Textbooks describe six ways that a synovial
(diarthrotic) joint might move:
Ball-&-socket joint:
This joint allows for freedom of rotation
as well as back-and-forth movement in all planes. It allows for the most freedom in
movement of any other joint. I tried to show this flexibility in the animation, but
there's even more flexibilty in movement than I could show.
Condyloid joint:
The drawing tries to show you that the
bones can move about one another in many directions-- except that they cannot
rotate. Keep in mind that this joint is named for a condyle-containing joint.
A condyle is a curved process that fits into a fossa on another bone for its
articulation. You also find this type of joint at the mandible-to-temporal bone
joint. Think about all the movements we can make with our lower jaw-- we have a lot
of flexibility, except we can't rotate our jaw!
Plane (or Gliding) joint:
Although these joints appear to offer a
lot of flexibility in movement direction, they do not offer a great distance
in movement. But they can move in many directions and they can rotate.
Hinge joint:
Hinge joints offer ease in movement, but
only provide for movement in one plane (no twisting, no sliding side-to-side). Keep
in mind that although a good example of a hinge joint is at your elbow, there are two
bones in your forearm that interact at the elbow joint. Only one of them, the ulna,
makes a hinge joint. When you are in the anatomical position and you bend your elbow
as if bringing your palm to your shoulder, that is the movement of the hinge joint.
If you instead, from the anatomical position, twist at the elbow so that your palm faces
posteriorly, that is NOT the hinge joint (it is a pivot joint, see below).
Pivot joint:
This joint is one where one bone spins
around on another bone. Although only one direction of spin has been diagrammed
above, the spinning can occur in either direction. This type of joint is in our
elbow (for the twisting motion) and is between our first two cervical vertebrae (as in the
figure from your book, this allows for you to shake your head "no").
Saddle joint:
Most students have a hard time
distinguishing this joint from the condyloid joint or plane
joint. But it is easy! In the
saddle joint, both of the bones that meet have odd shapes, but they are totally
complementary to one another. (Remember, in the condyloid joint, one bone is
concave and the other is convex). So in the saddle joint, each bone has both
concavities and convexities, but they fit nicely.
Every synovial joint fits one of these
categories. You will not have to specifically identify each joint of the body as
fitting into one or another of these categories. But, you should be familiar with
each, and have some idea of which allows for the most movement options. You should
also know of an example of each of the six.
Other places to look for joints:
An image of four of the types of joints (ball-and-socket,
gliding, hinge, and saddle) is available at Body Online, and then you go from the
home page and click on the button underneath all the systems on "images" and
scroll down to "Joints and Mechanical Equivalents."
Another website where you can find out more about 4 types of
these joints (the movie didn't work for me) is this website from
University of Leeds.
Here's a website specifically on the shoulder
joint-- and the movies here actually work!
