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Arch Phys Med Rehabil. 2004 Jun;85(6):1026-30.

Computerized biofeedback knee goniometer: acceptance and effect on exercise behavior in post-total knee arthroplasty rehabilitation.

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  • 1Rehabilitation Institute of Chicago, 345 E. Superior Street, Rm. 1124, Chicago, IL 60611, USA.



To assess device accuracy, patient acceptance, and effect of a computerized biofeedback knee goniometer (CBG), on patients' compliance with active range of motion (AROM) exercises after total knee arthroplasty (TKA).


Two-stage study: measurement validation on asymptomatic controls and an unblinded, multiple crossover trial.


Inpatient rehabilitation.


Asymptomatic controls (n=14) and post-TKA inpatients (n=11).


For measurement validation, CBG-angle measurements were compared with manual, clinician-obtained angles. To assess motivational effect, the CBG was worn after TKA; on alternating days, it either monitored AROM silently (no feedback) or provided audiovisual feedback about reaching preset range of motion (ROM) goals and prompted the patients to exercise when idle.


To assess accuracy, the device's readings were compared with manual measurements. Patient satisfaction was determined by a self-report questionnaire; exercise compliance was assessed by calculating activity rate and stratified interactivity intervals.


CBG readings reproduced clinician measurements reliably between 0 degrees and 100 degrees (eta(2)=98.5%). Auditory feedback was more helpful than visual feedback for motivating exercise. During feedback-on days, the mean total activity rate +/- standard deviation was 15.1+/-10.9 activity counts per hour, and the interactivity interval was 6.7+/-5.7 minutes. The activity rate was higher on feedback-off days-22.5+/-11.1 counts/hour (P=.11)-and the mean interactivity interval was 3.6+/-2.7 minutes (P=.07).


The CBG provided reliable, unbiased estimates of clinician measurements of joint angle within the range of 0 degrees to 100 degrees. The CBG was accepted well by most patients. Surprisingly, slightly more ROM activity was noted during feedback-off days than feedback-on days.

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