10.1 Significance and Function of the Lumbar Spine
The embryonic curves change during early childhood development in two sections of the vertebral column. The lumbar spine represents one of these sections. The mobile sections of the vertebral column (cervical and lumbar spines) become lordotic. The thoracic spine and the sacrum remain in their original kyphosis. The cervical and lumbar spines also possess deep prevertebral muscles (e.g., psoas major, adductor longus).
10.1.1 Supporting the Weight of the Body
From a kinetic point of view, the lumbar spine supports the weight of the upper body, the head, and the arms. As already described, approximately 60% of the body’s weight in an upright posture is transmitted from the lumbar spine onto the S1 end plate. The lumbar spine adapts to this loading with wider and more solid material in the bones, collagen, and fibrous cartilage (structural stability/force closure).
10.1.2 Spatial Alignment of the Upper Body
The lordotic sections of the spine provide spatial orientation for the parts of the body they support. The lumbar spine supports, props up, and turns the upper body. The cervical spine supports and aligns the head in relation to its surroundings.
10.1.3 The Importance of Stability for Standing and Lifting
The intervertebral disks, ligaments, and muscles are in particular responsible for stability in the vertebral column and achieve this using compression and tension banding. The erector spinae are not very active in the upright posture. Their activity increases when the body’s center of gravity moves anteriorly, for example when:
It is important that the tissues provide the mobile parts of the chain with force closure to enable controlled movement. For this reason, science of human movement states that: “stiffness is a precondition for movement.” In a multisegmental system such as the vertebral column, stability is maintained by reducing the range of available mobility in individual segments so that the entire system can move harmoniously. The trunk extensors become inactive after approximately 60° of trunk flexion due to the ligamentous structures taking over the job of decelerating movement. The thoracolumbar fascia is the most important ligamentous structure (see ▶ Fig. 10.32).
10.1.4 Movement in the Trunk
The lumbar spine is an organ designed for flexion, with movement mainly occurring in the sagittal plane. It is just as natural to move out of the lordosis to bend the trunk backward and forward as it is to develop the lordotic form when standing. The lumbar spine is anatomically constructed and equipped for flexion. It is irrelevant whether the movements are proper flexion or just a straightening out of the lordosis for palpation.
Certain anatomical structures assist the lumbar spine in its movement in the sagittal plane:
The alignment of the lumbar vertebral joints superior to L5 makes extensive movement in the sagittal plane possible (▶ Fig. 10.1).
Thick intervertebral disks make extensive tilting movements possible in the lumbar segments.
Structures that decelerate movement and absorb forces: ligamenta flava, interspinous ligaments, thoracolumbar fascia.
The exceptionally strong intrinsic muscles of the lateral tract (iliocostalis, longissimus).
Fig. 10.1 Schematic illustration of the alignment of the lumbar zygapophysial joints (ZAJs). Compare this to ▶ Fig. 10.9.
10.1.5 Development of Energy Needed for Locomotion
According to Serge Gracovetsky (1989), the impulse for walking arises in the lumbar spine and is based on the mobility and activity in the muscles that cause rotation (the multifidi and external oblique). The legs only follow and reinforce this movement. Examples from evolution (fish, amphibians) demonstrate how important lateral flexion is for locomotion. In human beings, the lumbar spine uses lateral flexion and coupled rotation to transfer the trigger for locomotion onto the pelvis and the legs, whereby a lumbar lordosis and a certain walking speed are important. The impulse and energy arise solely in the legs when gait is slow; this requires a great deal of strength.
10.1.6 Junction between the Rigid and Mobile Vertebral Column
The junction between the lumbar spine and the sacrum is a region of anatomical and pathological turbulence. Anatomical variations in the number of vertebrae (e.g., hemisacralization) as well as a multitude of pathological conditions are frequently found here. This distinctive feature is probably due to typical biomechanical loading in addition to the lumbar spine acting as the junction between the freely mobile vertebral column and the rather rigid pelvis, in particular the sacrum.
This region is supported by different anatomical structures:
10.2 Common Applications for Treatment in this Region
Most symptoms in the lumbar region are directly or indirectly related to the intervertebral disks. It is a known fact that the primary and most secondary intervertebral disk pathologies tend to be found in the lower lumbar segments of L4/L5 and L5/S1. The primary intervertebral disk symptoms range from internal rupturing to the different forms of protrusions and prolapses of intervertebral disk substance (▶ Fig. 10.2). These symptoms possess a large potential for self-healing. The initial physical therapy management of acute back pain aims to assess the primary pain and relieve affected neural structures, thereby supporting self-healing. The first inflammatory stage ends after a few days. Physical therapy then addresses the increased muscle tension, adaptive postures, immobilization, decreased proprioception, and, when necessary, the repositioning of the intervertebral disk substance.
The therapeutic approaches to treatment always address the entire lumbar spine. Precise palpation techniques only have limited use here. For instance, it is generally not necessary to ascertain which segment is affected by provoking pain with palpation or assessing the local mobility. It is important to assess whether there is excessive muscle tension in the paravertebral muscles for the treatment of subacute disk-related symptoms. This provides therapists with a sensible basis when they are deciding which treatment to use. When patients present with these sets of symptoms, therapists are therefore required to systematically palpate the muscles and have knowledge of surface anatomy (see the section “Palpating the Consistency of Muscle [Assessment of Muscle Tension]” in Chapter 8).
The secondary pathological intervertebral disk conditions behave completely differently. Surface anatomy is often required in this case. Degenerative changes to the lumbar disks cause a surprisingly large range of symptoms. The intervertebral disks can be the source of pain and can be responsible for the involvement of sensitive ligamentous and neural structures (▶ Fig. 10.3).
These types of pathological disorders are mainly in the form of local segmental instability, chronic intervertebral disk irritation, disorders and diseases in the zygapophysial joints, and varying degrees of stenoses. Of course, combinations of these pathological conditions are possible. Just think of the neighboring hypermobile and hypomobile segments that are frequently present.
There are several different approaches to therapeutic management. The main aim of these approaches is pain relief and stabilization. Detailed anatomical orientation is an important foundation for segmental assessment and for the reliable use of local segmental techniques.
The roles of surface anatomy here are the following:
To locate the affected segments using pain provocation.
To identify the affected segments by differentiating them from the neighboring segments (locating their level).
To assess the segmental stability and mobility using angled or translation tests.
Competence in palpation is obtained from the consequential use of surface anatomy. It enables the therapist to provide exact information on the functional characteristics of the lumbar spine and therefore substantiates the treatment plan and the targeted use of pain-relieving and/or mobilizing techniques.
10.3 Required Basic Anatomical and Biomechanical Knowledge
The following information represents only a selection of information available on local anatomy and biomechanics. Several areas, such as the construction and function of the intervertebral disks or neuroanatomy, are not discussed in order to stay on the topic of surface anatomy. These sections primarily discuss the anatomical details required for palpation. A basic knowledge of movement segments according to Junghanns is of advantage.
10.3.1 Anatomical Definitions
The inferior section of the freely moveable vertebral column, the lumbar spine, usually consists anatomically of five freely moveable vertebrae. However, this is not the case in every individual. As already mentioned above, the lumbosacral junction is quite variable and anatomically turbulent. Töndury (1968, in von Lanz and Wachsmuth, 2004a) wrote about the entire spectrum of variation in the anatomy with respect to the anatomical boundaries of all sections of the vertebral column (▶ Fig. 10.4 ): “Only approximately 40% of all people have their boundaries in the normal location.” The boundaries between the thoracic spine and the lumbar spine as well as the lumbosacral junction are of interest here.
When S1 is separated from the sacrum, it takes on the role of a lumbar vertebra and is labeled anatomically as lumbarization. This results in the lumbar spine possessing six vertebrae. The anatomist defines the superior variation or sacralization as the fusion of L5 with the sacrum. This can be present partially or on both sides (▶ Fig. 10.5). In this case, only four freely mobile vertebrae exist. It becomes quite confusing when the therapist considers that there is even more variety in the number of sacral vertebrae. The terms refer therefore to the possible variations (lumbarization or sacralization) in the freely moveable lumbar vertebrae (von Lanz and Wachsmuth, 2004a):
Five lumbar vertebrae → common number in the lumbar spine.
Four lumbar vertebrae →hemi-/sacralization in 3 to 12%.
How Does this Affect Palpation?
A focus of surface anatomy along the vertebral column is defining the exact location, the level of a structure. Topographical knowledge provides the therapist with expected norms. These norms are transferred onto the living body during palpation. What does it mean when our confidence in topographical orientation—our knowledge of anatomy that we learn during training—becomes lost in the variation?
Variations in the anatomy of the lumbar spine make it difficult to locate the L5 spinous process. When three protruding and pointed spinous processes are found at the lumbosacral junction, it is difficult to differentiate between L5 and S1 by simply looking at their shape. What options exist to confirm the location of a structure when no movement in L5 on S1 can be felt, as is seen when mobility is restricted or when hemisacralization is present? How can therapists remain confident that palpation is correct when the suspected S1 spinous process moves on S2? Is the location incorrect or is a lumbarization present?
Fortunately, constants also exist in anatomy. Certain structures have a constantly recurring shape, always react to pressure in the same way, and behave typically when they move (changes due to pathological conditions are not included here):
The L5 spinous process is always smaller than the L4 spinous process.
The T12 spinous process is always smaller than the L1 spinous process.
Posteroanterior pressure applied to a spinous process moves the vertebra slightly anteriorly (▶ Fig. 10.6).
Rotation (in a coupled movement pattern) in one segment leads to the development of a palpable step between two neighboring spinous processes.
10.3.2 Shape of the Inferior Lumbar Vertebrae and Intervertebral Disks
From an anatomical point of view, the lumbar lordosis is supported by the wedge-shaped construction of the vertebral bodies, especially at L5 and most notably at the L5/S1 intervertebral disk (Bogduk, 2000) (▶ Fig. 10.7).
The lumbar spine is usually positioned in its physiological lordosis when it is being palpated. This is independent of the patient’s starting position (SP) (prone, side-lying). It may be the most natural position, but it does make the palpatory process more difficult. A lordotic lumbar spine offers certain conditions for palpation:
The palpation demonstrates that the superior section of the sacrum is definitely tilted anteriorly and its angled surface can be distinguished.
When the erector spinae are prominent, all spinous processes can only be reached at their tips and somewhat to the side.
The L5 spinous process is mostly found deep in the tissues and in close proximity to L4 and S1.
The thoracolumbar fascia and the back extensors are relatively relaxed.
Further sections will explain which lumbar spine positions are favorable or less favorable for precise palpation.
10.3.3 Detailed Anatomy of Bony Structures
The thick vertebral bodies (VBs) are generally shaped like a bean or a kidney. Each VB is a tube made of the bone’s cortical substance filled with the bone’s spongy substance. The VB is enclosed superiorly and inferiorly by hyaline end plates. These end plates are nowadays included functionally as a part of the intervertebral disk (Bogduk, 2000). The vertebral arch connects immediately posterior onto the vertebral body. All vertebral processes are attached to the arch:
These processes point directly posterior and are strongly developed (▶ Fig. 10.8). They are the only osseous structure in the lumbar spine that the palpating finger can reach with certainty. The shape of the lumbar spinous processes is typical and can be well differentiated from the neighboring sections of the vertebral column during palpation.
Aylott et al. (2012) demonstrate that the length and width of the spinous processes increase with age (approx. 0.5 mm/10 years for both length and width). Aylott measured an average height (superior-inferior dimension) of 27 mm for the L1 to L4 spinous processes in men. The height of the L5 spinous process was only 17 mm. All of the measurements were around 3 mm less in women. The study conducted by Shaw et al. (2015) on approx. 3000 cadaveric lumbar vertebrae provides additional information about the length of the L1 to L4 spinous processes (from the edge of the vertebral foramen to its tip), stating an approximate length of 30 mm, while the L5 spinous process is 25 mm. Slope at L1 to L4 was approximately 15° and at L5 approximately 24° (▶ Fig. 10.8).
Thus, the following observations can be made about the L5 spinous process: It is shorter, and has a shorter and steeper slope than the other lumbar spinous processes (Shaw et al., 2015). When palpating the L5 spinous process it almost seems to point posteriorly. It can generally be well located. The therapist may get confused between neighboring spinous processes when the S1 spinous process is pronounced. This can make it more difficult to allocate a segment to a specific level.
The Shape and Alignment of the Lumbar Spinous Processes
The novice therapists may initially be surprised by the size and morphology of the lumbar spinous processes. The L1-L4 spinous processes are rather broad (superior-inferior dimensions) and have an exceptionally irregular shape with indentations along their posterior aspect, giving them an undulating appearance (▶ Fig. 10.9). The spinous processes are often expected to be smaller than they actually are.
Bursae are regularly found between the neighboring lumbar and thoracic spinous processes. As with the other sections of the vertebral column, the therapist should not expect the lumbar spinous processes to always form a straight line. The lumbar spinous processes can protrude laterally away from the mid-line by up to a few millimeters and up to 1 cm in the thoracic spine and still be seen as a normal variation in anatomy.
The palpatory differentiation of spinous processes by locating the interspinous space is made considerably more difficult by their undulating form. Aids must be used once again to ensure that structures have been allocated to the correct level. Provided the condition of tissues does not make palpation difficult in study partners and patients, the long spinous processes can be correctly differentiated from the pointed L5 and the T12 spinous processes after gaining some experience. The T12 spinous process is likewise very thin.
Therapists and physicians often directly connect the position of the spinous processes with a local pathological condition. A spinous process that deviates from the mid-line is mostly interpreted as a rotational malpositioning of the respective vertebra. However, this cannot always be the case due to the large variation in anatomy. A palpatory finding must always be supported by local mobility tests and provocation tests to conclude the presence of a segmental pathological condition.
Lumbar Transverse Processes
The lumbar transverse processes are remnants of ribs from the times of somitic composition. This arrangement can still be observed in the thoracic spine and is the reason why the transverse process is labeled the costal process. All transverse processes are strongly developed and extend directly sideways from the vertebral arch. According to von Lanz and Wachsmuth (2004a), the L3 costal process is the widest. In rare cases (4–8%), L1 can possess an oversized process that is described in literature as a lumbar rib (von Lanz and Wachsmuth, 2004a). This makes it more difficult to differentiate the thorax from the lumbar spine when using palpation.
A multitude of muscles attach onto the transverse processes (Dvořák et al., 1998). As with the spinous processes, the transverse processes are therefore perfect levers for acting forces moving the lumbar vertebrae into lateral flexion and rotation (▶ Fig. 10.10). The transverse processes separate the posterior intrinsic back muscles topographically from the anterior deep abdominal muscles (e.g., psoas major).
Muscular or dynamized connective-tissue structures are currently regarded as functionally very important in the stabilizing treatment of the lumbar spine. These structures insert on the costal processes:
Transversus abdominis over the middle layer of the thoracolumbar fascia.
The attempt to reach the transverse processes using palpation is only conclusive on slender people. The transverse processes are located several centimeters anterior to the superficial surface of the back and are completely covered by the thick, prominent back extensors. Only the tips of the L3 and possibly the L4 transverse processes can be reached. This is achieved by applying significant posteroanterior pressure lateral to the back extensors and superior to the iliac crests, then palpating in a medial direction in the hope of coming across a hard structure.
The purpose of this maneuver is questionable, alongside the technical difficulties associated with this procedure. This technique is not suitable for diagnosing the alignment of the structure or for the selective provocation of pain and will therefore not be discussed later.
These are some of the most important functional parts of the vertebra. The largest variety of terms is also used to describe these joints (e.g., facet joints, vertebral joints). The thickness and construction of intervertebral disks enable segments to move. In principle, the zygapophysial joints (ZAJs) determine how this potential for movement is used. The alignment of these joints dictates the direction and partially the range of segmental movement. It is well known that the superior articular process of the inferiorly positioned vertebra (more concave) forms a ZAJ with the inferior articular process of the superiorly positioned vertebra (more convex) (▶ Fig. 10.11).
The position of the lumbar joint facets between T12/L1 and L4/L5 is uniformly described in manual therapy literature (Dvořák et al., 1998): In relation to the vertebral bodies, the superior joint surfaces are arranged upright and converge at an average angle of 45° from posterolateral to anteromedial (▶ Fig. 10.12). This angle gradually decreases in the more superior vertebrae (Bogduk, 2000).
This results in the lumbar spine’s affinity to movement in the sagittal plane, enables the lumbar spine to laterally flex, and prevents axial rotation. The latter movement can best be visualized by looking at the axes for lumbar movement found in the disk (see the section “Basic Bio-mechanical Principles” below).
The L5/S1 joint facets orient themselves more in the frontal plane, somewhat increasing this segment’s ability to axially rotate.
The principle of anatomical variation continues in the lumbar ZAJs.
Joint surfaces of the same level can be shaped differently with different spatial alignment without being pathological. Individual differences in the shape of the ZAJs between sides is labeled “facet tropism” (Jerosch and Steinleitner, 2005) (▶ Fig. 10.13). This means that the previously described spatial alignment of the joint surfaces is to be understood as only representing the average and that there are differences between the left and right side in each segment.
The ability to palpate the vertebral column is mainly used to assess segmental mobility and to ascertain the level of individual structures. To be able to do this, the therapist must be aware of the possible range of motion in the sections of the vertebral column.
The influence of differently formed joint facets on the palpation during movement will be clarified later. It can be presumed that facet tropism does not affect the degree of symmetrical movement in the lumbar spine (flexion and extension). When the anterior tilt of the vertebra is different on the left and right side during flexion, this cannot be felt because sagittal movement is simply perceived as an opening or closing of the spinous processes (▶ Fig. 10.14). A difference in movement between the sides where the vertebra moves asymmetrically does not change the palpable range of motion.
This is different for asymmetrical lateral flexion or rotation movements, where the effect of differently formed joint positions and shapes is important. The range of motion in segmental lateral flexion and rotation to the left and to the right can therefore differ, even in healthy segments. For this reason, the therapist compares sides when assessing the range of local motion while still being aware of what is happening in the neighboring segments (▶ Fig. 10.15).
The ZAJs and their capsules stand out in anatomical specimens with their astoundingly large ball-like form. Their position is approximately at the level of the inferior edge of a spinous process. To palpate the ZAJs, the therapist must overcome a layer several centimeters thick (25–35 mm) consisting of the thoracolumbar fascia and the multifidus (Bjordal et al., 2003) (▶ Fig. 10.16). In my opinion, it is not possible to locate the joint by palpating the contours, feeling the different consistencies of the tissues, or through the use of palpation under movement. Pain can be provoked by applying pressure to the soft tissue. However, it is not possible to definitely attribute the pain on pressure to the involvement of the ZAJs.
10.3.4 Detailed Anatomy of the Ligaments
Four ligamentous systems can be differentiated from one another in the lumbar spine:
Columns of segmental ligaments.
Vertebral Body Ligaments
Both longitudinal ligamentous columns accompany the entire vertebral column: the anterior and the posterior longitudinal ligaments. These ligaments are also part of the basic ligamentous structures found in a segment (▶ Fig. 10.17).
The anterior longitudinal ligament (ALL) is found anterior to the foramen magnum and extends down to the sacrum where it attaches inseparably onto the periosteum. It becomes increasingly wider more inferiorly. Superficial layers skip over four to five vertebrae. Deeper layers connect two neighboring vertebrae (Bogduk, 2000). All sections of the ligament are attached to the middle of the vertebral body and are not firmly connected to the intervertebral disk’s anulus fibrosus. This ligament helps to restrict lumbar extension and prevent an increase in lordosis.
The posterior longitudinal ligament (PLL) is also made up of two layers. The superficial layer runs in a longitudinal direction and is thin. The deep layer runs in a transverse direction and is wider. It connects to the anulus fibrosus, reinforcing the disk. This ligament passes from the occiput to the coccyx, just like the anterior longitudinal ligament. The ligament has special nomenclature in its upper cervical section and at the lumbosacral junction. In comparison to the ALL, the PLL possesses a high number of nociceptors and acts as an alarm bell for certain pathological conditions in the intervertebral disk.
Columns of Segmental Ligaments
A row of short ligaments is found between the vertebral arches and the protruding processes, each connecting two vertebrae.
In young people, the ligamenta flava (▶ Fig. 10.18) are mainly made of elastic fibers. They extend between the laminae of the vertebral arch and line the posterior side of the vertebral canal. These ligaments are under tension even in an upright posture. When the trunk is flexed, these ligaments are placed under increasing tension, save energy, and help the vertebral column to return to an upright posture, therefore reducing the required muscle power. The anterior section of the zygapophysial joint capsules is formed by the ligamenta flava.
The intertransverse ligaments are quite thin and membranelike in the lumbar spine. They connect the transverse processes—called the costal processes here—and are placed under tension when contralateral lateral flexion and rotation are performed.
The interspinous ligaments (▶ Fig. 10.18) stretch between the spinous processes of two neighboring vertebrae. The literature describes the alignment of the fibers quite differently. The details vary from a vertical alignment, via the anterosuperior course of fibers (Netter, 2004), to the posterosuperior course of fibers (Bogduk, 2000), demonstrating the need for clarification in descriptive anatomy. All authors agree that these ligaments limit flexion and rotation.
The supraspinous ligament (▶ Fig. 10.18) is found superficial to the spinous processes and is basically the only ligament that can be palpated in the lumbar spine. This structure should not be seen as a ligament. Rather, it should be viewed as a doubling of the thoracolumbar fascia. Vleeming commented on this (personal communication, 2003): “The supraspinous ligament is really an anatomical specimen artifact.”
The following relationships are currently being discussed:
The superficial layers of this fascia meet at the midline.
The connecting line is reinforced with ligament-like structures.
A section is attached to the periosteum of the spinous processes.
The other section is found in the interspinous space, forms the interspinous ligaments, and even extends into the ligamenta flava deep inside the movement segment.
As already described, it is very difficult to palpate the posterior aspect of the spinous processes due to their irregular contours and undulating shape. The presence of the supraspinous ligament makes it even more difficult to feel the interspinous space when searching for the boundaries to the neighboring vertebra using palpation. The supraspinous ligament is absent between L5 and S1 (Heylings, 1978, in Bogduk, 2000). This may contribute to the fact that the lower edge of L5 can be palpated well (see the section “Local Bony Palpation” below).
Additional Lumbar Ligaments
The iliolumbar ligaments (▶ Fig. 10.19) are the most important complex of ligaments that have contact with the lumbar spine but arise elsewhere. They run from different points on the L4 and L5 costal processes to the anterior aspect of the iliac crest and the ala of the ilium. The individual sections vary in their construction and are connected to the lumbar segmental ligaments and the sacroiliac ligaments (Pool-Goudzwaard et al., 2001).
The iliolumbar ligaments are also described in the anatomical literature (von Lanz and Wachsmuth, 2004a) as a continuation of the intertransverse ligaments, partially as a reinforcement of the thoracolumbar fascia (middle layer), as well as fibrotic parts of the quadratus lumborum. The position of these structures becomes apparent when the ligament is seen on an anatomical specimen. They are hidden beneath the several-centimeters-thick layer of intrinsic back muscles and lie in a tight corner between the transverse processes and the pelvis.
Individual fibers run along the frontal plane and restrict lateral flexion and rotation at L4-S1. The fibers are also arranged in a variety of ways in the sagittal plane ( ▶ Fig. 10.19 and ▶ Fig. 10.20 ), limiting flexion and extension (Yamamoto et al., 1990) and helping to prevent the lowermost free vertebra from gliding anteriorly (Bogduk, 2000).
Muscle activity can most likely assist the deep lumbar stability to a large extent by placing these ligaments under tension.
The iliolumbar ligaments help to control lateral flexion and rotation, especially at L5-S1. This action must be considered when palpating during movement.
Some textbooks (Chaitow, 2001) recommend palpating these ligaments for diagnostic purposes.
Readers should form their own opinion as to whether diagnostically conclusive palpation through the thoracolumbar fascia and the erector spinae, 5 to 7 cm deep, is possible.
The collagenous fibers of the thoracolumbar fascia define the appearance during the inspection of an anatomical specimen of this region. The significance of the sacroiliac (SI) joint has already been described in Chapter 9 on “Posterior Pelvis.” It is mentioned there that the superficial parts of the gluteus maximus radiate into the fascia. The collagenous fibers of the latissimus dorsi and gluteus maximus cross over the mid-line when they do this and are connected diagonally with each other (see the section “Ilium—Posterior Superior Iliac Spine” in Chapter 9).
More dynamizing structures are added to this in the lumbar region:
Superficial layer: serratus posterior inferior.
The superficial layer of the fascia, the aponeurotic area of origin for the latissimus dorsi, extends from the thoracolumbar junction to the iliac crests, covering the entire lumbar spine and sacral areas. The latissimus aponeurosis turns into a solid ligamentous plate (▶ Fig. 10.21). According to Vleeming (personal communication), the tensile loading capacity amounts to 500 kg and the plate is up to 1 cm thick.
The fibers within the fascia have a meshlike construction and do not only correspond to the continuation of the latissimus fibers that come from a superolateral position and point inferomedially. The fascia is at its widest at the level of L3, where it measures approximately 12 cm in width. It is narrowest at the level of T12.
Below T12, the fibers radiate into the fascial fibers on the contralateral side. They continue over the sacrum as the posterior sacroiliac ligament.
The middle fascial layer is also a solid aponeurosis. It stretches between the most inferior ribs, the L1-L4 costal processes, and the iliac crests (▶ Fig. 10.22). It separates the back extensors from the quadratus lumborum. In contrast to the superficial layer, the middle layer appears to be a site of origin for the lateral tract muscles and the quadratus lumborum. The foundation for this strong tendinous plate is the aponeurosis, which is the site of origin for the transversus abdominis (von Lanz and Wachsmuth, 2004a). The fibers from the internal oblique, in particular, radiate into this.
Barker et al. (2006) found in a study that the tension in the middle fascial layer significantly increases segmental stiffness and the resistance to flexion. According to their conclusions, tension in the fascia plays a significant role in segmental stability.
Richardson et al. (1999) also state that the multifidus and transversus abdominis provide basic stability for the lumbar spine (▶ Fig. 10.23). They described the relationship between delayed activation of the transversus abdominis and lumbar symptoms.
The muscle is normally activated approximately 4 ms before the trunk or the limbs start moving. Core stability is first built up before proceeding with further action. The muscle is activated too late in patients suffering from back pain. Based on these results, Richardson et al. (1999) developed an exercise program that is currently a source of discussion and used for therapeutic approaches.
Both layers of the thoracolumbar fascia are connected immediately lateral to the back extensors at the lateral raphe (▶ Fig. 10.24). Both of the fascial layers and the serratus posterior inferior form an osteofibrous channel with the vertebral arch and the processes. This channel is the guiding sheath for the erector spinae. The anatomy of this can be recognized by looking at the loose connective tissue superior to the sacrum positioned between the back extensors and the fascia. The osteofibrotic guiding sheath bundles up the back extensors and holds these muscles on the vertebral column when the muscles contract.