Fibrous joints and skull sutures
A fibrous joint is held by fibrous connective tissue (tough tissue packed with collagen) with no joint cavity (fluid-filled space), so it is very stable with very little movement.
Remember
Fibrous joints bind the bones with fibrous connective tissue and have no joint cavity, so they are very stable with very little movement, as in the skull sutures.
Memory aid
think of a suture as a stitch
The word suture means to bind or sew, and fibres stitch the skull bones together.
Joints trade mobility against stability, and a fibrous joint sits at the stable end. The bones are connected directly by fibrous connective tissue, with no joint cavity between them. Because the bones are bound so firmly, the joint is very stable and allows very little movement.
The skull sutures are the classic example: narrow seams between the skull bones. Most skull bones are joined this way, which suits a structure that protects the brain. The mandible (lower jaw) is the exception, because it is not joined to the rest of the skull by a suture.
Sutures are one of three kinds of fibrous joint. In syndesmoses, two bones are held by a ligament or by an interosseous membrane (a broad sheet of connective tissue), as between the radius and ulna in the forearm. In gomphoses, a tooth is anchored in its socket.
A newborn's skull has some much wider gaps between the bones. These fontanelles (the soft spots) are still made of fibrous tissue. They give the skull some flexibility during birth and allow the skull and brain to grow afterwards. They narrow during the first year, and once the connective tissue is reduced to a narrow layer the joint is called a suture.
Cartilaginous joints (bones joined by cartilage, a tough but flexible tissue) are immobile or allow slight movement, and synovial joints (bones moving within a fluid-filled capsule) allow free movement. Fibrous joints are immobile or almost immobile, although some sutures may allow slight movement.
Key facts
- Joining tissue
- fibrous connective tissue, with no joint cavity between the bones.
- Movement
- very little, so the joint is very stable.
- Three kinds
- sutures (skull), syndesmoses (for example the forearm and leg) and gomphoses (teeth in their sockets).
- Where sutures lie
- between most of the skull bones, but not the mandible.
- Newborn skull
- fontanelles are wide areas of connective tissue that give flexibility at birth and narrow in the first year.
- Other joint types
- cartilaginous joints united by hyaline cartilage (smooth, glassy cartilage) are immobile, those united by fibrocartilage (tough cartilage packed with collagen fibres) allow slight movement, and synovial joints have a fluid-filled cavity and allow free movement.
Exam traps
- A joint united by hyaline cartilage is not a fibrous joint: the joining tissue is cartilage rather than fibrous connective tissue, even though it also allows very little movement.
- The name fibrocartilage sounds like fibrous, but fibrocartilage is a type of cartilage, not fibrous connective tissue, so a joint united by a pad of it belongs with the cartilaginous joints and allows slight movement.
- A syndesmosis is a fibrous joint, but the bones are held together by a ligament or an interosseous membrane, as in the forearm and leg, not between skull bones.
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