title: Validation of a novel activity monitor in impaired, slow-walking, crutch-supported patients.
abstract: BACKGROUND
  A growing need in clinical practice of rehabilitation and orthopaedic medicine is for objective outcome tools to estimate physical activity. Current techniques show limited validity or are too demanding for routine clinical use. Accelerometer-based activity monitors (AMs) have shown promise for measuring physical activity in healthy people but lack validity in impaired patients.
  
  
  OBJECTIVE
  This study aimed to validate an accelerometer-based AM in impaired, slow-walking, crutch-supported patients after total joint arthroplasty (TJA).
  
  
  METHODS
  Shortly after TJA, patients who were safely mobilized with 2 crutches and 8 healthy participants completed a trial of different activities while wearing the AM on the lateral upper leg and being videotaped. Outcome variables (e.g., time walking, number of gait cycles, sit-stand-sit transfers) were compared to video recordings, and sensitivity, predictive value and mean percentage difference (MPD) values were calculated.
  
  
  RESULTS
  We included 40 patients (mean age: 65±9 years; mean BMI: 30±6kg/m2; male:female ratio: 18:22) and 8 healthy participants (mean age: 49±20 years; mean BMI: 23±0.7kg/m2; male:female ratio: 5:3). The AM showed excellent sensitivity (>95%) and predictive value (>95%) in identifying activities (e.g., walking, sitting, resting) and detecting the number of gait cycles and sit-stand-sit transfers (mean percentage difference: ±2%). Detection of number of steps ascending and descending stairs and cadence was more difficult but still showed good results (mean percentage difference: ±7%).
  
  
  CONCLUSIONS
  This is the first validation study to assess physical activity with an AM in impaired, slow-walking, crutch-supported patients. The AM was a valid tool for measuring physical activity in these patients. The tool may help in evaluating and optimizing rehabilitation programs for patients after TJA, those recovering from stroke or chronic impaired patients.
authors.affiliation: Department of orthopaedics, Atrium medical center Heerlen, 5, Henri Dunantstraat, 6419PC Heerlen, The Netherlands. Electronic address: simon_van_laarhoven@hotmail.com.
authors.forename: Simon N
authors.initials: SN
authors.lastname: van Laarhoven
authors.affiliation: Department of orthopaedics, Atrium medical center Heerlen, 5, Henri Dunantstraat, 6419PC Heerlen, The Netherlands.
authors.forename: Matthijs
authors.initials: M
authors.lastname: Lipperts
authors.affiliation: Department of orthopaedics, Atrium medical center Heerlen, 5, Henri Dunantstraat, 6419PC Heerlen, The Netherlands.
authors.forename: Stijn A A N
authors.initials: SA
authors.lastname: Bolink
authors.affiliation: Department of orthopaedics, Atrium medical center Heerlen, 5, Henri Dunantstraat, 6419PC Heerlen, The Netherlands.
authors.forename: Rachel
authors.initials: R
authors.lastname: Senden
authors.affiliation: Department of orthopaedics, Atrium medical center Heerlen, 5, Henri Dunantstraat, 6419PC Heerlen, The Netherlands.
authors.forename: Ide C
authors.initials: IC
authors.lastname: Heyligers
authors.affiliation: Department of orthopaedics, Atrium medical center Heerlen, 5, Henri Dunantstraat, 6419PC Heerlen, The Netherlands.
authors.forename: Bernd
authors.initials: B
authors.lastname: Grimm
mesh_terms: D061725:Accelerometry / Q000295:instrumentation* / Q000379:methods; D000328:Adult; D000368:Aged; D019643:Arthroplasty, Replacement / Q000534:rehabilitation*; D016022:Case-Control Studies; D003446:Crutches; D015444:Exercise; D005260:Female; D006801:Humans; D007866:Leg / Q000502:physiology; D008297:Male; D008875:Middle Aged; D011187:Posture / Q000502:physiology; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016138:Walking / Q000502:physiology*
keywords: Activity monitor; Arthroplasty; Outcome assessment; Physical activity; Rehabilitation