Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.


Validity of Portable Devices To Assess Physical Activity in Patients with Total Knee Arthroplasty.

Almeida1,  Gustavo J. M., Brower2,  Kelly S., Celik2,  Derya, Chang2,  Hua-Chen, Piva1,  Sara R.

University of Pittsburgh, Pittsburgh, PA
University of Pittsburgh

Total knee arthroplasty (TKA) is one of the most successful surgeries to reduce pain, improve function, and health-related quality of life in end-stage knee osteoarthritis. Thus, patient expectations on having a more active lifestyle after surgery are increasing, and accurate/valid measures of physical activity (PA) are needed to monitor these changes. To date, there is limited information about the validity of portable PA monitors in patients after TKA. The aim of this study was to compare measures of energy expenditure (EE) given by the SenseWear armband (SWA) (Bodymedia, Pittsburgh, PA) and the Actigraph (ACT; Pensacola, FL), against measures of EE estimated by indirect calorimetry. In addition, we aimed at characterizing PA of patients with TKA measured by the SWA and ACT in a free-living condition.

EE (kcal/min) was estimated by indirect calorimetry (MedGraphics VO2000), and by the SWA and ACT simultaneously. Patients performed several standardized activities in a laboratory setting while concurrently wearing the SWA on the arm, the ACT on the waist, and the facemask of the indirect calorimeter. Each activity was performed during 7 minutes (see table). To characterize PA in a free-living condition, patients wore the SWA and ACT over 8 consecutive days. Pearson correlation or Spearman coefficients were calculated according to data distribution.

Table. Correlation coefficients between energy expenditure measured by indirect calorimetry and the Sensewear Armband (SWA) and the Actigraph (ACT)

 Indirect Calorimetry (kcal/min)
 Lying downSeating ReadingSeating TypingStanding TalkingStanding Moving ArmsMoppingUsual walkSlow walkFast walk
SWA (kcal/min)0.80**0.68**0.71**0.82§**0.4§*0.75**0.310.400.52*
ACT (kcal/min)0.63**0.60**0.46*0.61**0.330.170.76**0.67**0.68**
§Spearman's rho;
*p <= .05;
**p <= .01

21 patients, 14 females (67%), with unilateral TKA underwent one testing session. Mean age and BMI were 68±7 and 29±4 respectively; time after surgery was 3.3±0.3 years; and physical function measured by the Western Ontario and McMaster Universities Osteoarthritis Index 14.6±9.6, indicating only moderate functional limitations. During the standardized activities (Table) the correlations between EE measured by indirect calorimetry and SWA ranged from moderate to high (r=.31 to.82), and between indirect calorimetry and ACT they ranged from weak to high (r=.17 to.76). In a free-living condition, patients wore the SWA and ACT for 97% of the time each day (23:20hr/24hr). Daily values of physical activity EE (PAEE) measured by the SWA (145 [73–260]kcal/day) was lower than the one measured by the ACT (268 [222–281]kcal/day). The correlation between these two measures was weak (rho=.22, p=.37).

Results of correlations between measures from the portable PA monitors and indirect calorimetry support the validity of the SWA and the ACT to measure EE in patients with TKA in a laboratory setting. The SWA was more accurate in measuring EE during non-walking activities, whereas the ACT was more accurate in measuring EE during walking activities. Measures of PA EE given by the SWA and ACT in a free-living condition did not agree. When assessing EE in patients with TKA, it is essential to consider type of PA monitor to use according to type of activity performed. Studies comparing SWA and ACT to a reference standard measure of PA in free-living condition are warranted.

To cite this abstract, please use the following information:
Almeida, Gustavo J. M., Brower, Kelly S., Celik, Derya, Chang, Hua-Chen, Piva, Sara R.; Validity of Portable Devices To Assess Physical Activity in Patients with Total Knee Arthroplasty. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :2061
DOI: 10.1002/art.29826

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