Assessing the patient-specific functional scale's ability to detect early recovery following total knee arthroplasty

The Patient-Specific Functional Scale (PSFS) has received considerable attention over the last 2 decades; however, validation studies have not examined its performance in patients after total knee arthroplasty (TKA). The purpose of this study was to investigate the ability of the PSFS to detect change in patients post-TKA by comparing PSFS change scores with Lower Extremity Functional Scale (LEFS) and pooled impairment change scores. One hundred thirty-three patients participating in a post-TKA exercise class were assessed at their initial and discharge visits. Initial assessments occurred within 28 days of arthroplasty; follow-up assessments occurred within 80 days of surgery. At both assessments, participants completed the PSFS, LEFS, and the P4 pain measure, and their knee range of motion (ROM) and extensor strength were measured. The ability to detect change was expressed as the standardized response mean (SRM) and as a correlation between the PSFS change scores and 2 reference standards: (1) LEFS change scores and (2) pooled impairment change scores. The pooled impairment measure consisted of pain, ROM, and strength change scores. The SRMs were PSFS 4.60 (95% confidence interval [CI]=4.00, 5.36) for the PSFS and 2.28 (95% CI=2.04, 2.60) for the LEFS. The correlation between the PSFS and pooled impairment change scores was 0.12 (95% CI=-0.04, 0.25), and the correlation between the PSFS and LEFS changes scores was 0.18 (0.02, 0.34). The order of measure administration was not standardized, and fixed activity set does not reflect clinical application in many instances. The results suggest that the PSFS is adept at detecting improvement in patients post-TKA but that the PSFS, like other patient-specific measures, is likely to be of limited value in distinguishing different levels of change among patients.