Page 27 - ASOP ROT Study Guide

socket joints hip joints

"universal
Joint"

Compound knee joint condylar joint (condyles of femur join with
joints / condyles of tibia) and saddle joint (lower end
modified of femur joins with patella)
hinge joints

4 . 8 Joint Stability

Immobile and slightly mobile joints are very stable - they do not allow the bones to move out of
their correct position. Synovial joints must allow the bones to move relative to each other but must
also maintain the bones in their correct position in the joint. The stability of synovial joints is
determined by:

♦ the shape of the bone surfaces in the joint
♦ the arrangement of ligaments around the joint
♦ the muscles (or tendons of muscles) which cross the joint

Immobile joints
The bones are held firmly together by short collagen fibers. These joints are known as fibrous
joints and allow no movement. Examples are found in the skull and at the distal ends of the tibia
and fibula (the distal tibio-fibular joint).

Slightly mobile joints
The bones are held together by fibrocartilage. These joints are known as cartilaginous joints.
Examples are found between the vertebrae and between the innominate bones of the pelvis. The
latter joint is called the symphysis pubis and it allows a little "give" which is desirable, particularly
when giving birth!

Very mobile joints
The bones are held together by ligaments and muscles. The bones may also be shaped to fit well
together at the joint thus helping to hold the bones in place but also allowing certain types of
movement. These joints are called synovial joints (see Figure 12) and allow a wide range of
movements. Examples of this type are the hip and knee joints. The ends of the bones in asynovial
joint are covered with articular cartilage. A sleeve of tough fibrous material called the capsule is
attached to the bones and encloses the joint. The inner layer of the capsule is lined with asynovial
membrane which produces synovial fluid. The synovial fluid fills the synovial cavity, lubricating the
joint and providing nutrients to the articular cartilage. These joints in particular allow us the
movement that is not only a major factor in our survival but also a prime source of our enjoyment
of life.

4 . 9 Joint Complications

A living joint has the capacity to regenerate its surface in response to wear and to restore a smooth
articulating surface after damage, provided that the damage is superficial. The mechanism of
repair is dependent on a good blood supply to the deeper layers of the cartilage and on nutrition
from the synovial fluid.

In certain situations this balance of wear and repair breaks down - There is either too much wear or
too little repair. This is of course a simplistic way of describing the problem but it serves as a
useful way of thinking about joint diseases such as arthritis. Arthritis is a word which only really