Introduction
The musculoskeletal system is a primary cause of poor performance in athletic horses, and its management is at the heart of equine medicine.1,2 Within this system, the axial skeleton and more specifically the back are important contributors to poor performance and financial loss in racehorses. Back pain and axial stiffness have been frequently overlooked in the race industry, as the poor specificity of clinical signs and imaging challenges make diagnosis of back conditions difficult.3–5 However, over the past decade, veterinarians have gained awareness regarding this condition, and various treating modalities have been developed. These include many scientifically validated medical and surgical treatments.6–9 Unfortunately, all these treatments are invasive or considered doping by racing authorities in France and other European countries, and most of them cannot be applied within 2 weeks of a race. Training management is also an essential part of the management of back problems but is not always applicable in racehorses.5
Considering these constraints, a growing interest for alternative therapies has developed. Some alternative therapies, such as chiropractics and osteopathy, rely on mobilization and tension relief.10–15 Others, such as extracorporeal shockwave therapy or laser, aim for pain relief.16–23 However, the use of some of these techniques prior to racing has also been restricted due to their short- or long-term consequences. Acupuncture has been a part of traditional Chinese medicine for centuries and has evolved over time. It is commonly used in modern veterinary medicine to treat pain and many other specific painful conditions. Acupuncture points are located close to major nerves, blood vessels, or lymphatic vessels at sites of muscle or fascia penetration, bone foramina, or neurovascular bundles.24,25 Stimulation of a point results in tissue damage, activation of the inflammatory cascade, and neural excitation, causing the release of various neurotransmitters that can have local or peripheral effects such as increased local microcirculation or muscle spasm relief.24–28
Studies29–33 have been performed on various types of acupuncture techniques used in treatment of axial stiffness in horses, with positive clinical results. However, few of them were randomized and controlled, and none involved racehorses. The objective of this study was to evaluate the short-term effects of acupuncture on the clinical signs of axial stiffness in steeplechase racehorses. We hypothesized (1) that the trainer and rider would find the signs of axial stiffness from horses treated with acupuncture improved for up to 2 weeks, compared with signs in untreated horses, and (2) that back mobility would be improved for treated horses compared with back mobility in control horses 2 days after treatment.
Methods
Horses
Twelve healthy steeplechase racehorses that were 2 to 5 years old, were free of lameness on visual evaluation, and presented clinical signs of axial stiffness, including back stiffness, shortened strides at the canter, or poor hind limb propulsion, were included in this exploratory study out of 43 horses at training at the facility. Horses that had received any medical or physical treatment < 3 weeks prior to the study or that had raced < 4 days prior to the study were not included. The study took place at a single facility where all horses were housed and trained. Written informed consent was obtained from the owner and trainer of the horses. This protocol was approved by the ComERC/ENVA Ethical Committee (Permit No. 2019-07-19).
Study design
The horses were randomly assigned to either the acupuncture treatment group (n = 6) or to the control group (6) using an Android app (Randomizer; Giannis Macheras). Each horse was ridden 3 days prior to treatment and a questionnaire was submitted to the trainer and rider, blinded to the treatment groups (Supplementary Table S1). On day 0 (D0; baseline) before treatment and day 2 (D2) after treatment, the back mobility of all horses was evaluated and graded on dynamic examination at the trot and then free jumping at the canter. On day 1, all horses were turned out in the walker. From days 3 to 6 and from days 8 to 13, all horses underwent an identical training program including walker, routine paddock turnout, and ridden exercise at the canter. All horses were ridden by the same rider with identical equipment during each exercise session. On days 7 (D7) and 14 (D14), the horses underwent their regular training, and a questionnaire was submitted to the trainer and rider still blinded to the treatment groups. A summarized timeline of the study is presented (Figure 1).
Primary outcome
As the trainer and rider’s opinion is the criterion used in equine practice to evaluate the response to back treatments, it was selected as the primary outcome. The axial mobility was evaluated by the trainer and the rider based on the horses’ flexibility and mobility at the canter and above the jumps, both from a visual and ridden perspective, and a consensual grade was attributed following an exercise session. This was divided into different categories to assess response to treatment in the most global way possible. Therefore, behavior was included to evaluate the willingness of the horse to perform the expected exercise, balance and rectitude to assess any potential compensatory patterns manifested by crookedness, head and neck pendulum to evaluate the fluidity of the pendular motion of the head or lack thereof that could be considered as stiffness, back and pelvic mobility, and overall amplitude and relaxation over the jumps as an evaluation of flexibility and ability to jump adequately. The horse behavior, balance and rectitude, head and neck pendulum, back and pelvic movement, stride length, and mobility during the jump were graded separately from 0 to 4, then summed to obtain a first combined score out of 20. The horses’ overall performance was also spontaneously subjectively graded out of 20 to obtain a second score. A total combined score out of 40 for D0, D7, and D14 was then obtained by addition of both scores (Supplementary Table S1).
Secondary outcomes
Visual evaluation—Previously described criteria, which took into account the thoracic and lumbosacral flexibility, hind limb propulsion, and stride length, were used to evaluate dorsal flexibility during in-hand examination of the horses in a straight line at the trot (3 to 4 m/s) and then free jumping at the canter in both directions on soft ground.8 All examinations were videotaped to allow final review after completion of the study by specialists in equine locomotion (JMD, VC, LB) who were blinded to the treatment groups. The video recordings from D0 and D2 of each horse were successively reviewed, and a subjective improvement grade of the dorsal flexibility was independently established by each observer for each condition of the examination as follows: –1, severe degradation; –0.5, mild to moderate degradation; 0, no change; 0.5, mild to moderate improvement; and 1, marked improvement. Grades were then fixed by consensus agreement, during which horses with different grades assigned by the observers were reviewed and discussed (Supplementary Table S2). A final dorsal flexibility improvement score was established by adding the trot and free jumping at canter grades together.
Quantification of the thoracolumbar mobility using inertial measurement units—Horses were equipped with 6 wireless inertial measurement units (IMUs; ProMove-mini wireless IMUs; Inertia Technology BV; triaxial accelerometer ± 16 X g, triaxial gyroscope ± 2,000°/s) placed on the head, withers (at the midlevel), thoracolumbar junction (at the level of the last rib), pelvis (at the level of the tuber sacrale), and 2 distal metacarpal areas (Supplementary Figure S1). They recorded at 200 Hz during 2 round trips on a straight line of 30 m on regular hard ground at the trot. The handler was the same person for the duration of the experiment for all horses.
Data were analyzed using custom-written Matlab2020a (The MathWorks) scripts. The dorsoventral acceleration signal was integrated twice to obtain displacement values and was high-pass filtered using a fourth-order Butterworth filter with a cutoff frequency set to 1 Hz chosen after checking that the filter suppresses the slow drift without distorting the shape of the signal.34 From the vertical displacement of the withers (W), thoracolumbar junction (TL), and pelvis (P), 2 variables were extracted for each inertial sensor: UP was the mean upward displacement (in cm) during the propulsion phase from the lowest point reached by the sensor at the end of the absorption phase to the highest point reached at the end of the propulsion phase, and DOWN was the mean downward displacement during the absorption phase from the highest to the lowest point (Figure 2).
Thoracolumbar mobility was assessed at the trot using a biomechanical beam model loaded in flexion by the weight of the abdominal mass (Figure 3). The displacements of the W and P sensors reflecting the displacement of the trunk were considered as fixed points to isolate the relative displacements of the TL sensor. The relative thoracolumbar mobility was then obtained by subtracting the average of the W and P displacement values to each TL value of UP and DOWN (Supplementary Table S3) such as presented in the following equation:
Acupuncture treatment
Treatment was tailored to each horse and performed by a certified acupuncturist (EJ) after systematic diagnostic palpation consisting in detailed digital pressure along the 6 neck meridians and along the thoracolumbar muscular groove where the bladder meridian runs, ending with specific points of the croup and gluteofemoral region. This systematic palpation highlighted hyperalgesic points associated with mobility restrictions along the spine itself, or referred pain from a limb or internal imbalances. Clinical signs and treatment for each horse are summarized (Supplementary Table S4). Puncture was performed via acupuncture needles or 21-gauge hypodermal needles that were left in place for around 10 minutes. The treatment was well tolerated by all horses. Immediate response to treatment was evaluated by palpation, and the treatment was adjusted if any residual sensitivity remained. No treatment of any kind was performed on the control group. Owners, trainer, and rider were absent from the barn during selection of the horses and treatment.
Statistical analysis
A binary classification of the primary outcome was performed, and the Fisher exact test was used. The 2 following categories were selected: (1) improvement, when the differences of the D7 – D0 and the D14 – D0 values were > 8; and (2) no improvement, when the D7 – D0 and/or the D14 – D0 values were ≤ 8. The threshold of 8 (20% of the highest score [40]) was chosen to consider the improvement as clinically relevant, to take into account a possible placebo effect, and to avoid a transient random effect.
For the secondary outcomes, the Mann-Whitney test was used due to sample size. The relative improvement of the thoracolumbar mobility measured with IMUs between D0 and D2 in each treatment group was evaluated by calculation of the difference in values between D2 and D0 relative to D0, such as presented in the following equation:
Data collected were centralized via Microsoft Excel, version 16.0 (Microsoft Corp). All statistical analyses were performed using R software, version 3.4.3 (R Foundation for Statistical Computing). Results are expressed in means and SDs or median with IQR, depending on the normal distribution of the data assessed visually.
Results
Population
Horses from both groups were similar in breed, age, exercise level, race earnings, and median values of baseline trainer and rider score, as well as propulsion UP and absorption DOWN (Table 1). Gender distribution was not similar in both groups, with 4 of 6 of the control group being female versus 5 of 6 in the treated group. One of the horses from the control group was excluded from follow-up after day 6 due to wound injury.
Characteristics of the population.
Criteria | Control group (n = 6) | Treated group (n = 6) |
---|---|---|
Breed (% [n]) | ||
Thoroughbred | 83 (5) | 17 (1) |
French Chaser | 83 (5) | 17 (1) |
Age (y [mean, SD]) | 3 ± 0 | 3 ± 0 |
Sex (% [n]) | ||
Gelding | 33 (2) | 67 (4) |
Female | 17 (1) | 83 (5) |
Earnings | ||
Absent | 100 (6) | 0 (0) |
Present | 100 (6) | 0 (0) |
Trainer and rider score D0 (median, IQR)/40 | 15.2 (9.5–17.6) | 11 (10.2–11.7) |
Propulsion (UP) D0 (mean, SD) | –1.3 (–0.1) | –1.5 (0.03) |
Absorption (DOWN) D0 (mean, SD) | 1.3 (–0.2) | 1.5 (0.04) |
Passive mobilization amplitude (median, IQR) | 1.5 (1, 20) | 2.5 (2, 3) |
Passive mobilization sensitivity | 1 (1, 1) | 0.5 (0, 1) |
D0 = Baseline before treatment. UP/DOWN = Relative dorsal flexibility obtained with inertial measurement units (IMUs) by subtracting the average of the withers and pelvis upward/backward mean vertical displacement values (cm) during the propulsion/absorption phase to each thoracolumbar value collected in Supplementary Table S2.
Evaluation of the locomotion
All the results are presented (Table 2). No adverse event occurred during the study period that could have impaired the general movement symmetry of the horses, and no subjective gait change was noticed over the study period. According to the primary outcome (rider and trainer’s evaluation of the locomotion), there were significantly more horses improved on D7 and D14 in the treated group (6/6) compared to the control group (1/6; P = .01).
Compiled results from data analysis of the primary criterium (trainer and rider score) and subjective (dorsal flexibility improvement score) and objective (UP and DOWN IMU measurements) secondary criteria.
Horse | ACUPUNCTURE | Horse | CONTROL | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Trainer and rider score (/40) | Dorsal flexibility subjective improvement score (trot/canter) | UP improvement relative to D0 | DOWN improvement relative to D0 | Trainer and rider score (/40) | Dorsal flexibility subjective improvement score (trot/canter) | UP improvement relative to D0 | DOWN improvement relative to D0 | ||||||
D0 | D7 | D14 | D0 | D7 | D14 | ||||||||
1 | 12 | 22 | 26.5 | 1 (0.5/0.5) | 0 | 0 | 7 | 16.5 | 17.5 | 20 | –1 (0/–1) | –0.1 | 0.1 |
2 | 15 | 26 | 26 | 0.5 (0.5/0) | 0 | –0.1 | 8 | 7 | 32 | 32 | 0 (0/0) | –0.1 | 0 |
3 | 11 | 39 | 39 | 0.5 (0/0.5) | –0.2 | 0.2 | 9 | 14 | Excluded | 0.5 (0.5/0) | 0 | 0.1 | |
4 | 7 | 37 | 40 | 1 (1/0) | –0.6 | 0.7 | 10 | 22 | 22 | 22 | –0.5 (–0.5/0) | –0.4 | 0.4 |
5 | 11 | 23 | 23 | –0.5 (0/–0.5) | –01 | 0.1 | 11 | 18 | 18 | 18 | 0 (0/0) | –0.5 | 0.4 |
6 | 10 | 39 | 39 | 0.5 (0.25/0.25) | 0.1 | –0.1 | 12 | 8 | 11 | 20 | –0.5 (0/–0.5) | –0.2 | 0.1 |
Median [IQR] or mean (SD) | Horses > 20% improved (D7 and D14): 6 (100%)* | 0.50 [0.5 to 0.88] * | –0.1 (0.2) | 0.1 (0.3) | Median [IQR] or mean (SD) | Horses > 20% improved (D7 and D14): 1 (20%)* | –0.25 [–0.5 to 0.0] * | –0.2 (0.2) | 0.2 (0.1) |
*Significant differences between groups (P < .05).
See Table 1 for remainder of key.
Among the secondary outcomes, horses receiving the acupuncture treatment showed a significant improvement between D0 and D2 in their dorsal flexibility at the trot and free jumping at the canter compared to control horses (P = .04). There were no statistically significant differences between treatment groups in the improvement of the mean relative thoracolumbar mobility measured with IMUs during the propulsion (UP) and absorption (DOWN) phases between D0 and D2 (Table 2).
Discussion
The purpose of this study was to evaluate whether a single acupuncture treatment improved clinical signs of axial stiffness in steeplechase racehorses from 2 days after treatment and up to 2 weeks. Our results were divided into primary and secondary outcomes to avoid multiple statistical testing. In previous studies,8,22 response to treatment as assessed by riders or trainers has already been considered relevant as an efficacy clinical variable in several controlled trials evaluating axial stiffness treatments and was selected as the primary outcome to reflect field practice. According to the results of those studies, acupuncture treatment significantly improved the horses’ locomotion and behavior when the horse was ridden at training compared to the control group 7 and 14 days after treatment.
Among the secondary outcomes comparing the improvement of both groups 2 days after treatment, only the subjective visual assessment of back mobility by expert clinicians demonstrated a significant improvement both at the trot and free jumping at the canter for the acupuncture group compared to the control group. No significant difference occurred considering the relative mobility of the thoracolumbar region with IMU objective measurements. This may be due to the fact that acupuncture treatment altered the horse’s overall locomotion pattern and made its movements more flexible, without specifically affecting the thoracolumbar segment. Indeed, the subjective visual assessment took into account the thoracic and lumbosacral mobility as well as hind limb propulsion or stride length.8 On the other hand, the present study used IMUs to measure the amplitude of the vertical displacements of the back over a whole stride, while several studies with motion capture have shown half-stride asymmetry of back movement, which were not captured in our model.35 Even if horses were judged nonlame by experts during the study period, mild gait asymmetry might have been missed by human perception.36 It would then be interesting in a future study to highlight such asymmetry within strides, all the more so since in a previous blinded crossover pilot study37 of 8 pasture horses that were sound or mildly lame on inclusion, acupuncture appeared to change horses’ gait symmetry, measured with a quantitative sensor-based gait analysis system. However, in that study and others38 aiming to calculate movements of the back using IMUs, the methodology of quantification differed from the present study in a number of ways. First, the number and general positioning of the sensors were different. Second, data analysis was based on symmetry indexes highlighting the asymmetry of back movements between the two halves of each stride (differences between the values obtained from each half-stride), while the present study analyzed the general amplitude of the thoracolumbar sensor displacement during a whole stride (average of all upward or downward vertical displacements). Finally, the vertical displacements from the TL sensor isolated from the displacement of the trunk by subtraction were analyzed here, whereas other studies focused on minimal and maximal height reached by the thoracic and pelvic sensors for the whole horse. Our results are therefore not comparable in their current state, but a dedicated analysis of similarly placed sensors with an extraction of symmetry data from the horses of the present study would be interesting as a future study.
Objective systems of quantitative measurement of back mobility at the trot to evaluate the effectiveness of back treatment have already been reported with kinematic systems, but to our knowledge, this study is the first one to use an IMU-based system.39 Accuracy of dorsoventral displacement from IMUs similar to those used in this protocol, placed along the spine of horses trotting over ground, was verified with a good correlation to the gold standard motion capture in a previous study.38 In that study, sensor data were also found to be reproductible between trials and between strides, thus allowing for data pooling. Quantification of flexion-extension angles might bring more accuracy than measures of vertical displacements to assess back movements, and the future development of algorithms for quantifying thoraco-lumbo-sacral flexion-extension angles from IMUs will bring additional information that might further improve the evaluation of back mobility. IMU systems demonstrated good reliability for quantification of flexion-extension movements in horses’ backs compared to motion capture systems.40 In this study, more sensors were placed over the back, with 2 flexion-extension angles calculated between 3 IMUs. The suitability of the method used in the present study for assessing changes in back mobility and discriminating sound horses from stiff horses needs to be validated on a large number of horses before drawing conclusions on the results. It would also be interesting in such a study to compare subjective visual assessment of back mobility to IMU-based systems. The growing number of studies using IMUs to assess back movements and the new sensor generations with improved ease of use suggest that IMUs will be more consistently used in the future in the field to assess back mobility and complete the diagnostic approach used to characterize axial stiffness. In our study, no diagnostic imaging techniques were used, to reflect the situation in racehorse stables. In France, these horses are rarely ensured, and the use of expensive imaging techniques is limited, therapeutic strategies being usually preferred as a first step. In addition, it is not uncommon for axial pain or stiffness to be poorly correlated to lesions on conventional imaging.4,41
Several studies report beneficial effects of acupuncture for the treatment of chronic axial stiffness. These studies26,30–32 have been performed using various types of acupuncture techniques. Among them, dry-needle stimulation, aquapuncture, and electro-acupuncture are the most commonly used in the West. Electro-acupuncture has been used successfully for treating axial stiffness in performance horses, and research suggests that it is more efficient than dry-needling or aquapuncture.26 However, many of these studies lack control groups, blinded evaluation, and randomization, which are essential elements to ensure an objective interpretation of the results. Nevertheless, a limited number of recent and rigorous studies32,33 have demonstrated the effectiveness of acupuncture, especially electroacupuncture, in the treatment of axial stiffness in horses. Xie et al,33 in a study of electroacupuncture versus phenylbutazone or saline, demonstrated a higher effectiveness of electroacupuncture to improve thoracolumbar pain scores after 3 sessions, with effects that lasted at least 2 weeks. In that study, however, the discipline, level of activity, and performance of horses were unknown. Because this technique is easier to perform in the field and therefore reflects routine practice, only 1 dry-needling acupuncture treatment was performed in our study.
Our study did have limitations, such as the evaluation of short-term effects of acupuncture only whereas axial stiffness is a chronic and recurring problem. It would be interesting in the future to study more precisely the duration of the effect of acupuncture and to evaluate the interest of repeating the treatments at regular intervals and with a crossover study design. Additionally, our sample size was limited to 12 horses, which may have influenced the impact of confusion bias despite the random attribution of each horse to either group. For example, both groups were not comparable regarding sex, while other studies42 have reported that the analgesic effect of acupuncture may be different in males and females. Other factors that could potentially influence axial stiffness, such as saddle fit, were not explored in this study, as its purpose was to evaluate the effect of acupuncture alone.43 Additionally, the saddles used were identical for all horses throughout the duration of the study. Further studies on a greater number of horses would be necessary to confirm our results.
Subjective evaluations from all reviewers blinded to treatment groups concur and are in favor of a positive effect on locomotion of a single acupuncture treatment on performing steeplechase racehorses showing clinical signs of axial stiffness. These results suggested that this nonconventional therapy could be used as a nondoping treatment option. The results should, however, be considered with caution given the limitations of the study.
Supplementary Materials
Supplementary materials are posted online at the journal website: avmajournals.avma.org
Acknowledgments
This work was supported by Boehringer Ingelheim Animal Health (France, Europe) through the “Bourses aux idées” organized by the Ecole Nationale Vétérinaire d’Alfort (ENVA) on April 4, 2019.
The authors declare that they had no conflicts of interest.
The authors thank M. Guillaume Lassaussaye and his team for their participation in this study.
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