Knee adduction moment associates with pain irritability and frequency in people with severe radiographic knee osteoarthritis

BACKGROUND: Pain irritability is the change in pain intensity after a task. The primary purpose was to determine the associations of knee adduction moment (KAM) with pain irritability and frequency in knee osteoarthritis, across varying radiographic severities. The secondary purpose was to compare pain measures between severities. METHODS: 93 adults with clinical knee osteoarthritis (59 females, 34 males) participated. Kellgren-Lawrence grades (doubtful, mild, moderate, severe) were scored from x-rays acquired in a standardized weight-bearing position. The external KAM peak (Nm/kg) and impulse (Nm•s) were computed from kinematic and kinetic data from 10 barefoot walking trials at a self-selected speed. Pain measures included frequency and intensity from the Intermittent and Constant Osteoarthritis Pain (ICOAP) questionnaire. Pain irritability was the change in intensity on the Numeric Pain Rating Scale from before and after walking six minutes. Regression analyses evaluated the association of KAM with pain measures for each radiographic severity. Pain measures were compared between severities. FINDINGS: In severe, KAM impulse was positively associated with ICOAP constant pain (p = 0.035) and intermittent pain (p = 0.044). KAM impulse was not associated with any pain measure in other radiographic severity groups. Peak KAM was not associated with pain measures. Pain irritability was greater in severe compared to both mild (p = 0.004) and doubtful (p = 0.019) severities of knee osteoarthritis. INTERPRETATION: Greater loading of the medial knee during walking was associated with constant and intermittent pain in severe radiographic knee osteoarthritis. Pain irritability was higher in severe compared to mild disease.