Tissues of the Posterior Aspect of the Trunk


Fig. 1

Once the epidermis removed (SKIN), the superficial adipose tissue (SAT) and deep adipose tissue (DAT) appear, separated by the fascia superficialis (FS)



Numerous authors describe it as comprising “fatty lobules” [28] or being “more or less impregnated with fat” [15, 24], while the most common nomenclature define the FS as including all the adipose which accompanies it [14]. Lockwood [29] proposed to include the adipose layers in the term superficial fascial system (SFS). We will use Lancerotto’s [28] and Stecco’s [30] definition of the FS, that is to say, the FS refers to the membranous layer within the SFS only.


Composition and Location of the FS


The FS is surrounded by fat and separates the superficial layer of adipose tissue (SAT) from the deep layer of adipose tissue (DAT). Compared to the superficial layer of adipose tissue, the deep layer has smaller fatty lobules, and the transversal liaisons of its septae are more obliquely oriented. Their size varies depending on the location in the body, the sex, as well as the adiposity of the subjects (“thin in the thoracic region, it can reach several centimetres in the lumbar region”) [28] (Fig. 2).

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Fig. 2

The fascia superficialis (FS) is attached to the latissimus dorsi (LD) via connective fibres (ARROWS) that protect the nervous fibres and blood vessels (BV) by limiting the sliding motion


Several authors and anatomists [14, 27, 28] describe that this membranous layer (the FS) can be made of one to several fine and horizontal membranous sheets. It is made of areolar connective tissue [27] and does not have clearly identified cranial or caudal borders [28]. In cases where there is more than one membranous sheet, they are separated by variable quantities of fat (Fig. 3).

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Fig. 3

In the lumbar region, the fascia superficialis (FS) is merged with the adipose tissue (FS/AT) and remains closely linked to the fascia profundis (FP). The FS is made up of fat lobules embedded in a connective mesh transversally linking and unifying different layers, while ensuring an important degree of deformability


Additional fibrous septums arise from the FS and form a three-dimensional mesh of transversal or oblique interlinking through the SAT and DAT. This network forms a honeycomb-like structure [28, 85] on which are attached the fatty lobules of the SAT and DAT. In the SAT, this network of septae is called retinacula cutis superficialis.


The collagen fibres of the FS are associated with elastin fibres that provide a great deformability to the fibro-elastic structure [21, 27]. The FS appears as well-defined, continuous and well-organised membrane or layer, of aspect predominantly membranous, with irregular islands of fat cells. Microscopically, it appears lamellar [4] or honey-comb-like [28, 85].


Function


The mechanical roles of the FS are to cover, maintain and shape the fat of the trunk, and to connect the skin to the underlying structures while allowing sliding motion of soft tissues to occur with movement.


Furthermore, the fatty lobules of the FS ensure a mechanical protection to compression. The fatty lobules provide a resilience to compression that guaranties the protection of the underlying structures and the restitution of the initial form [27, 28].


In addition, some skeletal muscles attach only to the superficial fascia, such as the platysma muscle or the muscles of facial expressions that enable humans to smile, frown and cry [15].


Fascia Profundis (FP)


The fascia profundis is situated deeper than the fascia superficialis and is directly in contact with the bones and muscles (Fig. 4).

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Fig. 4

Removal of the epidermis and of the fascia superficialis (FS) exposes the superficial lamina of the posterior layer of the fascia profundis (sPLF). The fascia superficialis (FS) and the sPLF are connected by connective fibres that protect nerves and blood vessels by limiting the sliding motion


It is found in the literature by the name of deep fascia, thoracolumbar fascia [23, 31, 32], lumbodorsal fascia [24], tendon of the latissimus dorsi [33], or lumbar aponeurosis or fascia [26, 3335]. It is described by Gray [36] as being made up of the lumbodorsal fascia, the lumbar aponeurosis and the vertebral fascia. Its close relationship with the muscles and the bones justifies that it is described as a “false aponeurosis” or “tendinous membrane” by Rouviere [20] and of “aponeurosis of the latissimus dorsi” by Cunningham [24].


Depending on the nature of its constitution and on where it is situated on the trunk, it will act as a means of docking for the contractile fibres on the bones, or act like a flexible sheath or like a rigid shell. The posterior layer and the middle layer, together with the postero-lateral region of the vertebral column, constitute an “osteofascial” compartment [17] that encloses the muscle group called erector spinae.


Lumbosacral Region


In the sacral region, below the level of L5, the fascia profundis, or thoracolumbar fascia, is a thick aponeurotic structure which attaches to the sacrum and laterally to the posterior iliac spines.


It comprises the aponeurosis of the Multifidus (M), L and IC muscles, as well as the aponeurosis of the latissimus dorsi. It is called by some authors the thoracolumbar composite (TLC).


Cranially to L5, the fascia profundis splits into three layers: the posterior layer (PLF), the middle layer (MLF) and the anterior layer (ALF).


Posterior Layer of the Fascia Profundis, Lumbosacral Region


The posterior layer of the fascia profundis (PLF) appears as a large, pearly white membranous sheet—a colour that is characteristic of this tissue. It is a dense, fibrous connective tissue. The fibres are parallel to one another within the matrix. Their orientation is oblique, cephalic or lateral.


The PLF is made up of the aponeurosis of the latissimus dorsi (LD), the aponeurosis of the serratus posterior inferior (SPi) and the posterior aponeurosis of the extensors (L+IC).


The aponeurosis of the latissimus dorsi (LD) and of some of the extensors (L+IC) emerge from the thoracolumbar composite (TLC) of the sacral region, and they define two layers or laminae:


The posterior aponeurosis of the LD and the aponeurosis of the SPi become the superior lamina of the PLF (sPLF) . It allows the insertion of the contractile fibres of the latissimus dorsi. The insertion roughly follows a line, starting between the median third, the posterior third of the iliac crest and the spinous process of T7.


The anterior aponeurosis of the LD and of the aponeurosis of the SPi, as well as the posterior part of the retinacular sheath that surrounds the paraspinal muscles (L+IC) becomes the deep lamina of the PLF (dPLF) .


Middle Layer of the Fascia Profundis, Lumbosacral Region


The aponeurosis of the QL and of the M, L and IC muscles separate from the thoracolumbar composite (TLC) of the sacral region. The middle layer of the PLF is made up of the anterior fascia of the M muscle, the posterior fascia of the QL, and the aponeurosis of the transversus abdominis (Tra) and internal oblique (IO).


The middle layer of the PLF is located in the plane of the costiform processes of the lumbar vertebrae.


Cephalically, it inserts on the inferior edge of the 12th rib and on the lumbo-costal ligament [22]; however this information varies depending on the authors.


At the L2 level, the middle layer will merge with the anterior layer. We will refer to the resulting layer as the anterior layer. The term “middle layer” therefore only exists in the lower lumbar region and in the cervical region.


Anterior Layer of the Fascia Profundis, Lumbosacral Region


From its differentiation with the TLC and up to the level of L2, the anterior layer of the PLF is made up of the anterior sheath of the QL muscle and extends laterally with the sheath of the psoas muscle (P), [33]. Going cranially from L2, the middle layer merges with the anterior layer that is then made up of the anterior fascia of the multifidus muscles (M), and the surrounding sheath (anterior and posterior) of the QL [24, 36, 37].


The anterior layer is not taken into account identically by all the authors that can describe two or three layers to the fascia profundis in the lumbar region. Authors describing two layers do not include this anterior layer and refer to it as the transversalis fascia [23].


It inserts caudally on the superior edge of the iliolumbar ligament and on the iliac crest [22]. The cephalic insertion of the deep layer varies according to authors. It is described as being on the arcuate ligament [22] or the lateral arcuate ligament (lateral lumbocostal arch) or medial arcuate ligament (medial lumbocostal arch) [20]. Medially, it merges with the fascia iliaca, and with the sheath of the psoas muscle [20, 24] and inserts on the costiform processes of the lumbar vertebrae, laterally and posteriorly to the fascia iliaca [22]. Its lateral insertion is on the lateral raphe.



The Lateral Raphe


The lateral raphe is made up of the merging of the posterior, middle and anterior layers, laterally to the QL muscle. It extends antero-laterally via the connective sheaths of the transversus abdominis (TA) and internal oblique (IO) abdominal muscles.


Thoracic Region


In the thoracic region , the fascia profundis consists of the posterior and anterior layers of the lumbosacral region. In between them, an additional fibrous element separates the extensors (L+IC+S) from (M+R): the intermediate layer.


Posterior Layer of the Fascia Profundis, Thoracic Region



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Fig. 5

Bilateral removal of the skin reveals the posterior layer of the fascia profundis (sPLF). It covers, on both sides of the vertebral column (Spine), the latissimus dorsi (LD), its aponeurosis (“asterisk”), and the inferior fibres of the trapezius (Ti—dashed line)


In the thoracic region, the superficial lamina of the posterior layer (sPLF) covers the inferior fibres of the trapezius muscle (T). It is made up of the posterior aspect of the sheath of the trapezius muscle and therefore inserts on the spinous processes of the lower vertebrae (Fig. 5).


In the thoracic region , the deep lamina of the posterior layer (dPLF) is made up of:



  • the anterior sheath of the rhomboid muscle (Rh) , then also includes the anterior sheath of the levator scapulae (LS) and of the serratus posterior inferior (SPi) and superior (SPs) (in continuity with this of the LD and SPi).



  • the posterior sheath of the spinalis muscle (in addition to this of the L+IC) then also includes this of the splenius muscle (Sp).



The Deep Lamina of the Posterior Layer of the Facia Profundis in the Thoracic Region


This connective layer is visible underneath the DL in the thoracic region . It contains thin and spaced-out pearl white fibres, the density of which varies according to the spinal level and the individual.


The fibres, parallel to one another, are arranged transversally from the spinous processes of T10 to C7 and do not reach the ribs. They provide aponeurotic properties to this structure. However, since they do not serve the purpose of docking of the contractile fibres as the superficial lamina does with the trapezius muscle, Loukas [32] does not consider this layer as an aponeurosis (Fig. 6).

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Fig. 6

The opening of the superficial lamina (sPLF) reveals the aponeurotic fibres of the LD (“asterisk”) connecting the latissimus dorsi (LD) and Trapezius (Ti) muscles


Laterally, the deep lamina extends with the sheath of the splenius, subscapularis, teres major and teres minor muscles. Its large side is on the spinous processes of T10 to T2. According to Rouviere [20], its large side has a common spinal origin with the aponeurosis of the LD and a part of the Trapezius muscle. The two layers merge near the median axis. The smaller side is located at the costal angles of the 4th to 9th ribs, and varies of one to two rib levels according to authors (Fig. 7).

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Fig. 7

Strong connective fibres (arrow) accompanying nerves and blood vessels between the deep lamina (dPLF) and the superficial lamina (sPLF)


Cunningham [24] considers that it continues laterally in the intercostal area through the intercostal aponeurosis. This sheet is named differently according to the authors and to the level on the trunk:



  • Intermediate aponeurosis of the serratus muscle [33, 38, 39].



  • Vertebral aponeurosis [26, 35, 40, 41]



  • Aponeurosis of the serratus posterior muscle [42]



  • Lumbodorsal fascia (posterior layer) [17, 36, 43]



  • Dorsal fascia [34]



  • Lumbar fascia [24, 44]



  • Thoracolumbar fascia (TLF) [17, 24, 4448] (Figs. 8 and 9)


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Fig. 8

Removal of the latissimus dorsi , Trapezius and Rhomoidus muscles show the deep lamina dPLF. A window in the dPLF shows the iliocostalis (IC) and longissimus (L) muscles, the aponeurotic fibres of which are visible below the transparent dPLF. S scapula, aponeurotic fibres (“asterisk”)


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Fig. 9

The opening of the deep lamina (“asterisk”) reveals the longissimus (L) and iliocostalis (IC) muscles. The sacral region (S) is covered by the thoracolumbar composite, the superficial part of which is represented by the aponeuroses of the latissimus dorsi (white part)


The generally admitted inferior spinal insertions globally correspond to the insertion of the serratus posterior inferior (SPi) . Its superior insertion is controversial. According to some authors [20, 21, 39, 42] it links the superior edge of the SPi to the inferior edge of the serratus posterior superior (SPs), which justifies the denomination of (intermediary) aponeurosis of the serratus.


For others, [35, 38, 44, 46, 48] it goes underneath the SPs to extend through the connective sheath of the splenius muscles (Sp) and therefore is part of the deep cervical fascia. According to Drake [22], it goes in front of the SPs before merging with the superficial layer of the deep cervical fascia (Fig. 10).

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Fig. 10

The fibres of the deep lamina (dPLF ) are situated deeper than the superficial lamina (sPLF) and the latissimus dorsi (LD). The fibres of the dPLF are parallel to one another, and the dPLF is denser caudally (plain arrow) than cranially (dashed arrow)


The dPLF follows the shape of the costal arc. It forms the arch of the vertebral grooves, separating the superficial longitudinal spinal muscles from the transverse and oblique muscles [26, 41]. Embryologically, this connective sheet is the separation between the dorsal epimere that gives rise to the epaxial muscles, which form the deep muscles of the back (spinalis, longissimus, iliocostalis, rotatores (R) and multifidi), and the ventral hypomere that gives rise to the hypaxial muscles of the lateral and ventral body wall in the thorax and abdomen and extending to the shoulder girdle (latissimus dorsi, trapezius, rhomboidi, levator scapulae) (Figs. 11 and 12).

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Fig. 11

The removal of the superficial lamina (sPLF) and of the latissimus dorsi (LD) reveals the serratus posterior inferior muscle (Spi) and the deep lamina (dPLF). The fibres of the dPLF cover the iliocostalis (IC) and longissimus (L) muscles in the costal region (R). It also shows the trapezius (Ti) and rhomboidus (Rh) muscles that insert on the scapula (S)


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Fig. 12

The latissimus dorsi (LD ) is closely linked to the serratus posterior inferior (Spi) muscle via its aponeurotic fibres that extend to the spine (Spine). The fibres of the dPLF are oriented in the same direction


Its close links with the abdominal muscles internal oblique and transversus seem to allow the transmission of the force that they develop to participate in the extension of the spine [49].


Intermediate Layer of the Fascia Profundis, Thoracic Region


Within the erector spinae or paraspinal muscles compartment, the intermediate layer is not a perfectly identified real layer but a sliding plane between more superficial longitudinal muscles (L + IC + E) and deepest muscles (M + R + Ssp).


Anterior Layer of the Fascia Profundis, Thoracic Region


The anterior layer of the fascia profundis does not have major changes in the thoracic region compared to the lumbosacral region. In the thoracic region, the anterior layer is in continuity with the extension of the sheath of the QL.


Cervico-Cranial Region


Posterior Layer of the Fascia Profundis, Cervico-Cranial Region


In the cervico-cranial region, the superficial lamina of the posterior layer (sPLF) is in continuity with the thoracic region and is therefore made up of the posterior aspect of the sheath of the trapezius muscle.


Cranially, from the upper nuchal line, it merges with the connective sheath of the skull.


LD wraps the latissimus dorsi in the thoracic region. In the cervico-cranial region, this same layer wraps the trapezius. It forms the superficial blade of the nuchal fascia and merges, from the superior nuchal line, with the connective sheath of the skull.


Intermediate Layer of the Fascia Profundis, Cranio-Cervical Region


The sheaths of the iliocostalis cervicis and longissimus cervicis muscles reach the transverse processes of the cervical vertebrae from C2.


The sheath of the longissimus capitis muscle becomes one with the connective sheaths of the skull from the mastoid process.


Middle Layer of the Fascia Profundis, Cranio-Cervical Region


At the T4 level, the middle layer emerges from the anterior layer. It is made up of the anterior fascia of the M+SSp and the posterior fascia of the Lcol+Lcap.


Anterior Layer of the Fascia Profundis, Cranio-Cervical Region


The sheaths of the scalene musles (Sc) insert on the superior edge of the first two ribs, and on the cervical vertebrae on their costiform process (anterior tubercle) and transverse process (posterior tubercle).


The sheaths of the suboccipital muscles reach the connective sheath of the skull from the inferior nuchal line.


Innervation


The connective tissues of the back compose an envelope that individualises anatomical structures. Being continuous, this envelope homogenises and links the different anatomical structures. It has therefore a fundamental role in providing nervous information. Each of the layers that composes the connective tissues of the back has a specific organisation, constitution, appearance, function and relation. In consequence, their innervation is also variable and specific [13].


This informative function is insured by the sensitive information which remains not well-known in its distribution and function. It appears difficult to study with precision the sensitive innervation of the connective tissues, since they can have ramifications in the tissue as well as in the muscles or the skin. There are four types of sensory fibres in the connective tissues of the back that originate from different sensory receptors. These receptors differ in size, configuration, organisation, form and density. They are not specific to this region and are found throughout the whole body.


Sensory innervation is essential from the first weeks of the embryological development [50], and connective tissues have an essential role in the organisation and formation of the nerve fibres and of the muscles [51].


We will consider the sheath of the muscles as being part of their aponeurosis. All these aponeuroses compose the thoracolumbar fascia described above. This part will focus on the sensory innervation of the thoracolumbar fascia, the nervous endings of which are located within the muscle sheaths and aponeurosis. This description is not limited to the TLF and is applicable to the connective tissues in general.


Fibres and Receptors


The thoracolumbar fascia is innervated by the dorsal ramus of the spinal nerve [5254]. The dorsal ramus has myelinated motor fibres (Aα, Aβ and Aγ), unmyelinated vasomotor fibres (C) and sensory fibres.


There are 4 types of sensory fibres, carrying information from the endings located in the muscle sheaths and aponeuroses to the dorsal horn of the spinal cord.



Sensory Fibre Types Found in the Connective Tissues of the Back


Type I sensory fibres have the largest diameter (12–20 μm) and are distributed in two sub-groups: type Ia sensory fibres that originate as annulospiral endings in muscle spindles, and type Ib sensory fibres that originate as Golgi tendon organs, Meissner corpuscles or Merkel corpuscles. They have the thickest myelin sheath and have therefore the highest conduction velocity (79–114 m/s) [55].

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Apr 25, 2020 | Posted by in ORTHOPEDIC | Comments Off on Tissues of the Posterior Aspect of the Trunk
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