---
title: "Radioulnar Joint | Anatomy and Physiology I"
description: "Radioulnar joint is the pivot joint between the radius and ulna that lets your forearm pronate and supinate in Anatomy and Physiology I."
canonical: "https://fiveable.me/anatomy-physiology/key-terms/radioulnar-joint"
type: "key-term"
subject: "Anatomy and Physiology I"
unit: "Unit 9"
---

# Radioulnar Joint | Anatomy and Physiology I

## Definition

The radioulnar joint is the synovial pivot joint between the radius and ulna that lets your forearm rotate. In Anatomy and Physiology I, it is the joint behind pronation and supination.

## What It Is

The radioulnar joint is the part of your forearm that lets the radius turn around the ulna, which is why your hand can rotate palm up and palm down. In Anatomy and Physiology I, you usually see it described as a synovial pivot joint, because one bone spins around another at a fixed point.

There are actually radioulnar joints at both ends of the forearm. The proximal radioulnar joint sits near the elbow, where the head of the radius meets the radial notch of the ulna. The distal radioulnar joint sits near the wrist, where the radius and ulna also have to stay coordinated as the forearm rotates. Together, these joints let the radius move while the ulna stays relatively stable.

That movement is what makes pronation and supination possible. Pronation turns the forearm so the palm faces down or back, and supination turns it so the palm faces up or forward. A simple way to picture it is to hold your elbow still and rotate your forearm, like turning a doorknob or twisting a screwdriver. The motion is not happening at the elbow hinge alone, it depends on the radius crossing over the ulna.

The joint is stabilized by structures that keep the bones lined up while still letting them rotate. The annular ligament wraps around the head of the radius at the elbow, and the interosseous membrane runs between the shafts of the radius and ulna to help hold them together and distribute force. The quadrate ligament also helps limit excess rotation at the proximal joint.

This is a good example of how anatomy and function match. The radioulnar joint is small compared with the shoulder or elbow, but without it you would lose the precise forearm rotation needed for writing, using tools, and everyday gripping tasks.

## Why It Matters

The radioulnar joint shows how joint structure determines movement in Anatomy and Physiology I. If you know it is a pivot joint, you can predict that rotation is the main motion, not bending or straightening like at the elbow.

It also helps you separate nearby joints that work together but do different jobs. The humeroulnar and humeroradial joints mainly handle elbow flexion and extension, while the radioulnar joints handle pronation and supination. That distinction comes up when you label diagrams, describe movement in a lab, or explain why a forearm injury can limit more than one motion.

This term also connects anatomy with everyday function. A person can flex and extend the elbow fairly well and still struggle with opening jars, turning a key, or using a screwdriver if the radioulnar joint is restricted. That makes it a useful term for case questions about fractures, dislocations, and limited range of motion.

It is also a bridge term for learning the skeletal system as a system, not a list of bone names. The radius, ulna, annular ligament, and interosseous membrane all have to work together for smooth rotation. Once you understand that setup, a lot of upper limb movement starts to make more sense.

## Connections

### Pronation

Pronation is one of the two main motions produced by the radioulnar joint. When you pronate, the radius rotates over the ulna so the palm faces down or back. This is the movement you use when typing with your palms down, placing your hand flat on a table, or lowering a spoon into soup with the palm turned inward.

### Supination

Supination is the opposite rotation, and it depends on the same radioulnar joints. In supination, the palm faces up or forward, and the radius and ulna return to a more parallel position. It is easier to feel this motion if you hold your elbow at your side and turn your palm from up to down and back again.

### Synovial Joint

The radioulnar joint is a synovial joint, so it has a joint cavity, articular cartilage, and a capsule that support smooth movement. Knowing it is synovial helps you predict why the surface is low-friction and why synovial joints are built for mobility rather than simple bone-to-bone rigidity.

### [Gliding Joints](/anatomy-physiology/key-terms/gliding-joints)

Gliding joints also involve relatively small movements, but the motion is different. Gliding joints allow flat bone surfaces to slide past each other, while the radioulnar joint is a pivot joint designed for rotation. Comparing the two helps you avoid mixing up small joint motions that look similar on a diagram.

## On the AP Exam

A lab practical or diagram question may show the forearm and ask you to identify which joint allows palm-up and palm-down rotation. You would name the radioulnar joint and connect it to pronation and supination, not elbow flexion. A movement question might ask which bones are involved, so you should point to the radius and ulna and describe how the radius rotates around the ulna. If a case question mentions trouble turning a screwdriver after a forearm injury, that is a clue that radioulnar motion has been affected. You may also need to tell the difference between rotation at the forearm and bending at the elbow, since those are easy to confuse on multiple-choice items and in anatomy images.

## Radioulnar Joint vs Elbow Joint

The elbow joint and the radioulnar joint work together, but they do different jobs. The elbow mainly handles flexion and extension, while the radioulnar joint handles rotation of the forearm. If a question asks about turning the palm up or down, the radioulnar joint is the better answer.

## Key Takeaways

- The radioulnar joint is the synovial pivot joint that lets the forearm rotate.
- Its main motions are pronation and supination, which change the position of the palm.
- The proximal and distal radioulnar joints work together so the radius can rotate around the ulna.
- Ligaments like the annular ligament and the interosseous membrane help stabilize the forearm during rotation.
- If forearm rotation is limited, everyday actions like turning a key or using a screwdriver can become difficult.

## FAQs

### What is the radioulnar joint in Anatomy and Physiology I?

It is the synovial pivot joint between the radius and ulna that allows forearm rotation. You use it for pronation and supination, not for bending the elbow. In A&P, it is one of the clearest examples of how joint shape matches joint movement.

### What movement does the radioulnar joint allow?

It allows pronation and supination of the forearm. That means your palm can turn down or up because the radius rotates around the ulna. If a question asks about twisting motions rather than flexing or extending, think radioulnar joint.

### How is the radioulnar joint different from the elbow joint?

The elbow mainly does flexion and extension, while the radioulnar joint does rotation. They sit close together and work as a unit during arm movement, which is why they are easy to mix up. A good clue is the motion being described.

### Why is the radioulnar joint considered a pivot joint?

It is called a pivot joint because one bone rotates around another bone at a relatively fixed point. In the forearm, the radius spins around the ulna instead of sliding in many directions. That is what makes palm-up and palm-down motion possible.

## Related Study Guides

- [9.5 Types of Body Movements ](/anatomy-physiology/unit-9/5-types-body-movements/study-guide/biuQWSVXuy7GkxV4)

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