Association of Chronic Pain with Radiologic Severity and Central Sensitization in Hip Osteoarthritis Patients

Purpose: Pain and joint deformity are the most common symptoms of hip osteoarthritis (OA). However, no significant association between pain and severity of radiographic lesions has been reported. Recently, central sensitization has been suggested as an underlying mechanism of pain in OA. We investigated the involvement of radiologic severity or central sensitization in the clinical manifestation of hip OA with various degrees of joint deformity. Patients and Methods: We included 39 patients with hip OA and divided them into two groups according to the severity of the hip pain: strong/severe (numerical rating scale, NRS >= 6) and mild/moderate (NRS<6). We assessed the radiologic severity of OA using the Kellgren-Lawrence (K-L) scale and minimum joint space width (mJSW). We conducted quantitative sensory testing (QST) that included pressure pain threshold (PPT) and temporal summation of pain (TSP) at hip, tibialis anterior (leg), and extensor carpi radialis longus (arm) on the affected side. We examined the difference of radiologic assessment and QST results between each group and the correlation of the NRS with the radiologic assessment and QST results. Results: There was no significant difference in the K-L scale and mJSW between patients with strong/severe and mild/moderate joint pain. Strong/severe pain patients demonstrated a lower PPT at all measurement sites and higher TSP at the hip and leg than the mild/moderate pain patients. In addition, NRS was significantly negatively correlated with PPT and positively correlated with TSP at all measurement sites, but not with the K-L scale and mJSW. Conclusion: We reported no significant difference in radiologic severity between patients with strong/severe and mild/moderate joint pain. By contrast, we found a significant difference in central sensitization represented by QST between strong/severe and mild/moderate joint pain groups. These results suggest that central sensitization may be involved in the joint pain of patients with hip OA who complain of severe pain despite less severe joint deformity.