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Synovial joints allow an individual to achieve a wide range of movements.
Learning Objectives
- Identify the different types of synovial joints
Key Points
- Synovial joints achieve movement at the point of contact of the articulating bones.
- Synovial joints allow bones to slide past each other or to rotate around each other. This produces movements called abduction (away), adduction (towards), extension (open), flexion (close), and rotation.
- There are six types of synovial joints. Some are relatively immobile but more stable than mobile joints.
Key Terms
- synovial joint: Also known as a diarthrosis, the most common and most movable type of joint in the body of a mammal.
- abduction: The movement that separates a limb or other part from the axis, or middle line, of the body.
- flexion: The act of bending a joint. The counteraction of extension.
- adduction: The action by which the parts of the body are drawn toward its axis.
A synovial joint, also known as a diarthrosis, is the most common and most movable type of joint in the body of a mammal. Synovial joints achieve movement at the point of contact of the articulating bones. Structural and functional differences distinguish synovial joints from cartilaginous joints (synchondroses and symphyses) and fibrous joints (sutures, gomphoses, and syndesmoses). The main structural differences between synovial and fibrous joints are the existence of capsules surrounding the articulating surfaces of a synovial joint and the presence of lubricating synovial fluid within those capsules (synovial cavities).
Several movements may be performed by synovial joints. Abduction is the movement away from the midline of the body. Adduction is the movement toward the middle line of the body. Extension is the straightening of limbs (increase in angle) at a joint. Flexion is bending the limbs (reduction of angle) at a joint. Rotation is a circular movement around a fixed point.
Body Movements I: Image demonstrating the various joint movements.
There are six types of synovial joints. Some are relatively immobile but more stable than mobile joints. Others have multiple degrees of freedom, but at the expense of greater risk of injury. The six types of joints include:
- Gliding joints: only allow sliding movement
- Hinge joints: allow flexion and extension in one plane
- Pivot joints: allow bone rotation about another bone
- Condyloid joints: perform flexion, extension, abduction, and adduction movements
- Saddle joints: permit the same movement as condyloid joints and combine with them to form compound joints
- Ball and socket joints: allow all movements except gliding
Six Types of Synovial Joints: Image demonstrating the six different types of synovial joints.
