Max Aebi & Robert Gunzburg 
Arthroplasty of the Spine [PDF ebook] 

Joint replacement is a logical step in the treatment of severe joint pathologies with irreversible lesions resisting conservative therapy. At the spinal level, arthrodesis became, very early, the gold standard of treatment for severe intervertebral disc pathologies. The next logical step was to envision functional replacement, and this step was taken as early as 1956, when the first intervertebral implant was described. However, it took many more years and a great variety of proposed implant designs before clinical applications could be attempted.