Beyond Cartilage Repair: The Role of the Osteochondral Unit in Joint Health and Disease

Abstract

In this comprehensive review, we are providing a holistic overview of osteochondral tissue development, disease, pain localization, as well as structural evaluation and current repair strategies. This review is intended to serve as a broad introduction to this multidisciplinary research area. It is a thorough examination of the biological aspects of the osteochondral unit from a tissue engineering perspective, highlighting the importance of the subchondral bone in chondral and osteochondral lesion repair and pain relief.

Keywords: bone; cartilage; crosstalk; osteochondral unit; tissue engineering.

FIG. 1.

Diagram of endochondral ossification and the formation of the osteochondral unit. Inset: Histological view of the osteochondral unit (stained with Toluidine Blue and von Kossa).

FIG. 2.

Proposed mechanism of crosstalk within the osteochondral unit. Small molecules can diffuse through blood vessels and the canalicular network in healthy synovial joints (A). In osteoarthritic joints, in addition to the formation of osteophytes, subchondral bone cysts, and cartilage degeneration, angiogenesis and the formation of fissures may cause an increase in transport of inflammatory, osteoclast, and cartilage degradation factors (B).

FIG. 3.

Innervation of the osteochondral unit. In synovial joints, sensory neurons innervate the healthy subchondral bone and show a normal expression of TrkA and CGRP (A), which are important effectors in the transmission of nociception. In osteoarthritic joints, neurons increase in number and size, and TrkA and CGRP are upregulated (B). TrkA, tropomyosin receptor kinase A; CGRP, calcitonin gene-related peptide.