No matter how sturdy the bone is, it is still by definition a rigid structure. You cannot bend or twist your bone; however all of these can be done with the joints. The joints allow movements between the bones and are protected against friction by a cartilage. Joints are classified functionally as synarthroses or immovable joint, amphiarthroses or partly movable and diarthroses or freely movable.Credit: http://www.teachpe.com/anatomy/joints.php
Fibrous joints are classified as synarthroses or immovable joint but somehow, there are fibrous joints that are part movable. These joints are formed when the two bones meeting together are connected with a fibrous tissue. Sutures or rigid joint of the skulls are immovable fibrous joints and the best example of this is the teeth in your socket which is held in place only by a ligament.Credit: http://www.body-motion.co.uk/injuries/kneearthritistreatment.htm
Also referred to as synchondroses or temporary joints, these are immovable joints typically seen during growth. Another way of defining cartilaginous joint is the connection of one bone to another bone by a cartilage and is classified as partly movable to immovable.Credit: http://commons.wikimedia.org/wiki/File:Illu_synovial_joint.jpg
This joint is freely movable within ligamentous limits and the bony architecture. The synovial joint is abundant with synovial fluid which is formed by the synovial membrane that lines the joint capsule. Synovial fluid lubricates the cartilage, thereby protecting the bone against friction from the meeting of the bones. Another function of the synovial fluid, aside from lubrication, is a cushion against shocks.
6 Types of Synovial Joint
Ball and SocketCredit: http://commons.wikimedia.org/wiki/File:Ball-socket_joint.png
Ball and socket joints are best seen in the shoulder and at the hip. It offers a wide array of movement and can be moved in all directions. It performs abduction, adduction, flexion, extension, circumduction, internal and external rotation.
A hinge joint differs from ball and socket joint in the aspect that it only allows movement in one plane, unlike the ball and socket which allows movement in all direction. The ankles and elbow joints are examples of hinge type of joint which only allows flexion and extension movements.
A saddle joint allows movement up and down, back and forth. The two concave articulating surfaces allow all motions except rotation. It is more versatile compared to the hinge joint.
Known by many name like condylar or condyloid joint, it appears like a configured or customized ball and socket joint in which significant rotation is largely excluded. The wrist joint is an example of an ellipsoid joint and the movement it permits is similar to that of the ball and socket but to a lesser degree.
Basically it is a joint that has a ring around a peg, the pivot joint allows movement around an axis. An example of this is the radius and the ulna able to twist around.
To put it simply, the two bones meeting together has flat surfaces so they slide past each other. Examples of this type of joint are the facet joints of the vertebrae, the intercarpal and intertarsal.
Various forces are at work to help keep our bones well oiled. As we age, bone resoprtion accelerates, decreasing bone mass and predisposing us to injury. Even the basic knowledge of the anatomy of bones can spell the difference between a painless aging and a painful aging.