Intervertebral spacer as an adjunct to anterior lumbar fusion. Part I. Design, fabrication, and testing of three...

Failure of anterior lumbar fusions are common, because the bone graft is required to provide mechanical stability during creeping substitution and replacement with host bone. Support of the interspace with mesh, cages, plates, and rods results in an improved rate of fusion. The objective of this study was to develop an anterior interbody implant to stabilize adjacent vertebral segments during spinal fusion. Three prototypes of an intervertebral spacer for anterior lumbar stabilization were designed, fabricated, and tested in vitro. The implants were inserted vertically between adjacent vertebral bodies in fresh frozen cadaver swine and baboon spines after disc excision and vertebral body preparation. In vitro cyclic testing of the three prototypes implanted in porcine and baboon spines to 100,000 cycles showed no displacement of the implant at 560-N axial and 16-Nm torsional loading. Three-point bending cyclic fatigue testing of the porous coated cylindrical implants (prototype 3) showed a maximum strength of 9,700 N in axial compressions. Analysis of the motion profiles at the site of implantation confirmed less axial displacement at the implant level compared with the uninstrumented levels above and below, but similar torsional displacements. Biomechanical testing of the three prototypes of anterior implants as well as radiographic, microstructural, and motion analysis confirmed implant stability and structural integrity in vitro. Based on these findings, implantation of a porous coated implant in baboons was undertaken as described in Part II (Nasca et al., this issue).