Fig. 2

Histological evaluation of tissues organization. a OA synovial tissue is composed by different cell types and matrixes organized in synovial lining layer (LL) and sublining layer (SLL). b Dense net of blood vessels (black arrows) was found in SLL together with loose connective tissue (blue stain). c Histological grading for synovial membrane thickening in OA. d Synovial membrane thickening (ST) with reactive neo vascularization. e Histological grading for synovial villous expansion in OA. f OA synovial membrane presenting villous hypertrophy (SV). g Histological grading for tissue fibrosis. h Synovial membrane-like interface tissue showing fibrosis characterized by intense deposition of collagen fibers (blue stain). i Histological grading for tissue necrosis. Masson’s trichrome (a, b, d, f, h) staining. Scale bars correspond to 500 μm (b, f, h), 200 μm (d) and 50 μm (a). Semi-quantitative histological evaluation of tissue architecture was performed in specimens retrieved from 11/15 OA and 19/20 AL patients. ***p < 0.001. Chi square test was used to compare OA and AL groups