Correlation of the squat-and-smile test against other patient-reported outcome scores in knee pathology

Abstract

Background The use of patient-reported outcome measures (PROMs) for knee pathology may be affected by socioeconomic factors, language barriers and time constraints in busy outpatient clinics. The squat-and-smile test (SST) is an example of such a test that has previously been validated for femur fractures. The aim of this study was to validate the SST against other PROMs in patients with knee pathology. Methods Patients presenting to a subspecialist knee clinic in a large hospital in sub-Saharan Africa were approached to participate. They were asked to squat and the depth of the squat as well as the need to support themselves were classified into four categories. To describe their pain, participants also selected one of three smiley faces (unhappy, neutral, smiling). These test scores were correlated to the patient’s Knee injury and Osteoarthritis Outcome Score (KOOS), Tegner Lysholm score and EQ-5D scores. Results Seventy patients (median age 53.4 years) were included. The squat depth correlated moderately with the KOOS score (r=0.56) and poorly with the EQ-5D and Lysholm scores (r=0.46; r=0.43). The need for squat support had poor correlations with the KOOS, EQ-5D and Lysholm scores (r=0.29; r=0.31; r=0.31), as did the smiley face component (r=0.40; r=0.32; r=0.30). Conclusion For patients with knee pathology, the squat depth correlates moderately with other PROMs. It could therefore be used in settings for which conventional PROMs have limited application. Support needed to squat, and a visual analogue scale of smiley faces, had poor correlation when compared to other knee PROMs and should not be used for the assessment of knee pathology.