The lumbosacral spine plays a central role in sustaining the postural stability of the body; however, the lumbar spine alone is not capable of sustaining the normal loads that it carries daily (Crisco et al. 1992). To stabilize the lumbar vertebrae on the sacral base requires the assistance of a complex myofascial and aponeurotic girdle surrounding the torso (Bergmark, 1989; Cholewicki et al. 1997; Willard, 2007). On the posterior body wall, the central point of this girdling structure is the thoracolumbar fascia (TLF), a blending of aponeurotic and fascial planes that forms the retinaculum around the paraspinal muscles of the lower back and sacral region (Singer, 1935; Romanes, 1981; Clemente, 1985; Vleeming & Willard, 2010; Schuenke et al. 2012). This complex composite of fascia and aponeurotic tissue is continuous with paraspinal fascia in the thoracic and cervical regions, eventually fusing to the cranial base. Numerous trunk and extremity muscles with a wide range of thicknesses and geometries insert into the connective tissue planes of the TLF, and can play a role in modulating the tension and stiffness of this structure (Bogduk & Macintosh, 1984; Vleeming et al. 1995; Barker & Briggs, 1999; Vleeming & Willard, 2010; Crommert et al. 2011; Schuenke et al. 2012).
Integration of the passive connective tissues and active muscular structures of the lumbopelvic area, and the relevance of their mutual interactions in relation to low back and pelvic pain. Muscular forces are transmitted through associated endo- and epimysial connective tissue matrices into the surrounding skeletal system via ligaments, tendons and aponeuroses. Moments and reaction forces generated by muscles and their associated passive structures combine to provide equilibrium at the multiple degrees of freedom of the lumbar spine and sacroiliac joints. The passive structures also interact with the muscular system through their role as sensory organs, thereby adding a component of feedback control to the system (Solomonow, 2010; Vleeming & Willard, 2010).
The TLF is a critical part of a myofascial girdle that surrounds the lower portion of the torso, playing an important role in posture, load transfer and respiration
TFL is a complex arrangement of multilayered fascial planes and aponeurotic sheets.
Fascia is an important and often misunderstood concept in medicine. Fascia is an organ system. Fascia is composed of irregularly arranged collagen fibers, distinctly unlike the regularly arranged collagen fibers seen in tendons, ligaments or aponeurotic sheets .
Conversely, tendons, ligaments and aponeuroses have a pronounced regular arrangement of collagen fibers thus specializing the tissue to resist maximal force in a limited number of planes, while rendering them vulnerable to tensional or shear forces in other directions. Where as fascia with its irregular weave of collagenous fibers is best suited to withstand stress in multiple directions.
TFL is composed of aponeurotic structure and fascial sheeth.
Structure of TLF
The TLF is a girdling structure consisting of several aponeurotic and fascial layers that separates the paraspinal muscles from the muscles of the posterior abdominal wall. The superficial lamina of the posterior layer of the TLF (PLF) is dominated by the aponeuroses of the latissimus dorsi and the serratus posterior inferior. The deeper lamina of the PLF forms an encapsulating retinacular sheath around the paraspinal muscles. The middle layer of the TLF (MLF) appears to derive from an intermuscular septum that developmentally separates the epaxial from the hypaxial musculature. This septum forms during the fifth and sixth weeks of gestation. The paraspinal retinacular sheath (PRS) is in a key position to act as a ‘hydraulic amplifier’, assisting the paraspinal muscles in supporting the lumbosacral spine. This sheath forms a lumbar interfascial triangle (LIFT) with the MLF and PLF. Along the lateral border of the PRS, a raphe forms where the sheath meets the aponeurosis of the transversus abdominis. This lateral raphe is a thickened complex of dense connective tissue marked by the presence of the LIFT, and represents the junction of the hypaxial myofascial compartment (the abdominal muscles) with the paraspinal sheath of the epaxial muscles. The lateral raphe is in a position to distribute tension from the surrounding hypaxial and extremity muscles into the layers of the TLF. At the base of the lumbar spine all of the layers of the TLF fuse together into a thick composite that attaches firmly to the posterior superior iliac spine and the sacrotuberous ligament. This thoracolumbar composite (TLC) is in a position to assist in maintaining the integrity of the lower lumbar spine and the sacroiliac joint
Compartmentalization of paraspinal muscles
the paraspinal muscles are depicted as being contained in a fascial compartment ; however, terminology and descriptions concerning the layers of this compartment vary considerably. Some authors consider the compartment to be a continuous sheet of fascia wrapping around the paraspinal muscles and attaching to the spinous process posteromedially and transverse process anterolaterally. Paraspinal muscles are contained in a sealed osteofibrous compartment attached to the spinous processes on the midline and the transverse processes anterolaterally.
Paraspinal muscles are contained in a sealed osteofibrous compartment attached to the spinous processes on the midline and the transverse processes anterolaterally . On the lateral extreme of the compartment, it is joined by the thick aponeurosis of the TrA; this junction point is termed the lateral raphe.
The fascia covering the paraspinal muscles forms a continuous sheath to which the aponeurosis of the TrA contributes laterally.
The TLF is a structural composite built out of aponeurotic and fascial planes that unite together to surround the paraspinal muscles and stabilize the lumbosacral spine.
MUSCULAR ATTACHMENT OF TLF
The latissimus dorsi has a broad attachment through the thoracolumbar fascia from the lower six thoracic spinous processes, all of the lumbar spinous processes and sacrum, and the iliac crest. The thoracolumbar fascial attachment of the latissimus dorsi muscle provides the mechanism for this muscle to affect the lumbopelvic alignment.
Contraction of the latissimus dorsi muscle creates an extension force on the spine and tilts the pelvis anteriorly. If the muscle is short, the back extends as a compensatory movement when shoulder flexion stretches the muscle to the limits of its length. Consistent with the concept of relative flexibility if the latissimus dorsi is stiffer than the abdominal muscles, which limit lumbar extension, the back extends when the latissimus dorsi stretches, even when the muscle is not short. In the patient with low back pain that occurs with extension, the shortness or stiffness of this muscle contributes to pain when he or she reaches overhead.
The lateral iliocostalis muscles and the medial longissimus attach to TFL and insert cranially to ribs.The lateral fibers of the internal oblique originate from the middle one third of the intermediate line of the iliac crest and thoracolumbar fascia. TrA originates from TLF along with lower six ribs and iliac crest. Through its attachment to the TLF TrA contributes to stabilisation of lumbar spine.
Innervation of the TLF
While most neuroanatomical studies of lumbar region explored the discs facet joints and spinal ligaments, there is a comparable lack of histological studies and related knowledge about the innervations of TLC. The density of nerve fibres in the PLF appears to be even higher than that of underline muscle studies confirm that the posterior layer contains sensory nerves terminationg in this tissue.
Several studies performed on rats suggest that the PLF is innervated by the dorsal rami of spinal neves.Tagichi et al(2008) report that the sensory endings project to spinal cord areas that are located in the dorsal horn to three segments cranially relative to the location of the terminal endings. This innervation pattern appears to be congruent with the underlying musculature. The similarity in the innervations pathways of the fascia corresponding with the segmental innervation of these underlying muscles (‘myotomes’) suggests that the overlaying fascia may also contain a segmentally related pattern of innervation. In reference to the posterior layer of the TLF, Tesarz et al. (2011) have suggested the term ‘fasciotomes’ for such segmental innervations fields. Verification of a clear segmental innervations could have implications for the potential role of the lumbar fascia in low back pain.
The high density of sympathetic fibres
The presence of a network of sympathetic nerves in human TLF was first reported by Hirch(1963). More recently a high density of sympathetic neurons was found in this fascia of humans. These sympathetic nerves accompanied blood vessels. This suggests that these nerves have a strong vasomotor component. If some of these fibres.
If some of these fibers are ergoreceptors or other mechanosensitive interoceptors, which are sensitive to muscle contraction, it is possible that they could exert a modulating effect on vasomotor activity and sympathovagal balance systemically in response to movement (De Meersman et al. 1998). Stimulation of those vasomotor fine nerve endings could serve as a cause of ischemic pain.
Staubesand et al. (1997), as well as Tesarz et al. (2011), proposed that a close relation could exist between the sympathetic nervous system and the pathophysiology of fascial disorders. This could potentially explain why some patients with low back pain report increased intensity of pain when they are under psychological stress.
Hstological examinations do not yet allow one to come to conclusion as to whether this tissue does in fact contain sufficient proprioceptive innervation. An improved understanding of the proprioceptive capacity of human TLF could possibly increase their effectiveness.
Potential nociceptive role
The sensory innervation of the TLF suggests at least three different mechanisms for fascia-based low back pain sensation: (1) microinjuries and resulting irritation of nociceptive nerve endings in the TLF may lead directly to back pain; (2) tissue deformations due to injury, immobility or excessive loading could also impair proprioceptive signaling, which by itself could lead to an increase in pain sensitivity via an activity-dependent sensitization of wide dynamic range neurons; and finally (3) irritation in other tissues innervated by the same spinal segment could lead to increased sensitivity of the TLF, which would then respond with nociceptive signaling, even to gentle stimulation. Wether or not each of these scenarios (or various combinations of them) manifest in low back pain, or how often they occur remains to be examined more closely in the future. Clarification of these questions could provide useful contributions for the treatment and prevention of back pain.
Distribution of nerve terminals in the TLF Only superficial sublayer have appreciable evidence of innervations.
Tonus/ stiffness regulation of lumbar fascia
Myofibroblasts are connective tissue cells with an increased contractile force, and are responsible for wound closure (Grinnell, 1994) as well as pathological fascial contractures such as morbus Dupuytren contracture (Shih & Bayat, 2010) or frozen shoulder (Bunker & Anthony, 1995; Ko & Wang, 2011). While the short-term contractile ability of myofibroblasts is considerably weaker compared with skeletal muscle fibers, an incremental summation of their cellular contractions together with remodeling of the surrounding collagenous matrix could lead to a strong tissue ‘contracture’ over time (Tomasek et al. 2002).
Immunohistochemical examination of samples from the TLF in two cases of patients with low back pain demonstrated a myofibroblast density comparable to that found in frozen shoulders. It is an intriguing thought that some cases of low back pain may be associated with a similar stiffening of the TLF, in which case such a condition could be described as ‘frozen lumbars’. High sympathetic activity might be a contributing factor for stiffness and loss of elasticity in the TLF. Other contributing factors could be genetic makeup, the presence of inflammatory cytokines and presence of frequent micro-injuries.
The lumbosacral region can be conceptualized as the union of three large levers: the spine and the two legs. These movement arms are united by TLC (thoraco lumbar composite which contains fascia and poneurosis).
This fascial and aponeurotic composite is affected through the attachments of several large groups of muscles: the bridging muscles from the upper extremity; muscles of the lower extremity; and the torso muscles including both epaxial and hypaxial components.
The bridging muscles of the upperlimb are trapezius and LD, bridging the gap between d extremiry and the TLF. Through this lumbosacral region is biomechanically coupled to the arms.The muscles of lowerlimb that can reach the TLF include Glut Max and biceps femoris.
The torso muscles involved in influencing this fascial and aponeurotic composite include the lumbar epaxial muscles and hypaxial muscles such as the TrA and the internal oblique, and possibly a small part of the external oblique.
Biomechanical properties of TLF
Researchers found that successive stretches produced an increase in the stiffness of the fascia, which showed signs of recovery towards baseline within a rest period of 1 h. It was also demonstrated that isometrically stabilized stress on the tissue resulted in gradual tightening of the tissue. The tightening was deduced from the observation that it required an increased load to maintain the initial strain on the tissue. This last finding is fascinating as it suggests that in vitro isolated connective tissue samples somehow change their own physical properties without the help of the normally attached muscles. Following attempts to eliminate the obvious sources of the tightening, such as changes in hydration, ionic balance and temperature, the authors propose the presence of muscle fibers in the fascia inducing this effect in vitro.
These findings could have significant implications for practitioners specialized in the treatment of the locomotor system, particularly those using techniques such as manual medicine.
When the spine is placed in full flexion, the TLF increases in length from the neutral position by about 30% (Gracovetsky et al. 1981). The expansion in length of this tissue is accomplished by a tightening in width. This deformation places ‘strain-energy’ (Elasticity) into the tissue, which should be recoverable in the form of reduced muscle work when the spine moves back in extension. Back muscles(extensors) have to use less energy to come back to original position.
Based on its physical properties, the deformation of the TLF offers an interesting mechanism for increasing efficacy of the extensor muscles of the back and stabilizing the spine. Any muscle or group of muscles that can resist the narrowing of the TLF by applying laterally directed traction force to the lateral margins of this structure is essentially applying an extensor force to the lumbar spine. The TLF is arranged in a position making it capable of creating a sizable extensor moment, which is especially important because passive (non-muscular) tissue develops less compressive strain on the intervertebral than active contraction of muscles.
Muscles and TLF
Several muscles of various dimensions attach to the TLF and its caudal composite. Examples include the Latismus dorsi (LD), gluteus maximus and the abdominal muscles, primarily the TrA. Biomechanical studies have supported the concept that tension applied by the surrounding muscles, especially the TrA, can be transmitted through the TLF to stiffen the lumbar spine and increase the force-closure of the sacroiliac joint. Flexion of the spine stretches the TLF, diminishing its lateral dimensions. Resistance to lateral retraction of the TLF by the abdominal muscles, acting through some combination of the MLF and PLF, will stiffen this tissue and increase resistance to flexion as well as enhance the extensor moment of the lumbar region , contraction of the paraspinal muscles has been demonstrated to increase the intracompartmental pressure and thereby contribute to the hydraulic amplifier effect supporting the lumbar spine.
Finally, increased tone in the lumbar multifidus muscle should act to increase the tension created by the TLC between PSIS bilaterally. This increased medially directed tension would lead to force-closure of the sacroiliac joint, thus stabilizing the pelvis.
Model of the TLF and its associated muscles and aponeuroses. This is a posterior view of the sacral region. The TLF and its associated aponeuroses have been dissected off the pelvis and flattened in the schematic diagram. The central region of the diagram represents the combined region of the aponeuroses, and has been termed the TLC. This region is the thickest and best positioned to resist lateral movements of the posterior superior iliac spine (PSIS). The PSIS and the lateral sacral tubercle (ST) are connected via the long dorsal sacroiliac ligament. The aponeurosis of the TrA joins the structure at the lateral raphe (LR), and the sacrotuberous ligament (STL), covered by the TLC, is seen ending on the ischial tuberosity (IT).
The PLF could play an important role in transferring forces between spine, pelvis and legs, especially in rotation of the trunk and stabilization of lower lumbar spine and sacroiliac joint (Fig. 19). The gluteus maximus and the LD merit special attention because they can conduct forces contralaterally via the posterior layer of the TLF. Because of the coupling between the gluteus maximus and the contralateral LD via the PLF, one must be cautious when categorizing certain muscles as arm, spine or leg muscles. Rotation of the trunk is mainly a function of the abdominal muscles. However, a counter-muscle sling in the back, in contrast to the abdominal sling, helps to preclude deformation of the spine. Rotation against increased resistance will activate the posterior oblique sling of LD and gluteus maximus (Vleeming & Stoeckart, 2007). However, these muscles have a higher threshold value compared with the abdominal Muscles.
Stay tube for for Part 2 Treatment approach for Thoraco Lumbar Fascia…………………
- The thoracolumbar fascia: anatomy, function and clinical considerationsH. Willard,1 A. Vleeming,1,2 M. D. Schuenke,1 L. Danneels2 and R. Schleip3
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