Calcific tendinitis (also known as calcific tendinopathy or tendonitis) is a self-limiting condition due to the deposition of calcium hydroxyapatite within tendons, usually of the rotator cuff. It is a common presentation of hydroxyapatite crystal deposition disease (HADD). 

Calcific tendinitis is common, however, the intra-osseous extension is a rare complication. This is important because it could be mistaken for a bone tumor (such as osteoid osteoma, or chondroid lesions) or an inflammatory process (osteomyelitis). The mechanism of cortical erosion and the intraosseous migration of calcific deposits is not entirely understood. It could be attributed to enzymatic actions that may facilitate the lysis of the cortical bone and the dissemination of calcific deposits subcortically. Intraosseous migration can be cortical erosion, subcortical calcium extension, or intramedullary diffusion.

Plain x-ray and CT are helpful to identify the calcific tendonitis and the intra-osseous extension, while the MRI helps to identify the surrounding marrow edema.

On follow-up exams, a complete resolution of the radiological findings might occur.