded in the walkway 1 m apart, with the middle sensor positioned at the middle of the platform, were used to determine velocity and acceleration as horses were trotted over the platform.

For force platform gait analysis, horses were led by hand at a trot along the walkway and across the platform at a comfortable speed. Ground reaction forces were recorded with standard softwared during each pass. Additional passes were performed until 5 valid measurements were obtained for each limb. A pass was considered valid if the forefoot and ipsilateral hind foot hit the platform consecutively, velocity was between 1.80 and 2.60 m/s, and acceleration was between −0.5 and 0.5 m/s2.

Values for PVF and VI for the first 5 valid passes for each limb were averaged to obtain values for analysis. All values were normalized by dividing by the horse's body weight. Data evaluated were PVF and VI.

ESWT—For ESWT, horses were lightly sedated with detomidine (0.01 mg/kg [0.0045 mg/lb], IV). Hair was clipped from the area to be treated, except that in horses with navicular syndrome, hair was clipped from the heel bulbs, excess sole over the frog was pared, and the foot was soaked in water for at least 8 hours.

In horses with navicular syndrome, the ESWT protocol consisted of administration of 1,000 shocks with a focused shock wave generatore to the navicular region through the frog, with a 35-mm focal depth and energy density of 0.15 mJ/mm2, and administration of an additional 1,000 pulses through the area between the heel bulbs, with a 20-mm focal depth and the same energy density. For horses with osteoarthritis, coupling gel was applied for ESWT. The ESWT protocol consisted of administration of a total of 800 shock waves divided among 4 sites (ie, caudolateral, dorsolateral, dorsomedial, and caudomedial), with a 20-mm focal depth and energy density of 0.14 mJ/mm2, and administration of an additional 800 shock waves divided among the same 4 locations but with a 5-mm focal depth and the same energy density.

Statistical analysis—Results of the 3 gait analyses performed prior to any treatments were averaged to obtain baseline values. The matched-pairs t test was used to compare baseline values with values obtained following use of local anesthesia to eliminate the lameness and with values obtained 8 hours and 1, 2, 3, 4, 5, 6, and 7 days after ESWT. The within-group t test was used to compare PVF and VI between horses with navicular syndrome and horses with osteoarthritis at each time point, and the Wilcoxon nonparametric test was used to compare lameness grades assigned prior to treatment with grades assigned on day 7. Analyses were performed with standard software.f For all analyses, values of P < 0.05 were considered significant.

Results

Six horses had navicular syndrome. Of the remaining 3, 1 had osteoarthritis of the distal interphalangeal joint, 1 had osteoarthritis of the metacarpophalangeal joint, and 1 had osteoarthritis of the middle carpal joint. No complications associated with ESWT were identified.

Mean PVF and mean VI were not significantly different between horses with navicular syndrome and horses with osteoarthritis at any time during the study. Therefore, data for all 9 horses were combined for subsequent analyses. Lameness grade prior to any treatment (mean, 2.67; range, 2 to 3) was not significantly (P = 0.848) different from lameness grade on day 7 at the end of the study (mean, 2.61; range, 2 to 3).

Baseline PVF was significantly (P = 0.006) lower than PVF after use of local anesthesia to eliminate the lameness (Figure 1). Peak vertical forces 8 hours (P = 0.003) and 2 days (P = 0.016) after administration ESWT were significantly higher than baseline PVF. In addition, PVF 2 days after administration of ESWT was not significantly (P = 0.14) different from PVF after use of local anesthesia.

Figure 1—
Figure 1—

Mean peak vertical force (A) and vertical impulse (B) in 9 horses with chronic unilateral forelimb lameness. Gait analysis was performed following use of local anesthesia to eliminate the lameness, prior to treatment (baseline), and 8 hours (day 0) and daily for 7 days after ESWT of the affected area. Error bars represent SE. Values marked with a star were significantly (P < 0.05) different from baseline values. Arrow indicates that value was not significantly different from value obtained following use of local anesthesia to eliminate the lameness.

Citation: Journal of the American Veterinary Medical Association 229, 1; 10.2460/javma.229.1.100

Similarly, baseline VI was significantly (P = 0.009) lower than VI after use of local anesthesia to eliminate the lameness (Figure 1). Vertical impulses 8 hours (P = 0.024) and 2 days (P = 0.023) after administration of ESWT were significantly higher than baseline VI. However, VI was significantly lower at all times after administration of ESWT than after use of local anesthesia to eliminate the lameness.

Discussion

Results of the present study suggest that in horses with naturally occurring unilateral forelimb lameness, use of ESWT results in a period of acute improvement in lameness severity that persists on average for 2 days. We recommend, therefore, that in horses undergoing ESWT, exercise should be controlled for a minimum of 2 days after treatment to prevent further injury.

For the present study, we selected horses that had grade 2 or 3 lameness, as we believed that such horses had lameness of adequate severity that any improvement associated with ESWT would be evident. Thus, it is possible that horses with grade 1 lameness would not be affected by ESWT. In addition, we selected horses for the present study with chronic lameness to decrease the likelihood of spontaneous improvement. In so doing, however, we potentially selected horses that would be less likely to respond to ESWT. In these horses, for instance, adhesions of the deep digital flexor tendon, osteophytes, cartilage erosions, and other anatomic changes may have made it less likely that ESWT would have resulted in analgesia and, subsequently, an improvement in lameness. In addition, because we only included horses with chronic lameness, we could not determine whether similar responses would be seen in horses with acute lameness. In horses with experimentally induced osteochondral fragments in which ESWT was initiated 14 days after the fragment was created, lameness was less severe and protein content of the synovial fluid was lower by day 28 in joints treated with ESWT than in untreated control joints.14

There is a documented dose response associated with ESWT,15–17 with no apparent effect at low energy levels and pulse numbers, desirable effects at midrange energy levels and pulse numbers, and destructive effects at high energy levels and pulse numbers. Horses in the present study were treated with a shock wave generator that is widely available to veterinarians in the United States, and energy levels and pulse numbers were typical for this type of application.1,14 We did not determine, however, whether altering energy level or pulse number would affect the lameness response following treatment.

The purpose of the present study was to evaluate the acute period of analgesia associated with ESWT, as reflected in improvements in lameness severity, and no attempts were made to identify the mechanism leading to such analgesia. However, it is apparent from our data that maximum analgesia is not immediate, as illustrated by the fact that the improvement in lameness severity peaked 2 days after treatment. It would be unlikely that destruction of nerves or nerve receptors would result in this type of response.

In the present study, graphs of PVF and VI showed increases in both values from baseline to day 2. However, significant differences were found, compared with baseline values, only 8 hours and 2 days after treatment. Values obtained 1 day after treatment were not significantly different from baseline values, but the P value (0.07) was close to our cutoff for significance.

Importantly, results of the present study relate only to the use of ESWT and not to the use of RPWT.

Focused ESWT involves the use of shock waves with maximum pressures as high as 100 MPa and durations as short as 1 ms; with focused ESWT, the maximum pressure is focused at a focal point within the tissues.18 In contrast, RPWT involves pressure waves with lower peak pressures (approx 7 MPa) and longer pulse durations (> 4 ms).18 In addition, with RPWT, the maximum pressure is exerted on the surface of the tissues and dissipates from that point. Importantly, results of a previous study19 involving force platform gait analysis of horses with navicular syndrome following RWPT were different from results of the present study.

Peak vertical force and VI have been identified as the best measures of lameness severity and subclinical gait abnormalities in horses.20 In the present study, PVF and VI values measured after use of local anesthesia to eliminate the lameness were similar to those reported for healthy horses.20 Mean baseline PVF (8.19 N•kg−1) and VI (1.8 N•s•kg−1) values for these horses were somewhat higher than values reported previously20 for PVF (6.3 N•kg−1) and VI (1.1 N•s•kg−1) in lame horses, even though mean lameness grade for horses in the present study (2.67) was higher than mean lameness grade for horses in the previous study (2.5). These discrepancies likely reflect differences in velocity during gait analysis. In the present study, velocity was maintained between 1.8 and 2.6 m/s, whereas velocity range in the previous study was 2.5 to 3.5 m/s. Because horses in the present study were evaluated multiple times, absolute values were less important than the changes that occurred over time.

The clinical importance of an increase of 1 N•kg−1 in PVF or 0.14 N•s•kg−1 in VI from baseline to day 2 is difficult to assess. However, the fact that mean PVF 2 days after administration of ESWT was not significantly different from mean PVF after use of local anesthesia to eliminate the lameness would suggest that this change was clinically important.

ABBREVIATIONS

ESWT

Extracorporeal shock wave therapy

PVF

Peak vertical force

VI

Vertical impulse

RPWT

Radial pressure wave therapy

a.

Ogden JA, Ogden DA. Electrohydraulic SWT: bimodal response (abstr), in Proceedings. 5th Int Soc Musculoskelet Shockwave Ther 2002;21.

b.

BP600900, Advanced Medical Technology Inc, Watertown, Mass.

c.

Mek 92-Tpad retroflective photocell, Sircon Controls, Missisauga, ON, Canada.

d.

Acquire, version 7.3, Sharon Software Inc, Dewitt, Mich.

e.

Equitron, SanuWave, Marietta, Ga.

f.

JMP statistical software, version 5.1, SAS Institute Inc, Cary, NC.

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