Chapter 11 Abdominal Region

11.1 Significance of the Region

The abdominal wall provides the anterior and lateral cover of the visceral organs. The muscle tone of the abdominal muscles is functionally opposed to the diaphragm. During inhalation and contraction, muscle tone relaxes slightly. It increases during exhalation. The abdominal muscles support and effect an abdominal press. Owing to the great distance of the rotational axes of the lumbar and thoracic segments and the very good lever, the oblique abdominal muscles, compared to parts of the back extensors, are very good trunk rotators.

The activity of the abdominal wall muscles clamps the hip bones ventrally and thus contributes to the stability of the sacroiliac joints. In an electromyography (EMG)-supported study, Cowan et al. (2004) demonstrate the relationship between groin pain and delayed onset of transversus abdominus, confirming a positive effect of the abdominal muscles on the stability of the symphysis. The activity of the abdominal muscles therefore plays a role in the treatment of symphyseal instabilities, such as those occurring during and after pregnancy. The significance of timely activity of the transverse abdominal muscle for lumbar stability has already been discussed in the Chapter 10.3.5 on functions of the lumbar muscles.

11.2 Common Applications for Treatment in this Region

Abdominal massage is used in adults and young children to promote overall relaxation. The ability of abdominal massage to promote bowel activity is also known. Colon massage is a very effective method for supporting bowel activity in an atonic colon (Reichert, 2015), although its use has largely been supplanted by drug therapy.

Individuals with spinal cord injury have impaired vegetative functions such as bowel movement and micturition. Patients with paraplegia may have to learn to manually trigger the bladder.

Respiratory therapy commonly focuses on respiratory depth and rhythm. The initial goal is to instruct the patient to perform relaxed abdominal breathing, which is the normal form of breathing during low physical activity. Abdominal breathing also has a calming effect, serves as a suction/force pump for venous transport in the abdominal region, and slightly shifts the abdominal organs as an additional stimulus for intestinal peristalsis.

Manual lymph drainage is the most suitable therapy for treating impaired lymph drainage from the leg and groin. For a better preparation of the lymphatic drainage, a deep abdominal drainage should be carried out in advance. The section below aims to provide precise and in-depth guidance for therapeutic understanding of the abdominal region, such as those required for colon massage and manual lymph drainage.

Muscle recruitment and strengthening play an important role both in treating patients with deep back, pelvic, and groin complaints as well as in postpartum pelvic floor exercises. Prior to the actual strengthening, the patients’ perception of their body must be sensitized and the proper timing of the activity must be fine-tuned.

In Western Europe, the abdomen is seldom the object of massage or physical therapy. Therapeutic diagnostics of functional impairment of the internal organs tends to be performed by observing tissue changes as defined by dermatomes. Palpation and auscultation of the abdominal and pelvic region tend to be performed by internists or surgeons. In Traditional Chinese Medicine (TCM), however, this is quite different. Abdominal wall diagnosis plays a key role in TCM (Greten, 2017). Inspection and palpation focus on pain and guarding or tension of the abdominal wall, among other things, the muscle tone at the intercostal arch, the upper abdomen, the periumbilical region, and the lower abdomen.

When it comes to palpating the groin region, Winkel (2004) states that the therapist is not directly responsible for performing specific palpation to confirm an inguinal hernia. However, when examining the groin region, the therapist must not overlook an inguinal hernia.

11.3 Required Knowledge (Topographic and Morphologic)

In the section below, anatomical aspects of the abdominal wall and the internal organs are presented if they are of therapeutic interest and are palpable. For this reason, various organs are not described below. For more detailed information, the anatomical literature in this book’s reference list may be consulted. To enhance description and understanding of the positions of muscles and organs, the trunk wall is subdivided into regions using lines and levels.

11.3.1 Boundaries of the Abdominal Wall

  • Superior boundary: Inferior margin of the thorax with the intercostal arch and xiphoid process

  • Inferior boundary: Iliac crest, inguinal ligaments, and pubic symphysis

  • Lateral boundary: Medial axillary line (▶ Fig. 11.1)

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Fig. 11.1 Boundaries of the abdominal wall: 1 = costal arch, 2 = xiphoid process, 3 = iliac crest, 4 = inguinal ligament, 5 = pubic symphysis, 6 = medial axillary line.

11.3.2 Regions of the Abdominal Wall

  • It is easiest to subdivide the regions of the abdominal wall by designating structures to the left and to the right of the linea alba—the tendinous, abdominal section of the anterior median line where the rectus sheaths meet. In some women, this line becomes pigmented in the second trimester of pregnancy. The darker color becomes significantly lighter or disappears completely after the pregnancy (Schmailzl and Hackelöer, 2002).

  • Two lines connecting bony structures are used to subdivide the abdominal region transversely.

  • The connecting line of the inferior margins of the 10th rib shows the position of the subcostal plane.

  • The epigastric space, which contains the hepatic field and the gastric field, is located above this plane. Superior to the subcostal plane, the medial abdominal region is located with the umbilical region and the lateral abdominal regions. This subdivision is undertaken by the medioclavicular line, where the lateral margins of the abdominal rectus muscles are approximately located.

  • The anatomical literature does not agree on the second transverse subdivision of the abdominal region. Some authors, such as Rauber and Leonhardt (1987), connect the highest points of the iliac crests. Here, the interspinous plane, the line connecting the two anterior superior iliac spine (ASIS), is demonstrated. Superior to this plane, the inguinal regions are located laterally and at the center, the pubic region.

Fig. 11.2 shows the subdivision of the abdominal regions.

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Fig. 11.2 Regional divisions of the abdominal wall: 1 = medioclavicular line, 2 = subcostal plane, 3 = epigastric space, 4 = umbilical region, 5 = lateral abdominal region, 6 = interspinous plane, 7 = pubic region, 8 = inguinal region.

11.3.3 Deep and Superficial Abdominal Muscles

The deep abdominal muscles are the muscles that delimit the abdominal region posteriorly (▶ Fig. 11.3):

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Fig. 11.3 Deep abdominal muscles and rectus muscles.

  • Psoas major and minor muscles.

  • Quadratus lumborum muscle.

Psoas Major and Minor Muscles

The psoas muscles are primarily known as the agonists of hip flexion. In the closed chain, the psoas major muscle, in conjunction with the abdominal muscles, serves to elevate the trunk from the supine position. During this activity, it exerts enormous lordotic tension on its origin sites, the L1–L4 vertebral bodies, transverse processes, and vertebral disks. With the compressive force component that arises additionally, it is known in the realm of physical therapy as an “evil muscle” with a generally negative impact on the lumbar spine, although this reputation is unjustified. With its unilateral innervation, it contributes to active lateral bending of the lumbar spine.

Quadratus Lumborum Muscle

This multilayer muscle stretches between the 12th rib, the lumbar transverse processes, and the iliac crest. It combines several functions. It supports forced exhalation and provides synergy for lateral bending (in both cases, by lowering the 12th rib). During walking, it controls the position of the pelvis in the frontal plane and in so doing works together with the contralateral gluteus minimus muscles. Its stabilizing influence on the lumbar spine and the layers of the thoracolumbar fascia was debated for a certain time but never consistently or conceptually implemented. Ploumis et al. (2011) describe the relationship between muscle atrophy of the back extensor muscles and the deep abdominal muscles in patients with chronic low back pain.

The superficial abdominal muscles delimit the abdominal space laterally and anteriorly. On each side there are three flat and one subdivided muscle. From superficial to deeper-lying these are:

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Fig. 11.4 External oblique.

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Fig. 11.5 Internal oblique.

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Fig. 11.6 Transverse abdominal.

Together, these muscles, in interaction with the pelvic floor and the diaphragm, are responsible for exerting adequate pressure on the internal organs and ensuring they are held together. When lifting heavy objects, the abdominal region forms a firmly encased stable soft tissue bladder through exhalation.

The abdominal press actively exerts pressure on the intestines (Schünke et al., 2005). This supports, for example, the emptying of the rectum (defecation), the bladder (micturition), and the stomach (vomiting). During the expulsive phase of labor, the abdominal press supports the contractions of the uterus (bearing down pains).

These muscles control the posture of the upright upper body. During forced walking, they, along with the oblique back muscles, limit the rotation movements of the upper body. The transverse and oblique abdominal muscles are stretched over the iliac bones and thus help stabilize the sacroiliac joints (Chapter 9.3.6). The influence of the transverse abdominal muscles on the deep lamina of the thoracolumbar fascia and consequently on lumbar stability has already been mentioned a number of times (see the section on thoracolumbar fascia in Chapter 10.3.4).

Rectus Abdominis Muscles

Both of the rectus abdominis muscles run at the level of the 3rd to 7th ribs to the pubic tubercle next to the symphysis (▶ Fig. 11.3). They lie in a connective tissue sheath formed by the aponeuroses of the flat abdominal muscles. These aponeuroses meet at thelinea alba, which separates the two rectus muscles. The transverse intersections evoke the earlier development of ribs and permit separate innervation of the individual muscle bellies. This enables the rectus abdominis muscles to alternatively pull the rib cage inferiorly and/or set the pelvis upright.

External Oblique

This flat muscle developed from the external intercostal muscles (▶ Fig. 11.4) after the ribs withdrew from the abdominal region in the course of evolution. Rauber and Leonhardt (1987) describe that its fibers generally extend from superior-lateral to inferior-medial, like the trajectory of a hand being slid into a pants pocket. It arises from the 5th to 12th ribs with muscular attachments (Schünke et al., 2005). As it does so, the attachments interdigitate with those of the serratus anterior at what is referred to as Gerdy’s line (Schünke et al., 2005). They become particularly prominent when the muscle is forced to exert flexion and rotate the trunk heterolaterally against resistance.

Internal Oblique

This muscle’s fibers embody the continuation of the internal intercostal muscles and also have their basic superolateral to inferomedial course (▶ Fig. 11.5).

The muscle belly of the internal oblique is generally covered by the external oblique and is thus not actually directly palpable. With the external oblique of the contralateral side, it completes an anterior diagonal muscle loop.

Transverse Abdominal

The section on the thoracolumbar fascia has already discussed (Chapter 10.3.4) this structure’s position and lumbar impact in detail. The muscle’s stabilizing effect is based on the connection between the linea alba and the lumbar transverse processes via the thoracolumbar fascia (▶ Fig. 11.6). If the anterior side of the muscle has a stable base, it can reverse the fixed point and mobile points and impact the lumbar spine rather than the abdomen.

Directly medial to the anterior superior iliac spine (ASIS), its aponeurosis can be accessed unimpeded with palpating fingers. When working with patients, this access is used when practicing deliberate recruitment of the muscle. To perceive its activity, the therapist only has to ask the patients to pull in their belly button.

The muscle bellies of all flat abdominal muscles are located on the lateral wall of the trunk. Anteriorly and medially, they each transition into an aponeurosis that inserts into either the linea alba and/or the iliac crest. Between the medial border of their muscle bellies and the outer edge of the rectus abdominalis muscle on one side the linea semilunaris is located around the level of the medioclavicular line (▶ Fig. 11.2). Lower-lying organs, especially the portions of the colon, can be accessed at this point without the resistance of the muscle bellies.

The oblique muscles contract during lateral bending on the same side against resistance (Rauber and Leonhardt, 1987). With the direction of the trunk rotation, the two oblique muscles can be distinguished:

  • Trunk rotation toward the contralateral side = external oblique.

  • Trunk rotation toward the ipsilateral side = internal oblique.

11.3.4 Organs of the Abdominopelvic Cavity

Abdominal Cavity

The abdominal cavity is bordered by the rib cage, diaphragm, abdominal muscles, vertebral column, and the iliac bones (Frick et al., 1992). In an inferior direction, it continues as the pelvic cavity, which is finally closed by the pelvic floor. The abdominal cavity contains the intestinal organs, as well as the liver and pancreas, which are both glands. Like the mediastinum in the thoracic cavity, the abdominal cavity also has a connective tissue compartment for large conductive pathways (e.g., aorta) behind the abdominal cavity.

The peritoneum completely encloses the organs located in the abdominal cavity and separates the organs and the abdominal wall by a gap. The inside of the peritoneum produces a serous fluid that lubricates the shifting of the organs against each other and the wall. A few milliliters of fluid are sufficient for this. Since only low volumes of gases occur in the organs of the abdominal cavity, they are not compressible, but are highly deformable. Every change in the shape of an organ causes the shape and position of the adjacent organ to change.

Shifts occur through abdominal breathing and changes in body position or posture, for example. The muscle tone of the abdominal and pelvic floor muscles is regulated such that the peritoneum can ideally surround the organs without compressing them. When there are changes in the volume of the abdominal cavity through the filling of the stomach and bowels and/or through breathing, the muscle tone of the abdominal muscles adapts accordingly.

Anatomy textbooks on the internal organs set the separation of the upper and lower abdomen at around the level of L2 (Rauber and Leonhardt, 1987; Frick et al., 1992). This corresponds approximately to the position of the inferior edge of the transverse part of the colon.

The upper abdomen extends through the curvature of the diaphragm from the level of T9 to the level of L2 and is mostly enclosed by the thorax. Located here are the liver, gallbladder, spleen, the largest part of the pancreas, stomach, and upper part of the duodenum. The lower abdomen extends from the level of L2 to the pelvic inlet plane (S1 – symphysis): lower part of the duodenum, head of the pancreas, and small and large intestines.

Upper Abdomen

The position of the organs in the upper abdomen (▶ Fig. 11.7) is dependent on breathing and posture. Age-related loss of elasticity of the lungs causes the organs to drop. Precise determination of the position of the lungs is only possible with imaging techniques (Rauber and Leonhardt, 1987).

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Fig. 11.7 Organs of the upper abdomen.


The stomach is where the enzymatic degradation of food through gastric acid takes place. Resorption plays only a minor role in this process. Gastric acid destroys bacteria in food and thus has an important protective function.

The shape and position of the stomach are highly variable. Rauber and Leonhardt (1987) describe its position as running asymmetrically in the upper abdomen from the upper left to the lower right. Most of the stomach is located on the left of the median plane. The stomach opening (cardia) is located at around the level of T11. Anatomical descriptions report three different most common shapes. In the lower half of the epigastric region, the stomach can be palpated on the left of the median plane.


The spleen is a lymphatic organ that can influence blood composition in multiple ways:

  • As an important immune organ, it is filled with specific defense cells.

  • It removes old red blood cells (“lymph node of the bloodstream”) and stores platelets.

The approximately fist-sized organ is shaped like a coffee bean. It is 10 to 12 cm long, 6 to 8 cm wide, and weighs 150 to 200 g. A fibrous capsule delimits the otherwise soft tissue from its surroundings. The spleen is located in a fossa behind the stomach and is located directly in front of the 9th to 11th ribs and directly below the diaphragm. The longitudinal axis falls laterally following the course of the 10th rib. The spleen has two surfaces facing the diaphragm and the bowels. The anterior pole does not usually protrude beneath the ribs. If the spleen is enlarged, this pole is difficult to access and the patient must breathe in deeply (Rauber and Leonhardt, 1987) while in the left semi-side-lying position (▶ Fig. 11.36).


As a multifunctional organ, the liver, weighing around 2,000 g, is the body’s largest gland and an important storage and excretory organ. The most important functions of the liver are as follows:

  • Producing bile as an exocrine product for emulsion of fats in the duodenum.

  • Synthesizing the body’s own substances from low-molecule components.

  • Storing up to 1 L of blood and 400 g of glycogen. This corresponds to a caloric value of around 1,600 kcal.

  • “Detoxifying” the blood, for example, converting ammonia into urea.

The liver occupies the largest space in the upper abdomen. It is mainly located on the right of the median plane behind the ribs. Enclosed in a firm connective tissue capsule, it has a smooth exterior. The shape of the liver is primarily determined by the adjacent organs. Rauber and Leonhardt (1987) report that the typical triangular shape is present in only 65% of all people. The superior surfaces adjoin the interior thorax and diaphragm. The third side (visceral fascia) faces the intestines. The inferior margin starts at the lateral right in the plumb-line of the medial axillary line and rises parallel to the costal arch in a left medial direction. Directly inferior to the xiphoid process in the upper epigastric region (hepatic field) it lies directly on the abdominal wall and can be accessed by applying pressure.

The movements of the liver are primarily dependent on breathing. As the lungs are connected with the diaphragm and the chest wall, the liver is firmly attached to the diaphragm through adhesive strength. The diaphragm thus “carries” the entire weight of the liver and in doing so relieves the rest of the intestines and the pelvic floor. Due to the attachment to the diaphragm, the liver follows its movements during breathing. In Rauber and Leonhardt (1987), the movement mechanism is described as follows: During exhalation, the diaphragm and liver are pressed into the rib cage through the contraction of the abdominal wall muscles and, at the same time, are sucked into the rib cage by the “pull of the lungs.” The extent of this movement is dependent on the depth of the breath and can be between 1.5 and 7 cm. The superior border is at the level of the fourth intercostal space during exhalation.


The gallbladder measures 8 to 12 cm by 4 to 5 cm. It is a sac that collects bile and discharges it as needed. The portion closest to the abdominal wall is the fundus of the gallbladder at the inferior margin of the liver. It is located in the corner between the exterior margin of the rectus abdominis and the right costal arch and thus lies on the colon at the right colic flexure.

Lower Abdomen

Large Intestine

The primary activities taking place in the large intestine are the resorption of water and salts, as well as thickening and fermentation of the intestinal contents. Slow peristalsis moves the intestinal contents, with only few movements effectively directed analwards. Frick et al. report that only two to three of these movements a day are especially pronounced (1992). In addition to local stretches and contractions, peristaltic waves occurring at a rhythmic interval of three to six per minute play an important role in the transportation of the intestinal contents.

The large intestine is divided into three parts (▶ Fig. 11.8): caecum, colon, and rectum. The large intestine is approximately 110 to 165 cm long and extends from the ileocecal valve (Bauhin’s valve) to the anal canal and rectum. Bauhin’s valve was named after Caspar Bauhin (1560–1624), professor of medicine and anatomy in Basel (Rauber/Kopsch).

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Fig. 11.8 Large intestine.

The nomenclatures “large intestine” and “small intestine” do not always accurately describe the actual structure. Rauber and Leonhardt (1987) point out that when the large intestine is contracted, it can be thinner (“smaller”) than the small intestine. The special structural features of the large intestine are three thin longitudinal ribbons of muscle (taeniae coli), transverse constrictions, and bulges in the wall (haustra of colon).

The caecum is approximately 6 to 8 cm long and its position varies widely. Its position is generally described as medial and superior to the ASIS. It is located directly below the abdominal wall, to which it is fused, and the iliacus. The ileocecal valve forms the junction of the terminal ileum and the ascending colon. The appendix (vermiform appendix) is around 1 finger length long and the diameter of a pencil and is positioned medial at the inferior end. Its position also varies widely. It is frequently found on the posterior caecum. The appendix is known as the site of acute or chronic inflammation. Its common position was described by Charles McBurney (1845–1914), a surgeon in New York. The so-called McBurney’s point is located on a line between the ASIS and the navel and at this point, on the border of the lateral third (McBurney, 1889).

The colon is commonly subdivided as follows: ascending colon, transverse colon, descending colon, and sigmoid colon (S-shaped part).

The ascending colon is directly connected to the caecum and extends to below the liver. It lies on the right posterior abdominal wall and is attached to it. With the right-angled right colic flexure, it passes directly into the transverse colon. The colic flexure is covered by the liver and, according to Rauber and Leonhardt (1987), its location varies between T3 and L4.

The course of the transverse colon avoids the overlying liver and stomach and is thus located below the hepatic and gastric fields of the epigastric area. It therefore runs in a convex arch inferiorly, ascending slightly toward the left up to below the spleen, where the left colic flexure is located. The flexure has a sharp bend and presents natural resistance to the movement of the intestinal contents. It is attached to the diaphragm with ligaments. The overall length can be seen between the angle of the right rectus margin and costal arch up to the angle of the left rectus margin and costal arch. This means that the transverse colon can only be directly accessed through the rectus abdominis muscles. The position of the transverse colon is highly dependent on body position (it is higher while lying than standing), how full the abdominal cavity is (pregnancy), and the extent to which the transverse colon itself is filled. The position of the left colic flexure varies between T10 and L3. The Cannon-Böhm area is located medial to the left colic flexure and on the transverse colon and constitutes the termination of the innervation area of the vagus nerve.

The descending colon descends retroperitoneally from the left colic flexure to the iliac crest, where it becomes the sigmoid colon between the iliac crest and the level of S1. Several small intestinal loops are situated between this part of the colon and the anterior abdominal wall.

The sigmoid colon is 45 cm long on average (Rauber and Leonhardt, 1987). Its location is also dependent on how full it is. It curves on itself toward the right and then bends downward into the pelvic space.

At the level of S2 to S3, the sigmoid becomes the rectum. It is 12 to 15 cm long and initially lies on the anterior side of the sacrum. While the term “rectum” may suggest that the structure is straight, this is not the case; it has three bends and terminates in the anal canal, which is 3 to 4 cm long.

Pelvic Cavity

The pelvic cavity contains the urinary bladder, the rectum, and the internal sex organs. Its inferior side is closed by the muscle and connective tissue plates of the pelvic floor.

Urinary Bladder

As the only accessible organ of the pelvic cavity, only the urinary bladder will be discussed here. It is located below the peritoneum, behind the symphysis, and on the pelvic floor (▶ Fig. 11.9). In the female pelvic cavity, the uterus is located directly behind the urinary bladder, while in the male pelvic cavity, the rectum is in this position. Superiorly, the sigmoid colon lies on the urinary bladder.

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Fig. 11.9 Position of the bladder in the median section.

The size of the urinary bladder obviously depends on the extent to which it is filled. While up to 700 mL of urine can be deliberately retained, the urge to urinate sets in starting with 350 mL. As the bladder fills, the vertex of the bladder rises to over the symphysis. If muscle tone is weak, bladder emptying may be impaired, which can lead to urinary retention.

Abdominal Aorta

The abdominal aorta is located in the retroperitoneal space. It enters the abdominal cavity through the aortic hiatus at the level of T12. Further below, it runs in front of the lumbar vertebral bodies somewhat left of the median plane. In the abdominal cavity, it gives off a number of paired and unpaired branches. At the level of L4, it is divided into two pelvic arteries (common iliac arteries) that course along the medial borders of the psoas major muscles. These finally become the femoral arteries, which course below the center of the inguinal ligament into the anterior thigh area.

The proximity to the lumbar vertebral bodies allows the pulsation of the aorta to be felt posterior to the spinous processes with the patient in prone position. If very distinct pulsation of the aorta can be felt while palpating the abdominal wall (left next to the median line) of the patient in supine position, the aorta should be examined for a possible aneurysm (Ferguson, 1990).

11.3.5 Anatomy of the Groin

The area of the groin comprises the transition from the abdominal cavity to the proximal thigh. Deep in the groin, large muscles and important vessels leave the abdominal cavity and enter the thigh (▶ Fig. 11.10). To this end, the space below the inguinal ligament is divided into separate sections for the iliopsoas muscle and femoral nerve and the femoral artery and vein (Chapter 5).

Dec 4, 2021 | Posted by in GENERAL SURGERY | Comments Off on Chapter 11 Abdominal Region
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