The subjective knee value is a valid single-item survey to assess knee function in common knee disorders

Introduction: The patient’s perspective plays a key role in judging the effect of knee disorders on physical function. We have introduced the Subjective Knee Value (SKV) to simplify the evaluation of individual’s knee function by providing one simple question. The purpose of this prospective study was to validate the SKV with accepted multiple-item knee surveys across patients with orthopaedic knee disorders. Materials and methods: Between January through March 2020, consecutive patients (n = 160; mean age 51 ± 18 years, range from 18 to 85 years, 54% women) attending the outpatient clinic for knee complaints caused by osteoarthritis (n = 69), meniscal lesion (n = 45), tear of the anterior cruciate ligament (n = 23) and focal chondral defect (n = 23) were invited to complete a knee-specific survey including the SKV along with the Knee Injury Osteoarthritis Outcome Score (KOOS) and the International Knee Documentation Committee subjective knee form (IKDC-S). The Pearson correlation coefficient was used to evaluate external validity between the SKV and each patient-reported outcome measure (PROM) separately. Furthermore, patient’s compliance was assessed by comparing responding rates. Results: Overall, the SKV highly correlated with both the KOOS (R = 0.758, p < 0.05) and the IKDC-S (R = 0.802, p < 0.05). This was also demonstrated across all investigated diagnosis- and demographic-specific (gender, age) subgroups (range 0.509–0.936). No relevant floor/ceiling effects were noticed. The responding rate for the SKV (96%) was significantly higher when compared with those for the KOOS (81%) and the IKDC-S (83%) (p < 0.05). Conclusion: At baseline, the SKV exhibits acceptable validity across all investigated knee-specific PROMs in a broad patient population with a wide array of knee disorders. The simplified survey format without compromising the precision to evaluate individual’s knee function justifies implementation in daily clinical practice. Level of evidence: II, cohort study (diagnosis).