Types of joints

Types of joints

A joint is any point of contact between two bones (Figure 9.13). Joints are essential for every movement performed by the bony skeleton, sometimes also playing a protective role, and — because the force generated by muscles is transmitted through them — a joint functions as the fulcrum of a lever, making the day-to-day activities of living and getting around (ambulation) possible. Joints are classified into three types based on how much movement they allow:

1. Fibrous joints (Synarthroses) — immovable, fixed joints with no gap between bones. Example: the sutures of the flat skull bones.
2. Cartilaginous joints (Amphiarthroses) — slightly movable joints where the bone surfaces are separated by cartilage, permitting only limited movement. Example: the joints between adjacent vertebrae of the vertebral column.
3. Synovial joints (Diarthroses) — freely movable joints where the articulating bones are separated by a fluid-filled cavity containing synovial fluid, which lubricates the joint and reduces friction. This is by far the largest and most functionally varied group, and is further divided by the shape of the articulating surfaces:
   • Pivot joint — e.g. between the atlas and the axis (permits rotation).
   • Plane/gliding joint — e.g. between the carpals (permits sliding movement).
   • Saddle joint — e.g. between a carpal and a metacarpal. …