Synovial biopsy and tissue sampling in the management of RA

Synovial tissue (ST) biopsy has evolved from an experimental procedure into a clinically relevant tool that provides unparalleled access to the inflamed joint in RA. Initially performed through blind needle and arthroscopic techniques, the adoption of minimally invasive ultrasound-guided biopsy has enabled safe, reproducible and patient-acceptable tissue sampling across large and small joints. Histopathological evaluation, including the Krenn Synovitis Score and recognition of distinct pathotypes, has provided diagnostic and prognostic insights, while comparative analyses have highlighted shared inflammatory pathways with OA and PsA. The integration of high-dimensional technologies such as bulk and single-cell transcriptomics, spatial profiling and proteomics has uncovered novel stromal and immune cell subsets and linked tissue signatures to therapeutic outcomes. Landmark biopsy-driven trials (R4RA and Synovial Tissue Research in Arthritis Pathobiology [STRAP]) have demonstrated the feasibility of stratifying treatment on the basis of synovial biology, positioning synovial biopsy as a cornerstone in the long journey towards precision RA management.