A joint is a point of contact between two or more bones, or between a bone and a cartilage.
A joint is a point of contact between two or more bones, or between a bone and a cartilage. Joints are important because they facilitate movement of the body parts. Adjacent bones and cartilage articulate with one another to form a joint. A joint acts as a pivot and the muscles create the necessary force needed for movement. Classification of Joints: There are two ways of classifying joints.
Structural classification – Bones may be connected to each other by a fibrous tissue or a cartilage or they may be connected within a fluid filled cavity. There are three types of joints:
Examples : Bones of skull are joined by fibrous tissue forming a cranium. These joints are called sutures. Another fibrous joint is seen in gomphoses of teeth which is a joint between teeth and bony sockets.
Examples : Joints between adjacent vertebrae, joint between the first rib and sternum (also called synchondrosis).
Example : The joints between the carpals of wrist and tarsals of foot.
Example : The joint in the elbow, knee and ankle.
Example : The joints in the hip and shoulder.
Example: The joint between the first (atlas) and second (axis) cervical vertebrae is a pivot joint. It allows the head to turn from side to side.
Example : Joint between radius of forearm and bones of the wrist.
Example : The joint between thumb and palm. Each synovial joint allows movement in specific direction. Some allow movement in only one direction while some allow movements in multiple directions. The muscles and ligaments also play an important role in these joints. Ligaments, tendons and fluid filled sacs called bursae are also present around these joints. Functional classification : This classification is based on the degree of movement allowed by the joint. These are further divided into three types:
Uniaxial joint – This joint allows movement in only one plane. Example : Elbow joint which allows only bending and straightening. Biaxial joint – This joint allows motion in two planes. Example : Joint of the knuckles where the joint allows movement in two axes; one bending and straightening of fingers and second spreading of fingers. Multiaxial joint – This joint allows motion in many directions; along all three axes. Example : Shoulder and hip joint where the limbs can move in forward- backward direction, sideways and can also rotate.
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