Articulations and Movement

Articulation

• site of union or junction between two or more bones, point of contact
• compromise between strength & mobility

Functional classification of joints by mobility:

1. Synarthroses - immovable, result of two separate ossification centers
   1. direct union of opposing surfaces or continuous fibrous c.t. connection
   2. no joint cavity
   3. ex. Sutures - irregular interlocking margins of skull bones
      • Gomphosis - tooth in socket
      • Synchondrosis - rigid cartilage bridge between two bones; epiphyseal plate, sternal ribs
2. Amphiarthroses - partial movement
   1. union by ligaments and possibly interposed fibrous cartilage pad
   2. partial joint cavity in cartilage pad
   3. hyaline cartilage covering articular surfaces
   4. ex.
      • Syndesmosis - ligament at distal ends of tibia and fibula
      • Symphysis - intervertebral disc, pubic symphysis
3. Diarthroses - free movement
   1. complex joint with joint capsule, ligaments and pads (cartilage or fat)
   2. joint cavity lined with synovial membrane and filled with synovial fluid
   3. ligaments form walls of cavity, hyaline cartilage covers articular surfaces
   4. ex. Majority of joints - ankle, knee, hip, shoulder, elbow, wrist, head

Figures in class

The greater the freedom of movement, the greater the chance of dislocation.

Range of movement at a joint is determined by:

1. extensibility of muscles - typical muscle is attached to two bones (origin and insertion) across movable joint
2. extensibility of ligaments - strong, collagen fibers, stabilize joint and limit excessive movement
3. architecture of joint surfaces - “fit”
4. elasticity of articular capsules and fluidity of pads
5. resistance of surrounding tissues