The pelvis is the kinetic and kinematic center of the musculoskeletal system. It is the center of the functional unit of the lumbopelvic-hip (LPH) region. The kinematic chains of the vertebral column and the lower limbs meet here. The pelvis must be able to withstand a variety of bio-mechanical demands, especially when the body is in upright position. Vleeming states (personal communication, 2002):
The pelvis has adapted itself to these demands throughout the phylogenetic evolution (▶ Fig. 9.1):
The large, protruding ala of the ilium provides a large area for the attachment of soft tissues and therefore the muscular prerequisites for an upright posture in standing: gluteal, back, and abdominal muscles. This protruding area of the ilia envelops and protects several organs.
The sacroiliac (SI) joint has increased greatly in size; the ligamentous apparatus has become considerably stronger. The load-transferring area between the SI joint and the acetabulum or the ischial tuberosities has been reduced in length and strengthened.
The sacrum has remained in the same position in the sagittal plane, tilting inward toward the abdominal cavity. This allows lumbar lordosis and enhances shock absorption. Ligaments stabilize the sacrum’s position.
Mobility in the SI joint is related to age and gender. The range of motion is governed by hormones, among other things, in females. Pelvic movement enables the birth canal to dynamically adapt during delivery.
The increase in hip-joint mobility, especially in extension, is also the result of phylogenetic development. The femoral head is integrated into the body’s plumb line. During walking, the trochanter point is transported forward during the mid-stance phase.
The pelvic muscles have been strengthened and their endurance improved. This allows the body to economically maintain upright positions and ensures that standing on one foot is safe. The pelvis absorbs impulses arising from the legs and increases the range of hip-joint motion by rapidly transferring movement up into the lumbar spine.
The pelvis is frequently the focus of treatment for symptoms in the LPH region (lumbar spine, pelvis, hip) due to the intensive strain that the pelvis experiences during different tasks. Therapists have a special task when assessing patients: to find out why the patient is suffering from pain in the buttocks or the groin.
Certain assessment techniques and forms of treatment are thus applied to the gluteal region. Apparently, over 50 provocation and mobility tests have been described for the SI joint at an international level (Vleeming et al., 2006). Each study group for manual therapy uses their own individual test. International standardization is not yet foreseeable. When these tests are being conducted or the patient is being mobilized, it frequently makes sense that certain osseous reference points (iliac crests, anterior and posterior iliac spines) are palpated accurately and their position compared with the other side.
The sacrum and the ilium are often mobilized in opposite directions during assessment and treatment (▶ Fig. 9.2). It is very important that the hand position is well placed and secure.
Some peripheral nerves can be irritated locally as they pass through the gluteal region on their way to their target organ. In the case of the sciatic nerve, this can occur at two locations (▶ Fig. 9.3):
A piriformis compression syndrome occurs only when at least a portion of the sciatic nerve passes through the muscle belly of the piriformis. According to Vleeming (personally communication, 2003), the fibular part passes through the piriformis muscle belly in only 4 to 10% of all people (▶ Fig. 9.4). A sustained muscle contraction alone is not expected to compress the nerve as the muscle is smooth and fibrous on the side facing the nerve. Also, the 4-cm-long muscle belly cannot expand so much during contraction that it compromises or stretches the nerve.
The trigger-point treatment, based on the work of Travell and Simons (1998), is concerned with the location of locally hardened muscles that may act as independent pain generators. Dvořák et al. also dealt with the subject of tender points within manual diagnostics. These points provide the clinician with information regarding the spinal level of sacroiliac and lumbar aggravation (Dvořák et al., 2008).
Dvořák labeled tender points as tendinoses and zones of irritation. Local surface anatomy is used here to find the appropriate muscular structure or to link the point that is tender on palpation to its respective muscle.
Muscle pathologies are treated using classical massage techniques, such as kneading (▶ Fig. 9.5), local frictions (▶ Fig. 9.6), or a variety of specialized techniques. These techniques can be conducted more accurately when the therapist has a good knowledge of the available area and can correctly feel the muscular structure being sought.
Precise palpation is also used to confirm bursitis by applying local and direct pressure (▶ Fig. 9.7) (e.g., when presented with a type of snapping hip) or to perceive muscle activity in the pelvic floor directly medial to the ischial tuberosity (▶ Fig. 9.8).
The pelvis is the anatomical and functional center of the “lumbopelvic region.” Two movement complexes meet at the sacrum: the vertebral column and the pelvis. This means that vertebral movement is directly transmitted onto the pelvis, and vice versa.
Several points on the pelvis are of static and dynamic significance: the base of the sacrum, iliac crest, SI joint, pubic symphysis, and the ischial tuberosity. The different types of loading are dealt with here, for example, by transferring the load in sitting or standing. Important ligamental structures and muscles insert here.
Surprisingly, anatomical literature does not always agree on the bony compilation of the pelvis. Netter (2004) only includes the two pelvic bones. In total, the pelvis should be understood to be a bony ring consisting of three large parts: two pelvic bones (consisting of the ilium, ischium, and pubis) and the sacrum (▶ Fig. 9.9).
Immobile: Y-formed synostosis in the acetabulum as well as a synostosis between the ischial ramus and the inferior pubic ramus, the bony connection between the originally distinct sacral vertebrae at the transverse ridges.
The mobile connections allow a certain amount of flexibility in the pelvis, absorbing the dynamic impulses coming from a superior or inferior direction. Shock absorption is an important principle for the lower limbs and is continued in the pelvis. This flexibility also creates a gradual transition from the more rigid pelvic structures to the mobile lumbar segments.
The gender-specific characteristics of the pelvis are presented in almost every anatomy book. In summary, these characteristics are based on the difference in form and are most distinctly seen in the ala of the ilium and the ischial tuberosities. In total, the male pelvis is described as being long and slender and the female pelvis as being wider and shorter. The dimensions of the female pelvis are therefore seen as a phylogenetic adaptation to the requirements of the birth canal during childbirth.
Naturally, these different characteristics in the bony anatomy of the pelvis also have a meaning for local surface-anatomy. They determine what is to be expected topographically when searching for a specific structure (▶ Fig. 9.10 ):
However, identifying the L4 level requires very precise palpation of the bony edge. Chakraverty et al. (2007) and Pysyk et al. (2010) have cautioned that manual palpation tends to access a higher level (L3 or L3/L4)
As with the iliac crests, the anterior superior iliac spine (ASIS) is preferably located to determine levels within the pelvis. It can be assumed that the female ASISs are found significantly further apart than their male counterparts. Therefore, it is necessary to search for them more laterally.
The inferior pubic rami meet at a significantly smaller angle in the male pelvis. It is therefore expected that the ischial tuberosities can be palpated significantly more medially in the male pelvis than in the female pelvis.
The coxal bone is the largest fused bony entity in the musculoskeletal system once skeletal growth has been completed. Two surfaces extend superiorly and inferiorly from a central collection of bony mass in the acetabular area:
Superior surface = ala of the ilium. This surface is entirely osseous. Its borders are strengthened by strong edges and projections (iliac crest and diverse spines). Although the middle of the ala of the ilium is osseous as well, it tends to be thinner and can be perforated in some cases.
When planes are drawn at a tangent over these superior and inferior surfaces, these planes are seen to be found at a 90° angle to each other (▶ Fig. 9.11).
The protruding edges, spines, and flattened areas of both surfaces of the coxal bone act as possible sites of origin or insertion for muscles and ligaments. Anatomical specimens show that the ilium is almost completely enclosed by the small gluteal muscles and the iliacus. The obturator membrane is likewise located between the obturator externus and the obturator internus. Thus, a series of active dynamic forces act on the coxal bone.
Other sections with significantly spongy thickening (▶ Fig. 9.12) can be identified in addition to the above-mentioned bony edges at the edge of both coxal bones and the central bony mass:
The sacrum is the third and central part of the bony pelvis. It is well known that the sacrum is a fusion of at least five originally distinct vertebrae. The final ossification into a single bone occurs in the fifth decade of life. Remnants of cartilaginous disks are existent prior to this.
The location and position of the vertebral column’s kyphotic section at the pelvis can be identified in the median cut of the pelvis. The recognizable tilt of the sacrum into the pelvic space can be calculated by using the angle between the transverse plane and a line extending from the end plate of S1 (Kapandji, 2006). This generally amounts to approximately 30° (▶ Fig. 9.13).
The sacrum’s distinctive form becomes evident in the posterior view (▶ Fig. 9.14). It is characterized by various structures:
The posterior aspect demonstrates additional interesting details (▶ Fig. 9.15 ):
Generally, it is possible to look through the bony model in four places on each side. The sacral foramina are found posteriorly and anteriorly at the same level and allow the anterior rami and the posterior rami of the spinal nerves to exit from the vertebral column and into the periphery.
Long ridges are found over the entire remaining posterior surface. These ridges are formed by the rudiments of the sacral vertebrae that have grown together. The median sacral crest is the most important of these ridges for palpation. The rudiments of the sacral spinous processes can be seen here as irregular protrusions and can be palpated well. All other crests and the posterior foraminae are hidden under thick fascia and the multifidus muscle.
The apex of the sacrum forms the sacrum’s inferior border. It lies in the middle, slightly inferior to the line connecting the two inferolateral angles. The mobile connection to the coccyx is found here. This is interchangeably labeled a synovial joint or a synchondrosis (with the intervertebral disk) in literature (▶ Fig. 9.16; Rauber and Kopsch, 2003).
Great variations are seen in the construction of the inferior sacral area. The median sacral crest usually runs down to the level of S4. Normally no rudiments of the spinous processes can be observed at the S5 level. Instead, an osseous cleft can be seen: the sacral hiatus. According to von Lanz and Wachsmuth (2004a), this posterior cleft is only found in approximately 46% of the population at the level of S5 and extends to the level of S4 or S3 in 33.5%. This makes accurate palpatory orientation on the inferior sacrum significantly more difficult.
The S5 arch leading to the hiatus is incomplete and is covered by a membrane (▶ Fig. 9.17). Small osseous horns (sacral horns) form its borders on the side. These horns are easily palpable in most cases but vary greatly in size and are irregularly shaped. They face two small osseous protrusions in the coccygeal bone, the coccygeal cornua, which are also palpable.
The covering membrane at the level of S5 is a continuation of the supraspinous ligament and continues onto the coccyx as the superficial posterior sacrococcygeal ligament. The membrane covers the vertebral canal as it peters out inferiorly. It is palpated as a firm and elastic structure, which clearly distinguishes it from the osseous borders.
Additional ligamentous connections between the sacrum and coccyx are (▶ Fig. 9.18 ):
These ligamentous structures are traumatically overstretched when people fall onto their buttocks and especially onto the coccyx. Their tenderness on pressure can be treated successfully using transverse frictions to relieve pain when they are directly palpated.
The anterior sections of the capsule (anterior sacroiliac ligaments) are very thin (< 1 mm) and have little mechanical relevance (personal correspondence from the IAOM study group). They perforate easily when joint pressure is increased (arthritis). They are not stretched during the iliac posterior test (SI joint test) as the entire function of the ligament is found posterior to the joint.
The interosseus ligaments are very short, nociceptively supplied ligaments that act as pain generators in the presence of sacroiliac pathologies (e.g., instability or blockages). Their function is to maintain the traction in the respective SI joint.
It is easiest to understand the function of the nutation restrictors by looking at the stress on the sacrospinous and sacrotuberous ligaments when the body is in a vertical position (▶ Fig. 9.19). Approximately 60% of the body’s weight bears down on the S1 end plate. This is positioned quite anterior to the nutation/counternutation axis so that the base of the sacrum tends to fall farther into the pelvic space. This tendency is counteracted by the posterior and anterior ligaments positioned very close to the joint. The tip of the sacrum tends to lever itself anteriorly and superiorly. This movement is counteracted by the sacrospinous and sacrotuberous ligaments.
The long posterior sacroiliac ligament (▶ Fig. 9.20) connects both posterior superior iliac spines (PSISs) with the respective edge of the sacrum. It is approximately 3 to 4 cm long, 1 to 2 cm wide, and extends inferiorly into the sacrotuberous ligament. It is the only ligament that counteracts counternutation. It has been described by Vleeming et al. (1996) and already published several times. It has also been mentioned by Dvořák et al. (2008).
The significance of the pelvis as central element in the musculoskeletal system has already been described. To understand the exceptional significance of the SI joint, the functional relationship between the various kinematic chains should first be clarified.
The L5, sacrum, and ilium form a kinematic chain. No bone moves without the others moving. It is nearly impossible to clearly attribute the effects of pathology and treatment to a specific level. The iliolumbar ligaments (especially the inferior short, stiff sections) are important for the linkages within this chain.
The SI joint biomechanics are controlled by the symphysis. Extensive, opposing movements of the iliac bones primarily meet up at the symphysis. SI joint instability can also affect the symphysis. We therefore differentiate the SI joint instability types into those without loosening of the symphysis and those with loosening of the symphysis.
Few topics concerning the musculoskeletal system are discussed as controversially as the SI joint. Views and opinions about the SI joint vary between the individual manual therapy study groups as well as between manual therapists and osteopaths. The significance given to the SI joint therefore depends on each therapist’s personal criteria and individual point of view.
The construction of this joint cannot be compared with any “traditional” joint (▶ Fig. 9.21):
Movement primarily occurs around a frontotransversal (transversal) axis and is very slight (according to Goode et al. , approximately a maximum of 2°). These movements are labeled nutation and counternutation (▶ Fig. 9.22). The extent of joint mobility is influenced by hormones, particularly in women (Brooke, 1924 and Sashin, 1930). Mobility also increases when SI joint disorders are present, for example, with arthritis.
The complexity of this joint also makes it easy to understand why comparatively few good studies exist that examine standardized assessment methods and treatment techniques. More than 50 tests have been described for assessment alone.
The SI joint is held together by its structure and the strength of tissues. This can be seen in the frontal plane by looking at the general alignment of the joint surfaces. According to Winkel (1992) the joint surfaces are tilted at approximately 25° from the vertical (▶ Fig. 9.23).
The sacrum’s wedge shape permits the auricular surface to support itself on the similarly shaped iliac joint surface (force closure). Nevertheless, the joint’s construction and the friction coefficient of the uneven and roughened surface are not sufficient to stabilize the sacrum’s position.
It therefore becomes clear that additional strength is needed to keep the joint surfaces together (holding the joint together with the strength of tissues). In particular, this is the function of the interosseous sacroiliac ligaments. These ligaments lie immediately posterior to the joint surfaces and are made of short, very strong, and nociceptively innervated collagen fibers. The SI joint is held together more by the joint structure in males and the strength of tissues in females.
The interosseous ligaments are supported by muscular structures and other ligamentous structures that generally act as nutation restrictors. These structures therefore qualify as further SI joint stabilizers:
The anterior abdominal muscles (especially the oblique and transverse sections) pull on the ilia anteriorly and place the interosseous ligaments under tension (▶ Fig. 9.24).
The posterior and anterior sacroiliac ligaments, together with the sacrospinous and sacrotuberous ligaments, primarily restrict the nutation of the sacrum. Loading tightens these ligaments and likewise increases the compression of the SI joint.
Several sections of the iliolumbar ligaments cross over the SI joint in the middle. Lumbar lordosis increases the SI joint surface compression (▶ Fig. 9.25).
Pool-Goudzwaard et al. (2001) described in a study the stabilizing role of the iliolumbar ligaments on the SI joint. Gradual transection of the ligaments resulted in a significant increase in SI joint mobility in the sagittal plane.
The ligaments also contribute to sacroiliac movements being transmitted onto the lower lumbar segments and vice versa. Movement within the pelvic ring and movement in L4-S1 must always be regarded as a kinematic chain.
The dominating concept until several years ago was that the SI joint, as a classic amphiarthrosis, was not supplied with its own muscles. This presumption is correct as regards the mobility function. However, it can be put on record that force closure, in the form of a multitude of dynamized ligaments and muscles, holds the joint surfaces together and stabilizes the SI joint.
The interplay between muscles and ligaments near joints has been known for a long time now. The knee joint is a perfect example of this. The extension of muscles into capsular-ligamentous structures is called ligament dynamization. Two examples of pelvic ligaments are presented here to demonstrate how intensive the contact is between muscles and the functional collagen in this region.
We know that the hamstring muscles are most active at the end of the swing phase during gait. The hamstrings slow down the anterior tibial swing a few milliseconds before heel contact, decelerating knee extension.
The long head of the tensed biceps femoris often merges with the sacrotuberous ligament via large bundles of collagen (also without contact with the ischial tuberosity) and dynamizes the ligament (▶ Fig. 9.26). The biceps femoris activity prevents the sacrum from fully nutating and stabilizes the SI joint directly before the landing phase.
Each of the muscles is able to dynamize the fascia. The fascia forms a diagonal sling between the latissimus dorsi and the contralateral gluteus maximus (▶ Fig. 9.27). The force of the sling acts perpendicular to the joint surfaces, stabilizing the SI joint and the inferior lumbar spine during strong rotation. Consequently, the participating muscles and the fascia belong to the primary SI joint stabilizers. This sling can be especially trained using trunk rotation against resistance.
This fascial layer is also connected to the supraspinous ligament and the interspinous ligament up to the ligamenta flava. Vleeming (personal communication) comments on this: “The entire system is dynamically stabilized.”
Muscles also dynamize the middle and deep layers. It is well known that the transversus abdominis tightens the middle layer (see also the section “Detailed Anatomy of the Ligaments,” in Chapter 10).