Table 2 ∣.
Risk factors and activators of synovial inflammation in OA
| Risk factor or activator |
Clinical relevance | Ref. |
|---|---|---|
| Obesity | Patients with obesity have a higher prevalence and severity of synovial inflammation assessed by conventional MRI | 25 |
| T2DM | Higher rates of ultrasonography-detected synovitis and effusion in patients with T2DM with end-stage knee OA who underwent arthroplasty compared with patients without T2DM, independent of patient BMI | 139 |
| Metabolic endotoxaemia | The presence of LPS in both plasma and synovial fluid from patients with OA correlates with the presence of activated macrophages in the joint capsule and synovium, radiographic severity (by 99mTc-EC20 SPECT–CT), and total WOMAC score | 158 |
| Microbiome — increased intestinal permeability and endotoxaemia | Pro-inflammatory Streptococcus species are associated with higher effusion on MRI and WOMAC knee pain, independent of BMI | 161 |
| Senescent cells | Positive correlation of the percentage of p16INK4A-expressing synoviocytes and IL-6 concentration in the synovial fluid with the degree of synovitis at the site of biopsy | 168 |
| Bioactive lipids | 11,12-DHET and 14,15-DHET levels are higher in OA knees versus unaffected knees of people with unilateral disease (P < 0.014 and P < 0.003, respectively) and are associated with radiographic progression over 3.3 years | 180 |
| HMGB1 | HMGB1 levels in the synovial fluid higher in patients with KL 4 than in those with KL 2 (P < 0.01) and KL 3 (P < 0.05) | 184 |
| Synovial fluid HMGB1 levels associated with the severity of synovitis and pain | 185 | |
| HSP70 | HSP70 levels higher in both serum and synovial fluid of individuals with knee OA than in healthy controls and both correlate with radiographic severity | 189 |
| MSU crystals | MSU crystals in the joint are associated with increased synovial fluid concentrations of IL-1β (r2 = 0.34, P < 0.0001) and IL-18 (r2 = 0.41, P < 0.0001), OA severity and radiographic progression, and osteophyte formation (P = 0.001 and P < 0.0001, respectively) | 204 |
KL, Kellgren and Lawrence; LPS, lipopolysaccharide; MSU, monosodium urate; OA, osteoarthritis; SPECT, single-photon emission computed tomography; T2DM, type 2 diabetes mellitus; WOMAC, Western Ontario and McMaster Universities Osteoarthritis Index.