Learn the structural and functional classifications of joints. Understand synovial, cartilaginous, and fibrous joints. Anatomy quiz included.
Joints of the body are classified both by movement and function. Some classification terms sound similar but refer to different aspects of joints. For example, “synarthroses” are joints that do not move, but “synovial” refers to a class of movable joints with a distinct structure. Though both words have the root “syn” they mean very different things. Test your understanding of joint anatomy with a quiz at the end of the article.
Functional Classification of Joints
Functional classes of joints:
- synarthroses – joints which do not move
- amphiarthroses – joints which move slightly
- diarthroses – joints which move freely
Synarthroses and amphiarthroses are found mainly in the axial skeleton, whereas moveable joints, diarthroses, are found in the limbs.
Structural Classification of Joints
The following classes of joints refer only to the structure of a joint, not to the movement. Remember that a joint of the body will have both a structural and functional classification. For example, the knee joint is functionally classified as a diarthrosis which moves freely but structurally classified as a synovial joint.
Structural Classes of Joints
- fibrous joints – sutures, syndesmosis and gomphosis
- cartilaginous joints – synchondrosis and symphysis
- synovial joints – plane, hinge, pivot, condyloid, saddle, ball and socket
Types of fibrous joints include sutures, syndesmosis and gomphosis. Fibrous joints connect bones with a layer of dense regular connective tissues.
- Sutures are joints in the skull which allow for growth in children but become fully closed in the adult human body. Closed sutures are called synostoses.
- Syndesmosis involves ligaments, which connect bone to bone. The amount of movement in a syndesmosis is related to the length of fibers in the joint. Short ligaments allow little to no movement, whereas longer ligaments (longer fibers) allow for greater movement.
- Gomphosis are the immobile joints where the teeth connect into the jawbones.
Cartilaginous joints connect bones with cartilage, creating synarthroses or amphiarthroses. Types of cartilaginous joints are distinguished by the type of cartilage used in the joint:
- synchondrosis is made of hyaline cartilage
- symphysis are made of fibrocartilage
Examples of synchondroses include joints between the ribs and sternum. Symphyses examples are the joints in the intervertebral discs and the pubic symphysis.
Synovial joints are diarthroses, or freely movable joints. The structure of synovial joints is more complex than fibrous or cartilaginous joints. Articulation of synovial joints includes cartilage, a joint cavity, an articular capsule, and a synovial membrane with synovial fluid. Synovial joints are distinguished by the type of movement allowed by their structure.
Types of synovial joints:
- plane – gliding joints such as the bones in the wrist (nonaxial)
- hinge – joints which move in one direction like the elbow (uniaxial)
- pivot – joints which rotate around one axis
- condyloid – joints which move in four directions (biaxial)
- saddle – joints shaped like saddles which move in four directions (biaxial)
- ball and socket – joints which move in multiple directions (multiaxial)
Joint Classification Summary and Anatomy Quiz
Remember that each joint of the body has both a structural and functional classification. Though classifications sound similar, they sometimes refer to completely different aspects or elements of a joint. Test your knowledge with a quiz below.
- What is the functional and structural classification of the knee joint?
- What are the elements of a synovial joint?
- What type of movement does a saddle joint allow for (and what type of joint is it)?
- What types of cartilage are found in the cartilaginous joints? What functional classifications are possible in cartilaginous joints?
- What are fibrous joints made of? How do you know if a fibrous joint can move or not?
(Answers: 1. diarthroses, synovial 2. cartilage, joint cavity, capsule, synovial membrane, synovial fluid 3. biaxial (synovial) 4. hyaline cartilage, fibrocartilage. synarthroses, amphiarthroses 5. dense connective tissue/ligaments, longer fibers allow for movement whereas shorter fibers do not.)
Marieb, Elaine, Patricia Brady and Jon Mallatt. Human Anatomy, sixth ed. Pearson Education. 2011)