The trigger point is a local area of somatic dysfunction that behaves in a specific manner. They develop when there is localized shortening of a fascicle of muscle fibres in which a group of sarcomeres remain in a state of contraction. This contracture can be palpated as ’taut band’ that is painful on palpation and gives rise to referred pain from the target area. The pain can be quite sharp in quality which can produce a jump sign or aggressive behaviour such as biting when the trigger point is stroked. Due to a reduction in vascularization and a heightened sympathetic tone there is a lowered peripheral temperature in a trigger point.
There are many different causes for trigger point formation, they can develop in a muscle when it is subject to direct trauma, acute strain, sustained stress, overwork, hormonal and nutritional imbalances. Nerve disorders such as interneuron dysfunction in both nerve plexus and in the spinal cord can allow trigger points to develop and become active. Dysafferentation is also a cause that develops with antagonist muscle imbalance such as the flexor and extensors imbalance associated with an injured or painful joint.
As discussed above trigger points behave in a specific manner, they can develop silently before developing into stronger active points where they become tender to palpation. Once they become strong active points they can develop spill over or satellite points adjacent too, this can make trigger point evaluation much more difficult.
In the acupuncture work up the information gathered from trigger points can allow the acupuncturist to pinpoint the region of pain in the body. Often time in performance horses the main cause of trigger point formation is from referred pain in joints and soft tissues, this causes predictable trigger point formation on the body which can be mapped out. However this is not always the case and the other causes discussed above should be considered in determining the trigger point information. Even with anti-inflammatory treatment a joint trigger point most often will still remain active until treatment of the point or a reduction in stress and rest is used.
Dry needling and aqua-puncture with substances such as vitamin B12 and saline are very effective methods of treatment for acupuncture. These two forms of acupuncture cause a local release of build up intracellular potassium which depolarises the trigger point and stimulates the nerve feed back loop responsible for the trigger point formation. Other benefits from acupuncture and trigger point therapy include muscle strengthening and restoration of full muscle length which benefits proper joint function and smooth joint function.