Subchondral bone abnormalities in the knee: imaging techniques, regional anatomy, and pathology

The subchondral bone is an integral structural component of the knee with key roles in shock absorption and load distribution. Injuries to the subchondral bone, which may occur secondary to various etiologies including trauma, degenerative disease, or repetitive overuse, are commonly encountered in clinical practice. Radiographs are generally performed as an initial imaging test to identify any gross osseous abnormalities. However, magnetic resonance imaging (MRI) is the modality of choice for the accurate evaluation and characterization of subchondral bone abnormalities, such as osseous contusion, insufficiency fracture, stress response, osteonecrosis, arthropathy, and neoplasm. Similarly, osteochondral derangements, including osteochondral fracture and osteochondritis dissecans, are also accurately identified with MRI. Therefore, knowledge of the MRI appearance of both normal anatomy and derangements of the subchondral bone are necessary for accurate diagnosis. This article aims to provide a review of the imaging features of subchondral bone abnormalities in the knee, highlighting key diagnostic findings and recommended practices in radiologic terminology and reporting.