Angiogenesis in osteoarthritis and spondylosis: successful repair with undesirable outcomes

Abstract

Osteoarthritis and spondylosis are frequently described as “wear-and-tear” arthritis, apparently contradicting modern management, which focuses on continuing and progressive exercise. Laboratory findings, including the growth of new blood vessels, encourage comparisons with repair processes. This review aims to place recent evidence in the context of previous work emphasizing the dynamic nature of tissues in these conditions. Synovitis has now become recognized as a common and important feature of osteoarthritis, and vascular growth is enhanced in osteoarthritic synovia when infiltrating macrophages generate angiogenic factors. As the molecular balance between angiogenic and antiangiogenic factors is disturbed, new blood vessels are permitted to grow into normally avascular structures, such as the articular cartilage and intervertebral disc. Angiogenesis is a key factor in new bone formation in osteophytes and at the osteochondral junction, thereby contributing to radiologic disease progression. Innervation of new blood vessels may contribute importantly to chronic pain. Reconceptualizing osteoarthritis and spondylosis as reparative processes provides a pathologic model consistent with current advice to exercise, when exercise facilitates repair. Repair does not, however, lead to normal tissue, and understanding the mechanisms by which changes in joint innervation may occur as a consequence of angiogenesis should lead to novel therapies that alleviate the common symptoms of these highly prevalent conditions.