Characterizing symptom burden in knee osteoarthritis: the predominant role of Kellgren-Lawrence grade 4 in functional decline and pain severity.

Knee osteoarthritis (KOA) causes pain, functional impairments, and sleep disturbances. This study aimed to assess differences in pain pattern, insomnia, function, and muscle strength across Kellgren-Lawrence grades in patients with KOA. In this cross-sectional study, 82 patients (65.8 ± 7.8 years) were categorized into Kellgren-Lawrence Grade 2 (n = 20), Grade 3 (n = 20), and Grade 4 (n = 42). Pain (VAS, ICOAP), insomnia (ISI), knee function (KOS-ADLS), functional performance (Timed-Up and Go [TUG], Five Times Sit-to-Stand [FTSST]), and isometric muscle strength were evaluated. Comparisons were performed using ANCOVA, adjusting for age and BMI. Groups differed significantly in age and BMI (p < 0.001 and p = 0.024), with higher values in Grade 4. Significant between-group differences were observed in VAS (p = 0.006), ICOAP-constant pain (p = 0.037), ICOAP-total pain (p = 0.035), TUG (p = 0.021), KOS-ADLS (p = 0.015), and quadriceps strength of the affected knee (p < 0.001) and hip adductor strength (p = 0.046). No significant differences were found for ICOAP-intermittent pain, ISI, or non-affected knee quadriceps strength (p > 0.05). Pairwise comparisons showed that Grade 4 patients had significantly worse outcomes than Grade 2 in VAS (p = 0.013), ICOAP-constant pain (p = 0.041), and total pain (p = 0.047), and TUG (p = 0.025), as well as reduced quadriceps strength of both affected (p < 0.001) and non-affected (p = 0.019) knees. Differences between Grades 2 and 3 were limited to VAS (p = 0.026), while Grades 3 and 4 differed only in KOS-ADLS (p = 0.022). Higher Kellgren-Lawrence grades were associated with greater pain, poorer function, and reduced quadriceps strength, particularly in Grade 4, emphasizing the clinical relevance of radiographic grading in characterizing symptom burden in KOA.