Posterior Approach to the Sacroiliac Joint
Posterior Approach to the Sacroiliac Joint
The posterior approach to the sacroiliac joint is a simple, safe approach that does not endanger any vital structures. Its uses include open reduction and internal fixation of disruptions of the sacroiliac joint, open reduction
and internal fixation of fractures of the ilium near the joint, and treatment of infections of the sacroiliac joint or surrounding bones. The popularity of this approach has diminished with the increasing use of percutaneous screw fixation techniques. It is still, however, invaluable if adequate imaging is not possible or if alternative techniques, such as plating, are used.
It should be noted that reduction of fractures and dislocations is difficult through this approach, especially the correction of vertical displacement. Vertical displacement should be corrected by longitudinal traction, preferably preoperatively.
Achieving fixation of these fractures is technically demanding because of the shape of the joint and the presence of the sacral nerve roots arising from the sacral foramina. Practice the direction of screw placement on a bone model before surgery is attempted. During surgery, strict radiologic control of screw fixation using two-plane C-arm imaging is mandatory. Safe screw fixation can also be facilitated by the use of computer-assisted surgery, if such technology is available to the operating surgeon.
Position of the Patient
Place the patient prone on the operating table. Position bolsters longitudinally to support the chest wall and pelvis; the bolsters should allow the chest wall and abdomen to expand without touching the table. Take great care during preparation and draping to exclude the contaminated anal region from the operative field.
Landmarks and Incision
Palpate the subcutaneous posterior iliac crest which terminates in the posterior superior iliac spine.
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Figure 7-16 Make a curved incision, beginning 3 cm distal and lateral to the posterior superior iliac spine. Cross the posterior superior iliac spine and continue along the crest to its highest point.
Incision
Make a curved incision overlying the posterior iliac crest, beginning 3 cm distal and lateral to the posterior superior iliac spine. Extend the incision
from this spot to the posterior superior iliac spine and then continue along the crest to its highest point (Fig. 7-16).
Internervous Plane
No internervous plane is available for use. Both the gluteus maximus and gluteus medius muscles must be detached partially from their origins, but their individual neurovascular pedicles are preserved easily.
Superficial Surgical Dissection
Divide the subcutaneous tissues in line with the skin incision. Anteriorly, small cutaneous nerves (the superior cluneal nerves) may have to be cut, but they are of little clinical significance. Cut down into the outer border of the subcutaneous surface of the iliac crest to reveal the layer of fascia that covers the gluteus maximus muscle. Detach the origin of the gluteus maximus from the crest and carefully reflect the muscle downward and laterally (Fig. 7-17). Two vital structures penetrate this muscle from its deep surface. First, branches from the inferior gluteal artery, which emerges from the pelvis, with the piriformis muscle through the greater sciatic notch, penetrate the muscle. In addition, the inferior gluteal nerve emerges through the notch beneath the piriformis to supply the muscle. Because it is imperative that these two structures be preserved, they limit the inferior mobilization of the muscle. As the gluteus maximus muscle is reflected, the gluteus medius and piriformis muscles will be uncovered.
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Figure 7-17 Divide the subcutaneous fat and reflect the skin flap to reveal the fascia overlying the gluteus maximus and gluteus medius.
Deep Surgical Dissection
Gently elevate the gluteus medius muscle from the outer wing of the ilium. The muscle cannot be elevated much because its deep surface is tethered by its neurovascular bundle—the superior gluteal nerves and vessels (Fig. 7-18). In cases of trauma, the ruptured sacroiliac joint or fracture is easily visible but reduction is extremely difficult. To evaluate any reduction, detach part of the origin of the piriformis muscle from around the greater sciatic notch and insert a finger through the notch to palpate the joint from its anterior surface. The surface of the joint will feel smooth if it has been reduced (Fig. 7-19).
Dang
Nerves
The inferior gluteal nerve enters the deep surface of the gluteus maximus muscle. Overzealous downward retraction of the muscle can cause a traction injury to this nerve.
The superior gluteal nerve enters the deep surface of the gluteus medius muscle. This limits the forward retraction of this muscle, restricting the exposure of the outer wing of the ilium. Excessive retraction of the muscle will injure the superior gluteal nerve.
The sacral nerve roots are not endangered by the surgical approach but can be injured by inaccurate screw fixation across the sacroiliac joint. Accurate x-ray control of screw placement is mandatory.
Vessels
Branches of the superior and inferior gluteal arteries run with their respective nerves and also are in danger.
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Figure 7-18 Reflect the gluteus maximus muscle and the gluteus medius from the outer surface of the pelvis.
How to Enlarge the Approach
Local Measures
There are no local measures for enlarging this approach.
Extensile Measures
Extend the skin incision anteriorly and elevate the gluteus medius and gluteus minimus muscles from the outer surface of the iliac wing. This will enable more extensive fractures of the wing and the ilium to be dealt with. It should be noted that anterior approaches give much better exposure of these structures (see ilioinguinal approach, page 378).
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Figure 7-19 Detach part of the origin of the piriformis and insert a finger through the greater sciatic notch to palpate the sacroiliac joint from its anterior surface.
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.
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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.