INTERVERTEBRAL SPACER AS AN ADJUNCT TO ANTERIOR LUMBAR FUSION - PART I - DESIGN, FABRICATION, AND TESTING OF 3 PROTOTYPES

Failure of anterior lumbar fusions are common, because the bone graft is required to provide mechanical stability during creeping substituti on and replacement with host bone. Support of the interspace with mesh , cages, plates, and rods results in an improved rate of fusion. The o bjective of this study was to develop an anterior interbody implant to stabilize adjacent vertebral segments during spinal fusion. Three pro totypes of an intervertebral spacer for anterior lumbar stabilization were designed, fabricated, and tested in vitro. The implants were inse rted vertically between adjacent vertebral bodies in fresh frozen cada ver swine and baboon spines after disc excision and vertebral body pre paration. 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 b ending cyclic fatigue testing of the porous coated cylindrical implant s (prototype 3) showed a maximum strength of 9,700 N in axial compress ions. Analysis of the motion profiles at the site of implantation conf irmed less axial displacement at the implant level compared with the u ninstrumented levels above and below, but similar torsional displaceme nts. Biomechanical testing of the three prototypes of anterior implant s as well as radiographic, microstructural, and motion analysis confir med implant stability and structural integrity in vitro. Based on thes e findings, implantation of a porous coated implant in baboons was und ertaken as described in Part II (Nasca et al., this issue).