Advances in Spinal Interbody Cages.

Since the late 1980s, spinal interbody cages (ICs) have been used to aid bone fusion in a variety of spinal disorders. Utilized to restore intervertebral height, enable bone graft containment for arthrodesis, and restore anterior column biomechanical stability, ICs have since evolved to become a highly successful means of achieving fusion, being associated with less postoperative pain, shorter hospital stay, fewer complications and higher rates of fusion when than bone graft only spinal fusion. IC design and materials have changed considerably over the past two decades. The threaded titanium-alloy cylindrical screw cages, typically filled with autologous bone graft, of the mid-1990s achieved greater fusion rates than bone grafts and non-threaded cages. Threaded screw cages, however, were soon found to be less stable in extension and flexion; additionally, they had a high incidence of cage subsidence. As of the early 2000s, non-threaded box-shaped titanium or polyether ether ketone IC designs have become increasingly more common. This modern design continues to achieve greater cage stability in flexion, axial rotation and bending. However, cage stability and subsidence, bone fusion rates and surgical complications still require optimization. Thus, this review provides an update of recent research findings relevant to ICs over the past 3 years, highlighting trends in optimization of cage design, materials, alternatives to bone grafts, and coatings that may enhance fusion.