sentences:  A better understanding of facet function and facet-mediated pain, possibly through classification of facet degeneration, may be needed to support the use of such devices.More recently, an August 2014 critique in the journal "Neurosurgery" has suggested that research aside, at least in the United States the regulatory process has led to "time lag inherent in the design, development and implementation of new technologies" such as artificial facet replacement, noting that both ACADIA and TOPS were still not FDA-approved within the U.S.In the short-term, study literature has provided "insufficient support" for the prosthesis, with pessimal results for the procedure.