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Individual Patient-reported Activity Levels Before and After Joint Arthroplasty Are Neither Accurate nor Reproducible

Vaughn, Natalie H., MD; Dunklebarger, Mitchell F., BS; Mason, Mark W., MD

Clinical Orthopaedics and Related Research®: March 2019 - Volume 477 - Issue 3 - p 536–544
doi: 10.1097/CORR.0000000000000591

Background Patients often are asked to report walking distances before joint arthroplasty and when discussing their results after surgery, but little evidence demonstrates whether patient responses accurately represent their activity.

Questions/purposes Are patients accurate in reporting distance walked, when compared with distance measured by an accelerometer, within a 50% margin of error?

Methods Patients undergoing THA or TKA were recruited over a 16-month period. One hundred twenty-one patients were screened and 66 patients (55%) were enrolled. There were no differences in mean age (p = 0.68), proportion of hips versus knees (p = 0.95), or sex (p = 0.16) between screened and enrolled patients. Each patient wore a FitBitTM Zip accelerometer for 1 week and was blinded to its measurements. The patients reported their perceived walking distance in miles daily. Data were collected preoperatively and 6 to 8 weeks postoperatively. Responses were normalized against the accelerometer distances and Wilcoxon one-tailed signed-rank testing was performed to compare the mean patient error with a 50% margin of error, our primary endpoint.

Results We found that patients’ self-reported walking distances were not accurate. The mean error of reporting was > 50% both preoperatively (p = 0.002) and postoperatively (p < 0.001). The mean magnitude of error was 69% (SD 58%) preoperatively and 93% (SD 86%) postoperatively and increased with time (p = 0.001).

Conclusions Patients’ estimates of daily walking distances differed substantially from those patients’ walking distances as recorded by an accelerometer, the accuracy of which has been validated in treadmill tests. Providers should exercise caution when interpreting patient-reported activity levels.

Level of Evidence Level III, diagnostic study.

Department of Orthopaedics and Rehabilitation, Penn State Health, Milton S. Hershey Medical Center, Hershey, PA, USA

The research group (MWM) received funding from a departmental Penn State Orthopaedics Research Initiation Grant.

N. H. Vaughn, 30 Hope Drive, PO Box 859, EC089, Hershey, PA 17033, USA, email:

All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research® editors and board members are on file with the publication and can be viewed on request.

Clinical Orthopaedics and Related Research® neither advocates nor endorses the use of any treatment, drug, or device. Readers are encouraged to always seek additional information, including FDA approval status, of any drug or device before clinical use.

Each author certifies that his or her institution approved the human protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research.

Received June 22, 2018

Accepted November 13, 2018

© 2019 Lippincott Williams & Wilkins LWW
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