Synovial Joint Movements

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.

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Image demonstrating the various joint movements.

Image demonstrating the various joint movements, including (a) and (b) angular movements, flexion and extension at the shoulders and knees; (c) angular movements, flexion and extension of the neck; (d) angular movements, flexion and extension of the vertebral column; (e) angular movements, adduction, abduction, and circumduction at the upper limb at the shoulder; (f) rotation of the head, neck, and lower limb.

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.

Image demonstrating the six different types of synovial joints, including pivot joint between C1 and C2 vertebrae, hinge joint (elbow), saddle joint (between first metacarpal bone and trapezius carpal bone), plane joint (between tarsal bones), condyloid joint (between radius and carpal bones of wrist), and ball and socket joint (hip).