The Knee injury and Osteoarthritis Outcome Score reflects the severity of knee osteoarthritis better than the revised Knee Society Score in a general Japanese population

The purposes of this study were to examine population-based reference data for sex- and age-related differences between the 2011 revised Knee Society Score (KSS2011) and the Knee injury and Osteoarthritis Outcome Score (KOOS), to assess the correlation between those scores and radiographic knee osteoarthritis (OA), and to validate the use of the scores in a general Japanese population.

This cross-sectional study included 963 volunteers (368 males, 595 females; mean age: 54.7 years). Participants were classified into five subgroups by age: under 40, 40s, 50s, 60s, and over 70 years old. The KSS2011 and KOOS were determined using self-administered questionnaires. Weight-bearing radiographs of the bilateral knee were taken and graded according to the Kellgren–Lawrence (KL) scale. The mean KSS2011 and KOOS were compared among age groups. Correlations between the severity of knee OA and each score were assessed using multiple regression analysis.

The overall KSS2011 tended to gradually decrease with age. Most subscales of the KSS2011 did not show sex-related differences. Similarly, the overall KOOS and all its subscales steadily decreased by approximately 20 points per decade with age. Most subscales of the KOOS were significantly decreased in females over 50. The KL grade was significantly related to both the overall KOOS (β = −0.42, p < 0.001) and KSS2011 (β = −0.13, p = 0.001), though the correlation to the KOOS was stronger.

The overall KSS2011 and KOOS appear to decrease with age. In this population, the KOOS reflects the severity of knee OA better than the KSS2011.