Evaluation of Articular Cartilage and Bone Marrow

Introduction: Preoperative evaluation of cartilage and bone marrow abnormalities relies on physical exam and imaging studies. Radiographs have a low sensitivity for cartilage damage and marrow abnormalities; MRI is the imaging method of choice. Physical Exam: The first steps in diagnosis are history and physical examination. Prior surgery or trauma suggest focal cartilage abnormality, whereas chronic, poorly localized pain suggests cartilage wear. Physical exam should include visual inspection, assessment of active and passive range of motion, palpation of painful regions, and evaluation of analgesic gait. Additional tests such as Wilson sign, ligament laxity maneuvers, and patellar tracking may be indicated. MRI of Cartilage: Each MRI sequence provides specific advantages and disadvantages in evaluating the knee structures and should be thoughtfully applied based on clinical concern. When MRI is acquired appropriately, it accurately evaluates cartilage injury, cartilage degeneration, and inflammatory arthritis. Artifacts such as magic angle, volume averaging, chemical shift, incomplete fat suppression, and patient motion can make MRI evaluation more difficult, and must be considered to arrive at the correct diagnosis. MRI of Bone Marrow: As bone matures, the marrow progresses from primarily hematopoietic to primarily fatty marrow, but it may reconvert to erythropoietic marrow during adulthood when there is increased hematopoietic demand. Erythropoietic bone marrow can be distinguished from marrow edema/abnormal marrow fluid by its signal characteristics. In the setting of trauma, bone marrow edema follows the line of force, and may have a bandlike, stellate, or semicircular configuration. When a stress reaction progresses to a stress fracture, an incomplete or complete fracture line develops in the center of the region of abnormal bone marrow. In the setting of cartilage degeneration, marrow edema tends to parallel the subchondral bone plate underlying the area of cartilage loss. Neoplasm or infection also shows abnormal marrow fluid but is distinguished by a round or ovoid shape. In adolescence, bone marrow edema may form along the physis due to increased stress on a bone at a time of decreasing flexibility.