The pathologic processes central to rheumatoid arthritis (RA) and several other forms of inflammatory arthritis take place in the synovium. Mononuclear cell infiltration, synovial hyperplasia, neovascularization, and joint effusion are hallmarks of inflammatory arthritis. Extensive research, therefore, has been and continues to be focused on the diseased synovium. Evaluation of synovial tissue also plays an important role in differentiating potential causes of inflammatory arthritis in the clinic .

The proliferation of bedside musculoskeletal ultrasound continues to improve the practice of rheumatology. One of the most exciting applications is procedural guidance. Ultrasound-guided synovial biopsy (UGSB) is a bedside procedure that can be mastered by rheumatologists. The procedure aids in the evaluation of patients with inflammatory arthritis of unclear etiology and can be an essential tool in the armamentarium of inflammatory arthritis research. While previous biopsy techniques were confined to use in larger joints, UGSB can be performed on large, medium, and small joints. It is a safe and well-tolerated bedside procedure that can be performed with disposable materials. A physician with strong musculoskeletal ultrasound skills can learn the technique relatively easily, as the approach to needle biopsy is similar to the conventional image-guided arthrocentesis technique.

The foundations for the logistics of the UGSB procedure were developed in Europe and have been previously published [[1], [2], [3], [4], ∗[5], ∗[6], ∗[7], ∗[8]]. The authors of the manuscript at hand were taught the best practices for synovial biopsy by Stephen Kelly, Andrew Filer, and Costantino Pitzalis. In this manuscript, we present our recommendations for the best practices for synovial biopsy in the United States, based on our initial training in Europe in 2015 and our subsequent collective experience in performing synovial biopsies for both clinical and research indications over the past 7 years in the United States.