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Bones of the Arm: Humerus, Ulna & Radius
Bones of the Arm: Humerus, Ulna & Radius
Includes labeled diagrams, downloadable notes, anatomy quizzes, and interactive learning tools
The upper limb beyond the shoulder is formed by the humerus in the arm and two parallel bones in the forearm: the ulna and the radius. Together, these bones create the framework for movement at the shoulder, elbow, and wrist, while also providing attachment sites for muscles that control the hand and arm.
Humerus
The humerus is the longest and largest bone of the upper limb. At its proximal end, it has a large, rounded head that faces upward, medially, and slightly backward. This head articulates with the glenoid cavity of the scapula to form the shoulder joint.
Around the edge of the head is the anatomical neck, which separates it from the rest of the bone and provides attachment for the joint capsule.
Next to the head are two projections called the greater and lesser tubercles. The greater tubercle is located laterally and has areas for muscle attachment, while the lesser tubercle is found on the anterior side and also serves as a muscle attachment site.
Between these two tubercles is the intertubercular groove, also known as the bicipital groove, which allows passage of the tendon of the biceps brachii muscle.
Below the tubercles is the surgical neck, which connects the expanded upper end of the humerus to its shaft and is a common site of fractures.
The shaft of the humerus is cylindrical in its upper part and becomes flatter toward the distal end. Along the lateral side of the shaft is the deltoid tuberosity, a roughened area where the deltoid muscle attaches.
At its distal end, the humerus becomes flattened and forms structures important for the elbow joint. There are two main articular surfaces: the trochlea, which articulates with the ulna, and the capitulum, which articulates with the radius.
Above these are depressions that receive parts of the forearm bones during movement. The coronoid fossa and radial fossa accommodate the ulna and radius when the elbow is flexed, while the olecranon fossa receives the olecranon of the ulna when the elbow is extended.
The distal humerus also has the medial and lateral epicondyles, which serve as attachment points for muscles of the forearm. The medial epicondyle is larger because it gives rise to stronger flexor muscles.
Ulna
The ulna is the medial bone of the forearm (it runs parallel to the radius). Its proximal end is large and forms an important part of the elbow joint. It has a C-shaped trochlear notch that articulates with the trochlea of the humerus. This notch is formed by the olecranon process, which creates the tip of the elbow, and the coronoid process, which forms its lower part.
Just below the coronoid process is the ulnar tuberosity, a rough area for muscle attachment. On the lateral side of the ulna is the radial notch, where the head of the radius articulates to form the proximal radioulnar joint.
The shaft of the ulna extends downward and gradually becomes smaller. Along its lateral side is the interosseous border, where the interosseous membrane attaches and connects the ulna to the radius.
The distal end of the ulna consists of a small head and a styloid process, which provides attachment for ligaments and helps stabilize the distal radioulnar joint.
Radius
The radius is the lateral bone of the forearm, located on the thumb side (it runs parallel to the ulna). Its proximal end has a disc-shaped head with a shallow depression on top, which articulates with the capitulum of the humerus. The outer surface of the head is smooth and articulates with the radial notch of the ulna, forming the proximal radioulnar joint.
Just below the head is the neck, followed by the radial tuberosity, which is a rough, oval-shaped projection that serves as a muscle attachment point.
The shaft of the radius is slightly curved and becomes wider toward its distal end. Along its medial side is the interosseous border, which provides attachment for the interosseous membrane that connects the radius to the ulna.
The radius has three surfaces and three borders, and its shape allows it to rotate around the ulna during forearm movements.
The distal end of the radius is large and plays a major role in forming the wrist joint. It has a surface that articulates with carpal bones.
On its medial side is the ulnar notch, which articulates with the head of the ulna to form the distal radioulnar joint. On the lateral side is the styloid process, a pointed projection that provides attachment for ligaments supporting the wrist. This styloid process extends further down than the one on the ulna, which helps limit excessive sideways movement of the hand.
Need a recap? Take a look at the bones of the arm anatomy notes here.
Need a recap? Take a look at the bones of the arm anatomy notes here.
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References
References
Gray, H. (1918). Anatomy of the human body (W. H. Lewis, Ed.; 20th ed.). Lea & Febiger.
J. Gordon Betts, Kelly A. Young, James A. Wise, Eddie Johnson, Brandon Poe, Dean H. Kruse, Oksana Korol, Jody E. Johnson, Mark Womble, Peter DeSaix. (2013, April 25). Anatomy and Physiology. OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/8-2-bones-of-the-upper-limb.
Based on OpenStax, Anatomy and Physiology (2013), licensed under CC BY 4.0.
Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction.
Content paraphrased; adaptations were made.
Sobotta, J. (1914). Atlas and text-book of human anatomy (J. P. McMurrich, Ed.; W. H. Thomas, Trans.). W.B. Saunders Company.
Image Credis
Image Credis
Images used in this guide and games are from the following source:
Sobotta, J. (1914). Atlas and text-book of human anatomy (J. P. McMurrich, Ed.; W. H. Thomas, Trans.). W.B. Saunders Company.
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