Clinical Evaluation of Fortilink® TETRAfuse® Interbody Fusion Device in Subjects With Degenerative Disc Disease

Inclusion Criteria: * The subject is skeletally mature and at least 18 years of age. * The subject has degenerative disc disease (DDD) of the cervical spine with accompanying radicular symptom at one or two contiguous levels (Fortilink-C), or the subject has DDD and ≤ Grade 1 spondylolisthesis of the lumbar spine at one or two contiguous levels (Fortilink-TS and Fortilink-L). * Subject plans to undergo one of the following procedures: An anterior cervical interbody fusion at one to two continuous levels from C2-C3 to C7-T1 using autogenous or allogenic bone graft and supplemental fixation cleared and indicated for use at the proposed treatment level(s) (Fortilink-C), or An interbody fusion in the lumbar spine at one to two continuous levels from L1-L2 to L5-S1 using autogenous or allogenic bone graft and supplemental fixation cleared and indicated for use at the proposed treatment level(s) (Fortilink-TS and Fortilink-L). * The subject has undergone non-operative treatment of at least six weeks (Fortilink-C) or at least six months (Fortilink-TS and Fortilink-L) prior to treatment with the IBF system. * The subject is willing and able to provide informed consent. * The subject is willing and able to attend the protocol required follow-up visits and examinations. Exclusion Criteria: * The subject has an active infection * The subject has had prior fusion attempt(s) or is undergoing revision of a previously implanted system at the involved level(s). * The subject is a worker's compensation case, in active litigation related to the procedure or is a prisoner or ward of the state. * The subject meets one or more of the contraindications outlined in the IFU. * The subject is pregnant, nursing, or is planning to become pregnant in the next year. * The subject has documented evidence of current substance abuse. * The subject has other concurrent medical condition that, in the opinion of the investigator, does not make the subject a good candidate for the study.