Next Lesson - Muscles of the Shoulder
Core
This article will discuss five key bones that provide structure to the upper limb. The shape of these bones allows a wide range of movement at the shoulder, elbow and forearm. The following will be discussed:
- Scapula
- Clavicle
- Humerus
- Ulna
- Radius
This is a large, flat, triangular bone found posteriorly in the thorax. It articulates (forms a joint) with the humerus and clavicle. Together, the scapula and clavicle make up the shoulder girdle, which connects the arm to the trunk. The joint with the humerus allows the shoulder to move. It is the site of attachment for many muscles and is therefore vital for normal function of the shoulder. The scapula articulates with the head of the humerus via the glenohumeral joint (the ball-and-socket shoulder joint) and articulates with the clavicle via the acromioclavicular joint (where the acromion of the scapula, described below, meets the clavicle).
The scapula has two surfaces (costal and posterior) and a lateral angle, so there are three main regions to know:
- Costal surface - region facing the ribcage
- Lateral angle - region closest to the humerus that bears the glenoid fossa (a shallow hollow that forms the socket of the shoulder joint)
- Posterior surface - region that faces backwards, away from the ribcage
Some key bony landmarks of the scapula include the following. These are the places where muscles and ligaments attach and where joints form. A process or tubercle is a raised part of the bone, and a fossa is a hollow:
Coracoid Process - found on the costal surface, this is a projection that lies just inferior to the clavicle. It is the site of origin (the attachment that stays fixed when the muscle contracts) of coracobrachialis (an upper arm muscle) and of the short head of biceps brachii. The chest muscle pectoralis minor also attaches to it.
Glenoid Fossa - found on the lateral angle, it articulates with the head of the humerus to form the shoulder joint.
Supraglenoid and Infraglenoid Tubercle - regions found immediately superior and inferior to the glenoid fossa respectively. The long head of biceps brachii attaches to the supraglenoid tubercle and the long head of triceps brachii attaches to the infraglenoid tubercle.
Spine of the Scapula - found posteriorly, it divides the posterior surface of the scapula into two regions.
Supraspinous and Infraspinous Fossae - regions found just superior and inferior to the spine of scapula respectively. They give origin to supraspinatus and infraspinatus respectively, two of the rotator cuff muscles (a group of four muscles that move the arm and keep the head of the humerus in the shoulder socket).
Acromion - a projection/elongation of the spine of the scapula which articulates with the clavicle to form the acromioclavicular joint.
Diagram - Costal aspect of the left scapula
Creative commons source by Atlas of Human Anatomy by Professor Dr. Carl Ernest Bock, edited by Dr. Sachin Sudhakaran [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
Diagram - Posterior aspect of the left scapula
Creative commons source by Atlas of Human Anatomy by Professor Dr. Carl Ernest Bock, edited by Dr. Sachin Sudhakaran [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
Also known as the collarbone, this is a long bone which articulates with both the sternum and the acromion of the scapula. It allows for movement by forming the shoulder girdle with the scapula. It protects the nerves and blood vessels (the neurovascular structures) that pass behind it on their way to the arm. It also transmits force from the arm to the axial skeleton (the skeleton of the head and trunk), for example in a fall.
There are a few landmarks to know:
- Medial end (sternal end) - a region with a smooth joint surface (a facet) that articulates with the manubrium (the top part of the sternum).
- Shaft - allows for attachment of different muscles and is also the region most prone to fracture, particularly the middle third (about 80% of clavicle fractures).
- Lateral end - location of a small facet which articulates with the acromion.
Diagram - Anterior aspect of the left clavicle. The highlighted region in the middle illustrates the most common fracture site. The articulating surfaces are highlighted on either side, with the acromial end on the left and the sternal end on the right
Creative commons source by Atlas of Human Anatomy by Professor Dr. Carl Ernest Bock, edited by Dr. Sachin Sudhakaran [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
This is a long bone within the upper limb found between the shoulder and the elbow. It articulates with the scapula to form the shoulder joint and articulates with the ulna and the radius to form the elbow joint.
Some proximal bony landmarks include:
Head of the Humerus - region that articulates with the glenoid fossa of the scapula.
Greater Tubercle - a bony ridge that is found laterally on the humerus. It is the site of attachment for three of the rotator cuff muscles and can be palpated externally.
Lesser Tubercle - a smaller ridge, that is found more medial to the greater tubercle.
Intertubercular Sulcus - a groove that runs between the two tubercles that allows for the tendon of the long head of biceps brachii to descend.
Anatomical and Surgical Neck - these necks separate the head from the shaft. The anatomical neck is found proximal to the tubercles, whilst the surgical neck is found distal to the tubercles. The surgical neck is a common site for fractures of the humerus. These usually follow a direct blow or a fall onto an outstretched hand, and are especially common in older people with weakened bones (osteoporosis). The axillary nerve (which supplies the deltoid muscle over the shoulder) lies against the bone here and can be injured.
Diagram - Anterior view of proximal left humerus
Creative commons source by Atlas of Human Anatomy by Professor Dr. Carl Ernest Bock, edited by Dr. Sachin Sudhakaran [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
The shaft of the humerus is the site of attachment for many muscles. A fracture of the shaft of the humerus can damage the radial nerve (which supplies the muscles that extend the wrist), because the nerve lies very close to the bone. In fact, the radial nerve runs through a spiral groove found on the posterior humerus.
The distal end of the humerus is responsible for articulating with the ulna and the radius to form the elbow joint. Therefore, there are a few bony landmarks to know:
Capitulum - an anterior articulating region which articulates with the head of the radius. It is found lateral to the trochlea.
Trochlea - a large articulating region that is found medially and extends posteriorly. It articulates with the trochlear notch of the ulna to form the elbow joint.
Lateral and Medial Epicondyles - found on either side of the distal humerus, just proximal to the capitulum and trochlea, these are projections of the humerus that allow for sites of attachment of different muscles. The medial epicondyle is larger than the lateral epicondyle and is easily palpable. The ulnar nerve runs in a groove behind the medial epicondyle, close to the surface. A fracture of the medial epicondyle can injure the nerve. Because the nerve lies so close to the surface, a knock to the elbow can compress it and cause tingling in the hand, especially in the little and ring fingers (the 'funny bone' feeling).
Olecranon Fossa - found on the posterior humerus just proximal to the trochlea. It receives the olecranon (the tip of the elbow, part of the ulna) when the elbow straightens.
Coronoid Fossa - found on the anterior humerus and just proximal to the trochlea. It receives the coronoid process of the ulna (a projection at the front of the ulna, described below) when the elbow bends.
Radial Fossa - found on the anterior humerus and just proximal to the capitulum. It receives the head of the radius when the elbow bends.
Diagram - Anterior view of distal left humerus
Creative commons source by Atlas of Human Anatomy by Professor Dr. Carl Ernest Bock, edited by Dr. Sachin Sudhakaran [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
Diagram - Posterior view of distal left humerus
Creative commons source by Atlas of Human Anatomy by Professor Dr. Carl Ernest Bock, edited by Dr. Sachin Sudhakaran [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
One of two bones in the forearm, this long bone lies medially to the radius. It acts to provide leverage for elbow movement.
Proximally, there are a few key landmarks to allow for effective articulation with the humerus to form the elbow joint:
Trochlear Notch - a large depression that articulates with the trochlea.
Olecranon - a large projection that forms part of the trochlear notch. It is the tip of the elbow and can be easily felt through the skin (palpated). It is the site of attachment for the triceps brachii muscle (the muscle that straightens the elbow).
Coronoid Process - an anterior projection that also forms part of the trochlear notch.
Radial Notch - located laterally, this articulates with the radius to form the proximal radioulnar joint.
Diagram - Anterior surface of proximal left ulna
Creative commons source by Atlas of Human Anatomy by Professor Dr. Carl Ernest Bock, edited by Dr. Sachin Sudhakaran [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
Diagram - Posterior surface of proximal left ulna
Creative commons source by Atlas of Human Anatomy by Professor Dr. Carl Ernest Bock, edited by Dr. Sachin Sudhakaran [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
The ulna tapers off to its distal end. The shaft is the site of attachment for a few muscles. The shaft also has an interosseous (between the bones) border, the edge facing the radius, for attachment of the interosseous membrane (the sheet of tough tissue that joins the radius and ulna).
The distal end of the ulna is significantly smaller than the proximal end. The head of the ulna can be found here and it articulates with the ulnar notch of the radius, forming the distal radioulnar joint. There is also a narrow bony projection on the medial and posterior side, called the ulnar styloid process.
Diagram - Anterior surface of distal left ulna
Creative commons source by Atlas of Human Anatomy by Professor Dr. Carl Ernest Bock, edited by Dr. Sachin Sudhakaran [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
Like the ulna, this is another long bone in the forearm and is found laterally. It rotates around the ulna, allowing supination (turning the palm upwards) and pronation (turning the palm downwards) of the forearm at the proximal and distal radioulnar joints.
Proximally is the head of the radius - a disc-like structure, which articulates with the capitulum of the humerus. It also articulates with the radial notch of the ulna. The radial head rotates within the annular (ring-shaped) ligament at the proximal radioulnar joint. The radial tuberosity is a bony bump just below the neck of the radius. It is where biceps brachii attaches, and this muscle helps to turn the forearm palm upwards (supination).
The shaft provides attachment for muscles and the interosseous membrane, which connects the radius and ulna.
Distally, the radius articulates with the scaphoid and lunate bones (two of the carpal bones, in the wrist), forming the wrist joint. On the lateral surface, there is a radial styloid process. The medial surface is curved inwards (concave) to allow for articulation with the head of the ulna via the ulnar notch.
Diagram - Anterior surface of left radius
Creative commons source by Atlas of Human Anatomy by Professor Dr. Carl Ernest Bock, edited by Dr. Sachin Sudhakaran [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
For Pathologies and Conditions of the Upper Limb, check out our articles on Conditions of the Shoulder and Clavicle, Arm, Elbow and Forearm and Wrist.
Reviewed by: Dr. Thomas Burnell and Dr. Marcus Judge
Edited by: Dr. Maddie Swannack
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