Where does it hurt? Pain localization in osteoarthritis of the knee

To identify the most common sites of pain in symptomatic knee osteoarthritis (OA) and to investigate clinical, radiographic and psychosocial associations of pain occurring in different locations.

Sixty-eight outpatients with knee OA were interviewed in detail about their knee pain. Location of pain was recorded on a standard drawing of the knee. Validated instruments were used to measure pain severity, function, depression, anxiety, quality of life, fatigue, helplessness, self efficacy. Pain threshold was measured by dolorimetry and a knee examination performed. Radiographs (anterioposterior and lateral) were viewed if available.

Most (85.3%) patients reported either 'generalized' (N = 35, 51.5%) or 'medial' (N = 23, 33.8%) knee pain. There were no differences between groups in pain severity, demographic or psychosocial variables, pain threshold or radiographic location or severity. However, function was significantly worse in the 'generalized' group (WOMAC function score 48.9 +/- 20.8 vs 34.2 +/- 22.3; P = 0.01): this remained significant after adjustment for potential confounding factors. The difference in function was most marked for activities involving knee bending. Early morning stiffness was also greater in the generalized group.

Knee pain is not the same in all individuals with knee OA, confirming the heterogeneity of the condition. Location of pain is usually either generalized or medial. Patients with these patterns do not differ in demographic, radiographic or psychosocial variables but important differences in functional ability can be detected, suggesting differences in the underlying causes of pain and disability between the two groups.