Michael J. Lee, Thomas Stanley, Mark Dumonski, Patrick Cahill, Daniel Park, and Kern Singh
DEFINITION
The use of autogenous bone graft is considered by most surgeons to be the gold standard for achieving fusion in the spine.
Autogenous bone graft can be used at any spinal level, anterior or posterior.
The posterior ilium is most frequently harvested for nonstructural, cancellous bone graft.
Tricortical, structural bone grafts for cervical interbody fusions are typically harvested from the anterior ilium.
ANATOMY
Anterior ilium
The anterior ilium has a concave anterosuperior surface.
The anterior iliac crest becomes its thickest (iliac tubercle) 2 to 3 cm posterior to the anterior superior iliac spine (ASIS) (fig 1A).
The lateral femoral cutaneous nerve typically courses medial to the ASIS; however, it can infrequently cross lateral to the ASIS and be at risk for injury (fig 1B).
Posterior ilium
The posterior iliac crest thickness ranges from 14 to 17 mm.
The superior cluneal nerve passes over the iliac crest 7 to 8 cm lateral to the posterior superior iliac spine (PSIS) and is at risk for injury with a lateral incision (fig 1C).
The superior gluteal artery exits the pelvis from the greater sciatic notch and can be injured if bone harvesting approaches the sciatic notch (fig 1D).
SURGICAL MANAGEMENT
Positioning
A roll or bump of towels or a blanket beneath the ipsilateral ischial tuberosity can facilitate access to the anterior iliac crest.
FIG 1 • A. Ideal anterior iliac crest bone graft is obtained 2 to 3 cm posterior to the anterior superior iliac spine. B. The lateral femoral cutaneous nerve generally traverses medial to the anterior superior iliac spine. C. The superior cluneal nerves cross the posterior iliac crest 8 cm anterior to the posterior superior iliac spine. D. The superior gluteal artery exits from the greater sciatic foramen.
TECHNIQUES
SURGICAL APPROACH
Anterior Iliac Crest
A skin incision is made parallel to the iliac crest and is centered over the iliac tubercle.
The incision is carried down to the bone of the crest and the muscles are elevated subperiosteally to expose the wing of the ilium (TECH FIG 1).
The tensor fascia latae, gluteus medius, and gluteus minimus originate from the lateral aspect of the ilium. These muscles are innervated by the superior gluteal nerve.
The abdominal muscles are also attached to the iliac crest and are segmentally innervated. The incision over the crest is, therefore, internervous and safe.
Posterior Iliac Crest
The posterior superior iliac crest is palpable under the skin dimple in the superomedial aspect of the gluteal region.
TECH FIG 1 • The anterior iliac crest (arrow).
A vertical incision over the PSIS is made to minimize injury to the cluneal nerves.
An oblique or curved incision may be made over the posterior iliac crest. The cluneal nerves cross the iliac crest 7 to 12 cm anterolateral to the PSIS; therefore, the incision should be made medial to this cutaneous innervation.
The subcutaneous tissue is divided to the level of the iliac crest.
Using Bovie cautery, the iliac crest is incised.
The muscles are elevated subperiosteally from the posterolateral surface of the ilium.
The gluteus maximus, medius, and minimus originate from the lateral surface of the ilium. The superior gluteal nerve innervates the gluteus medius and minimus and the inferior gluteal nerve innervates the gluteus maximus.
The paraspinal musculature is innervated segmentally.
Posterior Iliac Crest: Midline Skin Incision
A midline spine incision may be extended distally and the posterior iliac crest approached laterally under the skin and subcutaneous fat. This avoids the use of a second skin incision.
The fascia overlying the PSIS is incised on the medial surface, where it is more robust; this facilitates fascial closure upon completion of the bone graft harvesting.
The PSIS is exposed on its outer surface with the aid of electrocautery via a subperiosteal dissection.
ANTERIOR TRICORTICAL ILIAC CREST BONE GRAFT
After exposure of the anterior iliac crest, an oscillating saw can be used to make parallel cuts through the inner and outer table (TECH FIG 2A).
Curved osteotomes can be used to make longitudinal cuts in the inner and outer tables to complete the tricortical bone graft harvesting (TECH FIG 2B,C).
TECH FIG 2 • A. An oscillating saw is used to make two parallel cuts in the anterior iliac crest (arrow). B. The void left by anterior iliac crest harvest (arrows). C. Resected tricortical anterior iliac crest bone graft.
POSTERIOR ILIAC CREST BONE GRAFT
Corticocancellous Strips
After exposure of the posterior iliac crest, adequate visualization can be obtained with the use of a Taylor retractor.
Caution should be taken to avoid penetrating the sciatic notch and potentially injuring the superior gluteal artery.
The removal of bone in the vicinity of the sciatic notch can weaken the thick bone that forms the notch, resulting in pelvic instability.
It is important to stay cephalad to the sciatic notch and remove bone only from the false pelvis. The false or greater pelvis is the portion of pelvis that lies cephalad to the pelvic brim, which defines the inner diameter of the pelvis.
For a landmark, an imaginary line dropped anteriorly from the PSIS with the patient in the prone position can be used as the caudal limit of bone removal (TECH FIG 3A).
Using a straight osteotome, multiple corticocancellous vertical strips can be cut from the iliac crest edge. A curved osteotome can be used to complete the cuts distally (TECH FIG 3B,C).
After removal of the corticocancellous strips, gouges or curettes can be used to harvest additional cancellous bone (TECH FIG 3D).
Uncapping the Posterior Superior Iliac Spine
With a rongeur, an osteotome, or both, the cap of the PSIS can be removed, allowing for harvesting of the cancellous bone between the two tables (TECH FIG 4A).
Using a curette or gouge, the cancellous graft is then harvested through this window (TECH FIG 4B).
TECH FIG 3 • A. Line directed anteriorly from the posterior superior iliac spine marks the caudal safe zone for bone grafting to avoid injury to the contents of the sciatic notch. B,C. Using osteotomes, several corticocancellous strips can be created from the posterior iliac crest. D. The void left after posterior bone graft harvesting.
TECH FIG 4 • A. The cap of the posterior superior iliac spine can be removed to expose cancellous bone. B. After removal of the cap of the posterior superior iliac spine, cancellous bone is exposed for harvesting (arrow).
ILIAC CREST GRAFT SITE RECONSTRUCTION
Several graft site techniques have been described to improve cosmesis and function and to potentially reduce the onset of chronic dysesthesias.
Malleable bone cement contoured to the void can be used, particularly when structural bone graft has been harvested (TECH FIG 5A).
Crushed allograft bone chips can also be packed into the ilium between the inner and outer table, allowing for bone reconstitution.
After filling the defect with allograft or demineralized bone matrix, malleable polymerized lactide sheets can be contoured to the defect to allow for reconstitution of the external iliac anatomy (TECH FIG 5B).
TECH FIG 5 • A. After bone graft harvest, cement can be molded to fit the void left from the harvest. B. A mesh sheet can be used to traverse the bone graft void to restore the crest.
COMPLICATIONS
Donor site pain is common after bone graft harvesting.
Most symptoms resolve within 3 months.
Chronic donor site pain persists beyond 3 months and can be debilitating.
Anteriorly, nerves at risk for injury include the lateral femoral cutaneous, ilioinguinal, and iliohypogastric.
Injury to the lateral femoral cutaneous nerve may give rise to meralgia paresthetica (paresthesias along the lateral thigh).
The ilioinguinal nerve may be injured when the abdominal wall is retracted medially from the anterior iliac crest. The nerve may be compressed beneath the retractor on the inner part of the wall of the ilium. Ilioinguinal neurologic injury is characterized by pain radiating from the iliac toward the inguinal and genital areas.
Posteriorly, nerves at risk for injury include the cluneal, superior gluteal, and sciatic.
The sciatic nerve may be injured when the dissection is extended down to the sciatic notch. A surgical instrument such as an osteotome may be passed deep to the sciatic notch to cause this injury. The bony rim of the notch should be palpated before the dissection is carried to this area.
Injury to the cluneal nerves gives rise to numbness to the buttocks or, more rarely, painful cluneal neuromas.
Injury to the superior gluteal artery is rare but may occur with bone graft harvesting too close to the sciatic notch, or via inappropriate placement of retractors or elevators.
If cut, the superior gluteal artery may retract into the pelvis.
If the superior gluteal vessel is lacerated, it can be compressed locally and exposed for ligation or clipping. A finger may be used to apply direct pressure to the vessel, against the bone.
If the bleeding vessel is still not accessible, the area should be packed and then accessed anteriorly via a retroperitoneal or transperitoneal approach.
Arterial occlusion by embolization or by use of a Fogerty catheter is another option.
The deep circumflex iliac artery, the iliolumbar artery, or the fourth lumbar artery may cause troublesome bleeding when working on the inner table of the ilium.
A hernia through the iliac bone graft donor site may occur after the removal of a full-thickness bone graft from that site. Symptoms may appear as an iliac swelling, sometimes associated with pain or symptoms of bowel obstruction. Strangulated hernia and valvulae are very rare occurrences.
Fracture
Removal of a large quantity of bone graft from the posterior ilium may disrupt the mechanical keystone effect of the sacroiliac joint and the posterior sacroiliac ligament, causing instability.
The ensuing instability transfers the stress forces to the pelvic ring, causing fractures of the superior and inferior pubic rami.
Patients with such instability may develop symptoms indistinguishable from other spinal disorders. History of clicking or thudding, as well as pain in the thigh and gluteal region, is characteristic.
Anteriorly, bone resection less than 3 cm from the ASIS may result in an avulsion fracture of the ASIS from the attached muscle groups (sartorius, tensor fascia lata).
The incidence of infection of the bone graft site ranges from 1% to 5%.
Careful subperiosteal dissection can limit hematoma formation. Hemostasis after bone graft harvesting with clotting agents (Gelfoam) should be used to limit hematoma formation.
The harvesting of tricortical grafts, particularly in thin patients, can result in a cosmetic deformity. Careful closure of fascial attachments should be performed to minimize soft tissue defects.
REFERENCES
1. Cowley SP, Anderson LD. Hernias through donor sites for iliac crest bone grafts. J Bone Joint Surg Am 1983;65A:1032–1035.
2. Ebraheim NA, Yang H, Lu J, et al. Anterior iliac crest bone graft: anatomic considerations. Spine 1997;22:847–849.
3. Kurtz LT, Garfin SR, Booth RE. Harvesting autogenous iliac crest bone grafts: a review of complications and techniques. Spine 1989; 14:1324–1332.
4. Robertson PA, Wray AC. Natural history of posterior iliac crest bone graft donation for spinal surgery: a prospective analysis of morbidity. Spine 2001;26:1473–1476.
5. Schnee CL, Freese A, Weil RJ, et al. Analysis of harvest morbidity and radiographic outcome using autograft for anterior cervical fusion. Spine 1997;22:2222–2227.
6. Silber JS, Anderson DG, Daffner SD, et al. Donor site morbidity after anterior iliac crest bone harvest for single-level anterior cervical discectomy and fusion. Spine 2003;28:134–139.