Harvest of Autograft for Spinal Fusion

Overview: Historical and Current Autogenous Bone Graft Harvest

Historically, bone autograft, most commonly iliac crest bone graft (ICBG), has been the established gold standard method of achieving spinal fusion because it contributes directly to the regenerated bone. Autografts offer many benefits not seen in other sources of bone grafting (e.g., allograft, xenograft, synthetic substitutes, etc.), including reduced cost to the patient, no risk of disease transmission or antigenic recognition, and ideal histological compatibility. Important characteristics of successful bone grafting include rapid incorporation into host tissue and adequate structural support (if desired), both of which are affected by the type of bone and the source of the graft. Cortical bone grafting provides more structural support than cancellous bone, whereas cancellous bone grafts allow for more rapid vascularization and incorporation into the surgical site. When harvesting bone from the patient, these characteristics dictate both the site of autograft harvest and the method of harvesting. Additional consideration must be given to the region of the spine being fused. For instance, anterior cervical surgery could necessitate a wedge graft that has sufficient strength to withstand compressive forces, whereas a posterolateral lumbar fusion will only require morselized cancellous bone to promote arthrodesis.

Among the viable bone autografts, ICBG and local bone grafts from the donor surgical site are among the most commonly used autografts today and will be discussed in detail in this chapter. Additional autograft harvest sites such as fibula, tibia, and rib have been successfully employed in the past for a variety of reasons. These reasons typically involved the dimensions of the graft, ease of access (for instance, a rib graft during thoracotomy), and strength; however, with industry advancement autografts from these sites have largely been replaced by more suitable alternatives and are mostly of historical interest or for fringe use.

Fibular grafts involve resection of the junction of the middle and distal thirds of the fibula, with careful preservation of the periosteum, as well as surrounding structures such as the peroneal nerve and peroneal muscles ( Fig. 170.1 ). As previously mentioned, use of these grafts largely depended on their ease of access, length, and compressive strength owing to their high cortical bone content. In fact, in compressive strength testing, fibular grafts were shown to be 4.5 times as strong as either anterior or posterior ICBG because of their high cortical content. Unfortunately, this characteristic leads to a prolonged revascularization and incorporation phase, making them unfavorable autograft options in the setting of expandable cages and suitable fibular allograft. Free vascularized fibular grafts have been described, but are technically challenging with longer operative time and hospital stays, with use limited to patients at very high risk for nonunion. ^, Rib grafts, although easily accessible during thoracic spine operations, provide little biomechanical stability and poor vascularization unless resected with their respective artery, resulting in a technically advanced grafting procedure with no true advantage compared with more currently accepted grafting techniques. Tibia grafts were occasionally used in the past but are seldom used today because of the risk of tibia fracture after harvest.