Secondary cartilaginous joints: pubic symphysis and vertebral bodies
A secondary cartilaginous joint, or symphysis, is a joint where a pad of fibrocartilage (a tough, fibre-rich cartilage) unites two bones, giving stability with slight movement.
Remember
The pubic symphysis (the joint between the two pubic bones) and the joints between vertebral bodies are secondary cartilaginous joints, where a fibrocartilage pad gives stability with slight movement, while hyaline cartilage (smooth, glassy cartilage) means a functionally immobile primary cartilaginous joint.
Memory aid
A firm cushion between two blocks
Picture a firm cushion between two blocks: the fibrocartilage pad holds the bones together but still gives a little.
A joint is classified by what unites its bones: fibrous tissue, cartilage or a fluid-filled cavity inside a capsule. Cartilaginous joints come in two kinds.
A primary cartilaginous joint, or synchondrosis, uses hyaline cartilage (smooth, glassy cartilage) and is functionally immobile. The growth plate (a plate of hyaline cartilage in a growing bone) is the classic example.
A secondary cartilaginous joint, also called a symphysis, uses fibrocartilage instead, and it allows slight movement. Fibrocartilage is a tough cartilage rich in collagen (the strong, rope-like protein that gives connective tissue its strength), so it withstands both squashing (compression) and pulling apart (tension). It holds the bones firmly together, yet it has a little give.
The pubic symphysis is the joint between the two pubic bones at the front of the pelvis. The joints between adjacent vertebral bodies (the main blocks of bone at the front of each vertebra) work in the same way, and in the spine the fibrocartilage pad is the intervertebral disc. The small movements at each disc add up along the column to give the spine its overall flexibility.
Ask what lies between the bones to classify any joint. A cartilage pad means a cartilaginous joint, fibrous tissue means a fibrous joint, and a fluid-filled cavity means a synovial joint. Within cartilaginous joints, a useful rule is that hyaline cartilage means a functionally immobile primary joint, while fibrocartilage means slight give.
Key facts
- Type
- a secondary cartilaginous joint, also called a symphysis.
- Tissue
- a pad of fibrocartilage unites the bones directly, and there is no joint cavity.
- Movement
- slightly movable, with stability.
- Examples
- the pubic symphysis and the intervertebral discs between vertebral bodies.
- Primary joints
- primary cartilaginous joints (synchondroses) use hyaline cartilage and are functionally immobile, as at a growth plate.
- Disc structure
- an intervertebral disc has a firm outer ring (the annulus fibrosus) and a softer jelly-like core (the nucleus pulposus).
- Pregnancy
- pelvic joints that are stiff or move unevenly can cause pelvic girdle pain, including pain at the front of the pelvis.
Exam traps
- Hyaline cartilage joining two bones does not make a secondary cartilaginous joint: it forms a primary cartilaginous joint, which is functionally immobile, whereas fibrocartilage gives the slight movement of a symphysis.
- A syndesmosis is a fibrous joint in which an interosseous membrane (a sheet of fibrous tissue between long bones) binds two bones, and it also allows slight movement. It is a near miss for slight movement, but fibrous joints are held by fibrous tissue rather than cartilage.
- Increased mobility does not make a joint synovial: the pubic symphysis is joined directly by fibrocartilage and normally moves only slightly, while synovial joints have a fluid-filled cavity within a fibrous capsule and move freely.
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