In fibrous joints the bones are united by dense connective tissue consisting
of collagen fibers which run between the bones.
There is NO JOINT CAVITY.
The degree of movement permitted depends on the length of the collagen fibers,
and on the shape and extent of the bone surface at the joint: most of the fibrous joints
are immovable - a few are slighly movable.
There are three subtypes of fibrous joints:
- 1. Suture:
- Bones are held together by a thin layer of dense fibrous tissue
and also by interlocking projections of the bones.
The connecting fibers
holding bones together are short. This type of joint occurs only
in the skull: cranial sutures.
In the fetal skull the bones are widely separated,
and the edges of adjacent bones are relatively smooth.
A fibrous membrane unites the bones forming a "soft spot" or fontanel.
This arrangement permits the bones of the fetal skull to overlap
slightly during delivery, and also allows for growth in size after birth.
As the diameter of the skull increases, bone is deposited
at the periphery of the cranial bones, gradually filling in the spaces.
During adulthood, the fibrous tissue ossifies and the skull
bones fuse into a single unit that provides a efficient protection for the brain.
- 2. Syndesmosis:
- Bones are held together by a cord or sheet of dense fibrous connective
tissue. The connecting fibers
holding bones together are long.
The tibia/fibula joint and the
interosseous membrane connecting the radius and ulna along their length are syndesmosis.
- 3. Gomphosis:
- It is a peg-in-socket fibrous joint.
The only examples are the articulations of teeth (the peg) with their alveolar sockets
in the mandible or the maxillae. The thin fibrous membrane that hold teeth
inside their alveolar sockets is called the periodontal ligament.
