Introducing the Subjective Knee Value for Daily Activity (SKV–d) and Sport (SKV–s) as Single-Item Measures to Assess Knee Function in Athletes

Background: Patient-reported outcome measures (PROMs) are essential for assessing knee function; however, their complexity can hinder efficiency. The subjective knee value (SKV) offers a simple alternative, but lacks distinction between daily activities and sports. Purpose: We propose the SKV for daily activity (SKV-d) and sport (SKV-s). This study aimed to validate the SKV-d and SKV-s as simple and accurate tools for assessing knee function. Study Design: Cohort Study (Diagnosis); Level of evidence, 3. Methods: A total of 79 consecutive athletic patients (mean age, 39 years; 49% women) with knee-related issues were included and categorized into 4 groups between September and November 2024. PROMs were collected according to clinic standards: knee osteoarthritis (n = 21), Knee Society Clinical Rating System (KSS) (Knee Score and KSS Function), anterior cruciate ligament injury (n = 19), International Knee Documentation Committee subjective knee evaluation form (IKDC-S), patellar instability (n = 12), Kujala Anterior Knee Pain Scale (AKPS), and focal cartilage lesion or isolated meniscal tear (n = 27). Patients completed the SKV, SKV-d, and SKV-s, along with the validated scores mentioned above. Validity, reliability, floor/ceiling effects, and differences among the 3 single-item scores were assessed. Results: The SKV-s correlated strongly with the AKPS ( rs = 0.71), moderately with the IKDC-S ( rs = 0.64) and the KSS Knee Score ( rs = 0.45), and weakly with the KSS Function ( rs = 0.28). The SKV-d correlated moderately with the IKDC-S ( rs = 0.65) and the AKPS ( rs = 0.50), and weakly with the KSS Knee Score ( rs = 0.15) and the KSS Function ( rs = 0.22). The SKV strongly correlated with the SKV-s ( rs = 0.83) and the SKV-d ( rs = 0.81). The SKV-s was significantly lower than the SKV (46.8 ± 27.8 vs 66 ± 20.7; P < .001) and the SKV-d (46.8 ± 27.8 vs 73.7 ± 23.3; P < .001). The SKV-d was higher than the SKV (73.7 ± 23.3 vs 66 ± 20.7; P < .001). Reliability was good for the SKV (intraclass correlation coefficient [ICC], 0.80), the SKV-s (ICC, 0.86), and the SKV-d (ICC, 0.81), with no significant floor/ceiling effects except for the SKV-d. Conclusion: The SKV-d and SKV-s demonstrated acceptable validity with the SKV, the IKDC-S, and the AKPS, and were reliable, with significant differences between each other and the SKV. Both the SKV-d and the SKV-s may help distinguish between daily activities and sports and for assessing knee function in athletes; however, they should not replace commonly used PROMs.