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7th Interaisciplinaiy Woria Congress on Low Back & Pelvic Pain The Aponeurotic Roots of the Thoracolumbar Fascia F.H. Willard, Ph.D, J.E. Carreiro, D.O Introduction Thoracolumbar fascia is a complex arrangement of connective tissue sheets enveloping the low back and reaching over the sacrum. It has received several detailed anatomical and biophysical studies of recent (Hu and others, 2010); however, the function of this complex system of interconnected tissue is still illusive. Part of the problem lies in our inability to understanding liow these layers integrate into the body to promote stability and facilitate motion. In this article we will review the major muscle groups and their associated fascial and aponeurotic sheaths that give rise to what is termed the thoracolumbar fascia (TLF). From these anatomical relationships a functional implication can be proposed. Dissection of the Thoracolumbar Fascia The fibromuscular layers of the lumbosacral region are arranged in a stacked array progressing from superficial to deep. Figure 1 presents a posterior view of the lower back of a 91 year-old male. The skin and pannicular (subcutaneous) fascia have been removed and the underlying structures stripped of their investing fascia to expose the latissimus dorsi and its associated aponeurosis, the superior aspect of the gluteus maximus and its aponeurosis as well as the fusion of these aponeurotic sheets to form the posterior layer of the TLF. In Figure 2, the latissimus dorsi and its aponeurosis have been removed to demonstrate the paraspinal muscles - iliocostalis laterally and longissimus medially -and the formation of the aponeurosis of the erector spinae. In the next step, the lateral two paraspinal muscles and their aponeurosis were removed (Figure 3) sparing just the inner most laminae of these muscles (Ic and Lo in the figure) to mark their position. The three white arrows in Figure 3 indicate the medial border of the aponeurosis of the transversus abdoiminis. At this border, the aponeurosis splits contributing to three separate layers: the outermost layer to which it fuses is the aponeurosis of the erector spinae (present on the right side of this figure), the innermost layer is the anterior layer of TLF (not seen in this figure) and the remaining layer - termed the middle layer of TLF - passes between the paraspinal muscles and the quadratus lumborum. The removal of the aponeurosis of the erector spinae reveals the underlying multifidus, the third and most medial muscle of the lumbar paraspinal group. The thin white fascial bands seen crossing the multifidus muscle on a diagonal represent its attachment sites to the deep surface of the aponeurosis of the erector spinae. In Figure 4, additional portions of the ilocostalis (Ic) and the longissimus (Lo) have been removed to expose the middle layer of TLF. Portions of the middle layer have been removed to expose the dorsal rami of the spinal nerves as they course through the middle layer. Finally, in Figure 5 (which involves a second specimen) all paraspinal muscles and the dorsal rami have been removed. Exposed are the lumbar zygapophyseal joints and the transverse processes of the lumbar vertebrae. The middle layer of TLF, derived from the aponeurosis of the transversus abdominis, is seen attaching to the tips of the transverse processes. In between the transverse processes, an arch is seen in the aponeurotic attachment. It is through this arch that the dorsal ramus gains entrance into the middle layer of the TLF. The irregular dense connective tissue (fascia) that normally fills the arch, surrounds the ventral rami and invests the psoas has been removed to expose these structures. This investing fascia represents the anterior layer of the TLF. Los Angeles, November 2010 3

The Aponeurotic Roots of the Thoracolumbar Fascia Aponeurotic Roots of the Thoracolumbar Fascia F.H. Willard, ... the superior aspect of the gluteus maximus and its aponeurosis as

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7th Interaisciplinaiy Woria Congress on Low Back & Pelvic Pain

The Aponeurotic Roots of the Thoracolumbar Fascia

F.H. Willard, Ph.D, J.E. Carreiro, D.O

I n t r o d u c t i o nThoracolumbar fascia is a complex arrangement of connective tissue sheets enveloping the lowback and reaching over the sacrum. It has received several detailed anatomical and biophysicalstudies of recent (Hu and others, 2010); however, the function of this complex system ofinterconnected tissue is still illusive. Part of the problem lies in our inability to understandingliow these layers integrate into the body to promote stability and facilitate motion. In this articlewe will review the major muscle groups and their associated fascial and aponeurotic sheathsthat give rise to what is termed the thoracolumbar fascia (TLF). From these anatomicalrelationships a functional implication can be proposed.

D i s s e c t i o n o f t h e T h o r a c o l u m b a r F a s c i aThe fibromuscular layers of the lumbosacral region are arranged in a stacked array progressingfrom superficial to deep. Figure 1 presents a posterior view of the lower back of a 91 year-oldmale. The skin and pannicular (subcutaneous) fascia have been removed and the underlyingstructures stripped of their investing fascia to expose the latissimus dorsi and its associatedaponeurosis, the superior aspect of the gluteus maximus and its aponeurosis as well as thefusion of these aponeurotic sheets to form the posterior layer of the TLF. In Figure 2, thelatissimus dorsi and its aponeurosis have been removed to demonstrate the paraspinal muscles -iliocostalis laterally and longissimus medially -and the formation of the aponeurosis of theerector spinae.

In the next step, the lateral two paraspinal muscles and their aponeurosis were removed (Figure3) sparing just the inner most laminae of these muscles (Ic and Lo in the figure) to mark theirposition. The three white arrows in Figure 3 indicate the medial border of the aponeurosis of thetransversus abdoiminis. At this border, the aponeurosis splits contributing to three separatelayers: the outermost layer to which it fuses is the aponeurosis of the erector spinae (present onthe right side of this figure), the innermost layer is the anterior layer of TLF (not seen in thisfigure) and the remaining layer - termed the middle layer of TLF - passes between theparaspinal muscles and the quadratus lumborum. The removal of the aponeurosis of the erectorspinae reveals the underlying multifidus, the third and most medial muscle of the lumbarparaspinal group. The thin white fascial bands seen crossing the multifidus muscle on adiagonal represent its attachment sites to the deep surface of the aponeurosis of the erectorspinae.

In Figure 4, additional portions of the ilocostalis (Ic) and the longissimus (Lo) have beenremoved to expose the middle layer of TLF. Portions of the middle layer have been removed toexpose the dorsal rami of the spinal nerves as they course through the middle layer.

Finally, in Figure 5 (which involves a second specimen) all paraspinal muscles and the dorsalrami have been removed. Exposed are the lumbar zygapophyseal joints and the transverseprocesses of the lumbar vertebrae. The middle layer of TLF, derived from the aponeurosis ofthe transversus abdominis, is seen attaching to the tips of the transverse processes. In betweenthe transverse processes, an arch is seen in the aponeurotic attachment. It is through this archthat the dorsal ramus gains entrance into the middle layer of the TLF. The irregular denseconnective tissue (fascia) that normally fills the arch, surrounds the ventral rami and invests thepsoas has been removed to expose these structures. This investing fascia represents the anteriorlayer of the TLF.

Los Angeles, November 2010 3

7th InteraisciplinaryWorta Congress on Low Back & Pelvic Pain

The muscles of the lumbosacral spineFour major muscle groups are positioned about the lumbosacral spine. Based on theirgeographic arrangement these groups are: superior posterior, inferior posterior, anterior anddeep muscles. The superior posterior group consists of the iliocostalis, longissimus andmultifidus, while the inferior posterior group contains gluteus maximus and medius and bicepsfemoris. The anterior group is composed of the rectus abdominis, external and internal obliquesand transversus abdominis. Finally, the deep group consists of the psoas and quadratuslumborum. An additional muscle extends its influence into the lumbosacral region and that isthe latissimus dorsi. This muscle effects lumbar region by way of its expansive aponeurosis thatfuses to the aponeurosis of the erector spinae muscles. The detailed descriptive anatomy of eaclimember of these muscle groups is presented in numerous textbooks of anatomy (Clemente,1985; Standring, 2008) and is beyond the scope of this review; however key features regarding^the contribution of these muscles to the aponeurotic roots of the TLF will be presented.

Superior posterior group - The three muscles of the superior posterior group are arrayed inlongitudinal bands positioned medial to lateral in the lumbar region (Figures 1, 2 and 3) . The jmedial most muscle, multifidus, begins at LI and extends into the sacrum and is separated fromithe other two muscles by a fascial septum thus creating an isolated muscle compartment. Theother two muscles, iliocostalis and longissimus, course from the cervical region to the crest olthe ilium. In the cervical and thoracic regions these two muscles are separated by fascial septae,however, in the lumbar region the two muscle frequently fuse together to form one large muscletermed the sacrospinalis (REF). Incomplete fascial septae partially separating the two musclesin the lower lumbar region can often be seen on MR imaging.

In the upper lumbar region, the iliocostalis and longissimus (or sacrospinalis muscle) forms alarge, flattened aponeurosis that extends to the crest of the ilium inferiorly and the lumbarspinous processes medially. In its medial projection, the aponeurosis of the erector spinaemuscles covers the posterior (outer) surface of the multifidus. These outer laminae of themultifidus have strong attachments to the inner surface of the aponeurosis. These attachmentscan be seen as whitish colored diagonal lines in Figure 3.

Inferior posterior group - Three large muscles of the lower extremity are related to theposterior aspect of the TLF. The superior and medial borders of the gluteus maximus arise froma flattened band of connective tissue termed the gluteal aponeurosis (Figure 1 and 6). This sheetof fibers extends upward from the superior border of the gluteus maximus to reach the crest ofthe ilium and medially from the attachment of the gluteus maximus to blend with the TLF overthe sacrum. Internally, the gluteal aponeurosis forms an attachment site for the gluteus medius.The inferior and medial border of the Gluteus maximis attaches to the outer layer of thesacrotuberous ligament. This ligament also act as an attachment site for the biceps femoris. Thislatter muscle has a superiorly directed tendon whose inferior fibers attach to the ischialtuberosity and superior fibers attach to the outer layer of the sacrotuberous ligament (Figure 7).This outer band of fibers covering the sacrotuberous ligament represents an inferior extensionof the TLF from the sacrum.

Anterior group - In the abdominal region, a multilayered fibromuscular band extends from theanterior midline around the torso to attach to the fascias of the lumbar spine. Laterally the bandconsists of three muscles, the external and internal oblique are superfical and the transversusabdominis forms the deep layer. Anteriorly all three muscles form aponeuroses that combineand then split forming the rectus sheath, this latter structure houses the rectus abdominis (Figure8). Inferiorly these muscles form the inguinal ligament and superiorly they attach to the ribswith the transversus abdominis interdigitating with muscular slips from the thoracoabdominaldiaphragm. The posterior border of the transversus abdominis ends by forming an aponeurosis4 Los Angeles, November 2010

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7th IttteraisdplinaryWorta Congress on Low Back GrPeMc Pain

structures while that posterior to the vertebral bodies contains the epaxial (paraspinal) musclesand their associated structures.

Aponeuroses are different and distinct from investing fasciaApnoeuroses are very succinctly defined in the 1948issue of Gray's Anatomy(Gray, 1948); hereI quote:

"Aponeuroses are fibrous membranes, of a pearly white color, iridescent, andglistening, which represent very much flattened tendons. They consist of closelypacked, parallel, collagenous bundles, and by this characteristic may be differentiatedfrom the fibrous membranes of fascia which have their collagenous more irregularlyi n t e r w o v e n . "

The text goes on to elaborate on how the aponeurosis, like a tendon, is part of the muscle, is inthe direct line of pull from the muscle and is further differentiate from fascial membrane thatenclose (invest) or guide the muscle. Multiple muscles can end in one aponeurotic sheet,similarly, an aponeurotic sheet can split to surround other structures such as muscles or bone.When this happens, the epitenon surrounding the aponeurosis blends with the epimysium of themuscle or the periosteum of the bone. Aponeuroses function to diffuse the tension generated bya muscle contraction over a wider range of territory than can be accomplished by a tendon orligament.

The investing fascias and the surrounding aponeurotic sheaths form a complex structurein the lumbosacral regionThe investing fascia of the epaxial musclesattaches laterally to the transverse processes of thevertebra; on the midline posteriorly it attaches to the spinous processes thus the posterior fascialtube is subdivided into two parallel tubes, left and right (Figure 11) by the spinous processesand interspinous ligaments. Overall, the fascial walls of these cylinders have been termedvertebral fascia, however regional names exist. The TLF begins superiorly as a regionaldelineation of the vertebral fascia (irregular connective tissue composing the epimysium of theparaspinal muscles). In the thoracic region it simply covers the paraspinal muscles, while in thelumbosacral region, this layer of fascia and its nomenclature, become extremely complex. Thevertebral fascia covering the iliocostalis and longissimus blends into the epitenon of theaponeurosis of the erector spinae muscles and then becomes compresses between thataponeurosis and the overlying aponeurosis of the latissimus dorsi. Laterally this aponeuroticcomplex is joined by the aponeurosis of the transverse abdominis to form the "posterior layer ofthe TLF" (Figure 9) Eventually all of these aponeurotic layers fuse to form a thick, inseparablecomposite sheet below the level of S2 (Figure 2 and 6). This composite (stllltermed posteriorlayer of the TLFis continuous laterally with the gluteal aponeuosis and inferiorly with thesacrotuberous ligament and the tendon of the biceps femoris (Figure 7).

Aponeurotic sheaths of the lumbar spineSeveral aponeuroses have been mentioned in the definition of TLF. A brief description of thesestructures will be presented.

Aponeurosis of the erector spinae muscles - The iliocostalis and longissimus muscles extendfrom the cervical and thoracic regions inferiorly to reach the crest of the ilixim. As thesemuscles enter the lumbar region, they form an aponeurosis on their superficial aspect. Mediallythis structure attaches to the spinous processes of the lumbar vertebrae (Figure 2 and 9) and thesuperspinous ligament. Laterally the aponeurosis attaches to the crest of the ilium in the regionof the posterior superior iliac spine (PSIS) and inferiorly it contributes to the composite ofT L F b e l o w S 2 .

6 Los Angeles^ November 2010

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Figure 4 Dissection of the aponeurosis of the transversusabdorninis II. In this view additional bands of the ihocostaUs

(Ic) and longissimus (Lo) have been removed to expose theunderlying layer of fascia. This fascia is termed the middlelayer of the thoracolumbar fascia and is derived from theaponeurosis of the transversus abdominis.

Figure 5 Deep dissection of the aponeurosis of the transversusabominis. The erector spinae muscles and the multifidus have beencomplete removed to expose the facet joints, transverse processes andthe aponeurosis of the transverse aMominis. This portion of theaponeurosis of the transversus abdominis is termed the middle layer ofthe TLF. The ventral rami of the lumbar plexus and the psoas musclecan be seen deep to the arches of the aponeurosis of the transversusa b d o m i n i s

Fig e 6 Superficial dissection of the glutealregion. The skin and subcutaneous fascia havebeen removed to reveal the attachment of thegluteus maximus and the gluteal aponeurosis. Inaddition the aponeurosis of the latissimus dorsihas been removed to expose the aponeurosis ofthe erector spinae muscles. A curved line is seenon the aponeiuosis of the erector spinae muscleswhere it fused inseparably with the aponeurosisof the latissimus dorsi. This combined or fused

portion of the TLF lies at the level of PSIS andbe low.

Figure 7 A deep dissection of the gluteal and sacral region. Thegluteus maximus and medius have been removed. The multifidusis seen lying between the two ilia at the level of PSIS. The TLFcovering the multufldus is seen to be continuos with the outerlayer of the sacrotuberous hgament.

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Figure 9 An axial plane diagram of theaponeurosis of the transversus abdominisin the liunbar region. The aponeurosisthe atissimus dorsi is seen to overlie the

aponeurosis of the erector spinae muscles.A thin layer of investing fascia, termed an

epitenon, separates these two structures.

Figure 8 A superficial dissection of the anterior abdominalwall. The extemal obhque is seen to form an aponeurosis thatsubsequently contributes to the rectus sheai. These is asimilarity between this relationship and the sphtting of theaponeurosis of the transversus abdominis to surround thequadratus lumborum and the paraspinal muscles (See Figure9).

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Figure 10 A histological section taken through a fetallimb. (Section from the University of MichiganHistology Website). This section demonstrates thecontinuity between investing fascias such as theepimycimn of muscle and the periosteum of bone.

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7th Itttenlisciplinary WorM Congress on Low Back & Pelvic Pain

Figure 11 The axia l cy l inders of fasciasurrounding the human torso. Image A is a axialplane CT scan of the thorax. Image B is adiagram outlining the hypaxial and epaxialcylinders of fascia surrounding the torso. Finally,image C is a hree dimensional model of these twofasc ia l co lumns. The ver tebra l co lumn is the

midline jimction of the two fascial columns.

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Figure 12 A posterior obUque view of a deep dissection inthe gluteal region. The gluteus maximus has been removed,s dissection demonstrates the continuity of the TLF withthe gluteal aponeurosis and with the scarotuberousUgament.

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Figure 13 An axial plane CT scan of a male pelvispproximately at the level of PSIS. The sacroiliac join isindicated by the two opposing black arrows. The body of themul t ifidus muscle is seen between the two i l ia . The TLF

covering the multifidus is indicated by the double curved fine.This portion of the TLC is composed of the fusedaponeuroses of the erector spinae and the latissimus dorsi (seetext for further explanation).

Figure 14 An axial plane section taken through thesacrum demonstrating the multifidus muscle with theoverlying layer of TLF. This portion of the TLC iscomposed of the fused aponeuroses of the erector spinaeand the latissimus dorsi.

Mu l t i fidus andfirecio? spinae muscles

Figure 15 Model of the TLF and itsssociated muscle and aponeuroses.This is a posterior view of the sacralregion. The TLF and its associatedaponeuroses have been dissected off offhe pe lv is and flat tened in theschematic diagram. The central regiono f t he d iag ram rep resen ts t hecombined region of the aponeurosesthat contribute to the TLF. This regionis the thickest and best positioned toresist lateral movements of PSIS. The

posterior superior iUac spine (PSIS)and the lateral sacral tubercle (LST)are shown to be connected by the longdorsa l sacro iUac l igament . Theaponemosis o f the Transversusabdominis forms the lateral raphe (LR)and the sacrotuberous ligament (STL)is seen ending on the ischial tuberosity(IT).

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7th IntenHsciplinary World Congress on Low Back Pelvic Pain

R e f e r e n c e s1. Clemente CD. 1985. Gray's Anatomy of the Human Body. Philadelphia: Lea & Febiger.2. Gray H. 1948. Anatomy of the Human Body. 25th ed. Philadelphia: Lea & Febiger.3. Hu H, Meijer OG, van Dieen JH, Hodges PW, Bruijn SM, Strijers RL, Nanayakkara PW, van Royen BJ, Wu

W, Xia C. 2010. Muscle activity during die active straight leg raise (ASLR), and the effects of a pelvic belton the ASLR and on treadmill walking. J Biomech 43(3):532-9.

4. Pel JJ, Spoor CW, Pool-Goudzwaard AL, Hoek van Dijke GA, Snijders CJ. 2008. Biomechanical analysis ofreducing sacroiliac joint shear load by optimization of pelvic muscle and ligament forces. Ann Biom Eng36(3):415-24.

5. Standring S. 2008. Gray's Anatomy, The Anatomical Basis of Clinical Practice. 40th ed. Edinburgh: ElsevierChurchill Livingston.

6. van Wingerden JP, Vleeming A, Buyruk HM, Raissadat K. 2004. Stabilization of the sacroiliac joint in vivo:verification of muscular contribution to force closure of the pelvis. Eur Spine J 13(3):199-205.

7. Vleeming A, Pool-Goudzwaard AL, Stoeckart R, van Wingerden J-P, Snijders CJ. 1995. The posterior layerof the thoracolumbar fascia: its function in load transfer from spine to legs. Spine 20(7):753-8.

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