Objectives: This study focused on the biomechanical implications of knee osteoarthritis (OA) and the association with pain. The plantar loading force distribution of the foot was determined and correlated to degenerative knee changes, function, pain intensity, and pain sensitization.
Method: Knee OA patients (n = 34) with moderate and mild knee pain were characterized and compared to matched controls (n = 16). The Plantar Foot Posture Index (FPI) and mean maximum plantar forces were determined by pressure-sensitive insoles. Pain intensity and function were assessed by the Western Ontario and McMaster Universities Arthritis Index (WOMAC) and the Brief Pain Inventory (BPI). Local knee pain sensitization was assessed by pressure pain thresholds (PPTs) from eight knee locations. Spreading sensitization was assessed by PPTs from two extra-segmental test sites. Temporal summation to repeated pressure stimulation (knee and extra-segmental stimulation) and conditioning pain modulation (CPM) were assessed, representing central pain mechanisms.
Results: The maximum force (MF) applied by the medial forefoot correlated to knee PPTs (r = 0.524, p < 0.001), CPM potency (r = 0.532, p < 0.001), and BPI (r = -0.325, p < 0.05) and WOMAC scores (pain r = -0.425, p < 0.01; stiffness r = -0.386, p < 0.01; function r = -0.378, p < 0.05). The MF applied by the medial hindfoot correlated negatively to scores on the FPI (r = -0.394, p < 0.01) and the Kellgren-Lawrence (K-L) grading scale (r = -0.330, p < 0.05). The MF applied by the medial forefoot correlated to extra-segmental PPTs (r = 0.554, p < 0.001) and the potency of CPM (r = 0.561, p < 0.0001). The MF applied by the lateral hindfoot correlated negatively to the PPT assessed extra-segmentally (r = -0.367, p < 0.05) and positively to CPM potency (r = 0.322, p < 0.05).
Conclusions: This study shows that mean maximum plantar foot force distribution in patients with painful knee OA is associated with specific pain mechanisms, function, radiological findings, and pain intensity.