Anterior Iliac Crest

The most anterior osteotomy for anterior iliac crest bone grafts should be made at least 2 to 3 cm behind the anterior superior iliac spine to avoid an avulsion fracture of the bone remaining anterior to the harvest site ( Fig. 35.1 ).1,2 The skin and fascia are incised parallel to the cortex of the iliac crest directly over the graft harvest site. Careful subperiosteal dissection should be performed to avoid injury to the ilioinguinal nerve, lateral femoral cutaneous nerve, blood vessels, or viscera.2,3 The periosteum of the iliac bone is incised with monopolar cautery; the linear incision is made longitudinally along the top of the iliac crest ( Fig. 35.2 ). A cuff of fascia and periosteum is elevated from the top and sides of the iliac crest with a Cobb periosteal elevator. This cuff of tissue is preserved to provide a secure fascial closure to reduce muscular pain when the patient ambulates postoperatively.

Bone grafts are harvested carefully with an oscillating saw or an osteotome after the medial and lateral surfaces of the graft harvest site have been exposed subperiosteally with a Cobb periosteal elevator. All bone cuts are made with sharp cutting tools while the surgeon visualizes the tips of the instruments directly to prevent complications. If bone grafts are used for mechanical reconstruction to bear loads (i.e., tricortical blocks), they should be harvested with an oscillating saw whenever possible. Osteotomes create microfractures, which can weaken the grafts. Hemostasis of the iliac crest donor bed is obtained with Gelfoam (Baxter, Deerfield, IL) or bone wax. A multilayer wound closure is performed. The fascial and periosteal tissues are reapproximated securely with interrupted sutures.

Portions of this chapter have been reprinted from Dickman CA, Maric Z. The biology of bone healing and techniques of spinal fusion. BNI Quarterly 1994;10(1):2–12. With permission from Barrow Neurological Institute.

Posterior Iliac Crest

Posteriorly, bone grafts are obtained from the medial 6 to 8 cm of the posterior iliac crest. A more lateral exposure can cause buttock numbness or painful neuromas from injuring the superior cluneal nerves. Tricortical grafts, cortical matchstick grafts, a large corticocancellous plate, or cancellous bone strips can be harvested posteriorly ( Fig. 35.3 ).

A curved skin incision is made over the medial iliac crest, beginning at the posterior iliac spine and continuing superolaterally. As with anterior osteotomies, careful anatomical tissue dissection must be performed under direct visualization to preserve the normal tissue planes whenever a bone graft is obtained. Tissue cuffs also are preserved during subperiosteal dissection of the bone surfaces to allow secure anatomical tissue closure.

All bone and soft tissue are dissected under direct visualiza tion to prevent complications.1,2,5,6 Monopolar cauterization and Cobb periosteal elevators are used to dissect the muscles from the iliac crest. Dissection of the bone surfaces should remain subperiosteal to avoid the branches of the gluteal arteries within the muscles. If the superior gluteal arteries are torn or cut, they can retract into the muscles and cause brisk, protracted bleeding. A Taylor (Aesculap, San Francisco, CA) retractor is useful for retracting soft tissues laterally from the ileum during graft harvest. The tissue dissection is restricted cephalad and lateral to the posterior iliac spine ( Fig. 35.4 ) to avoid the sacroiliac joint (medially) and the sciatic notch (inferiorly). The sacroiliac ligaments should be preserved to maintain stability of the sacroiliac joint.1,2,6 If a tricortical bone graft is needed, the anterior surface of the iliac crest should be dissected carefully with a curved Cobb periosteal elevator. The retroperitoneal fat pad is visualized, and within this fat pad, the ureter must be avoided. The muscles must be detached from the ventral, dorsal, and superior edges of the iliac crest to remove the tricortical graft.

Sharp instruments (e.g., osteotomes, oscillating saws, bone curettes, and bone gouges) are used to incise the bone to obtain grafts. These tools should be used with precision. After bone grafts have been harvested, meticulous hemostasis should be obtained with bone wax or Gelfoam. Bone wax provides an excellent method to obtain complete or almost complete hemostasis. However, bone wax inhibits bone healing and precludes accessing the same donor site if a new graft is needed in the future. Sheets of Gelfoam compressed onto the donor site provide reasonably good hemostasis and allow further grafts to be obtained from the same donor site if needed. Suction drains are placed if any blood persistently oozes from the graft donor site. All periosteal and fascial layers are closed to obliterate dead space, to reattach the muscles to their sites of origin or insertion, to prevent herniation of abdominal contents, and to reduce postoperative muscular pain.