Implantable devices useful for creating bony fusion particularly in intervetebral spinal fusion. The device is formed of bone and has a body portion with an upper flange member and an opposite lower flange member extending from the body portion. The upper and lower flange members are at least partially demineralized to create a flexible ligament extending from the body portion. In one application, the body portion is inserted into a disc space and the flexible ligament is secured to vertebrae on either side of the disc space. Techniques are also disclosed for making the implantable devices and for inserting the implantable device into an intervertebral disc space to promote interbody fusion.