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1. Structural classifications of the body joints are based on how the bones are held together and articulate with each other.
2. At fibrous joints, the adjacent bones are directly united to each other by fibrous connective tissue.
3. Similarly, at a cartilaginous joint, the adjacent bones are united by cartilage.
4. In contrast, at a synovial joint, the articulating bone surfaces are not directly united to each other, but come together within a fluid-filled joint cavity.
5. The functional classification of body joints is based on the degree of movement found at each joint.
6. A synarthrosis is a joint that is essentially immobile.
7. This type of joint provides for a strong connection between the adjacent bones, which serves to protect internal structures such as the brain or heart.
8. Examples include the fibrous joints of the skull sutures and the cartilaginous manubriosternal joint.
9. A joint that allows for limited movement is an amphiarthrosis.
10. An example is the pubic symphysis of the pelvis, the cartilaginous joint that strongly unites the right and left hip bones of the pelvis.
11. The cartilaginous joints in which vertebrae are united by intervertebral discs provide for small movements between the adjacent vertebrae and are also an amphiarthrosis type of joint.
12. Thus, based on their movement ability, both fibrous and cartilaginous joints are functionally classified as a synarthrosis or amphiarthrosis.
13. The most common type of joint is the diarthrosis, which is a freely moveable joint.
14. All synovial joints are functionally classified as diarthroses.
15. A uniaxial diarthrosis, such as the elbow, is a joint that only allows for movement within a single anatomical plane.
16. Joints that allow for movements in two planes are biaxial joints, such as the metacarpophalangeal joints of the fingers.
17. A multiaxial joint, such as the shoulder or hip joint, allows for three planes of motions.