The articulation of two or more bones allows various types of movement. The extent and type of movement determine the name applied to the joint. Bone structure limits the kind and amount of movement, others are freely moveable with a variety of movement ranges. The type and range of movements are similar in all humans; but the freedom, range, and vigor of movements are limited by ligaments and muscles.
The articulations are grouped into three classe based on their structure and the amount of movement possible.
Synarthrodial (immovable) joints
Found in the sutures of cranial bones and sockets of the teeth.
Amphiarthrodial (slightly movable) joint
Structurally, these articulations are divided into two groups.
Syndesmosis
Type of joint held together by strong ligamentous structures that allow minimal movements between the bones. Examples are the coracocalvicular joint and the inferior tibiofibular joint.
Synchondrosis
Type of joint separated by a fibrocartilage that allows very slight movement between the bones. Examples are the symphysis pubis and the costochondral joints of the ribs with the sternum.
Diarthrodial
Diarthrodial joints, also known as synovial joints, are freely movable. A sleevelike covering of ligamentous tissue known as the joint capsule surrounds the bony ends forming the joints. This ligamentous capsule is lined with a thin vascular synovial capsule that secretes synovial fluid to lubricate the area inside the joint capsule known as the joint cavity. In certain areas the capsule is thickened to form tough, noneelastic ligaments that provide additional support against abnormal movement or joint opening. These ligamnets vary in location size, and strength depending upon the particular joint.
in many cases, additional ligaments, not continuous with the joint capsule, provide further support. The articular surfaces on the ends of the bones inside the joint cavity are covered with layers of articular or hyaline cartilage. This resilient cartilage absorbs shock to protect the bone it covers. When the joint surfaces are unloaded or distracted, this articular cartilage slowly absorbs a slight amount of the joint synovlia fluid, only to slowly secrete it during subsequent weight bearing and compression. Additionally, some between their articulation can be divided into six groups.
Arthrodial (gliding) joint
Condyloidal (biaxial ball and socket) joint
Enarthrodial (multiaxial ball and socket) joint
Ginglymus (hinge) joint
Sellar (saddle) joint
Trochoidal (pivot) joint
