Recently MIT and Harvard have conducted studies of Mexican Indians who run 60 miles a day wearing nothing more than leather sandals. Studies found that these runners have a reduced amount of injuries than runners who run significantly less miles per week.
The reason for this reduction and injuries was not related solely to the fact that they were running barefoot. However the biomechanics required to run barefoot is what reduces the injuries.
Therefore if you are running in one of the newly designed barefoot running shoes, I would strongly recommend that you learn the technique of barefoot running prior to returning to your normal running distance.
Without changing your technique you will incur a whole host of new injuries. However, if done properly, this technique will reduce the stress and strain of your joints, and in particular with arthritic knees, allow you to run more comfortably.
The brand Newton will allow you to gradually transition to barefoot running.