Fig. 1

Schematic representation of epiphysial and vertebral bone phenotypes in musculoskeletal and rheumatic diseases. OA is characterized by increase bone remodeling and progressive subchondral thinning followed by sclerostation. Mechanical adaptation may lead to the formation of osteophytes at the joint margins. The bone phenotype in RA joints are usually showing as excessive bone erosions. Hallmarks of AS consists of ankylosis of the spine, but also pathological bone loss both systemically and locally. The bone phenotype in psoriatic arthritis is mixed but characterized by bone erosions similar to RA. These are often less severe and more asymmetric in terms of affected joints. PsA also presents with pathological bone formation in the axial skeleton such as syndesmophytes, and in the peripheral joints, as joint ankylosis, enthesophytes or periosteal bone formation