Applied Surgical Anatomy of the Bony Pelvis

Overview

The approaches described in this chapter obtain access via a subcutaneous portion of the bony pelvis. Thereafter, access is afforded by stripping the muscular coverings off the bone while remaining in a strictly subperiosteal plane. Using this technique, the approaches avoid vital structures and, therefore, are extremely safe. The further one proceeds from a subcutaneous part of the bone the more muscles must be stripped and the view obtained inevitably becomes poorer. For this reason, these approaches are limited in the exposure they provide. They cannot be extended and afford only limited access to certain portions of the bony skeleton.

Two superficial parts of the innominate bones are used for access. The iliac crest has the internal oblique and transversus abdominis muscle arising from its surface and the external oblique muscle inserting into it. The wing of the ilium itself is sandwiched between two masses of muscles, the glutei and tensor fasciae latae muscles on the outer side, and the iliacus muscle on the inner side. The pubic tubercles and upper parts of the superior pubic rami have the rectus abdominis muscle attached to them, and these must be detached for access to the superior surface of the structures.

Landmarks and Incisions

Landmarks

The anterior superior iliac spine is the site of insertion of the inguinal ligament and the sartorius muscle. The anterior third of the iliac crest is the site of origin for the external oblique, transversus abdominis, and tensor fasciae latae muscles.

The posterior iliac crest is easily palpable and is the site of origin of the external oblique muscle. The posterior superior iliac spine is marked by an overlying dimple. A line connecting these dimples crosses the sacroiliac joint at the level of S2. The pubic tubercle is the medial attachment of the inguinal ligament and the most lateral part of the body of the pubis.

Incisions

All the incisions described roughly parallel the lines of cleavage. Scars can be broad and ugly, however, but this rarely is of clinical significance because they usually are covered with clothing.

Superficial Surgical Dissection

In all approaches, superficial surgical dissection consists of incising down onto the superficial portion of the bone. In the iliac crest, this merely involves dividing the overlying fat. In the symphysis pubis, the rectus sheath must be opened. The rectus sheath is a tough fibrous structure derived from all three muscles of the anterior abdominal wall. The superior part of the rectus is enclosed by the sheath. 2 cm below the umbilicus the posterior portion of the sheath formed by the aponeurosis of the internal oblique muscle and the transversus abdominis ceases and the sheath which receives contributions from all three layers of the abdominal wall is only present anterior to the muscle. It forms a tough anterior covering to the underlying rectus muscle which is easy to repair (see Fig. 7-9).

Deep Surgical Dissection

Muscles can be stripped safely off both aspects of the anterior third of the iliac crest, but only from the outer aspect of the posterior third of the crest.

Dissection of the outer side of the ilium involves detaching the origin of the tensor fasciae latae. Covering this muscle is a thick layer of fascia that is continuous with the fascia covering the gluteus maximus muscle. The tensor fasciae latae, gluteus maximus, and the fascia can therefore be thought of as the outer layer of the buttock anatomy (Fig. 7-20). This is analogous to the position of the deltoid muscle in the shoulder. Deep to the structures are the origins of the gluteus medius and gluteus minimus muscles from the outer wing of the ilium. These can be lifted off the bone entirely to provide a view of the wing of the ilium. It is important to realize, however, that the rectus femoris muscle still remains between the surgeon and the hip joint, thus limiting the approach.

Figure 7-20 The superficial musculature of the posterior approach to the hip joint. The gluteus maximus predominates.

Gluteus Maximus. Origin. From posterior gluteal line of ilium and that portion of the bone immediately above and behind it; from posterior surface of lower part of sacrum and from side of coccyx; and from fascia covering gluteus medius. Insertion. Into iliotibial band of fascia lata and into gluteal tuberosity. Action. Extends and laterally rotates thigh. Nerve supply. Inferior gluteal nerve.

The inner surface of the ilium serves as origin for the iliacus muscle. This can be lifted off the bone safely, providing access down to the brim of the true pelvis.

The sacroiliac joint is a paradox. It is a true synovial joint, yet any movement is very difficult to demonstrate. The joint is reinforced heavily by anterior and posterior supporting ligaments. Approached from the front, the sacroiliac joint is perpendicular to the plane of dissection. Approached from the rear, the joint is overhung by the posterior iliac crest, making it oblique to the plane of dissection. It is critically important to appreciate this obliquity when planning the insertion of any screws that may be used to cross the joint.

In contrast, the pubic symphysis is not a synovial joint, but a secondary cartilaginous joint. Its superior surface is readily accessible once the insertion of the rectus abdominis muscle has been detached. Behind the symphysis pubis is a potential space filled with loose areolar tissue; this is known as the cave of Retzius. This potential space lies between the symphysis pubis and the bladder, and allows access to the inner surface of the pubis down to the muscles of the pelvic floor.