A, Autologous bone graft obtained from anterior iliac crest. B, The Medtronic cage has a cylindrical hollow center and a flat superior surface. Inset: Lateral view of a Medtronic cage. C, Solis cage has 1 mm titanium spikes bilaterally on both inferior and superior surface. Inset: Lateral view of a Solis cage. D, Bioabsorbable, self-retaining cervical fusion cage, composite of an interbody fusion cage and two anchoring clips. Inset: Lateral and dorsal views and of assembled bioabsorbable, self-retaining cervical fusion cage. (Image provided by International Journal of Nanomedicine. From Cao L, Duan PG, Li XL, et al. Biomechanical stability of a bioabsorbable self-retaining polylactic acid/nano-sized B-tricalcium phosphate cervical spine interbody fusion device in single-level anterior cervical discectomy and fusion sheep models. Int J Nanomed. 2012;7:5875-5880.)