Background The level of radiographic knee osteoarthritis (OA) is only moderately associated with the level of pain. As OA is a disease of the entire joint, ultrasonography (US) of cartilage and soft tissue structures might provide more insight in the complex process of pain in knee OA(1).
Objectives To investigate the cross sectional association between US findings and pain in knee OA.
Methods A single centre cross sectional observational study was performed. A total of 180 patients fulfilling the American College of Rheumatology clinical criteria for knee OA underwent US examination of the most symptomatic knee. The previously validated US protocol (2) comprised inflammatory (synovial hypertrophy, joint effusion, infrapatellar bursitis and Baker’s cyst), and mechanical aspects(medial meniscus protrusion, cartilage thickness). On inclusion, clinical data, data on pain (Knee injury and Osteoarthritis Outcome Score (KOOS) and Numerated Rating Scale (NRS) and knee X-rays were collected. Correlations between the different US features were tested. To evaluate the association between US features and pain, regression analysis was performed.
Results The study participants were predominantly female (67%). Mean age was 57 ± 9.2 years and the predominant Kellgren and Lawrence score was II (0-IV). The mean NRS was 6.1± 1.7 indicating moderate to high pain levels. The US findings were: (n,%): joint effusion : 30 (16.7%), synovial hypertrophy: 37 (20.6%), meniscal protrusion: 111 (61.7%), infrapatellar bursitis 10 (5.6%) Baker’s cyst: 47 (26.1%). Cartilage thickness measures were (mean, SD) 1.75 (0.56) mm, 2.26 (0.67) mm and 1.86 (0.50) mm respectively. Small statistically significant associations among US features were found for the three measures of cartilage thickness (r:0.45-0.50) and between synovial hypertrophy and joint effusion (V: 0.18). Regression analysis showed no association between US features and the level of knee pain. Post hoc analyses for inflammatory and mechanical symptoms yielded the same results.
Conclusions In this cohort of 180 patients with painful knee OA no association between US features and the level of knee pain was found.
The results in this study are in line with limited previous research, that also failed to demonstrate a robust cross sectional association between US features and the level pain in knee OA, although some differences between patients with and without knee pain in OA have been found. This cohort somewhat distinguishes itself from other cohorts in relatively high pain levels and moderate radiological damage. Longitudinal extension of the study will further assess whether US features can be predictive for future signs and symptoms of knee OA, and what the course is of US abnormalities in knee OA.
Keen HI, Wakefield RJ, Conaghan PG: A systematic review of ultrasonography in osteoarthritis. Ann Rheum Dis 2009; 68(5):611-9.
Bevers K, Zweers MC, van den Ende CH et al.: Ultrasonographic analysis in knee osteoarthritis: evaluation of inter-observer reliability. Clin Exp Rheumatol 2012; 30(5):673-8.
Disclosure of Interest None Declared