VMBO Year 3 · Support and movement · Section 5.3

Connections between bones

How are bones connected?

Bones must remain firmly connected while allowing the right amount of movement. This course distinguishes four types of connection: fusion, sutures, cartilage connections and synovial joints. Some allow almost no movement, some limited movement and some a wide range.

Four types of connection

Fused bones have grown into a single structure, as in the adult sacrum. Sutures, such as those between most skull bones, are strong fibrous connections with very little movement. Cartilage connections allow limited movement, for example in parts of the connections between ribs and sternum. Synovial joints, such as finger joints and knees, allow more extensive movement.

How does a synovial joint work?

The ends of the bones are covered with smooth articular cartilage, reducing friction and helping absorb pressure. A joint capsule encloses the joint. Its inner lining produces synovial fluid, which lubricates the surfaces. Ligaments reinforce the connection and help keep the bones aligned. In a ball-and-socket joint, one bone has a rounded head fitting into a socket in the other; other joints have different surface shapes.

Three joint types

• Ball-and-socket joint: permits movement in many directions, as in the shoulder and hip.
• Pivot joint: permits rotation, as in the connection between the radius and ulna used when turning the forearm.
• Hinge joint: mainly permits bending and straightening, as in the fingers. The knee is a modified hinge joint and also permits some rotation.