Introduction

Although Travell coined the term ‘myofascial’ in relation to trigger points (TrP), the myofascial literature rarely considers the role of fascia in defining the etiology of TrPs and therapy. In the TrP literature, including this publication and Travell and Simons’ two-volume Trigger Point Manual, muscles are usually presented as individual, stand-alone structures with defined origins and insertions, contractile functions, and referred pain patterns (Travell & Simons 1992, Simons et al. 1999). Viewing muscles independently from fascial structures is quite common in anatomy books, sports medicine, physical therapy and chiropractic publications, yet does not come close to reflecting the actual reality. While this outdated model is still acceptable for teaching the basics of TrP dry needling, current advances in fascial research have shown that the role of fascia can no longer be ignored. In Part I of this chapter, Langevin reported on the effect on needling procedures on connective tissue. In this section, we will explore a theoretical framework for the role of fascia in dry needling. Unfortunately, there is no substantial research into this area, which makes this chapter by default somewhat speculative.

Brief update on fascia

Every time a needle is inserted through the skin towards a TrP, the needle passes through multiple levels of fascia. Fascia is divided into superficial and deep fascia, reflecting their topographical relationships with the skin, and muscle-related fascial layers (Langevin & Huijing 2009, Findley et al. 2012). Superficial fascia consists of subcutaneous ‘loose’ or non-dense connective tissue, which contains collagen, elastin, and some fat tissue. Deep fascia is comprised of a connective tissue membrane that sheaths muscles, nerves, vessels, and certain organs. Deep fascia has no fat tissue. The deep fascia and muscles are separated by a layer of loose connective tissue rich in hyaluronan, which is thought to facilitate the free sliding of adjacent layers (Stecco et al. 2011). Hyaluronan is a glycosaminoglycan polymer of the extracellular matrix and has also been identified in between various muscle tissues in rats and humans (Laurent et al. 1991, Piehl-Aulin et al. 1991).

Muscle-related layers consist of epimysium, perimysium and endomysium. The epimysium consists of the fascia, which surrounds single muscles, and is directly connected with the perimysium, which surrounds muscle fiber bundles, and the endomysium, which surrounds deeper muscles fibers (Findley et al. 2012). The endomysium covers the full length of myofibrils until the myotendinous junction (Trotter & Purslow 1992, Trotter, 1993) and is the main aspect of the extracellular matrix involved in muscle flexibility (Passerieux et al. 2009).

The tension of the deep fascia is maintained by many muscular attachments. Muscles distribute a significant part of contractile forces onto fascial structures, which subsequently will increase joint stability and facilitate movement involving several other muscles (Findley 2012). Myofascial force transmission occurs between antagonistic muscles via the endomysium (Huijing 2009a, 2009b, 2009c). Interestingly, Maas Sandercock (2009) demonstrated that although the soleus muscle in a cat does have strong mechanical connections with synergistic muscles, the force transmission from the soleus muscle does not appear to be affected by length changes of its synergists, which means that not all muscles appear to use the same mechanisms for force transmission.

The most common cells found in connective tissue are fibroblasts, which play a significant role in the synthesis of collagen, ground substance, elastin and reticulin (Cantu & Stanborough 2012). Normally, fibroblasts are more or less shielded in the extracellular matrix, but their interactions with the collagen matrices are determined partially by the degree of tension in the matrix. Under high tension, fibroblasts feature stress fibers and focal adhesions, and appear lamellar in shape, while under low stress they are more or less rounded and somewhat dendritic in nature (Grinnell 2003, Langevin et al. 2005, 2010, 2011, Miron-Mendoza et al. 2008). Lamellar fibroblasts have a characteristic high matrix biosynthetic activity and they can differentiate in myofibroblasts, which feature a contractile apparatus of actin microfilaments and non-muscle myosin (Tomasek et al. 2002). Myofibroblasts are involved in wound closure, but are also active during muscle contractions (Yahia et al. 1992,1993) and the formation of Dupuytren’s contractures (Satish et al. 2011). Perimysium, especially, has a high density of myofibroblasts and they may play a significant role in muscle contractibility and possibly in the formation of TrPs (Schleip et al. 2005, 2006a, 2006b, 2008). If direct connections are present between TrPs and perimysium, would that suggest that myofascial TrPs are more prevalent in tonic muscles, since they contain more perimysium than phasic muscles (Schleip et al. 2006a)?

Collagen fibers in a particular layer are oriented in the same plane and direction; however, they are at a 78° angle with the fiber direction in adjacent layers (Purslow 2010, Benetazzo et al. 2011). This may have implications for manual TrP therapy. Chaudhry et al. (2007, 2008, 2012) found that a greater fiber angle makes collagen fibers more resistant to longitudinal stretching. Since the muscle fiber direction does not necessarily match the fascia fiber direction, further research should examine whether stretching exercises after manual TrP release or dry needling have evidence-based value and if so, what the optimal stretching methods entails.

Fascia and trigger points (TrPs)

As early as 1944, one effect of TrP injections was attributed to mechanical stimulation (Steinbrocker 1944). Dry needling is similar to injection therapy and generally thought to be equally effective (Cummings & White 200, Ga et al. 2007). Because the needle has to pass through the superficial and deep fascia to reach TrPs, the effects on these structures has to be considered on treatment outcomes, even though there is no research confirming or denying this hypothesis.

In Part I of this chapter, Langevin mentioned that rotation of solid filament needles can cause an ‘internal’ stretch of the tissues. In a previous paper, Langevin et al. (2001a) suggested that there may be a coupling between the needle and body tissues consisting of surface tension and electrical attraction. The electrical attraction is probably fairly weak, but may be sufficient to cause some initial winding of tissue around the needle and contribute to the mechanical effect of dry needling (Dommerholt 2012). Rotating a needle that has been placed in a taut band or a TrP is advocated in dry needling courses as the most direct method of stretching the taut band or muscle contracture (Gunn & Milbrandt 1977). As every muscle fiber bundle is surrounded by fascial layers, the question emerges whether rotation of the needle actually stretches the taut band and muscle fibers or the deeper connective tissue fibers, or perhaps both muscle and fascia (Langevin et al. 2001a). With needling rat abdominal explants, Langevin et al. observed pulling of the sub-dermal tissue without structural changes in the dermis and muscle (Langevin et al. 2001a). Does DN change the viscoelastic properties or behaviour of fascia? If so, fascial manipulation techniques should probably play a greater role in trigger point therapy as suggested by Stecco and others (Stecco 2004, Gröbli & Dommerholt 1997).

Taking this a step further, it is conceivable that fascial restrictions of the perimysium contribute to taut band formation. Perimysium seems to adapt more to changes in mechanical tension than other intramuscular connective tissues and is capable of increasing muscle stiffness (Passerieux et al. 2007). On the other hand, taut bands are palpated perpendicular to the muscle fiber direction and the direction of fascial fibers does not match the direction of muscle fibers. Stecco et al. (2011) speculated that changes in the density of loose connective tissue of the deep fascia and the hydrodynamics of hyaluronan may contribute to the development of myofascial pain.

Stretching connective tissue with a needle has been shown to stretch and reduce the tissue tension, flatten fibroblasts and remodel the cytoskeleton (Langevin et al. 2011). The mechanical stimulation by a needle may activate mechanotransduction (Langevin et al. 2001a). It is not known whether the instantaneous reduction of local and referred pain following DN or TrP injections is related to stimulation of fibroblasts. Langevin et al. (2001b, 2002, 2006) showed that the effects of acupuncture needling can at least partially be explained by stimulation of fibroblasts. Does stimulation of TrPs involve myofibroblasts and result in similar mechanical signalling and a reduction in nociception (Dommerholt 2012)?