Anterior Approach to the Sacroiliac Joint

The anterior approach to the sacroiliac joint offers safe, reliable access to that structure and allows anterior plates to be positioned accurately across the joint. It also permits the exposure of the inner wall of the ala of the ilium, allowing fixation of associated iliac fractures. Paradoxically, although the sacroiliac joint is one of the most posterior structures in the entire pelvic ring, the anterior approach allows greater exposure and

control than does the seemingly more logical posterior approach, because of the shape of the joint. Anteriorly, the joint is flat and directly available, whereas posteriorly it is overhung by the posterior iliac crest.

Position of the Patient

Place the patient in a supine position on the operating table and put a large sandbag under the buttock. This will push the iliac crest up toward the surgeon. Support the opposite iliac wing with a support attached to the operating table and then tilt the table 20 degrees away, allowing the mobile contents of the pelvis to fall away.

Landmarks and Incision

Landmarks

The anterior superior iliac spine and the anterior third of the iliac crest are subcutaneous and easy to palpate.

Incision

Make a long, curved incision over the iliac crest, beginning 7 cm posterior to the anterior superior iliac spine (at about the level of the iliac tubercle). Curve the incision forward until the anterior superior iliac spine is reached. Continue the incision anteriorly and medially along the line of the inguinal ligament for an additional 4 to 5 cm (Fig. 7-12).

Internervous Plane

No true internervous plane is available for use. The approach consists simply of stripping muscles off the inner side of the pelvis; because the bone is being approached via its subcutaneous surface, no muscle is denervated.

Superficial Surgical Dissection

Deepen the skin incision through the subcutaneous fat onto the subcutaneous surface of the iliac crest. Two techniques can be used to detach the iliacus from the deep surface of the iliac wing.

Bone block technique. Expose the deep fascia overlying the glutei and tensor fasciae latae muscles at the point where it attaches to the outer lip of the iliac crest. Incise the periosteum of the entire anterior third of the

iliac crest and gently strip the muscles off the outer wall of the pelvis to expose about 1 cm of the outer surface below the crest of the ilium.

Predrill the iliac crest for easy reattachment. Using an oscillating saw, transect the wing of the ilium at this level, cutting only the outer cortex and the cancellous bone underneath (Fig. 7-13). Next, crack the inner cortex with an osteotome. This allows the anterior superior iliac spine to be detached along with the transected portion of the iliac wing (Fig. 7-14).

Figure 7-12 Make a curved incision over the iliac crest, beginning 7 cm posterior to the anterior superior iliac spine.
Soft tissue release only. Start just posterior to the anterior superior iliac spine and detach the iliacus muscle and its overlying fascia from the

deep surface of the iliac wing. Begin by using sharp dissection and then develop the plane using a swab used as a tissue expander.

Deep Surgical Dissection

The iliacus muscle arises from the inner wall of the ilium; detach it by blunt dissection. If the bone block technique is used as the dissection is deepened, the detached anterior superior iliac spine, which still is attached to the lateral end of the inguinal ligament, must be mobilized. This block of bone and muscle must be moved medially; to accomplish this, divide some fibers of both the tensor fasciae latae and sartorius muscles (Fig. 7-15). Note that the lateral cutaneous nerve of the thigh is about 1 cm distal and medial to the anterior superior iliac spine, and may have to be divided to permit this mobilization.

Remaining strictly in a subperiosteal plane, strip the iliacus muscle off the inner wall of the pelvis to expose the underlying sacroiliac joint (see Fig. 7-15). The distance is surprisingly short. As the muscle is stripped off, some nutrient vessels will have to be detached from the inner wall of the pelvis. Bleeding usually can be controlled by bone wax.

The L4, L5 nerve roots and the lumbosacral trunk run along the anterior surface of the sacrum approximately 1.5 cm medial to the sacroiliac joint. Therefore do not continue the dissection more than 1.5 cm medial to the sacroiliac joint. If a standard 3.5 mm plate is used to stabilise the joint place the plate so that only one screw hole is placed medial to the joint. Using two holes of the same plate will endanger the nerve root (see Fig. 7-15, inset).

Mobilizing the iliacus muscle off the inside of the pelvis with a large bone block allows the muscles to be reattached securely with screws during closure. The muscle then resumes its anatomic position, and the dead space beneath it is obliterated. If the bone block technique is used, failure to securely reattach the iliac crest will produce impaired function, a poor cosmetic result, possible chronic pain, and a high risk of hematoma formation.

Figure 7-13 Strip the muscles from the outer wall of the pelvis. Predrill the iliac crest. Divide the outer cortex 1 cm below the crest using an oscillating saw.

Dang

Nerves

The lateral cutaneous nerve of the thigh may have to be divided during the mobilization of the anterior superior iliac spine. This will cause some

numbness of the lateral aspect of the thigh. Even if the nerve is not transected a neurapraxia due to retraction is common and patients should be warned that an area of numbness on the lateral aspect of the thigh may occur following surgery that in some cases may be permanent.

The L4, L5 nerve roots and the lumbosacral trunk crosses the anterior surface of the sacrum approximately 1.5 cm medial to the sacroiliac joint. If plates are applied too far medially on the sacrum the nerve will be damaged. This nerve root marks the medial limit of the approach.

Sacral Nerve Roots

The sacral nerve roots can be damaged at the point where they arise from the sacral foramina. For this reason, the dissection cannot be carried further medially than the sacral foramina. The sacral nerve roots are not usually exposed during this approach. They can be at risk at two stages of the operation. If sharp pointed retractors such as Hohmann are used medially, great care should be taken that the point of these retractors is not inadvertently inserted into a sacral foramen. Sacral nerve roots can also be entrapped under the medial end of plates applied to the anterior surface of the sacroiliac joint. Meticulous preoperative planning will allow you to know exactly how many screw holes can be inserted safely into the sacrum without endangering the sacral nerve roots. In most cases, only one screw can be inserted.

Figure 7-14 Crack the inner cortex using an osteotome to complete the iliac osteotomy.

Vessels

Relatively large nutrient vessels often are avulsed from the inner wall of the ilium. Bleeding from these vessels can be controlled by pressure or bone wax.

How to Enlarge the Approach

Local Measures

Paradoxically, the key to adequate exposure of the posteriorly placed sacroiliac joint is adequate anterior dissection. The lateral end of the inguinal ligament and its attached anterior superior iliac spine must be mobilized to visualize the sacroiliac joint adequately.

Extensile Measures

The approach may be enlarged into an extended ilioinguinal approach that provides access to the entire anterior column of the acetabulum. This approach is discussed later in this chapter (page 378).

Figure 7-15 Strip the iliacus from the inner wall of the pelvis to expose the underlying sacroiliac joint.