In cartilaginous joints the bones are united with each other by
cartilage.
Again, there is NO JOINT CAVITY.
There are two subtypes of cartilaginous joints:
- 1. Primary cartilaginous joints (= synchondroses):
- A plate of hyaline cartilage connects the bones at the joint.
Only hyaline cartilage is involved, and the joints are immoveable.
An example is the cartilaginous epiphyseal plate which
separates the epiphysis from the diaphysis in long bones during growth.
These joints are immoveable (synarthroses) and are obliterated by bone in the adult.
A second example is the joint between the first rib and the sternum.
- 2. Secondary cartilaginous joints (= symphyses)
- It involves both hyaline and
fibrocartilage. The articular surface of each bone is covered with a thin
layer of hyaline cartilage, and fibrocartilage unites these two layers.
Limited movement is permitted at such joints, depending on the thickness of the
fibrocartilage pad which can be compressed or stretched.
Two important examples are the pubic symphysis and the
intervertebral discs.
Normally this pubic symphysis joint permits little compression or stretching.
Hormonal influences during pregnancy alter its structure to permit greater
stretching as the child's head passes through the birth canal.
The intervertebral discs have special features associated with
their functions in weight bearing and in permitting bending of
the vertebral column.
A thin layer of hyaline cartilage covers the joint surface of each vertebra.
The intervertebral disc is a short cylinder.
Its peripheral region (annulus fibrosus) consists of dense fibrocartilage.
Centrally is a less dense region (nucleus pulposus)
which contains a considerable amount of watery fluid.
The adaptation of such a structure for shock absorbing as
well as permitting limited movement is obvious.
