as previously depicted in many atlases. The urogenital diaphragm exists only in humans because the

human pelvic outlet faces inferiorly, unlike that of quadrupeds.

Figure 72-16. A: The pelvic diaphragm (levator ani and the piriformis) and the urogenital diaphragm viewed from within the

pelvis. B: Hemisection of the pelvis revealing the levator ani, piriformis, obturator internus, and psoas muscles.

WHY DO HUMAN BEINGS DEVELOP ABDOMINAL WALL HERNIAS?

2 The most common hernias develop at sites where the abdominal wall has natural openings such as

the internal inguinal ring, the umbilicus, and the esophageal hiatus. Previous surgical entry sites

(incisional hernia) are also common areas where hernias develop. Factors that increase the pressure

in the abdominal cavity, such as obesity, heavy lifting, coughing with chronic lung disease, straining

during a bowel movement or urination (prostatism), chronic lung disease, and ascites, have

traditionally been considered important in the etiology, especially at these natural openings.

Developmental phenomena also play a role. For example, in the evolution from a quadruped to a

biped, the unprotected groin is more vulnerable to changes in intra-abdominal pressure, predisposing

to inguinal herniation. Major risk factors for the development of an abdominal wall hernias include

chronic obstructive pulmonary disease, smoking, high intra-abdominal pressure, collagen vascular

disease, thoracic or abdominal aortic aneurysm, peritoneal dialysis, matrix metalloproteinase (MMP)

abnormalities, and an increased type I: type III collagen ratio.

The role of heavy lifting, especially a single strenuous event, is an unsettled question and has

considerable medical–legal ramifications. There is minimal evidence that vigorous abdominal wall

activity is an independent risk factor for abdominal wall hernia development despite the overwhelming

opinion to the contrary in the lay literature.19–21 In a systematic review of existing evidence performed

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by Svendsen and colleagues, regarding the effects of occupational and mechanical exposures in relation

to inguinal hernias, a causal relationship could not be established between specific mechanical insults

and occurrence of inguinal hernia, hernia recurrence, and persistent pain after inguinal hernia

repair.22,23 According to the results of another register-based male cohort study in Denmark, increasing

cumulative exposure to daily lifting activities and prolonged standing or walking at work was associated

with an increased risk of having an indirect inguinal hernia repair.22,23 The authors hypothesized that

patent processus vaginalis may be more susceptible to changes in intra-abdominal pressures, whereas in

a direct hernia, other mechanisms may be involved in connective tissue degradation and weakening of

the transversalis fascia. Still, the role of mechanical activity in the development of abdominal wall

hernia is not completely clear, and further research is needed to determine if inguinal hernias can be

prevented and if the postoperative prognosis can be improved by reducing occupational mechanical

exposures.

Figure 72-17. The gluteal muscles and lateral rotators of the hip. External relations of the sciatic foramen are also evident.

Familial predisposition and the role of connective tissue diseases in hernia development have received

considerable attention in recent years. Particularly important for inguinal hernia is a family history as it

has been reported to increase the risk up to 8 times.24,25 Various connective tissue disorders, such as

osteogenesis imperfecta, Marfan syndrome, Ehlers–Danlos syndrome, and congenital hip dislocation, are

associated with hernias. Imbalances in collagen, the basic building block of the abdominal wall, are

believed to contribute to hernia disease. While type I collagen confers predominantly tensile strength,

type III collagen consists of thinner fibers and is regarded as a temporary matrix during tissue

remodeling. A decreased ratio of type I to type III collagens can be detected in fascial and skin

specimens obtained from patients with hernias. A similar phenomenon was discovered by Cannon and

Read in smokers when they performed biopsies of the rectus sheaths from adult smokers with inguinal

hernias and coined the term “metastatic emphysema.”26 The investigators also demonstrated

significantly greater levels of circulating serum elastolytic activity in patients who smoke.

Aside from primary defects in collagen synthesis, the imbalances in collagen in patients with hernia

can be attributed to altered extracellular matrix (ECM) which is maintained in a dynamic balance of

synthesis and degradation by a complex set of enzymes. MMPs,27 which are a group of 23 structurally

related zinc-dependent enzymes, protease with collagenolytic activity and have a pivotal role in the

integrity and composition of the ECM.

The association between MMP overexpression and abdominal wall hernia was initially demonstrated

by Bellon and colleagues, who studied the expression of MMP-1 and MMP-2 in the transversalis fascia of

patients with direct and indirect inguinal hernia. Since then, several studies have been conducted,

aiming at elucidating the role of MMPs in the development of primary and recurrent abdominal wall

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hernias. For this purpose, MMP levels in fascia, skin, hernia sac, and blood specimens of patients with

inguinal, incisional, and recurrent abdominal wall hernias have been measured. The expression of MMP

mRNA in cultured fibroblasts has also been investigated to evaluate cell–cell and cell–matrix interactive

mechanisms as causative factors for abnormal MMP production. In addition to this, in-vitro studies have

been performed to study the effect of different mesh materials on MMP expression on cultured

fibroblasts; in one such study, polypropylene has been shown to induce less MMP2 expression than

polygalactin. The function of MMPs is further regulated by a variety of endogenous regulators, the most

important ones are known as tissue inhibitors of MMPs (TIMPs).28–30 Studies have shown that an

imbalance between MMP and TIMP activity may have a role pathogenesis of abdominal wall hernias.31

Despite the increasing knowledge regarding MMPs in incisional and inguinal hernia, the exact role of

MMPs in the pathogenesis of hernia formation remains unclear. Most studies are small and not

completely controlled; and there is a remarkable heterogeneity among studies concerning the

characteristics of the study populations, the examined tissue specimens, and the biochemical assays

used. In addition to MMP and TIMPs, factors that have been implicated in hernia development include

deficiency of the elastic fiber system of the transversalis fascia, decreased tropoelastin and lysyl oxidaselike 1 synthesis, elastase overexpression and TGF-beta1 overexpression. It remains unclear whether

these alterations in hernia patients are a part of the “cause or effect” phenomenon. Another interesting

area of research are drug classes that can suppress MMP expression (e.g., tetracyclines, especially

doxycycline, aspirin, statins, and thiazolidinediones) and understanding their role in hernia prevention

and treatment.32

Figure 72-18. Reduction of a hernia by taxis. A: Applying pressure on the hernia directly occludes the neck. B: Elongating the neck

of the hernia while applying pressure allows reduction.

COMPLICATIONS OF HERNIAS

Hernia Accident

For years, surgeons have been taught that all hernias should be repaired at diagnosis to prevent a hernia

accident, which is defined as a bowel obstruction or incarceration with strangulation, because of the

perception that patients presenting with these complications have an unacceptable increase in mortality.

This thinking, however, has not stood up when tested in randomized controlled trials. For example, for

men with asymptomatic inguinal hernias, randomized controlled trials have shown that a strategy of

watchful waiting is safe.33

Incarceration

Incarcerated means “trapped” or “imprisoned.” Clinically, an incarcerated hernia is an irreducible hernia.

An incarceration is not in and of itself a surgical emergency. Many hernias are chronically incarcerated

due to adhesions of contents (e.g., omentum, bowel, ovary, etc.) to the hernia sac. The hernia itself is

not necessarily tense to palpation, and the overlying skin appears normal. Normal bowel sounds may be

heard within the hernia. It is important to differentiate an incarcerated hernia from a hydrocele of the

cord. One can get above the hydrocele with the examining fingers. One cannot get above a hernia,

however, as it communicates with the abdominal cavity. Hydroceles will transilluminate clearly, but a

hernia will not.

An acutely incarcerated, painful hernia must be managed carefully. An attempt at reduction is

reasonable unless there are signs of strangulation, which is not always obvious by clinical examination.

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Immediate surgical exploration is the safest approach when the diagnosis is not clear. The advantage of

reduction followed by elective repair is that edematous tissue associated with an acute incarceration can

return to normal, which presumably will translate into a better repair with less chance of infection.34 If

an attempt at reduction seems reasonable, the patient is sedated and placed in bed. The Trendelenburg

position should facilitate reduction of a groin hernia. An attempt should be made at the initial

examination to reduce the hernia. The maneuver of taxis entails grasping the neck of the hernia with the

fingers of one hand and then applying intermittent pressure on the most distal part of the hernia with

the other hand. Taxis has the effect of elongating the neck of the hernia so that the contents of the

hernia may be guided through this area back into the abdominal cavity with a rocking movement. Mere

pressure on the most distal part of the hernia causes bulging of the hernial sac around the neck, which

can occlude the neck and prevent it from being reduced (Fig. 72-18). The maneuver of taxis should not

be performed with excessive pressure or too vigorously. If the hernia is strangulated, gangrenous bowel

might be reduced into the abdomen or perforated in the process. One or two gentle attempts should be

made at taxis. If they are unsuccessful, this procedure should be abandoned. Rarely, the hernia together

with its peritoneal sac and constricting neck may be reduced into the abdomen (reduction en masse).

The patient would then have persistent obstruction after reduction of the hernia.

Intestinal Obstruction

One hundred years ago, the most common cause of intestinal obstruction was a hernia. At the present

time, hernia is third, after adhesive obstructions and cancer. Hernia is an important cause of obstruction

that is not infrequently missed on clinical examination. When a patient with an intestinal obstruction is

examined, great emphasis should be placed on adequate exposure of the entire abdominal wall and

groin area (from nipples to knees). Proper lighting is essential because previous scars can fade with

time and become barely perceptible. The patient with intestinal obstruction as a result of a hernia will

have a tense hernia that is irreducible. The abdomen itself will be distended, and high-pitched bowel

sounds with frequent rushes will be heard. If the process continues to the complication of strangulation,

these signs will disappear. Unlike adhesive small-bowel obstructions, partial small-bowel obstructions

secondary to hernia are rare. Most patients will have had vomiting and obstipation.

A plain roentgenogram of the abdomen will reveal the signs of an intestinal obstruction – dilated

loops of bowel with air–fluid levels and no bowel gas distal to the obstruction. Frequently on a plain

roentgenogram, one can see bowel shadows in the region of the hernia. A lateral view is often useful to

demonstrate this feature more clearly. Contrast studies are not usually necessary in this instance.

Computed tomography (CT) reliably demonstrates the hernia with characteristic features of obstruction

and should be considered if the clinical diagnosis is not certain (Fig. 72-19) because a distal intestinal

obstruction secondary to another cause (e.g., adhesions) may result in significant distention of a

coincidental nonobstructing hernia of the abdominal wall. Should the examiner focus attention

exclusively on the hernia, the real cause of the obstruction may be missed when the hernia is repaired.

Figure 72-19. Computed tomogram showing a left-sided inguinal hernia.

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