Articular System - Classification of Joints

Study Notes

Joints: Articulations where two or more bones connect via soft tissue.
Joint Functions:
- Enable movement, facilitated by muscles.
- Provide shock absorption, with cartilage, menisci, and synovial fluid.
- Establish stability, via ligaments and a joint capsule.
- Maintaining a balance between mobility and stability is crucial; one characteristic can be compromised to gain the other. Structures like menisci or articular discs can enhance stability.

Fibrous Joints: No joint cavity; bones connected by dense fibrous connective tissue. They permit little to no movement and provide shape and support. (Examples: sutures in the skull, gomphosis, syndesmosis).
Cartilaginous Joints: No joint cavity; bones connected by cartilage (hyaline or fibrocartilage). Permit limited movement and support. (Examples: Symphysis—pubic symphysis, intervertebral discs; Synchondrosis—sternocostal joint, epiphyseal plates).
Synovial Joints: Contain a joint cavity; bones are separated by a fluid-filled space. They are highly mobile.

Synarthroses: Permit little to no movement, typical of fibrous joints.
Amphiarthroses: Allowing moderate movement, characteristic of cartilaginous joints.
Diarthroses: High mobility. Typical of synovial joints.

Joint Capsule: An outer fibrous and inner synovial membrane that encapsulates the joint.
Synovial Membrane: Produces synovial fluid; this is impacted by stress and friction on the joint surfaces.
Synovial Fluid: A viscous fluid that reduces friction within the joint.
Hyaline Cartilage: Covers the articulating surfaces of bones within the joint; it is also supported nutritionally by the synovial fluid.
Ligaments: Fibrous structures that connect bones, either within or outside the joint capsule.
Menisci/Articular Discs: Structures that form congruency to increase stability (often found in diarthrotic joints).

Uniaxial Joints: Allow movement around one axis in one plane.
- Hinge Joints: Elbow, knee, and ankle joints—one surface is spool-like, other is concave shape.
- Pivot Joints: Atlantoaxial joint and superior/inferior radioulnar joints—one surface is ring shaped; the other surface rotates in the ring.
Biaxial Joints: Allow motion around two axes in two planes.
- Condyloid (Ellipsoid) Joints: Radiocarpal joints, metacarpophalangeal joints of fingers 2–5. (one bone concave, the other convex).
- Saddle Joints: Carpometacarpal joint of the thumb, sternoclavicular joint—(each bone has a convex and a concave part).
Triaxial Joints: Allow movement around three axes in three planes.
- Ball and Socket Joints: Glenohumeral (shoulder) and hip joints—(one bone has a convex ball-like surface that fits into the concave socket of the other bone).
Nonaxial Joints: Permit gliding/sliding movements; intercarpal joints, facet joints.