Lumbar spine fusion. Artwork of pins and screws inserted into a patient's lumbar spine in a case of spinal fusion. The pins hold together the patient's vertebrae. This may be done in cases of fractured vertebrae to allow them to heal, but in this case it is being done because the spine is degenerating. Degenerative disc disease is where the intervertebral discs have degenerated. Removing these and allowing the vertebrae to fuse reduces mobility but also removes the pain. Screws and pins are used to fix the vertebrae in place while they fuse.