Resident Physician Barrow Neurological Institute Phoenix, Arizona, United States
Introduction: 3D printed titanium cages have quickly become an implant of choice for spine surgeons due to complex porous features for bone ingrowth and greater surface area for minimizing subsidence. Surgeons are increasingly tempted to implant these cages without bone graft material, but strong supporting evidence still does not exist, and it is unclear how increased endplate surface area, resulting in a smaller graft aperture, influences fusion results. Here, we evaluate the effect of interbody endplate surface area and bone graft packing on spinal fusion.
Methods: Twenty-four levels of interbody fusion were performed in twelve adult sheep (L2-3 & L4-5) using 3D printed titanium interbody cages with bilateral pedicle screw fixation. Interbody cage designs evaluated had either a standard-aperture (low endplate surface area), small-aperture (medium endplate surface area), or no-aperture (high endplate surface area) packed with autologous iliac crest bone graft (ICBG). A fourth group was implanted without ICBG, utilizing the no-aperture cage. Fusions were evaluated at 16 weeks via manual palpation, microCT, and histology endpoints.
Results: Standard, small, and no-aperture cages packed with ICBG all resulted in strong fusion results (80%, 100%, and 83%, respectively) at 16 weeks by manual palpation, and these results were not significantly different. Implantation without ICBD resulted in a significantly lower fusion rate (33%, p< 0.05). Histological and microCT results supported those seen by manual palpation, with new bone bridging across the vertebral endplates for spines graded as fused by manual palpation.
Conclusion : Similar fusion results for standard, small, and no-aperture cage designs when packed with ICBG suggest that aperture size does not appear to influence fusion results in the sheep model. Significantly decreased fusion results when ICBG graft was not used suggests that graft material is necessary to predictably obtain fusion in this model.
