Joint structure and function
Joint structure and function describes how the body's articulations are built and how they move. Joints are classified structurally as fibrous, cartilaginous, or synovial, and functionally by how much movement they allow.
A joint (articulation) is any point where two or more bones meet. Joint structure and function is the study of how these connections are built and what movement each design permits — foundational knowledge for kinesiology, massage therapy, and clinical assessment.
Structurally, joints fall into three classes. Fibrous joints connect bones with dense connective tissue and allow little or no movement, like the sutures of the skull. Cartilaginous joints join bones with cartilage and permit slight movement, like the intervertebral discs and the pubic symphysis. Synovial joints — the most common type — feature a fluid-filled joint capsule, articular cartilage covering the bone ends, and supporting ligaments, allowing free movement. The parallel functional classification labels joints synarthrotic (immovable), amphiarthrotic (slightly movable), or diarthrotic (freely movable).
Synovial joints are further divided by shape, and shape dictates motion. Hinge joints (elbow, knee) allow flexion and extension in one plane; ball-and-socket joints (shoulder, hip) move in all planes plus rotation; pivot joints (atlas-axis) permit rotation; and condyloid, saddle, and gliding (plane) joints each allow their own characteristic movements. Knowing which motions a joint's architecture allows — and which it forbids — is the basis for describing range of motion and joint actions like flexion, abduction, and circumduction.
The MBLEx tests joint structure and function within its kinesiology content. Expect questions matching joints to their structural and functional classifications, identifying synovial joint types by example, and pairing joints with the movements they permit.
Key takeaways
- Joints are classified structurally as fibrous, cartilaginous, or synovial, and functionally as synarthrotic, amphiarthrotic, or diarthrotic.
- Synovial joints have a joint capsule, synovial fluid, and articular cartilage, and allow free movement.
- Synovial joint shapes — hinge, ball-and-socket, pivot, condyloid, saddle, and gliding — determine which movements are possible.
- Examples to memorize: skull sutures (fibrous), intervertebral discs (cartilaginous), shoulder and hip (ball-and-socket), elbow and knee (hinge).
- The MBLEx tests joint classifications and their permitted movements in its kinesiology section.