Plane joint: gliding between flat surfaces
A plane joint is a synovial joint whose relatively flat articular surfaces (the smooth, cartilage-covered ends of the bones) glide over each other in small movements.
Remember
Flat surfaces that glide over each other in small movements, limited by the joint capsule and ligaments, mean a plane joint.
Memory aid
Think of two flat sheets of paper sliding over each other.
Flat surfaces that glide, giving small movements limited by the capsule and ligaments.
A plane joint (also called a gliding joint) is a synovial joint, meaning a freely movable joint with a fluid-filled cavity. The two articular surfaces (the smooth, cartilage-covered ends of the bones that meet) are flat or only slightly curved. Nothing locks one bone into a groove or a socket, so the surfaces glide over one another, and the small slides can happen in several directions.
The movement stays small because the joint capsule (the fibrous sleeve that surrounds the joint) and nearby ligaments limit the gliding. A plane joint therefore gives up range of movement in return for stability.
Many of the intertarsal joints, the joints between the tarsal bones (the group of bones that form the back and middle of the foot), are plane joints. Examples include the intercuneiform joints between the wedge-shaped cuneiform bones. Together these small slides let the foot give slightly when it takes weight.
Plane joints are also found between the carpal bones of the wrist and at the second to seventh sternocostal joints, where the ribs meet the sternum. The first sternocostal joint, however, is a primary cartilaginous joint (a synchondrosis, where cartilage joins the bones), so it is not a plane synovial joint.
To place the other joint types, count the axes of movement (an axis is the line around which a bone moves). For example, a hinge joint bends and straightens about one axis, a pivot joint rotates about one axis, and a ball-and-socket joint moves about several.
Key facts
- Surfaces
- the articular surfaces are relatively flat, or only slightly curved.
- Movement
- small gliding movements in several directions, limited by the joint capsule and ligaments.
- Stability
- a plane joint gives up range of movement in return for stability.
- Foot examples
- the intercuneiform joints between the wedge-shaped cuneiform bones, and many of the intertarsal joints between the tarsal bones.
- Other examples
- the joints between the carpal bones of the wrist, and the second to seventh sternocostal joints.
- Chest wall
- the first sternocostal joint is a synchondrosis, not a plane synovial joint.
Exam traps
- The first sternocostal joint, where the first rib meets the sternum, is not a plane synovial joint, because it is a primary cartilaginous joint (a synchondrosis); the second to seventh sternocostal joints are the plane joints.
- Bending and straightening about a single axis is the movement of a hinge joint such as the elbow, because a plane joint slides instead of bending.
- Rotation about one axis belongs to a pivot joint, where a rounded bone turns inside a ring of bone and ligament, because a plane joint slides instead of turning.
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