 The objective of the KAROS study is to compare rehabilitation outcomes between 3 proposed protocols and a current standard of care protocol for the purpose of identifying better practice for outpatient rehabilitation among patients with single total knee replacement. The 3 advanced protocols involve use of an anti-gravity treadmill andor the patterned electrical neuromuscular stimulation PENS. Both medical modalities have been cleared by the FDA to be used in medical rehabilitation, including total knee replacement. 