13.5: Structural Joints: Cartilaginous Joints
As the name indicates, at a cartilaginous joint, the adjacent bones are united by cartilage, a tough but flexible type of connective tissue. Unlike synovial joints, these types of joints lack a joint cavity and involve bones joined together by either hyaline cartilage or fibrocartilage.
There are two types of cartilaginous joints:
Synchondrosis
A synchondrosis ("joined by cartilage") is a cartilaginous joint where bones are connected by hyaline cartilage. Synchondrosis may be temporary or permanent. A temporary synchondrosis is the epiphyseal or growth plate of a growing long bone. The epiphyseal plate is the region of growing hyaline cartilage that unites the "metaphysis" (flared section at the proximal or distal end of the shaft) of the bone to the epiphysis (end of the bone). Bone lengthening involves the growth of the epiphyseal plate cartilage and its replacement by bone, which adds to the diaphysis.
Examples of permanent synchondroses are found in the thoracic cage. One example is the first sternocostal joint, where the first rib is anchored to the manubrium by its costal cartilage. (The articulations of the remaining costal cartilages to the sternum are all synovial joints.) Unlike the temporary synchondroses of the epiphyseal plate, these permanent synchondroses retain their hyaline cartilage and thus do not ossify with age. Due to the lack of movement between the bone and cartilage, both temporary and permanent synchondroses are functionally classified as synarthrosis.
Symphysis
A cartilaginous joint where the bones are joined by fibrocartilage is called a symphysis ("growing together"). Fibrocartilage is very strong because it contains numerous bundles of thick collagen fibers, thus giving it a much greater ability to resist pulling and bending forces when compared with hyaline cartilage. This allows symphyses to unite the adjacent bones firmly but allow limited movement. Thus, a symphysis is functionally classified as an amphiarthrosis.
The intervertebral symphysis is a wide symphysis located between the bodies of adjacent vertebrae of the vertebral column. Here a thick pad of fibrocartilage called an intervertebral disc strongly unites the adjacent vertebrae by filling the gap between them. The width of the intervertebral symphysis is important because it allows for small movements between the adjacent vertebrae. In addition, the thick intervertebral disc provides cushioning between the vertebrae, which is important when carrying heavy objects or during high-impact activities such as running or jumping.
This text is adapted from Openstax, Anatomy and Physiology 2e, Section 9.3: Cartilaginous Joints
