Value of digital X‐ray radiogrammetry in the assessment of inflammatory bone loss in rheumatoid arthritis

Introduction Rheumatoid arthritis (RA) is a systemic inflammatory disease characterized by progressive joint destruction based on the synovitis of large and small joints (1,2). The small joints of the hands and feet are particularly affected in the majority of RA patients, leading to destruction of articular tissue, including cartilage and bone (2). Osteoporosis, a typical phenomenon of RA, occurs in two forms: periarticular osteoporosis, adjacent to the inflamed joints, and generalized osteoporosis, resulting in an increased risk of fractures. Periarticular osteoporosis is a specific feature of bone involvement in RA (3,4) and is one of the bone involvement criteria in addition to erosions in the American College of Rheumatology criteria for RA (5). The onset of periarticular bone loss in the hands and feet is an early sign of RA (6) and may precede erosions (7). Periarticular bone loss is mainly caused by the local release of inflammatory agents and is a direct consequence of the inflammatory process (8), whereas generalized bone loss is additionally influenced by immobility and treatment effects (e.g., glucocorticoids) (9–11). In the hand, inflammatory bone loss includes not only the direct periarticular region of the joints, but also the cortical bone of the metacarpal diaphysis, indicating that inflammation-induced bone loss is present independent of direct synovial contact (12–14). Immunologic aspects of periarticular bone loss in RA