Edema of the Bone Marrow Can Cause Pain in Osteoarthritis and Other Diseases of Bone and Joints

• Osteoarthritis
• Bone marrow diseases
• Edema
• Pain
• Joint diseases

Cartilage degeneration, although fundamental to the pathogenesis of osteoarthritis, is not the site of origin of pain, the predominant symptom of osteoarthritis. Peripheral nerves generally follow the path of blood vessels, and cartilage contains no nerves or blood vessels. Pain can originate in the synovium, the joint capsule, or intra-articular ligaments, as well as in the muscles and soft tissues, which surround and move the joint in osteoarthritis.

Ordinary radiographs show the effect of degeneration of joint cartilage as narrowing of the space between the surfaces of the articular bone (usually called the “joint space” or, more accurately, the “cartilage space”). However, patients can have considerable pain despite a normal-looking cartilage space, or pain can be mild despite marked narrowing. Likewise, other radiographic changes seen in osteoarthritis, including thickening of the subchondral bone (eburnation) and formation of osteophytes, do not correlate with the presence or the severity of pain. The clinical significance of joint pain can therefore be obscure and difficult to determine.

In this issue, Felson and colleagues (1) describe edema in the subarticular bone marrow adjacent to the knee, detected by T₂-weighted magnetic resonance imaging (MRI), in patients with painful osteoarthritis of that joint. Edema of the bone marrow has also been demonstrated in patients with traumatic bone injuries, including “bone bruises” and other forms of “overuse” (2); the pathologic process in the subarticular marrow of patients with osteoarthritis is probably an analogous phenomenon. Thinning and erosion of the cartilage in osteoarthritis decrease the …