This trial is being conducted at five centres in Spain by the Banc di Sang I Teixits and seeks to investigate whether the patient’s own stem cells can assist in recovery following back surgery. Participants with L4-5 spinal degenerative disease requiring fusion surgery will be assigned to either the control group where they will receive a bone graft during surgery, or the treatment group where they will receive their own mesenchymal stem cells. The stem cells will be collected from the patient’s bone marrow and expanded in the laboratory before they are used. Participants will be assessed for complications following treatment and for improvements in their condition using standard tests including radiography and tomography as well as a subjective patient symptom and disability scores. The trial is expected to enrol 62 patients and be completed by November 2014.