Muscle as pain generator: Myofascial trigger points, recognition, and treatment (Proceedings)

It is not possible to achieve designed goals of physical rehabilitation in the canine patient without adequate pain management. Often in these patients, pain is not only generated from the original injury or trauma of surgery but also additionally from the functional impairment(s) brought about by the primary issues. Changes in weight distribution or posture can overload compensating portions of the body. It is this overload, specifically of muscles, that may result in the development of myofascial pain in areas of the body other than the primary injury. Recognition and management of secondary problems become critical in the achievement of desired outcomes.

Examination for pain is separate but related to the physical, orthopedic and neurologic examinations. While the orthopedic examination mainly focuses on joints the pain examination incorporates this as well as what is between the joints, the myofascial tissues.

With articular dysfunction comes myofascial dysfunction and vice versa. Localization of pain in the myofascial tissues is followed by examination of the joint(s) that those painful muscles exert function. Myofascial pain can also be found in muscles that can become overloaded due to an injury and/or functional impairment. Examples of this the development of myofascial pain in the limb opposite the initial injured limb and myofascial pain in the muscles of the forelimbs seen with hind limb problems. Changes in body posture as the result of injury may result in the development of myofascial pain. Myofascial pain can also develop within muscles innervated by injured peripheral, spinal nerves and spinal cord segments.

In many patients the primary source of pain and dysfunction is known, therefore examination can focus on groups of muscles that would be suspect to be affected. Therapy plan can then include treatment directed toward both primary and secondary issues. In so doing restoration of normal function and the full benefit maybe appreciated.

Theories still exist as to the development of myofascial pain due to myofascial trigger points. Gerwin, Dommerholt and Shah expanded one of the original theories of motor endplate dysfunction described by Simons. Their conclusions were that in injured muscle there is release of substances that activate muscle nociceptors and cause pain and facilitate the release of acetylcholine, inhibits it breakdown and up-regulate acetylcholine receptors at the motor endplate. This loss of equilibrium results in a persistent muscle fiber contraction, as is characteristic of the myofascial trigger point (MTrP).

Muscle injury in the rehabilitation patient can possibly occur in one of several ways; 1) Low-level muscle exertions of muscle groups leading to muscle overuse. This can be brought about by adaptations in posture or protection of a painful joint, 2) overload of a muscle groups usually due to increase weight bearing possibly related to eccentric contractions.

In overuse due to low level muscle contractions, the Cinderella Hypothesis could explain the development of myofascial pain and MTrPs in dogs. The Cinderella hypothesis developed by Hagg in 1988 postulates that this type myofascial pain is caused by selective overloading of the earliest recruited and last de-recruited motor units. This results in metabolically overloaded motor units with subsequent activation of autogenic destructive processes and muscle pain.

Myofascial pain in muscle overload maybe the result of maximal eccentric exercise or eccentric exercise in unconditioned muscle. Eccentric contractions often occur during ambulation in a limb(s) that is compensating for decrease or non-weight bearing of another limb.

Clinical Application

Discussion of some of the more common clinical presentations of myofascial pain in the rehabilitation patient will help in understanding the principles discussed previously.

1. Myofascial pain in the upper forelimbs due to cranial weight shift associated with problems of the hind limbs.

Cranial weight shift with hind limb problems can produce overload of forelimb muscles especially the m. infraspinatus, m. deltoideus and m. triceps-long head. MTrPs will develop within these muscles making ambulation even more painful. Low-level muscle exertions due to postural changes while standing and eccentric contractions can occur during ambulation, especially in the patient with a hopping action in the hind limb. Additional muscles that can become painful are the dorsal cervical paraspinals, m. trapezius and any of extrinsic muscles of the forelimb.

2. Myofascial pain in the muscles of the contralateral limb.

Limited or non-weight bearing can overload muscles in the contralateral limb due to increased weight bearing during ambulation and standing. Both eccentric contractions and low-level muscle contractions can be the cause of muscle damage and subsequent development of MTrPs. In the forelimb is can be the same muscles as described in #1. In the hind limb it is mainly the cranial muscles of the thigh; m. Sartorius, m. tensor fascia latae, m. rectus femoris and the vastus group.

3. Myofascial pain in muscles that flex the coxofemoral joint in the limited or non-weight bearing hind limb.

In this situation the coxofemoral joint is held in slight to moderate flexion by activation of the hip flexors. This is accomplished by low-level muscle contractions in the iliopsoas (m. psoas major and m. iliacus), m. sartorius, m. tensor fascia latae, and m. rectus femoris. The low-level muscle contractions never allow adequate rest for first recruited muscle fibers resulting in overload and the formation of MTrPs. This is a common complication of the postoperative stifle patient and can produce add to and/or maintain severe and even non-weight bearing lameness. It also possible for these muscles to be overworked during ambulation by increased hip flexion needed to move the limb forward without adequate stifle extension.

Myofascial Trigger Point Therapy

     • Trigger point dry needling – MTrP

     • Trigger point injections

     • Manual trigger point release and massage

     • Therapeutic Laser

     • Extracorporeal Shockwave

     • Pulsed Electromagnetic Field therapy (PEMF)

Conclusion

The possibilities regarding the occurrence of myofascial pain in the rehabilitation patient are limitless. Thorough routine myofascial examination is needed so that proper supportive therapy can be instigated. Reducing the overall pain burden aides in the overall management of pain and thus in the rehabilitation patient accomplishment of goals.