The thoracolumbar fascia: anatomy, function and clinical considerations
F H Willard, A Vleeming, M D Schuenke, L Danneels, R Schleip, F H Willard, A Vleeming, M D Schuenke, L Danneels, R Schleip
Abstract
In this overview, new and existent material on the organization and composition of the thoracolumbar fascia (TLF) will be evaluated in respect to its anatomy, innervation biomechanics and clinical relevance. The integration of the passive connective tissues of the TLF and active muscular structures surrounding this structure are discussed, and the relevance of their mutual interactions in relation to low back and pelvic pain reviewed. 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. The three-dimensional structure of the TLF and its caudally positioned composite will be analyzed in light of recent studies concerning the cellular organization of fascia, as well as its innervation. Finally, the concept of a TLC will be used to reassess biomechanical models of lumbopelvic stability, static posture and movement.
© 2012 The Authors. Journal of Anatomy © 2012 Anatomical Society.
Figures
This is an axial plane CT with contrast taken through the chest at the level of the pulmonary trunk. The bridging muscles (muscles that cross between upper extremity and torso) have been shaded white. These muscles are in a common fascial sheath that extends from the extremity medially to surround the upper portion of the torso. This sheath reaches as far caudalward as the sternum anteriorly and the sacrum posteriorly. Inside the sheath are the hypaxial and epaxial muscle compartments of the thorax and abdomen, each surrounded by its own fascial sheath. ASer, anterior serratus; InfSp, infraspinatus; LD, latissimus dorsi; PMa, pectoralis major; PMi, pectoralis minor; Rh, rhomboid; SubScap, subscapularis; TMa, teres major; Tp, trapezius.
The hypaxial and epaxial myofascial compartments of the torso. (A and C) Axial plane CT scans taken through the thorax at the level T8 (A) and through the abdomen at the level of L1 (C). (B) A schematic drawing of the hypaxial cylinder separated from the twin epaxial cylinders by the vertebral column; it is derived from approximation between the two levels shown in (A and C). It illustrates the hypaxial myofascial compartment anteriorly surrounding the body cavity and the epaxial myofascial compartment posteriorly. The epaxial compartment is divided into two subcompartments by the spinous process of the vertebra. The hypaxial and epaxial compartments are separated by an intermuscular septum that medially attaches to the transverse processes of the vertebra. In the lumbar region, this septum forms the middle layer of the TLF.
This is a tracing of the hypaxial and epaxial myofascial compartments, illustrating the comparison between the two-layered and three-layered models of the TLF. The latissimus dorsi (LD) is seen lying on the external wall of the hypaxial compartment and extending over the epaxial compartment to reach its attachments on the midline. In doing so, the aponeurosis of the LD contributes to the superficial lamina of the PLF.
This is a posterior view of the lower thoracic and lumbar spine illustrating the construction of the superficial and deep lamina of the PLF. The LD has been sectioned to expose the underlying SPI. The aponeuroses of these two muscles combine to form the sPLF. The sPLF attaches to the deep lamina of PLF; both of these laminae have been removed over the lumbar region to expose the erector spinae muscles. The short arrow points to the curvature of the deep lamina as it wraps around the erector spinae muscles laterally forming the epaxial myofascial compartment. The paired long arrows, top and bottom, point to the sectioned edge of the deep lamina. Note that the deep lamina is thick and aponeurotic in nature at the lower lumbar level, but thin and fascial in nature in the upper thoracic region. Apo ES, aponeurosis of the erector spinae; IcL, iliocostalis lumborum; IcT, iliocostalis thoracis; LD, latissimus dorsi; LoT, longissimus thoracis; sPLF, superficial lamina of posterior layer of thoracolumbar fascia; SPI, serratus posterior inferior.
This is a series of photographs illustrating a superficial-to-deep dissection of the lower thoracic and lumbar region. (A) The panniculus of fascia following removal of the skin. (B) The panniculus has been removed to display the underlying epimysium of the latissimus dorsi (LD) and the gluteus maximus (GM). (C) The epimysium of the LD has been removed to display the underlying muscles and the aponeurotic attachments of the LD forming in part the superficial lamina of the PLF (sPLF). (D) The LD has been removed for the right side to reveal the underlying serratus posterior inferior (SPI) and its aponeurosis. (E) The LD and rhomboid muscles have been removed bilaterally and a window placed in the aponeurosis of the serratus posterior superior to expose the underlying paraspinal muscles (PS) and their investing fascia. Note the thin sheet of the deep lamina (dPLF) seen above the window. Finally, (F) the posterior serratus muscles remain on the right side, whilst the left side has had the dorsal aspect of the PRS removed to expose the paraspinal muscles and the aponeurosis of the erector spinae (apo ES) caudally. The apo ES first fuses with the overlying deep and then with the superficial laminae of the PLF to form a tough composite of dense connective tissue that extends over the sacrum and to which the GM is attached. The thoracolumbar composite (TLC) is seen in the last four photographs (C–F).
These are posterior views of the paraspinal muscles in the lumbosacral region. (A) The PLF has been removed to expose the iliocostalis lumborum (IcL) and the longissimus thoracis (LoT), as well as the aponeurosis of these two muscles (apo ES). A narrow rim of the deep lamina (dPLF) is seen at the point where the apo ES and the overlying TLF fuse to form the thoracolumbar composite (TLC). This fusion occurs at or slightly above the level of the posterior superior iliac spine (PSIS). (B) Erector spinae muscles of the lumbar region, IcL and LoT, have been removed to expose the more medially positioned multifidus lumborum (MuL). The opaque white bands (arrow) on the posterior surface of the MuL represent regions where the muscle bands fused with the inner aspect of the overlying apo ES. GM, gluteus maximus.
This is a posterior view of the lumbosacral region following removal of the gluteus maximus and the erector spinae muscles. Multifidus lumborum is seen inserting into the TLC. The composite extends caudally to cover the sacrotuberous ligaments and reach the ischial tuberosities.
This is a photograph of a transverse section taken approximately at level L3 and illustrating the fascial structures lateral to the paraspinal muscles. The specimen was embalmed using the Thiel method. This method maintains the non-linear load-deformation characteristics of biological tissue (Wilke et al. 2011). LIFT, lumbar interfascial triangle (Schuenke et al. 2012). The deep lamina of the PLF actually forms an encapsulating sheath around the multifidi and paraspinal muscles (PSM), this is the paraspinal retinacular sheath (PRS). In this image, the LIFT is under tension from forceps pulling laterally (far right side of the picture) and posteriorly (bottom of the picture). The aponeurosis of the transversus abdominis (ApoTrA) is seen to divide into a posterior (3) and anterior (2) layer before joining the PRS. The sheath is seen to form a continuous layer wrapping around the paraspinal muscles (1). This arrangement strongly suggests that the aponeurosis of the TrA and IO does not solely form the PLF and MLF, but splits to contribute to these layers by joining the PRS (a more detailed description of the composition of the fascial layers can be found in Fig. 10). Note in this specimen that the quadratus lumborum (QL) and the psoas muscle (Ps) are both strongly atrophied. Anteriorly of the QL a small part of the kidney (K) can be seen (specimen kindly supplied by the Medical faculty Ghent Belgium, Department of Anatomy).
A posterior oblique view of the lumbosacral region illustrating the aponeurosis of the erector spinae muscles (Apo ES), the deep lamina (dPLF) and the thoracolumbar composite (TLC). The Apo ES and dPLF fuse with the overlying posterior lamina (not shown) to form the TLC. Laterally, the dPLF will wrap around the border of iliocostalis lumborum (IcL) forming the PRS. This sheath creates a strong fascial compartment around the paraspinal muscles. On the lateral border of the IcL the dl is joined by the aponeurosis of the transversus abdominis (TrA) to form the lateral raphe. Also attached to the raphe in this specimen is the internal oblique (IO); the external oblique (EO) in this specimen did not reach the lateral raphe. The gluteus maximus (GM) attaches to the TLC beginning around the level of the posterior superior iliac spine (PSIS) and below. The gluteus medius (GMed) does not make an attachment to the TLC.
This is a transverse section of the posterior (PLF) and middle layer (MLF) of the TLF and related muscles at the L3 level. Fascial structures are represented such that individual layers are visible, but not necessarily presented to scale. Please note that the serratus posterior inferior (SPI) often is not present caudal to the L3 level. The transversus abdominis (TrA) muscle is covered with a dashed line on the peritoneal surface illustrating the transversalis fascia (TF). This fascia continues medially covering the anterior side of the investing fascia of the quadratus lumborum (QL). Anteriorly and medially, the TF also fuses with the psoas muscle fascia (not drawn). The internal (IO) and external obliques (EO) are seen external to TrA. SPI is highly variable in thickness and, more often than not, absent on the L4 level. Latissimus dorsi (LD) forms the superficial lamina of the PLF together with the SPI, when present. The three paraspinal muscles, multifidus (Mu), longissimus (Lo) and iliocostalis (Il) are contained within the PRS. The aponeurosis (tendon) of the paraspinal muscles (4) is indicated by stippling. Please note that the epimysium of the individual spinal muscles is very thin and follows the contours of each separate muscle within the PRS. The epimysium is not indicated in the present figure but lies anteriorly to the aponeurosis (4). The upper circle shows a magnified view of the different fascial layers contributing to the MLF. The picture shows that MLF is made up of three different structures: (1) this dashed line depicts the investing fascia of QL; (3) this dashed line represents the PRS, also termed the deep lamina of the PLF encapsulating the paraspinal muscles; (2) the thick dark line between the two dashed lines 1 and 2 represents the aponeurosis of the abdominal muscles especially deriving from TrA. Numbers 1, 2 and 3 form the MLF. The lower circle shows a magnified view of the different fascial layers constituting the PLF. The picture shows that on the L3 level the PLF is also made up of three layers, as the fascia of SPI is normally present on this level. (5) This dashed line depicts the PRS or deep lamina of the PLF encapsulating the paraspinal muscles; (6) the investing fascia of SPI is seen blending medially into the gray line marked (7) and representing the aponeurosis of SPI – posteriorly to the PRS; (8) this dark line represents the investing fascia of LD blending medially into the black line representing the LD aponeurosis (9) posteriorly to the SPI aponeurosis. Numbers 5, 7 and 9 form the PLF. Numbers 7 and 9 form the superficial lamina of the posterior layer (sPLF). LIFT is the lumbar interfascial triangle, as described by Schuenke et al. (2012). As indicated, the PRS encapsulates the paraspinal muscles; together with PLF and MLF and the lateral border of PRS, a triangle is formed normally also visible on axial lumbar MRIs. For further specification, see Fig. 8.
A posterior oblique view of the right lumbar region illustrating the removal of the LD to expose the serratus posterior inferior (SPI) and its associated aponeurosis (ApoSPI). Although the LD is firmly adhered to the SPI, it can be separated by careful dissection. These two aponeurotic structures combine to form the PLF. In this specimen, muscle fibers of the LD reach caudalward to the crest of the ilium. TLC, thoracolumbar composite.
A posterior view of the left thoracolumbar region illustrating the relationship of the serratus posterior inferior (SPI) and the deep lamina of the PLF covering the paraspinal muscles. (Note that the deep lamina represents the posterior wall of the PRS.) The bridging muscles from the extremity, such as the LD, trapezius and rhomboids have been removed in this specimen. (A) A window has been opened in the deep lamina to expose the erector spinae muscles. (B) The SPI has been elevated laterally and is being tensioned on the medial attachment of its aponeurosis. (C) The deep lamina (PRS) and aponeurosis of the SPI (ApoSPI) are being elevated with forceps to illustrate the loose connective tissue located between the paraspinal muscles and the surrounding PRS.
A posterior view of the back illustrating the attachments of the LD, trapezius and gluteus maximus to the TLF and thoracolumbar composite (TLC). The LD is the major component of the superficial lamina of the PLF (sPLF).
A comparison between drawings of three studies of the superficial lamina of the PLF: (a) Vleeming et al.; (b) Bogduk et al.; (c) Barker et al. (a–c) The same fiber direction of the superficial lamina. (a and c) A crosshatched appearance and the connections to the gluteus maximus fascia. (a) Along with variation in fiber direction there are changes in fiber density in the superficial lamina as well. Where the abdominal muscles join the paraspinal muscles, the orientation of the fibers change and they become denser. From the level of L4 to the lower part of the sacrum, the fiber density markedly increases. This density change corresponds to the area where the different fascial layers fuse to form the TLC.
A comparison between drawings of two studies of the deep lamina of the PLF: (a) Vleeming et al.; (b) Bogduk et al. (a and b) The same fiber direction; however, in (b) the dense parts of the deep lamina are coined as accessory ligaments. (b) The lateral raphe is indicated as a dotted vertical line, indicating the area where the abdominal muscles join the paraspinal muscles. (a) An increase of density in the same area. More caudally, it can be noticed that the sacrotuberous ligament partially fuses to the deep lamina. The fiber characteristics show increased density and an altered pattern in the region over the sacrum. This pattern is another indication that the various layers of the TLF and aponeurosis fuse into the TLC, as referred to in the text.
A schematic diagram of a human embryo demonstrating the epaxial and hypaxial myofascial compartments. The spinal nerve is seen dividing into its dorsal and ventral ramus. The dorsal ramus innervates the epaxial compartment, whilst the ventral ramus innervates the hypaxial compartment. Between the two compartments lies the intermuscular septum of connective tissue from which the middle layer of the TLF will develop (figure modified from: Bailey & Miller, 1916).
This is a posterior view of a deep dissection of the middle layer (MLF) of the TLF. The erector spinae muscles and the multifidus have been complete removed to expose the facet joints, transverse processes (TP) and the MLF. The MLF is composed of the aponeurosis of the TrA and the PRS, as well as the epimysium of the QL. The ventral rami of the lumbar plexus and the psoas muscle can be seen deep to the arches of the MLF. It is through these arches that the dorsal ramus gains access to the paraspinal muscles in the epaxial compartment.
Example of density of myofibroblasts in TLF comparable to frozen shoulder or Dupuytren contracture. Stress fiber bundles that are positively marked for α-smooth muscle actin (here in dark red) are used to identify myofibroblasts. Arrows indicate clearly visible myofibroblasts.
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).
An axial plane CT scan of a male pelvis approximately at the level of PSIS. The sacroiliac joint is indicated by the two opposing black arrows. The body of the multifidus muscle is seen in the sacral groove between the two ilia. The layer covering the multifidus at this level is the TLC and is indicated by the double curved line. At this level, the TLC is composed of the fused aponeuroses of the erector spinae and the LD (see text for further explanation). GM, gluteus maximus, G.med., gluteus medius; G.min., gluteus minimus; Mu, multifidus; Rec. abd., rectus abdominis. Adapted after Snijders et al. (1995).
Source: PubMed