Equine Myofascial Pain

Written by our guest: Maria Calatayud Bonilla
CHARTERED PHYSIOTHERAPIST- EQUINE PHYSIOTHERAPIST Spain; ICOFCV Col. 4048
Coordinator of Special Interest Group in Animal Physiotherapy of Spain (CGCFE)
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We tend to think that musculoskeletal pain occurs during the healing process of a disabling injury, but within the general category of musculoskeletal pain, myofascial pain is a common diagnosis. 

More specific than musculoskeletal pain

We tend to think that musculoskeletal pain occurs during the healing process of a disabling injury such as enthesitis, tendonitis, desmitis, fibrillar tears and fractures. Tendon injuries, for example, can severely debilitate a horse and completely throw out a training programme, just as they do in human athletes. But within the general category of musculoskeletal pain, myofascial pain is a common diagnosis.

Myofascial Pain Syndrome

Epidemiologically, a high percentage of patients present with myofascial pain caused by the presence of trigger points (TrPs).¹ We know that 80% of the world’s population will suffer some episode of myofascial pain during their lives², which has encouraged research in this field.

Myofascial pain is not completely limiting; it may not paralyze the patient’s activity, but it does present in the form of local pain, referred pain, palpation pain, stiffness, muscle weakness, dysfunction and alterations in the motor pattern. The main characteristic of Myofascial Pain Syndrome is the presence of TrPs³.

Maria Calatayud Bonilla

Myofascial Trigger Points

TrPs are nodules that are hypersensitive when palpated, located within a taut band of skeletal muscle. Simons⁴ describes three essential clinical diagnostic criteria for the presence of TrPs:

1. the existence of a taut muscular band,
2. a painful, hypersensitive spot in the taut band,
3. and pain referred to and recognized by the patient, caused by the stimulation of a sensitive spot.

In addition to these minimum criteria for diagnosis, six other confirmatory characteristics may be present:

1. response of local spasm when palpating the TrPs,
2. jumpiness (a “flight” reaction by the patient),
3. recognition of the pain by the patient,
4. predictable referred pain patterns,
5. weakness or muscle tension and
6. pain during the contraction or stretching of the affected muscle.⁵

In humans, the diagnosis for TrPs is currently clinical and relies upon the identification of the TrPs through palpation.⁶ 

Maria Calatayud Bonilla

Diagnosing myofascial trigger points through palpation.

Clinicians have the best tools to diagnose trigger points; thanks to their palpatory skills, they can confirm the presence of the taut band and locate the TrPs, and of course, in humans, patients can confirm the clinical signs caused by the TrPs and describe what they are feeling. However, clinicians still need to be well trained in palpation, and possess the necessary sensitivity to appreciate subtle changes in tissue. To detect TrPs takes a great deal of sensitivity and experience.

Active and latent trigger points

Various studies demonstrate good inter- and intra-examiner reliability when clinicians are both skilled in palpation and experienced.⁷ Palpation of the TrPs will activate referred pain, whether active or latent; the experience will differ according to the presence or absence of active pain. Latent TrPs produce pain only with external stimuli. In cases of both active and latent pain, it will be the patient who confirms the diagnosis; he will perceive the pain and describe it as “his pain”. Of course, this cannot happen with horses.

Defining pain

The International Association for the Study of Pain (IASP) defines human pain as “an unpleasant sensory and emotional experience associated with current or potential tissue damage or described in terms of such damage.” Zimmerman defines animal pain as “an aversive sensory experience that elicits protective motor actions, results in avoidance and may modify species-specific traits of behavior including social behavior.”⁸

Diagnosing pain in veterinary rehabilitation

In veterinary medicine, clinicians struggle with diagnosing pain, and the use of pain scales based on the animal’s behavior is becoming common, especially in research. We understand that a horse is presenting with myofascial pain when we locate the sensitive nodule within a taut band during palpation, and the horse reacts with a pain response, as described by various authors. Dalla Costa^{9 10} developed the Horse Grimace Scale as a tool to assess pain in horses after castration, and uses the same scale to assess pain in acute laminitis. In addition, scientific evidence confirms the use of algometry as a valuable tool to evaluate myofascial pain in horses. Both of these may be used in conjunction with observation; simply observe the horse’s facial and bodily response to pressure.¹¹

Maria Calatayud Bonilla

Myofascial pain in equine rehabilitation

In clinical practice, my main area of ​​interest is myofascial pain. An evaluation begins with the clinical history. Clinical signs that confirm the presence of pain could be refusal to be mounted, bucking, failure to bend, short striding, refusal to collect and difficulties during the canter and transitions. The static evaluation adds complementary information, but palpation is the fundamental tool to assess the affected muscles.

Evidence-based practice and equine myofascial pain

We see a great deal of research into myofascial pain in humans, but very little in animals. Great scope therefore exists for research into equine physiotherapy, which might be guided by advances in human research.¹² Physiotherapy is a focused approach to managing myofascial pain. From my own research, from the evidence I have read, and from experiences in my own clinical practice, I am convinced that physiotherapy is helpful to horses experiencing myofascial pain.

REFERENCES

1. Cummings, M., & Baldry, P. (2007). Regional myofascial pain: diagnosis and management. Best practice & Research Clinical Rheumatology, 21(2), 367-387.
2. Srbely, J. Z., Dickey, J. P., Lee, D., & Lowerison, M. (2010). Dry needle stimulation of myofascial trigger points evokes segmental anti-nociceptive effects. Journal of Rehabilitation Medicine, 42(5), 463-468.
3. Dommerholt, J. (2011). Dry needling—peripheral and central considerations. Journal of Manual & Manipulative Therapy, 19(4), 223-227.
4. Simons DG. New views of myofascial trigger points: etiology and diagnosis. Arch Phys Med Rehabil 2008;89:157–9.
5. Cagnie, B., Dewitte, V., Barbe, T., Timmermans, F., Delrue, N., & Meeus, M. (2013). Physiologic effects of dry needling. Current Pain and Headache Reports, 17(8), 348.
6. Rathbone, A. T., Grosman-Rimon, L., & Kumbhare, D. A. (2017). Interrater agreement of manual palpation for identification of myofascial trigger points. The Clinical Journal of Pain, 33(8), 715-729.
7. Barbero, M., Bertoli, P., Cescon, C., Macmillan, F., Coutts, F., & Gatti, R. (2012). Intra-rater reliability of an experienced physiotherapist in locating myofascial trigger points in upper trapezius muscle. Journal of Manual & Manipulative Therapy, 20(4), 171-177.
8. Ashley, F. H., Waterman‐Pearson, A. E., & Whay, H. R. (2005). Behavioural assessment of pain in horses and donkeys: application to clinical practice and future studies. Equine Veterinary Journal, 37(6), 565-575.
9. Dalla Costa, E., Minero, M., Lebelt, D., Stucke, D., Canali, E., & Leach, M. C. (2014). Development of the Horse Grimace Scale (HGS) as a pain assessment tool in horses undergoing routine castration. PLoS one, 9(3), e92281.
10. Dalla Costa, E., Stucke, D., Dai, F., Minero, M., Leach, M., & Lebelt, D. (2016). Using the horse grimace scale (HGS) to assess pain associated with acute laminitis in horses (Equus caballus). Animals, 6(8), 47.
11. Haussler, K. K., & Erb, H. N. (2006). Mechanical nociceptive thresholds in the axial skeleton of horses. Equine Veterinary Journal, 38(1), 70-75.
12. McGowan, C. M., Stubbs, N. C., & Jull, G. A. (2007). Equine physiotherapy: a comparative view of the science underlying the profession. Equine Veterinary Journal, 39(1), 90-94.