Controlled clinical studies were conducted in 1983 and 1989 in two clinical sites. The study was published in Environmental Medicine in 1991. The study was performed to assess the effectiveness of QuadraBloc™ in reducing lower back and knee pain in 54 patients at both sites. The study was a double blind, randomized, cross over study, using both active MagnaBloc™s*tm and inactive MagnaBloc™s*tm and neither the patient nor doctor knew which was which. Subjects were treated with either the QuadraBloc™ or the dummy device on two separate occasions.