In the last blog, we discussed the first model (The Radiculopathy Model) that helps explain why Dry Needling works. Now we will continue with the second of four models. This one is probably the most well-known one and there is a plethora of medical literature supporting it. Again, we will try to explain any concepts that are a little difficult to understand. These models really shed light into how our bodies work and they are great to learn about.
The Trigger Point Model
Myofascial Trigger Points (MTrPs, or TrPs for Trigger Points) are defined as ‘hyper-irritable spots in skeletal muscle that are associated with a hypersensitive palpable nodule in a taut band’ (Travell and Simons). The resultant pain/discomfort that one gets due to such points is referred to as myofascial pain syndrome (MPS). Simply put, MPS is defined as ‘sensory, motor, and autonomic symptoms caused by myofascial trigger points’ (Travell and Simons). Sensory symptoms refer to what you feel, motor symptoms refer to how the muscles work, and autonomic symptoms refer to the things that you do not realize. This seems a little odd, but consider what happens when you bang your arm really hard. You will feel the pain (sensory), the muscle might be painful and not contract properly (motor), and your heart rate goes up as does your respiration due to the ‘adrenaline rush’ (autonomic) of the injury.
MTrPs exist where there is macro (large) trauma and/or micro (small or repetitive use injury) trauma. These traumas cause an excessive release of calcium in the muscle and this leads to shortening of the muscle. When the damage goes untreated, the excessive shortening begins to cut off oxygen supply to the area, adversely affecting the cell’s ability to produce ATP. Without ATP, the muscle cannot relax. To go along with this, excessive acetylcholine (a neurotransmitter responsible for activating muscles) release is found in the areas of MTrPs. Along with the lack of ATP, the excessive acetylcholine helps to form the knotted, tight/taut muscle fibers associated with MTrPs. The acetylcholine cannot be broken down due to the altered function and toxic state in the MTrP. In effect, the toxicity is due the acidic environment and this acidity inhibits the breakdown of the acetylcholine. To top it all off, the area will also have a lot of byproducts of pathological muscle function such as serotonin, leukotrienes, prostaglandins, bradykinins, and more. These byproducts further the inflammatory and pathological state of the tissue, causing pain and dysfunction.
There are 2 types of MTrPs that we deal with (there are really four, but for conversation here, we will only cover the two most common): 1. Active TrPs that cause pain in the location of the actual TrP and refer pain or altered sensation (paresthesia) distally. 2. Latent TrPs, which do the same thing, but they must first be stimulated to do so.
So, where does Dry Needling come in with all of this information about MTrPs? With the TrPs model, taut bands, very tender spots on the band, a ‘jump’ sign (pain catches you so quickly that it makes your body jerk), and pain recognition are typically found if you have a skilled manual therapist applying the Dry Needling. It is interesting to note that trigger points, if active or latent, tend to show up in the same parts of the particular muscle(s) on everyone. So, a TrP found in the vastus lateralis muscle (lateral quadriceps muscle) on one person, if he/she has TrPs in that muscle, will tend to show up in the same place/places of the vastus lateralis on another person, if that person also has TrPs in that muscle.
Dry Needling is used to help diagnose and treat TrPs and it can be used to elicit the The Local Twitch Response (LTR). This is really the ‘meat and potatoes’ of Dry Needling according to the Trigger Point Model. The LTR is an involuntary spinal cord reflex contraction of the muscle fibers in a tight/taut band following treatment or needling of the band/TrP. According to the TrP model, when applying a deep type of therapy, such as Dry Needling, eliciting the LTR is necessary. In effect, the LTR confirms that the needle was put in the right place, and by doing so, likely resolution of the Trigger Point is achieved. This, in turns, help to eliminate pain and dysfunction in the area being treated.
Dry Needling Support Models Part 3 of 4 will discuss The Spinal Segmental Sensitization and Pentad Model. Please feel free to comment or ask any questions here on the blog.