Development of a Patient-Reported Measure of Function of the Knee.

Irrgang J J, Snyder-Mackler L, Wainner RS, et al (Department of Physical Therapy, School of Health and Rehabilitation Sciences and Department of Orthopaedic Surgery, School of Medicine, University of Pittsburgh, Pittsburgh, Pa; Department of Physical Therapy, University of Delaware, Newark, Del), J Bone Joint Surg Am. 1998;80:1132-1145.

The Knee Outcome Survey was developed as a patient-reported instrument for measuring the functional limitations experienced by individuals with various knee pathologies. The survey consists of 2 separate scales: the Activities of Daily Living Scale and the Sports Activity Scale. The purpose of this study was to assess the psychometric properties of the Activities of Daily Living Scale and, specifically, to determine its test-retest reliability, internal consistency, concurrent and construct validity, and responsiveness.

Two global measures of function and the Lysholm Knee Scale were used as concurrent measures of the construct measured by the Activities of Daily Living Scale. Data were collected from 397 patients who were referred to 9 different physical therapy clinics for evaluation and treatment of the knee over a 1-year period. Subjects consisted of 213 men and 156 women; the sex of the remaining 28 subjects was not recorded. Subjects ranged in age from 12 to 76 years (the mean and median ages were 33.3 years and 30.3 years, respectively). The median interval between the injury and the referral was 65 days (range=1 day to 26.5 years). The scale was completed by 67% (266) of the patients at 1 week of therapy, by 55% (218) of patients at 4 weeks of therapy, and by 45% (179) of the patients at 8 weeks of therapy. A second sample of 52 patients from 2 of the original 9 clinics was recruited for the assessment of test-retest reliability before and after treatment within the same day. All data were entered into a database for analysis.

Two dominant factors emerged from factor analysis: factor 1 represented a combination of symptoms and functional limitations, and factor 2 represented only symptoms. The internal consistency of the Activities of Daily Living Scale with its smaller standard error of measurement (coefficient alpha=0.92 to 0.93), was higher than that for the Lysholm Knee Scale (coefficient alpha=0.60 to 0.73). Validity was revealed by moderately strong correlations with the concurrent measures of function, including the Lysholm Knee Scale (r=0.78 to 0.86) and the global assessment of function as measured on a scale that ranged from 0 to 100 points (r=0.66 to 0.75). The 1-way repeated-measures ANOVA revealed significant improvement in the score on the Activities of Daily Living Scale during the 8 weeks of physical therapy. A post hoc Scheffe test indicated that the mean change in score at 8 weeks was significantly greater than that at 4 weeks and that the mean change in score at 4 weeks was significantly greater than that at 1 week. Patients who said the knee was somewhat improved had a significantly smaller change in the score, compared with those who said that it was greatly improved, both at 4 weeks and at 8 weeks. Test-retest reliability, as indicated by intraclass correlation coefficient (2,1), was 0.97.

Based on the results of this study, the authors concluded that the Activities of Daily Living Scale can be used to assess functional limitations resulting from a variety of pathologies affecting the knee. According to the researchers, the scale appears to be valid, reliable, and responsive for the measurement of function related to pathological disorders and impairments of the knee. However, they indicated that additional testing is needed to demonstrate the test-retest reliability of the scale over a longer time period and to determine the usefulness of the scale for other patient groups.

Eugene Pavone, PT Spring Valley, NY