The ball-and-socket joints at your shoulder and hip are the primary multiaxial joints in the human body. A multiaxial joint allows movement in three or more planes, giving it the widest range of motion of any joint type. Planar (gliding) joints, like those between the small bones in your wrists and ankles, are also technically classified as multiaxial, though their actual movement is much more limited.
What Makes a Joint Multiaxial
Joints are classified by how many axes, or directions, they permit movement. A uniaxial joint like the elbow hinge allows motion along one axis only: bending and straightening. A biaxial joint like the wrist allows motion along two axes: bending/straightening and side-to-side tilting. A multiaxial joint goes further, permitting movement along three or more axes. That means it can flex and extend, move side to side, and rotate.
This classification matters because it tells you what a joint can actually do. A multiaxial joint doesn’t just move in more directions; it can also combine those movements into circumduction, the circular “windmill” motion you can do with your arm. Circumduction is a sequential blend of flexion, extension, and side-to-side movement that traces a cone shape in space.
Ball-and-Socket Joints: Shoulder and Hip
The classic multiaxial joint is the ball-and-socket type. The rounded head of one bone sits inside a cup-shaped hollow of another, allowing the bone to swing forward and back, move side to side, and rotate along its length. Your body has two pairs: the glenohumeral joints at your shoulders and the hip joints.
Both share the same basic design, but they’re built for different jobs. The shoulder prioritizes mobility. Your upper arm bone can flex forward roughly 180 degrees, extend backward 45 to 60 degrees, lift out to the side about 150 degrees, and rotate inward 70 to 90 degrees or outward about 90 degrees. That enormous range is possible because the “socket” side of the shoulder is shallow, more like a golf tee than a deep cup. The ball of the upper arm bone is significantly larger than the socket holding it, which creates freedom of movement at the cost of structural security.
The hip takes the opposite approach. Its socket is deep and covers much more of the ball, making the joint inherently more stable but less mobile. Hip flexion typically ranges from about 80 to 140 degrees, while extension ranges from 5 to 40 degrees. You can still rotate, abduct, and circumduct at the hip, but with noticeably less range than the shoulder.
Planar Joints: Multiaxial but Restricted
Ball-and-socket joints aren’t the only multiaxial type. Planar joints, also called gliding joints, form where two relatively flat bone surfaces meet. Examples include the joints between the small carpal bones of the wrist, the tarsal bones of the foot, and the facet joints along your spine. These joints are classified as multiaxial because the flat surfaces can technically slide against each other in multiple directions. In practice, though, tight surrounding ligaments keep actual movement quite small. You won’t get anything close to the sweeping range of a shoulder from a gliding joint.
The Mobility-Stability Trade-Off
There’s a fundamental engineering principle at work in multiaxial joints: the more movement a joint allows, the less inherently stable it becomes. This trade-off is most visible at the shoulder. Because the socket is so shallow relative to the ball, the shoulder relies heavily on muscles, tendons, and ligaments to stay in place rather than on bony architecture alone. That makes it the most mobile joint in your body and also the most vulnerable to injury.
Common shoulder problems stem directly from this design. Dislocations happen when the ball slips out of its shallow socket. Rotator cuff tears involve the group of muscles and tendons responsible for holding the joint together during movement. Bursitis, tendinitis, frozen shoulder, and arthritis all reflect the wear that comes with a joint built to move in virtually every direction while supporting the weight and force of arm movements.
The hip, by contrast, dislocates far less often. Its deeper socket and heavier ligaments provide bony stability that the shoulder simply lacks. The price is a more restricted range of motion, which is fine for its primary roles of weight-bearing, walking, and running.
How Multiaxial Compares to Other Joint Types
- Uniaxial (one axis): Hinge joints like the elbow and knee. They allow flexion and extension only.
- Biaxial (two axes): Condyloid joints like the knuckles and saddle joints like the base of the thumb. They allow flexion, extension, and side-to-side movement, plus circumduction, but no true rotation.
- Multiaxial (three or more axes): Ball-and-socket joints (shoulder, hip) and planar joints (wrist bones, ankle bones, spinal facets). Ball-and-socket joints allow flexion, extension, abduction, adduction, rotation, and circumduction. Planar joints allow small gliding movements in multiple directions.
One movement that distinguishes multiaxial ball-and-socket joints from biaxial joints is true rotation, where the bone spins around its own long axis. When you turn your arm so your palm faces forward or backward, that’s the shoulder rotating the upper arm bone. This type of medial and lateral rotation occurs only at the shoulder and hip.