Synovial joints
What a synovial joint is
A joint is where two or more bones meet. A is a joint that moves freely. Its bone ends are covered in , and they are held together inside a , which is filled with .
- Synovial fluid lubricates the joint, reducing friction so the bones move smoothly.
- The joint capsule surrounds the joint and holds the fluid in.
- Cartilage cushions the ends of the bones (see Movement at joints).
The bones that meet and move against each other at a joint are its .
Key terms
Hinge joints and ball and socket joints
You need to know four synovial joints:
| Joint | Type | Articulating bones |
|---|---|---|
| Knee | Hinge | femur, tibia |
| Elbow | Hinge | humerus, radius, ulna |
| Shoulder | Ball and socket | humerus, scapula |
| Hip | Ball and socket | pelvis, femur |
A moves in one direction, like a door hinge: it bends and straightens. A has a rounded end of one bone sitting in a cup in the other, so it can move in every direction.
Common mistake
The patella and fibula aren't articulating bones of the knee in this course: the answer is the and .
Key terms
Why the type of joint matters in sport
- give strong, controlled movement in one direction: a runner's knees bend and straighten with every stride, and a netball player's elbows straighten to pass the ball.
- give the widest range of movement: a swimmer's shoulders can circle the arms in front crawl, and a footballer's hips let the leg swing forwards, backwards and to the side.
Because the shoulder can move so freely, it is also less stable than a hinge joint, so it can be easier to injure.