Outcomes of Allogenic Cages in Anterior and Posterior Lumbar Interbody Fusion
Spine arthrodesis is a generally accepted procedure for the management of patients with a variety of spinal disorders. The primary goal for spine fusion is to eliminate the instability of the spine, often caused by trauma, deformity, tumor, inflammation or infection, and common degenerative deterioration of the motion segments. In many clinical situations, the optimal solution in restoring the spine's integrity is through surgical intervention. There are many techniques of spinal fusion applicable to the lumbar spine. Posterior (PLIF) and anterior lumbar interbody fusion (ALIF) have been developed and employed to address these concerns alone or in combination with various internal fixation devices. The anterior column is often reconstructed with metallic intervertebral cages or biological implants (allografts or autograft bone) [16,31].
The success of every spine fusion procedure depends on the phenomenon of bone healing. Whether the healing process occurs depends on many factors, including the type of biological graft, host factors, technique, and the rigidity of the particular surgical construct. Bone grafts serve two main functions: they provide for the synthesis of new bone originating from the host cells (osteogenesis), and they can serve as mechanical/structural support . Graft bone cells have been shown to survive initial transplantation if properly handled to synthesize new bone.
Many studies have compared allografts with autografts in spinal arthrodesis for a variety of pathologic conditions. In adults, autografts are generally superior to allografts for achieving bone fusion. However, under certain circumstances, it may be advantageous to use an allograft. The usage of a structural allograft precludes the need for harvesting a graft from the patient and eliminates morbidity associated with donor site complications . These complications may include infection, pain, blood loss, secondary fracture, instability at the donor site, and possible neural damage. A recent retrospective study involving the Smith-Robinson technique compared the results of fibular allograft interbody fusions in 23 patients with tricortical iliac autograft fusions in 25 patients [5,17]. The results indicate that there was no significant difference in the fusion rates in autogenic bone grafting compared with allogenic bone grafting.
Preservation techniques can maintain the graft's mechanical properties and its ability to stimulate osteogenesis while eliminating its antigenicity . Frozen allografts are still somewhat immunogenic. Revascularization and remodeling are delayed compared with fresh autografts, but resorption and osteoconduction occur more rapidly and completely in these grafts. Freeze-drying reduces the immunogenicity of allografts even more, but alters their mechanical properties, resulting in a weaker structure. Although the initial inflammatory stage is diminished after transplantation of frozen or freeze-dried allografts, resorption and ultimately new bone formation will occur slowly.
This paper aims to provide a review of the two newly developed biological cages, the femoral ring allograft (FRA) spacer and the posterior lumbar interbody fusion (PLIF) spacer (Fig. 1). To aid in the understanding of the clinical outcome of these devices, this paper will review the biomechanics, development, and the screening process of these unique "biological cages."
Figure 1. Femoral ring allograft (FRA) and posterior lumbar interbody fusion (PLIF) spacers.