Osseous/Ligamentous

Lumbar spine

• Bones
o 5 lumbar vertebrae that have large bodies with a kidney shape, wider side to side then front to back as well as thicker anteriorly than posteriorly. This is due to the lordotic curve of this region (2).
o The bilateral pedicles coming off of the posterior superior aspect of the bodies continue as the transverse processes laterally (2).
o The TVPs in the lumbar region are different from that of the thoracic as they have the pedicle continuing into two processes. The first is the accessory processes, which is a small eminence at the roof of the other larger costal process which resemble small ribs (1).
o Continuing down the back, the lamina comes off posteriorly and inferiorly from the vertebral arch and continues as a broad, dorsal fin shaped spinous process. The lamina connects the pedicle to the spinous process (1).
o Together these extensions and their vertebral arches from the vertebral body form an almost triangular vertebral foramen for the spinal cord (1).
o The lumbar spine has superior and inferior articular processes which house the articular facets. The superior being oriented backward and medial with a concave surface, and the inferior facets face outward and lateral with a convex surface. This allows for the largely sagittal plane movement of the lumbar vertebrae (1)
o There is one more process, the mammary process, which sits on the lateral surface of the superior articular processes and is an attachment point for the deep intrinsic muscles. (1)
o The first lumbar vertebra is the marker of the transpyloric plane. This is because it is level with the pylorus of the stomach, it is also level with, the anterior end of the ninth rib, fundus of the gallbladder, celiac trunk (at the top end), superior mesenteric artery (at the bottom end, renal vessels, middle suprarenal arteries, and hila of kidneys. This also marks the termination of spinal cord and beginning of filum terminale (2)
o The fifth lumbar vertebra has a smaller spinous process and thick transverse processes which branch from the body as well as the pedicle. Its body is much deeper in front than behind, this allows it to articulate with prominence of the sacral articular surface at L5/S1 (2)
Ligaments
• Starting with the fibrocartilaginous intervertebral joints, we have the intervertebral discs which consist of a fibrous outer ring, the annulus fibrosus, and a gelatin-like centre, the nucleus pulposus.
o The annulus fibrosus can then be spit into an inner and outer zone. The outer zone, composed mostly of type 1 collagen fibers in criss crossing concentric laminae designed for high tensile strength and to withstand compressive forces. The outer zone then blends with the inner zone, a fibrocartilaginous tissues composed mostly of type 2 collagen fibers (being more cartilage based) which then attaches to the hyaline cartilage endplates of the vertebral bodies (1). In the lumbar spine, the annulus fibrosus is especially thicker anteriorly due to the lordotic curve and mechanical forces put onto it.
o The nucleus pulposus is a watery gel like structure composed of some nucleus pulposus cells, type 2 collagen fibers (cartilaginous), elastin fibers and water molecules (80-85% water) tightly bound to hydrophilic glycosaminoglycans side chains of abundant proteoglycans (3). These structural components create a tissue that constantly wants to expand against the annulus fibrosus and vertebral endplates, with a pressure that never reaches zero due to the water loving quality. This makes the nucleus propulsus very good at absorbing mechanical energy in the form of compressive forces (from axial loads). (4)
o These two structures together allow the intervertebral disc to take on compressive forces from axial loading, onto the nucleus propulsus of the disc, which distributes it relatively evenly through the cartilaginous end plates (plates of hyaline cartilage that cover the superior and inferior aspects of the disc, and bind the disc to the vertebral body), the body of the vertebrae below and the annulus fibrosus which takes the compressive force and transforms it into a tensile or tension force (think stretch on the fibrous tissue). One compression resistant tissue and one tension resistant tissue working together to distribute and transform forces. (1)
o Another interesting aspect of this hydrostatic, hydraulic system is that it regulates its own fluid volume. Fluid flows out of the disc when under a sustained load or compression force which exceeds the interstitial osmotic pressure of the surrounding tissues, reducing its height and bringing the bodies closer together as well as the intervertebral foramen closer together. Fluid is then brought back into the disc when the pressure is released, almost like a vacuum. Pressure increases, the fluid follows the path of least resistance, pressure decreases and the fluid does the same. The disc may be mostly avascular but can still change fluid volume through diffusion of surrounding vessels through the annulus fibrous and the vascular cavities (bone marrow spaces) of the vertebral endplates into the extracellular fluid around the disc (1).
• Next are the vertebral body ligaments, the anterior and posterior longitudinal ligaments
o The anterior longitudinal ligament runs from the occiput down to the sacrum (through the lumbar spine) attaching to the anterior side of the vertebral bodies and loosely to the intervertebral disks. It has broad superficial and deep fibers, the deep fibers attach each spinal segment, and superficial fibers which travel over several segments (1)
o The posterior longitudinal ligament starts as a continuation of the tectorial membrane of the atlanto-axial joint (occipitoaxial ligament which blends with cranial dura mater), attaches from the Clivus, which is a depression behind the dorsum sellae of the sphenoid bone and anterior aspect of the occiput, down the posterior surface of the vertebral bodies within the vertebral canal and into the sacral canal. Its width changes depending on if it is over the vertebral body (where it is narrower and attaches to the superior and inferior margins) or over the disk (where it becomes broader with lateral extensions attaching to the posterolateral sides of the annulus fibrosus) (1,2) .
o These two ligaments limit extension and flexion respectively but also play a role in maintaining the integrity of the annulus fibrosus from the anterior and posterior sides. Because there is less coverage laterally, and the annulus fibrosus is thinner posteriorly, the most common disk herniation in the lumbar spine is posterior lateral. (1)
• Then the vertebral arch ligaments
o The ligamentum flavum attaches through the laminae of each vertebra (except OA/AA) and helps reinforce the wall of the vertebral canal behind the intervertebral foramina. This ligament is thickest in the lumbar spine. It is a very different ligament as it contains more yellow elastic tissue, giving it recoil capability for maintaining upright posture in the sagittal plane, preventing hyperflexion and to pull the spine out of flexion. This elastic capability also stops the ligament from bulging into the spinal cord when it is brought off tension.(1,2)
o The intertransverse ligament attaches to the tips of transverse processes and limit sidebening of the vertebra. This ligament often blends with the intertravarsari muscle
o The interspinous and supraspinous ligaments connect the spinous processes of each vertebra. The interspinous ligament connects the root and apex of each spinous process and the supraspinous ligament connects the tips of the spinous processes. They are thicker in the lumbar region then others, and together they limit separation or hyperflexion of the vertebra.

Sacrum, Coccyx and Innominates



• Bones
o The sacrum is a single bone derived from the fusion of 5 sacral vertebra postnatally. It has a triangular shape with a concavity on the anterior side along with transverse ridges or lines where the vertebrae fused, and a convexity on the posterior side as well as 4 sacral foramina per side where the intervertebral foramina would be. The sacrum articulates with the fifth lumbar vertebrae at the top (or at its base) with a wedged shaped intervertebral disc between. These two bones allow for flexion/extension as well as sidebending and rotation with the superior facets of the sacrum facing posteriorly and slightly medially. Another articulation forms at the inferior end, or apex of the sacrum with the coccyx forming the sacrococcygeal joint which usually has a cartilaginous disk between. The lateral border of the sacrum, above where it meets the coccyx is the inferior lateral angle and can be an important landmark in palpation. The coccyx also takes on some characteristics of 3 or 4 rudimentary vertebrae, especially the most superior almost having transverse foramina. On the posterior surface of the sacrum there is a bony ridge called the median sacral crest which is where the spinous processes fused together. Just lateral to each side are the medial sacral crests which is where the articular processes fused together, and they continue downward as the inferior articular facets of S5 or the sacral cornua (which articulates with the coccygeal cornua or its superior articular facets) and continuous superiorly into the superior articular facets of L5/S1. There is an aperture between the sacral cornua called the sacral hiatus which opens into the sacral canal. If there was a fusion of the SP’s there also has to be a fusion of the TVPs which forms a lateral sacral crest. There are also rudimentary ribs associated with those TVPs which fuse to form the sacral wings (or ala of the sacrum), the superior lateral aspects of the bony sacrum. This is where the auricular (ear shaped) surfaces which articulate with the innominate bones, forming the sacroiliac joint (have considerable individual variation). Just behind the auricular surface of the sacrum, lies the sacral tuberosity or tubercles which is a rough surface with 3 impressions. The sacrum tilts forward at its base internally, forming the sacral promontory with a concave surface just below, increasing the space of the pelvic cavity, and ends at the coccyx which is the very end of the vertebral column (1,2)
o The innominate or hip bone is a fusion of the pubic, ischium and ilium bones postnatally. The uppermost portion of the innominate, or the ilium portion, forms the iliac crest, iliac fossa and 2/5ths of the acetabulum (which is the articular surface for the head of the femur). It has the bony landmarks of the anterior superior and inferior iliac spines anteriorly as well as the posterior superior and inferior spines posteriorly as well as the ischial spine and ischial tuberosity. It has a body and a wing or ala which are separated from each other by the arcuate line. The body of the ilium contains the auricular surface for the articulation with the sacrum (both have irregular cartilage covering, the sacrum side being twice as thick). The posterior and inferior portion of the innominate is formed by the ischium which also has a body as well as a superior and inferior ramus. It is the strongest portion of the innominate as it has the ischial tuberosity which takes on a lot of different forces, including that of our body weight in seated. The body forms 1/3rd of the acetabulum. The last and anterior portion of the innominate is the pubic bone. It also has a body, superior and inferior ramus. The superior pubic ramus, on its medial and superior surface has the pecten of the pubis, which is a line that continues posteriorly with the arcuate line (together are the iliopectineal line), and anteriorly with the pubic crest. These lines along with. the sacral promontory separates the lesser and greater pelvis (or false and true pelvis). Just anterior to the pubic crest is the pubic tubercle, an important bony landmark. The body of the pubic bone forms 1/5th of the acetabulum. The ischium and pubic bone through their rami, form a foramen anteriolaterally called the obturator foramen. The two pubic bones meet anteriorly with their symphyseal surfaces, forming the pubic symphysis which contains an interpubic disc (fibrocartilaginous pad) (1).
• Ligaments
o The interosseous ligament is very deep and attaches from the iliac tuberosity (just above the articular surface of the ilium) and runs medially to the sacral tuberosity (just above the articular surface of the sacrum. This ligament stabilizes the dorsal side of the joint and stops the joint from distracting excessively. The posterior sacroiliac ligament has upper and lower fibers. The upper fibers attach from the 2nd and 3rd transverse tubercles of the sacrum to the tuberosity of the ilium and has horizontal short fibers. The lower fibers attach from the 3rd tubercle of the sacrum to the posterior superior spine of the ilium and has oblique long fibers. This ligament also supports the joint posteriorly and also helps distribute the axial forces of the spine into the lower legs. The anterior sacroiliac joint is not as thick as the posterior. It attaches from the anterior lateral surface of the sacrum to the auricular surface of the ilium (1,2). This ligament stabilizes the anterior aspect of the joint and limits sacral nutation or flexion of the sacrum. The sacrotuberous ligament attaches from the lower sacral tubercles, the inferior margin of the sacrum and upper coccyx to the ischial tuberosity. It has some fibers continuing into the posterior SI ligament. The sacrospinous ligament attaches from the spine of the ischium to the lateral inferior aspect of the sacrum and coccyx and forms the greater sciatic foramen (1,2). These ligaments together stabilize the SIJ and also prevent hyper counternutation of the sacrum. Moving back up to the L5/S1 joint, there is the iliolumbar ligament. It attaches from the transverse process of L5 and sometimes L4, and travels inferiorly to the posterior and inner part of the iliac crest and blends with the anterior SI ligament to the sacrum. It is continuous superiorly with the thoracolumbar fascia which is a deep investing membrane attaching to the lumbar TVPs and SPs and an attachment site for many muscles (1,2) This ligament helps to tether the lumbar vertebra down into the pelvis, and limits motions of the SIJ and L5/S1.

Muscles/Fascia


• Working still deep to superficial we will start with the deep intrinsic musculature. I’ve seen the deep intrinsic muscles categorized in a few ways. More recent texts will split them into transversospinalis (semispinalis, multifidus, rotators) and then the segmental muscles (levator costarum, interspinales and intertransverse. We are going to be categorizing the deep intrinsics as multifidus, interspinales,intertransversarii and rotatores muscles(levator costarum only in thoracic spine).
o The multifidus muscle in this region attaches from the sacrum (as low as the sacral foramen), ilium (at the PSIS and posterior SI ligament) , mammillary processes of L1-5,to spinous processes 2-4 vertebrae above (superficial fibers span farther, this is a common theme among soft tissues). It is important to keep in mind that these muscles continue superiorly into the thoracic and cervical regions, but for the sake of this discussion, we will talk predominantly about their attachments in the lumbopelvic region. This tendinous muscle fills the groove just lateral to the SPs and travels upward and medially (2). Bilateral contraction of this muscle would extend the lumbar spine and flex or nutate the sacrum forward. Unilateral contraction would side bend to the same side and rotate to the opposite side, in regular Fryette’s spinal mechanics. It may also have potential to pull superiorly on the PSIS creating weak anterior innominate rotation and can create tension on the Posterior SI ligament.
o The interspinales muscle attaches to adjacent spinous processes all the way up the lumbar spine (some texts say also it attaches to the sacrum). It is still a paired muscle, one on each side of the interspinous ligament, this muscle though only seems to be present in the lumbar and cervical regions (soft tissue curves) (1,2). Bilateral contraction creates extension, and unilateral contraction would side bend to the same side.
o The intertransversarii muscle has a medial and lateral portion. The lateral portion attaches to adjacent costal processes in the lumbar spine, and the medial portion attaches to the mammillary processes (1,2). So, we have attachments closer to the facet joints and further on the lateral portions of the TVPs. This muscle often blends with the intertransverse ligament and creates sidebending to the same side with unilateral contraction, and bilateral extension.
o The rotatores muscles lie just deep to the multifidi and are similar in that they attach from the transverse processes (on the superior and posterior aspect) and run up medially to spinous processes (and their lamina) 1-2 levels higher (brevis and longus respectively) (1). This muscle is more developed in the thoracic spine as one of its major motions being rotation, and is fairly underdeveloped in the lumbar spine to the point where some resources say its non existent there. This muscle is a unilateral rotator and bilateral extensor of the spine (1,2).
o An important note is that these deep intrinsic’s are not major movers of the spine, and are more stabilizers of posture and positioning of the spine. Although we talked about their movement capabilities based on their attachment points, they are not necessarily involved in gross motions of the body, but protect and stabilize the spine as bigger muscles create those motions. They create minor motions within and across spinal segments and limit excessive movements of the facet joints (7). They are highly spindilated, meaning they have many muscle spindles per fiber, allowing them to read and react to small movements in joint position. The rotatores and interanseversarri muscles especially which are seen to have 4-7 times more spindles then even the multifudi muscles (6). These muscles are innervated by the posterior rami of the spinal nerves (with the exception of the lateral portion of the intertransversarii innervated by the anterior rami). Their blood supply generally comes from lumbar (from posterior abdominal aorta) and lateral sacral arteries (from posterior division of internal iliac artery) (1,2)
• Staying on the posterior side on the lumbar spine, moving slightly superficial and lateral lie the erector spinae muscles. The erector spinae muscle is actually 3 muscles consisting of the iliocostalis, longissimus and spinalis muscles.
o The iliocostalis lumborum muscle attaches from the lateral crest of the sacrum and the supraspinous ligament, posterior part of medial lip of iliac crest and superficial layer of the thoracolumbar fascia (therefore to SPs of lumbars and lower thoracic vertebra), travels upward and slightly laterally to attach to the angle of the lower 6 ribs, deep layer of the thoracolumbar fascia as well as the upper 2 lumbar TVPs (remember are almost like the ribs in the lumbar region) (1,2). The texts books say this muscle bilateral extends the spine and unilateral sidebends the spine to the same side, but based off the inferior pull on the posterior side of the rib, likely could exhale the lower six ribs and pull the inferior aspect of the sacrum superiorly, nutating the sacrum or unilaterally flexing that side as well as potentially anteriorly rotating the innominate in the sagittal plane (makes sense for a muscle to flex one region and extend another, compensation movement). This muscle also has interesting connections in the thoracic and cervical region which will be discussed in a future podcast.
o The next muscle medially is the longissimus thoracic muscle which attaches from the sacrum, iliac crest (common tendon for erector spinae), SPs of the lumbar vertebrae (superficial thoracolumbar fascia) and TVPs of the lower thoracic vertebra, upward and laterally to attach to ribs 2-12 between the tubercles and angles (medial to iliocostalis attachment), costal processes of the lumbar vertebrae (some sources say mammillary processes, others accessory processes) and TVPs of the rest of the thoracic spine. This muscle also is said to extend the lumbar spine or sidebend to the same side (1,2). Though just looking again at attachment points can influence the ribs, sacrum and innominate in a similar way as that of the iliocostalis muscle. Although, because its attachment is more medial on the rib, it would have less leverage to pull straight down. These two muscles could also potentially, depending on the angle and the motion capacity of the rib rotate the rib head posteriorly (on a transverse axis) and inhale in the sagittal plane, but this is just speculation.
o Lastly the spinalis thoracis muscle attaches from the lateral surface of the spinous processes of T10-L3 and travels superiorly to the lateral surfaces of spinous processes T2-8. This muscle also bilaterally extends and unilaterally sidebends the lumbar region (1,2). These muscles work together on the dorsal spine to hold our body upright and stabilize the spine similarly to that of the deep intrinsics. They will be innervated segmentally by the lateral branches of the posterior primary spinal rami and receive blood supply from posterior intercostal, lumbar, subcostal and lateral sacral arteries (1,2). A muscle I'm going to sneak with these is the posterior serratus inferior which attaches from the SPs of T11-L2 and thoracolumbar fascia up and laterally to the lower margin of ribs 9-12. This muscle helps with inhalation, but may have more important functions in proprioception (8).
• Staying in the lumbar region, there are muscles which run from the spine down into the innominates and lower limbs which include the iliopsoas, quadratus lumborum muscles and gluteal muscles which have great influence on this region.
o The iliopsoas muscle which is a combination of psoas major, minor and the iliacus muscle attach from the vertebral bodies, intervertebral disks and costal processes of T12-L5 and the iliac fossa and travels inferiorly to attach to the lesser trochanter of the femur. This muscle is interesting as it joins the leg to the spine and therefore the axial skeleton and the appendicular skeleton. Its action is to flex and externally rotate the hip when the spine is fixed, but can also create bilateral extension, unilateral sidebending to the same side and rotation to the contralateral side if the leg is fixed. It can also pull an individual out of the supine position if the legs stay fixed in almost a sit up movement because of its anterior attachment on the lumbar spine. Its iliacus attachment can also pull the innominate anteriorly into rotation. This muscle is innervated by the femoral nerve L2-4 and also from some direct spinal branches of anterior rami L1-4. it gets its blood from lumbar branches of the iliolumbar artery (1,2).
o The quadratus lumborum muscle attaches from the wings of the iliac crest to the 12th rib and costal processes L1-4 (the same as the psoas but a more posterior lateral orientation). This muscle extends the spine bilaterally, sidbends the spine to the same side unilateral and helps to fix the 12th rib during forced expiration and can help with inhalation (1,2). It can also potentially anteriorly rotate the innominate.
o Another muscle I want to include with these two is the respiratory diaphragm which attaches from the costal arch or margin (ribs 7-12), xiphoid process, L1-3 intervertebral disks (through the right and left crus, crus meaning leg), anterior longitudinal ligament, and some lateral attachments we will talk about here to the central tendon. The interesting connection with the iliopsoas and quadratus lumbar is through the right and left crus as well as 3 tendinous arcs. The right crus, on the right side, is lower and attaches from the bodies and disks of L1-3, the left only L1-2. Medially, these two crura meet at L1 and form the median arcuate ligament, which also forms the aortic hiatus, where the aorta travels through. The next arch just laterally is the medial arcuate ligament or psoas arcade from L2 body to the L2 costal process and allows passage for the psoas major muscle. The most lateral arch, the lateral arcuate ligament, attaches from the costal process of L2 to the 12th rib and allows passage for the quadratus lumborum muscle (1,2,8). This means the diaphragm allows for passage of the upper ends of these muscles into the lumbar spine, just at and around the thoracolumbar junction. Are there connections between the functionality of the lumbar spine, postural position and respiration? Neurologically we can see some overlap in the extrapyramidal system, something worth considering. What organs are in that region? Discussed in a future podcast.
o The gluteus maximus muscle is the only of the three glute muscles that attaches to the spine. It attaches to the lateral, posterior aspect of the sacrum and coccyx, posterior part of the gluteal surface of the ilium (posterior gluteal line of the inner upper ilum), thoracolumbar fascia (same as erector spinae) and sacrotuberous ligament. It then has upper and lower fibers, the upper fibers attaching into the iliotibial tract and the lower fibers into the gluteal tuberosity of the femur between the vastus lateralis and adductor magnus. This muscle extends and laterally rotates the hip, also anteriorizing the innominate (1,2). If the hip is fixed though, it helps support the pelvis ontop of the head of the femur and can pull the pelvis posteriorly helping to maintain the upright position of the trunk
• Moving to the pelvic diaphragm, there is the levator ani and coccygeus muscles. We are also going to include some external rotators here from the hip in this discussion. The levator ani 3 muscles, the puborectalis, pubococcygeus and iliococcygeus.
o The puborectalis attaches from the superior pubic ramus just lateral to the pubic symphysis and attaches to itself on the opposite side around the anorectal junction.
o The pubococcygeus attaches from the pubis lateral to puborectalis, and innserts onto the annococyygeal ligament (fibromuscular band attaching external anal sphincter to coccyx) and coccyx.
o The iliococcygeus attaches from the tendinous arch of the internal obturator fascia to the iliococcygeal raphe (where the two muscles meet in the middle), anococcygeal ligament and coccyx.
o The coccygeus muscle attaches from the inferior end of the sacrum to the ischial spine under the sacrospinous ligament . These muscles together support the pelvic visceral above (1,2).
o There are also 6 external rotators of the hip including the piriformis, obturator internus, obturator externus, superior gemellus, inferior gemellus and the quadratus femoris which also help to support this floor and influence the position of the sacrum and innominates.
• Lastly, we are going to discuss a few more muscles in relation to the anterior and posterior fascial compartments as there are some really interesting relationships. These are the muscles of the abdominal wall and the latissimus dorsi muscle of the upper limb.
o Starting deep is the transversus abdominis muscle which attaches on the inner surfaces of the lower 6 ribs and costal cartilages (interdigitating with the diaphragm), deep layer of thoracolumbar fascia, inner lip of the iliac crest (anterior 3/4ths), anterior superior iliac spine, lateral part of the inguinal ligament to the posterior layer of the rectus sheath , linea alba (vertical band of connective tissue), the pubic crest and pectineal line of the pubis (joining with the aponeurosis of the internal oblique forming the inguinal conjoined tendon). These muscle fibers run medially and slightly inferiorly as they travel to the front. It is responsible for compressing the abdomen, increasing abdominal pressure as well as ipsilateral rotation (1,2).
o The next muscle just superficial to the transversus abdominis is the internal oblique. It attaches from the deep layer of the thoracolumbar fascia, intermediate line of the iliac crest (anterior 2/3rds), lateral half of the inguinal ligament anterior superior iliac spine and the iliopsoas fascia, to the lower borders of the lower 3-4 ribs, anterior and posterior layers of the rectus sheath and linea alba as well as the junction of the cremaster muscle (in males). Its fibers run superiorly and medially. It also acts to compress the abdomen, increasing pressure of expiration as well as rotation to the ipsilateral side. It also sidebends the trunk to the same side and can bilaterally flex the trunk (1,2).
o The most superficial, the external oblique attaches from the outer surface of the lower 8 ribs to the outer lip of the iliac crest (anterior ½), anterior layer of the rectus sheath and linea alba. Its fibers run inferiorly and medially allowing the muscle to unilaterally sidebend the trunk to the same side and rotate to the opposite side and bilaterally compress the abdomen and flex the trunk (1,2).
o The muscle bellies of these three muscles, as they wrap from posterior to anterior, turn to an aponeurosis around the mid clavicular line. Aponeurosis are sheets of a type of deep fascia made of fibrous tissue that are vary similar to tendons that connect sheet-like muscles to bones or other muscles. These three aponeuroses come together in the midline forming the tendinous rectus sheath which encloses the rectus abdominis muscle. The external oblique aponeurosis forms the anterior layer, the superior 2/3rds of the internal oblique aponeurosis split into an anterior and posterior portion (lamina) at the lateral border of the rectus abdominis. The anterior lamina meets with the external oblique aponeurosis forming the anterior layer of the rectus sheath (anterior to rectus abdominis) and the posterior lamina meets the transversus abdominis aponeurosis forming the posterior layer of the rectus sheath (posterior to the rectus abdominis). At the level of the bottom ⅓ of the internal oblique just below the umbilicus, the three layers of aponeurosis then pass anterior to the rectus abdominis, all forming the anterior layer with only the transversalis fascia posterior. The aponeurosis of both sides then intertwines with each other at the midline with the anterior and posterior layers coming together to form the Linea alba (raphe). All layers of the abdominal wall fuse at the umbilicus. This make up creates some very interesting forces for movement and packaging for NAVL and Organs. For example, the aponeurotic fibers of the external oblique become continuous with the internal obliques on the opposite side forming a digastric muscle which rotates toward that internal oblique. The external oblique aponeurosis creates a thickened fibrous band from the ASIS to the pubic tubercle, which we call the inguinal ligament which then becomes continuous with the deep fascia of the leg (8). The rectus abdominis muscle attaches from the cartilages of the 5-7 ribs, xiphoid process of the sternum, down vertically through the rectus sheath to the pubis between the pubic tubercle and symphysis. This muscle is anchored by anterior attachments to the anterior rectus sheath at the tendinous intersections which separate the muscle bellies. There is also a small muscle associated in some people called the pyramidalis that attaches just anterior to the rectus abdomen on the pubis to the Linea alba. This muscle also compresses the abdomen and flexes the trunk/lumbar spine (1,2).
o There is also a posterior equivalent of this system on the back side, named the thoracolumbar fascia/aponeurosis. In the lumbar region it is thick and strong, it consists of posterior (coming off of the spinous process and median crest of sacrum and supraspinous ligament) , middle and anterior layers (coming off the TVPs to the iliac crest and 12th rib and iliolumbar ligament) that unit together laterally (where the obliques then attach) at the lateral ends of the intrinsic back muscles including and separating compartments. The psoas is anterior to the anterior layer, the QL is between the middle and anterior layers, the deep intrinsics and erector spinae are between the posterior and middle layers (forming an enclosure similar to the rectus sheath). Then superficial muscles like the latissimus dorsi, trapezius muscle, gluteus maximus, posterior serratus inferior attach to its posterior layer. This fascia is much like that of the anterior abdominal wall but the aponeurosis on the front creates a soft tissue attachment of the linea alba whereas the thoracolumbar fascia attaches into the vertebrae. Other then the external oblique, the internal oblique and transversus abdominis directly connect the thoracolumbar fascia with the rectus sheath. Their pull through the TL fascia influences the posterior sheath of the erector spinae. Then you have pull from the glutes, and upper limb via the latissimus dorsi making this region a huge coordinator of collective body movements. It compartmentalizes muscle groups and helps coordinate load anterior to posterior as well as different regions.
• Some other associated fascia’s
o On the anterior and lateral abdominal wall there is superficial and deep investing layers of fascia. The subcutaneous tissue or superficial fascia is a storage are for fat. The superficial fascia on the anterior abdominal wall is similar to that of other regions of the body, except below the umbilicus where there is a reinforcement of the deeper portion with elastic and collagen fibers forming another deep membranous layer of the superficial fascia. The superficial fatty layer is called camper's fascia and thee deeper membranous layer is called scarpa’s fascia but they are both apart of the subcutaneous tissue. Camper's fascia continuous inferiorly with the superficial fascia of the thigh. Scarpa's fascia continues into the perineal region as colles fascia, some texts say it does not continue into the lower limbs but others say it fuses with the fascia lata of the thigh
o The investing deep layers are the layers associated with the abdominal wall musculature and aponeurosis, are thin and not easily separated from the muscles, pretty much the epimysium. These three layers lie on top of each abdominal muscle.
o The internal aspect of the transversalis muscle is also lined with an endoabdominal fascia also called the transversalis fascia.
o That endoabdominal fascia continues to the posterior abdominal wall. There is then also the psoas fascia attached to the lumbar vertebra and pelvic brim. It is thickened superiorly forming taht medial arcuate ligament with the diaphragm we discussed earlier. The QL fascia is also present, and connects with the psoas fascia and the thoracolumbar fascia (8).

References:

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