Synovial Joints of Pectoral Girdle (Left)

Description

Synovial joints are specialized joints that permit free movement between two bones, called articulations. The bones are united by an articular capsule, composed of an outer fibrous membrane and an inner synovial membrane, that encloses the joint. Within the capsule is a potential space containing synovial fluid, produced by the synovial membrane, which helps lubricate the joint during movement. The synovial joints of the pectoral girdle (or shoulder girdle) include the acromioclavicular and sternoclavicular joints.

The acromioclavicular joint is formed between the acromion of the scapula and the acromial end of the clavicle. It is a synovial plane joint and the articular surfaces of the bones are covered by fibrocartilage and are surrounded by a fibrous joint capsule. The joint strengthened superiorly by the acromioclavicular ligament, posteriorly by fibers of the trapezius muscle, and anteriorly by fibers of the deltoid muscle.

The sternoclavicular joint is a synovial sellar (or saddle) joint and is the only articulation between the axial skeleton and the upper limb. The joint is located between the clavicle and the clavicular notches of the sternum and both the articulating surfaces are covered with fibrocartilage. The joint is reinforced by a number of ligaments, including the anterior and posterior sternoclavicular ligaments, and the costoclavicular ligament.