The Use of Interbody Cage Devices in the Lumbosacral Spine

Abstract

Interbody devices are aimed to restore disc height, place annular fibers in a normal tension, create sagittal balance, reduce facet joints subluxation, enlarge neuroforaminal space, and maintain a normal weight-bearing proportion through the anterior column. There is no convincing evidence from controlled studies, however, to show that correcting the mechanical deformation is actually associated with symptomatic relief of back pain in patients who have such devices implanted. An inherent problem with cylindrical designs is that the lateral width of a paired cage construct is at least double the cage height, and the distractive height is limited without destruction of the facet joint. Cage bed preparation requires endplate integrity preserved and bleeding bone exposed to the graft material. The 30-50% higher compressive strength for central rather than for peripheral trabecular bone adapts to the shifts in axial load. Before solid arthrodesis, micromotion through the segment is unavoidable and particulate debris results in release of mediators and subsequent loosening of the device-bony interface. Pedicle screw, translaminar screw or transfacet screw fixation substantially improves stabilization. Adverse conditions, such as a small-sized cage, inadequate seating, total facetectomy, a lack of posterior instrumentation and infection, can cause migration of interbody devices. Surgeons cannot rely on the cage material/biomechanical properties to overcome failed arthrodesis, and must strive for the optimal milieu of fusion. Although early research into alternative biomaterials for cage technology is promising, the optimal cage stiffness and the desired period over which the cage will biodegrade remain unknown.