I completed a rotation at Wisconsin and they had excellent exposure to spine with Dr. Zdeblick and Anderson among others. They are given a great mix of autonomy on "bread and butter" and assisting with new cutting edge stuff (ie disk replacement) and more complex cases.

There is only one spine fellow and with 4+ faculty doing spine cases, there is little/no butting of heads over cases. Plus with Zdeblick being the co-editor of Master Techniques in Orthopaedic Surgery: Spine, you are learning from some of the best.