Efficacy of a single-formula acupuncture treatment for horses with palmar heel pain

Abstract

Acupuncture is used without strong scientific evidence to treat many diseases of the horse, including palmar heel pain. Research is needed to provide evidence for the application of these treatments. Within the confines of our study, acupuncture did not reliably modulate palmar heel pain in horses.

Introduction

Palmar heel pain (also known as navicular disease or syndrome) is a common cause of bilateral forelimb lameness; “estimated to cause one third of all chronic forelimb lamenesses in the horse” (1). The syndrome most commonly affects horses over 6 y of age (2,3), although younger horses may also be affected (3). Quarter Horses, some Warmblood breeds, and Thoroughbreds may be overrepresented (3,4). There is no known gender predilection, although at 1 institution, geldings were more likely to be diagnosed (2). The etiology of palmar heel pain remains unknown but 2 main theories, abnormal biomechanical stresses and vascular compromise, have been suggested (3–8). Magnetic resonance imaging (MRI) may be considered the new gold standard of diagnosis, and has allowed for confirmation of the theory that many different osseous or soft tissue abnormalities (alone or in combination) may be affecting the horse with palmar heel pain (3,4,7). Magnetic resonance imaging is not readily available to all equine practitioners and may be beyond the financial means of some clients. Therefore, the diagnosis of palmar heel pain is frequently still based on clinical and radiographic examination. These non-specific diagnostic methods lead to the continued use of non-specific treatments for palmar heel pain, such as corrective shoeing and systemic non-steroidal anti-inflammatory drug administration. Although non-specific with regard to etiology, these therapies are applicable and helpful to many horses with palmar heel pain (3). Acupuncture, a similarly non-specific treatment, may be useful for alleviating the pain experienced by affected horses.

Indeed, acupuncture has been utilized to combat palmar heel pain (1,8,9), although peer-reviewed literature substantiating its efficacy is lacking. However, there is peer-reviewed literature that seems to support the efficacy of acupuncture as a treatment for pain associated with other conditions in the horse (10–12).

Many owners today are looking for non-invasive, drug-free ways to treat their horses. Acupuncture has gained great popularity as a way to provide this service, but there is little scientific evidence to suggest that it is effective for the treatment of palmar heel pain. The aim of this study was to investigate the efficacy of acupuncture for horses affected by palmar heel pain.

Materials and methods

Case selection

Client-owned horses with clinical disease were used for this trial. Horses may or may not have had a previous diagnosis of palmar heel pain and chronicity of lameness was not part of the selection process, although all horses included had a history of chronic forelimb lameness. To be included in the trial, horses had to have a forelimb lameness that was no more severe than a grade 3 out of 5 according to the American Association of Equine Practitioners lameness scale, meaning that horses which were lame at the walk or non-weight bearing were excluded from the trial. As well, the lameness had to improve substantially (at least 70%) to biaxial palmar digital (PD) perineural analgesia. Perineural analgesia was accomplished using 40 to 50 mg of lidocaine hydrochloride (Lidocaine Neat; Vétoquinol, Lavaltrie, Quebec) per site. Horses could be bilaterally or unilaterally lame, but needed to have the same blocking pattern on each limb if lameness was bilateral.

Horses were radiographed using 1 of 2 portable, digital X-ray units (truDR lx; Sound-Eklin, Carlsbad, California, USA or uno1; Cuattro Americas, Pekin, Illinois, USA). Horses with radiographic evidence of disease in the proximal interphalangeal joint or distal interphalangeal joint were excluded from the study as it has been shown that a PD block may decrease pain associated with these joints (3). As well, horses with evidence of modeling of the third phalanx were excluded. Acceptable radiographic changes included: modeling of the navicular bone, cyst-like lesions of the navicular bone, entheseophytosis of the navicular bone, dystrophic mineralization of soft tissue structures below the level of the distal interphalangeal joint, and abnormal hoof-pastern angle (as evidenced by “broken back” or “broken forward” angles at the distal interphalangeal joint). Horses were barefoot for the duration of the trial and were trimmed by the same farrier (TB). Anti-inflammatory medications were not permitted for use in the horses during the study period. If an anti-inflammatory drug had been recently administered to a horse that otherwise qualified for the study, a washout period of 2 wk was given (13). Twelve horses met the inclusion criteria, of which 9 completed the study. The study was approved by the University of Saskatchewan’s University Committee on Animal Care and Supply.

Of the 9 horses that completed the study, 8 were geldings and 1 was a mare. The ages ranged from 6 to 19 y with a mean age of 14.4 y. Breeds represented included: Paint (n = 4), Quarter Horse (n = 3), Thoroughbred cross (n = 1) and Paint cross (n = 1). Eight of the 9 horses included were bilaterally lame; only 1 horse was unilaterally lame. Owners gave informed consent for the use of their horses in this trial.

Radiographic evaluation

Standard radiographic projections were taken as part of the inclusion criteria and then again at the completion of the trial. Views included: lateral-medial, dorsal-palmar, 60° dorsoproximal-palmarodistal oblique and 45° palmaroproximal-palmarodistal oblique (skyline). Radiographs of both forefeet were obtained on each horse at the pre- and post-study assessments.

Experimental design

Horses were randomly assigned to the treatment group or the control group. Horses were trimmed to maintain heel mass and decrease breakover (3) and then given a 1 wk adjustment period. The trial period then commenced and was carried out over the next 4 wk. During this trial period, horses were kept in their home environment, on their regular diet, and at their normal level of activity.

Twice weekly visits on non-successive days were made to each horse. Horses in the treatment group received 20 min of dry needle and electroacupuncture at each visit; horses in the control group received no treatment. Acupuncture treatments were administered by a certified veterinary acupuncturist (SM). The same acupuncture points were applied to each horse in the treatment group. Acupuncture treatment points included: Bai Hui, Bladder (BL) 11, BL 13, Pericardium (PC) 1, Heart (H) 9, Lung (LU) 1, and LU 11 bilaterally, and electroacupuncture at Small Intestine (SI) 9 and Large Intestine (LI) 11 bilaterally. Sterile, single use acupuncture needles were used (Seirin Corporation, Shizuoka, Japan). Needle size was similar for all points (0.25 × 40 mm) with the exception of H9 and LU11 (0.25 × 15 mm). Electrical stimulation was provided in a mixed pattern at 2 to 5 Hz using a commercially available electrostimulator (Electro-Acupuncture Stimulator 4C; Pantheon Research, Venice, California, USA).

A second visit was made on the same day but at a different time by a clinician blinded to the treatment (KR). This clinician scored each horse’s lameness at each visit based on the AAEP lameness scale and applied electronic calibrated hoof testers developed and validated in our laboratory (unpublished data) to quantify hoof compression threshold (HCT) at 7 sites on the foot: toe, medial quarter, medial heel, lateral quarter, lateral heel, over the frog, and across both heels. Two modified hoof testers were purpose built for this project using strain gauges to measure applied forces. These modified hoof testers were validated on 20 horses with no evidence of musculoskeletal disease, prior to use in the current study. Serial lameness examinations were videotaped for further review.

At the end of the 4-week trial period each horse was given another week off and then lameness examination, blocking pattern, and radiographs were repeated to confirm no changes from the pre-study baseline.

Data analysis

Data were not normally distributed; therefore, non-parametric statistics were employed. Lameness grades were compared between groups using the Kruskal-Wallis one way analysis of variance (ANOVA), and HCT data were compared using the Mann-Whitney U-test (IBM SPSS Statistics 20.0, IBM Corporation, Armonk, New York, USA).

Results

Lameness evaluation

There was no significant difference in grade of lameness between treatment and control animals at initial assessment [right front (RF); P = 0.27, left front (LF); P = 0.66], nor at final assessment (RF; P = 0.44, LF; P = 0.27). All 4 horses in the control group maintained the same grade of lameness through the duration of the study or improved on 1 or both limbs by no more than 1 grade of lameness. Of the 5 horses in the treatment group, 3 showed improvement of 1 lameness grade on 1 or both limbs, 1 horse did not change, and 1 horse’s lameness worsened through the course of the study. Table 1 presents lameness grades for all of the horses in the trial at the initial and final assessments.

Table 1.

Lameness grades at initial and final assessments

	Grade at initial assessment		Grade at final assessment
Horse	Right front	Left front	Right front	Left front
1 (Control)	3	2	2	2
2 (Control)	2	3	2	1
3 (Treatment)	0	2	3	2
4 (Control)	3	2	2	2
5 (Treatment)	3	2	1	3
6 (Treatment)	2	2	1	2
7 (Treatment)	3	2	3	2
8 (Control)	3	1	3	1
9 (Treatment)	2	1	1	1

Hoof compression threshold

There was no significant difference in HCT’s between treatment and control groups at any of the 7 sites on the foot over the course of the study (P > 0.05). For the left front foot, calculated P-values ranged from 0.41 to 1.0 over the 7 sites. For the right front foot, calculated P-values ranged from 0.56 to 1.0 over the 7 sites.

Discussion

Acupuncture did not effectively modulate pain in horses with palmar heel pain under the conditions of the current study. There was no significant difference between horses in the treatment group and horses in the control group with regards to lameness grade or hoof compression threshold. To the authors’ knowledge, there is only 1 study of similar depth published in a peer-reviewed journal investigating the use of acupuncture and electroacupuncture for pain relief in horses with palmar heel pain (9). That study investigated 2 groups of horses; those with laminitis and those with navicular syndrome. In each disease group there were horses that showed improvement with acupuncture treatment but there were no statistically significant differences between treatment groups and controls, regardless of disease process. The current study used similar acupuncture points and treatment protocols and achieved similar results.

The major limitation of the current study includes patient numbers, which reduce statistical power and therefore possibly statistical significance. Our recruitment of eligible horses was greatly limited in that, under the conditions imposed by the Animal Care Committee, horses could not be enrolled in the study if at initial assessment they had a lameness grade of 4 out of 5 or greater on the AAEP Lameness Scale. Had horses with this degree of lameness been able to participate, we would have been able to include significantly more animals in the trial, and a different result might have been achieved.

Another significant limitation is the need to approach clinical trials such that all treated animals received the same treatment. Traditional acupuncture would have each horse diagnosed as an individual and then a specific acupuncture treatment applied as indicated for that individual; having each horse treated in exactly the same way is at odds with traditional acupuncture, and may have limited the efficacy in certain individuals. It would be difficult to design a study that allows for strict, scientific comparisons while using a traditional approach to acupuncture. This core dilemma between science and acupuncture is likely to continue limiting our ability to scientifically assess the efficacy of acupuncture.

The current study utilized electronic calibrated hoof testers to collect quantitative data, rather than force plate analysis, which is typically used for lameness studies (5,14). Electronic calibrated hoof testers are much more accessible to the average practitioner than a force plate for the quantitative evaluation of pain in the foot. Commercial products are available, and the use of hoof compression thresholds in lame horses has been validated (15). As has been previously reported when using calibrated hoof testers, there were few extreme values in the current study, which is evidence that the test is repeatable and consistent. Hoof compression thresholds, whether tested manually or robotically, seem to be a reliable and objective way of assessing foot pain in the horse.

Interestingly, it was noted throughout the course of the study that horses did not test across the heels as consistently as has been historically reported. Horses were much more likely to be positive to hoof testers across the toe, which may be a consequence of repeated overloading (3).

Lameness grade did not significantly change through the course of the study. Other researchers claim that palmar heel pain is a stable lameness with no significant variation over days or weeks (14). This lends credibility to our serial lameness scoring, and the fact that acupuncture did not appear to make a significant difference in level of comfort to the horses receiving that treatment.

In conclusion, acupuncture does not appear to be effective in relieving palmar heel pain in horses. A larger study and the use of MRI for more specific inclusion criteria may lead to different results.