Chapter 9.3 - Cartilaginous Joints

Joint Cavity: Cartilaginous joints lack a joint cavity entirely.
Articulating Tissue: Articulating bones are joined or connected by either hyaline cartilage or fibrocartilage.
General Mobility: Cartilaginous joints range functionally from completely immobile (synarthrotic) to slightly mobile (amphiarthrotic).

Structural Composition: A synchondrosis (plural: synchondroses) is a cartilaginous joint in which the articulating bones are united by hyaline cartilage.
Functional Mobility: Synchondroses are functionally classified as synarthrotic (completely immobile). The shared prefix syn- serves as an identifier linking synchondroses to their synarthrotic classification.
Perichondrium Characteristic: Unlike typical skeletal hyaline cartilage, articular cartilage found in these joints lacks an outer perichondrium.
Anatomical Examples:
- Epiphyseal Plate: A temporary hyaline cartilage joint present in growing bones that ossifies completely once longitudinal growth ceases.
- First Sternocostal Joint: The junction between the first rib and the sternum.

Structural Composition: A symphysis (plural: symphyses) features a pad or disc of fibrocartilage positioned between the articulating bones.
Biomechanical Role of Fibrocartilage: Fibrocartilage provides high tensile strength, resists compression, and functions as a shock absorber.
Functional Mobility: The presence of fibrocartilage allows for slight movement, making symphyses amphiarthrotic joints.
Co-occurrence of Hyaline Cartilage: Symphysis joints may also contain surrounding hyaline cartilage (such as in the intervertebral discs), but the articulating bones are fundamentally united by fibrocartilage.
Anatomical Locations:
- Pubic Symphysis: Located between the anterior portions of the pubic bones.
- Intervertebral Discs: Positioned between the centrums (bodies) of adjacent, unfused vertebrae.
- Vertebral Column Boundaries: Symphyses exist only between unfused vertebrae and are not present between fused vertebrae, such as those forming the sacrum and the coccyx.

Restricted Locations of Fibrocartilage: Fibrocartilage is very uncommon within the human body and is restricted to three specific locations:
- Intervertebral discs.
- Pubic symphysis.
- Knee joints.
Classification Caution Regarding Fibrocartilage: The presence of fibrocartilage within an articulation does not automatically designate the joint as a symphysis.
The Knee Joint: Although the knee contains fibrocartilage pads, it is classified structurally as a synovial joint, not a symphysis.

Mobility Comparison Between Synchondroses and Symphyses:
- Question: How does the mobility of a synchondrosis compare to that of a symphysis?
- Response: Synchondroses are synarthrotic (immobile), whereas symphyses are amphiarthrotic (slightly movable).
Cartilage Type in Synchondroses:
- Question: What type of cartilage is found in a synchondrosis?
- Response: Synchondroses contain hyaline cartilage.
Locations of Symphysis Joints:
- Question: Where are symphysis joints located?
- Response: Symphysis joints are situated between the pubic bones and between the centrums of most unfused vertebrae. They do not occur in fused vertebrae such as the sacrum and the coccyx.
Distinctive Cartilage in Symphyses:
- Question: What type of cartilage makes the symphysis joint unique?
- Response: Symphysis joints contain fibrocartilage, which is very uncommon in the body. While surrounding hyaline cartilage may also be present, the defining connective tissue uniting the bones is fibrocartilage.