Applied Surgical Anatomy of the Ilioinguinal Approach to the Acetabulum

Applied Surgical Anatomy of the Ilioinguinal Approach to the Acetabulum

 

 

Overview

 

The applied anatomy of this approach is conveniently divided into two parts.

1. Lateral and posterior to the anterior superior iliac spine. The dissection consists of detaching those muscles that arise from or insert into the iliac crest and the inner wall of the ilium using subperiosteal dissection.

2. Medial and anterior to the anterior superior iliac spine. The applied anatomy of the approach is that of the inguinal canal and its related structures. Because pathology in this area nearly always relates to herniae, both inguinal and femoral, it is usually an unfamiliar ground for orthopedic surgeons and, thus, is potentially hazardous.

 

Landmarks and Incision

Landmarks

The anterior superior iliac spine is the site of attachment to two important

structures. The sartorius takes its origin from it and the inguinal ligament uses it as a lateral attachment.

The anterior third of the iliac crest serves as the origin of the following three muscles.

1. The external oblique forms the outer layer of the muscles of the anterior abdominal wall. It inserts into the outer strip of the anterior half of the iliac crest.

2. The internal oblique forms the middle layer of the muscles of the anterior abdominal wall. It originates from the center strip of the anterior half of the iliac crest.

3. The tensor fasciae latae arises from the outer lip of the anterior half of the iliac crest.

The pubic tubercle is not easily palpated because it is covered by the spermatic cord in the male and the round ligament in the female.

Incision

This curved incision roughly follows the lines of cleavage in the skin. However, the extensive dissections involved may leave rather broad scars. They are nearly always hidden by clothing.

 

Superficial Surgical Dissection and Its Dangers

 

The dissection consists of the division of the fascia of the external oblique muscle and anterior rectus sheath. The external oblique, which is the outer layer of the abdominal muscles, arises from the lower eight ribs. It inserts as fleshy fibers into the anterior half of the iliac crest. However, from the anterior superior iliac spine, it becomes aponeurotic. The aponeurosis attaches to the pubic tubercle and medially becomes fused with the aponeurosis of the opposite external oblique muscle to form the anterior part of the rectus sheath. Therefore, the splitting of the fibers of the external oblique muscle and the incision of the anterior rectus sheath are both in the same plane. There is a free lower border of this muscle between the anterior superior iliac spine and the pubic tubercle. This free edge is called the inguinal ligament. The aponeurosis curls back on itself to form a gutter, and the free edge of this gutter is the origin of part of the internal oblique and transversus abdominis muscles.

Just above the pubic tubercle, there is a gap in this aponeurosis to allow the passage of the spermatic cord in the male and the round ligament in the female. This gap is known as the superficial inguinal ring (Fig. 7-

33). Dividing the fascia of the external oblique opens up the inguinal canal which is an oblique intramuscular slit running from the deep to the superficial inguinal rings. These contain the spermatic cord in the male and the round ligament in the female (Fig. 7-34).

The rectus abdominis muscle is enclosed in a sheath of fascia. In the region of this approach, however, the posterior layer of fascia is absent. The anterior rectus sheath also receives some tissue from both the internal oblique and transversus abdominis muscles.

The spermatic cord consists of the vas deferens accompanied by its artery and the testicular artery and vein. As these structures emerge through the abdominal wall, they get coverings from each layer they pass through (Fig. 7-35). The transversalis fascia covers the cord with a thin layer of tissue known as the internal spermatic fascia. Passing through the transversus abdominis and internal oblique, the cord gets covered with a layer of muscle known as the cremasteric muscle. As it passes through the external oblique at the superficial inguinal ring, it is covered by a thin layer known as the external spermatic fascia. The round ligament in the female is also covered by these three fascial layers. Both the spermatic cord and round ligament can be mobilized easily in the inguinal canal during the superficial surgical dissection.

 

Deep Surgical Dissection and Its Dangers

 

Once the spermatic cord has been mobilized the posterior wall of the inguinal canal is seen. In the lateral half of the inguinal canal, the rolled free edge of the external oblique aponeurosis gives origin to muscle fibers from both the internal oblique and the transversus abdominis. These muscle fibers arch up over the spermatic cord and fuse to form a conjoint tendon that is attached posterior to the spermatic cord into the pubic crest. Therefore, in the medial half of the inguinal canal, its posterior wall consists of this conjoint tendon which needs to be divided for access to the underlying structures. The spermatic cord exits from the abdominal cavity through the deep inguinal ring to enter the inguinal canal. Lateral to the deep inguinal ring, fibers of the internal oblique and transversus abdominis arise from the inguinal ligament and also have to be detached with a small cuff of the ligament to facilitate repair during closure (see Fig. 7-35). Medial to the deep inguinal ring lies the inferior epigastric artery which usually requires ligation. Deep to these muscles lies the thin transversalis fascia, extraperitoneal fat, and finally the peritoneum (Fig. 7-37).

The dissection completely disrupts the anatomy of the inguinal canal. Careful repair of all these structures on a layer-by-layer basis is important to prevent the development of an inguinal hernia.

Passing under the inguinal ligament from the abdomen into the thigh are the femoral nerve, the femoral artery, and the femoral vein, as well as the psoas and iliacus muscles (Fig. 7-36). The iliacus arises from the hollow of the iliac fossa, and runs into the thigh underneath the lateral part of the inguinal ligament. The psoas muscle arises from the anterior aspect of the lumbar spine and passes into the thigh below the middle of the inguinal ligament. Between these two muscles, the femoral nerve runs down into the thigh. It is intimately related to the iliopsoas and is mobilized with the muscle to avoid excessive retraction. Covering the muscle is a thick layer of fascia known as the iliopectineal fascia. This is attached deeply to the pubis and must be divided to allow access to the inner surface of the pelvis. This fascial layer separates the vascular bundle from the iliopsoas (see Fig. 7-29). Medial to the nerve, the femoral artery and vein enter the thigh. As these vessels leave the abdomen, they take with them a fascial layer derived from the extraperitoneal fascia. This is known as the femoral sheath. In addition to the artery and vein, the femoral sheath has a space in it, medial to the vein, known as the femoral canal. The function of the femoral canal is to allow the passage of lymphatic vessels and to make it possible for the vein to expand at times when the blood return from the leg becomes increased.

It is also, however, the site of a femoral hernia. Because the femoral artery and vein are enclosed in a common fascial sheath, they should be mobilized together. Separate mobilization of the femoral vein will traumatize it leading to possible thrombosis.

The bladder is separated from the pubic bones by a space known as the Cave of Retzius. It is occupied by very thin tissue, the bladder, and, in the case of the male, the prostate. The prostate can be easily mobilized from the back of the pubis. However, in cases of fracture, there may be pathologic adhesions in this area, and great care should be taken not to accidentally produce a bladder rupture. A full bladder will make safe access to this area impossible, and a urinary catheter inserted preoperatively is vital (Fig. 7-38).

 

 

Figure 7-33 The superficial musculature of the inguinal region. Just above the pubic tubercle, there is a gap in the aponeurosis of the external oblique to allow the

passage of the spermatic cord in the male and the round ligament in the female. This gap is known as the superficial inguinal ring (inset).

 

 

Figure 7-34 Dividing the external oblique muscle opens up in the inguinal canal. The spermatic cord is revealed covered by the cremasteric muscle, a muscle derived from the internal oblique muscle (inset).

 

 

Figure 7-35 As the testis migrates out through the anterior abdominal wall in fetal development, it and the vas deferens get coverings from each layer they pass

through. The external oblique provides the external spermatic fascia. The internal oblique and the transversus abdominis provide the cremasteric muscle. The transversalis fascia provides the internal spermatic fascia. The cord is retracted to reveal the posterior wall of the inguinal canal formed by the conjoint tendons (inset).

 

 

Figure 7-36 Deep to the inguinal ligament run the femoral nerve, the femoral vessel, as well as the psoas and iliacus muscles. Medial to the deep inguinal ring lie the inferior epigastric vessels (inset).

 

 

Figure 7-37 Division of the posterior wall of the inguinal canal reveals the extraperitoneal fat.

 

 

 

Figure 7-38 The medial aspect of the acetabulum can be exposed by retraction of the iliopsoas and the femoral sheath. The inner aspect of the superior pubic ramus can only be visualized by careful mobilization of the bladder.