Objective Measure of Activity Level After Total Knee Arthoplasty with The Use of the ‘Fitbit’ Device

Abstract

Objectives: The commercial release of non invasive, light weight, low cost accelerometers has great potential to more accurately assess activity level before and after knee arthroplasty from a small light weight wrist strap. These devices have been shown to be valid and reliable assessment tools for activity levels in normal subjects. This study examines activity levels before and after knee arthroplasty using a modern commercially available accelerometer known as a “FitBit”. Methods: Observational Series. Subjects undergoing knee arthroplasty under the care of the senior surgeon were invited to participate and wear the accelerometer for 5-7 days at 4 times periods: before surgery, day 1-3, 6 weeks and 12 month after arthroplasty. Preoperatively and at 12 months after TKR subjects completed the Knee injury and Osteoarthritis Outcome Score (KOOS), WOMAC Assessment, and British Orthopaedic Association Patient Satisfaction Scale. Results: 54 subjects were recruited to the study over a 12 month period. Prior to total knee arthroplasty, the mean number of recorded steps per day was 6600. Post arthroplasty the mean number of steps per day was 1200 in the first 3 days, 5700 at 6 weeks and 7200 at 1 year. Preoperative activity level was significantly correlated with preoperative Pain Score (p=0.003). Activity level within the first 3 days after surgery was correlated with 6 weeks activity level (0.473, p=0.004), and 1 year activity level (0.593, p=0.02), but not 1 year KOOS scores. Conclusion: Modern accelerometers present a novel way to objectively measure activity level before and after knee arthroplasty. Preoperative activity level is significantly associated with post operative activity level. One year after knee arthroplasty the mean number of steps per day is 7200, and 50% of subjects taking more than 7000 steps per day, which is the recommended daily average for those age 65+ years.