Flexion and extension radiographs will be obtained pre-operatively, at 6-months and 12-months after surgery. A CT scan will be obtained at 6 months, if fusion has occurred no CT is needed at 12 months, if fusion did not occur another computerized tomography (CT) scan will obtained at 12 months. From previous literature, successful fusion is defined as ≤2° of angular motion on lateral flexion and extension radiographs, the presence of bridging trabecular bone between the vertebrae being fused, and the absence of any radiolucent zones spanning more than 50% of the allograft surface. Two independent blinded radiologists will assess the radiographs. In the event of disagreement about fusion healing, a third independent reading will be obtained from a third radiologist.