Background Pain and fatigue are frequent symptoms of osteoarthritis (OA). However, the exact mechanism causing these symptoms remains unclear. Inflammation is important in OA pathophysiology. Associations between inflammatory aspects and clinical outcomes have been found. However, mainly (contrast-enhanced) MRI was used to assess synovial inflammation in these studies. Using this method, inflammation is assessed in an indirect way (e.g. infrapatellar fat pad signal enhancement, synovial fluid effusion and thickening of synovial tissue). Conversely, histological assessment of synovial inflammation is regarded as the gold standard. Using this method, specific aspects of inflammation can be distinguished and rated for severity.
Objectives To evaluate the associations of inflammation-related histological parameters of the synovium with pain and fatigue in knee OA patients.
Methods Fifty-nine patients fulfilling ACR criteria for knee OA were recruited from two prospective studies1,2 and gave consent for synovial biopsy using a mini knee arthroscopy. Biopsies were taken from visually inflamed areas of the synovium. Tissue sections were histologically assessed for 1) number of synovial lining cells (absolute); 2) sub-synovial infiltration; 3) fibrin deposition; 4) vascularization; 5) fibrosis; and 6) perivascular edema (scores 0–3).3 Average scores across sections were calculated for each parameter and for all parameters together. These data were combined with longitudinal clinical data from the prospective studies (WOMAC pain, SF36 vitality; 0=worst – 100=best). Associations between individual inflammatory features and clinical outcomes over time were assessed with mixed model analyses.
Results Patient characteristics are shown in Table 1. Relatively mild levels of inflammation were found, in line with previous research (median 1.1 [95% CI 0.9–1.6]).3,4 Longitudinal data was available for 56 patients. Age, gender, BMI and time since symptom onset were no confounders. No significant associations were found between any histological parameter and pain or fatigue over time (Table 2).
Conclusions This is the first study to examine different parameters of histologically assessed synovial inflammation in knee OA patients and their associations with clinical outcomes over time. We were unable to identify individual inflammatory aspects which associate with pain or fatigue. Additional research is required to identify the underlying mechanism for pain and fatigue in OA.
Ann Rheum Dis 2011 70:1191–6.
Scand J Rheum 2011 40:225–31.
Clin Rheum 2010 29:1185–90.
Arthritis Rheum 2005 52:3492–501.
Disclosure of Interest None declared