Interbody fusion cages

A method for enhancing spinal fusion in adjacent vertebrae of a patient through maximal bone graft material placement, the method comprising:

• providing an implant device for interbody fusion of lumbar or cervical vertebrae, the implant device comprising:
• a unibody cage structure having an enveloping cage volume and a minimized material volume, the cage structure comprising
• a first and a second generally planar ring member, each ring member formed from an opposing pair of lengthwise joists and an opposing pair of cross joists, the joists together forming a large opening through the ring member,
• the ring members fixedly sandwiched on a plurality of support members, the support members holding the ring members in a spaced apart relationship to thereby provide a large void volume relative to the enveloping cage volume, to thereby allow for receipt of a large volume of bone graft within the cage structure,
• wherein a ratio of the void volume to the enveloping cage volume is between about 0.7 to about 0.9;
• and
• inserting the implant between said adjacent vertebrae of said patient.