2. In what sense does these devices differ from the Wagner Resurfacing procedure?

The poor results of Wagner resurfacing are mainly caused by poor performing bearing couples (metal-on-poly, or ceramic-on-poly). Not by the resurfacing procedure itself. The main problem with young and/or active patients was the wear of polyethylene. Especially in the case of the Wagner prosthesis with a big metal head on a thin polyethylene socket, the wear is increased by a factor 4 to 10.