The humerus is a long bone, which is defined as a bone that is longer than it is wide
The other four types of bones are short, flat, irregular, and sesamoid. It runs from the scapula to the two bones
of the forearm, the ulna, which runs from the medial side of the elbow to the pinky
side of the wrist, and the radius, which runs from the lateral side of the elbow to the
thumb side of the wrist. The humerus can be divided into three sections
– the humeral upper extremity, body, and lower extremity. The upper extremity has a
rounded head, a narrow neck, and two projections called tubercles, or tuberosities. The body
of the humerus is fairly cylindrical in the upper half and more prismatic and flattened
in the lower portion. The lower extremity has two epicondyles, two processes (trochlea
and capitulum, and three fossae (radial fossa, coronoid fossa, and olecranon fossa).
Let’s discuss the humeral upper extremity first. The head of the humerus faces medially
and articulates with the glenoid fossa of the scapula. The groove that surrounds the
articular surface of the head of the humerus is called the anatomical neck. This is where
the articular envelope attaches. An articular envelope, also called a joint capsule, is
an envelope surrounding a synovial joint. Note that in addition to its true anatomical
neck, the constriction below the greater and lesser tubercles of the humerus, which is
the connection between the head and the shaft of the humerus, is termed its surgical neck
because it tends to be the location of fractures. The greater tubercle is a projection on the
lateral side of the humerus. It is larger than and posterior to the lesser tubercle.
The lesser tubercle is a smaller projection on the lateral side of the humerus. The bicipital
groove, also called the intertubercular groove, or sulcus intertubercularis, is a deep groove
separating the greater and lesser tubercles. The crest of the greater tubercle forms the
lateral lip of the bicipital groove, while the crest of the lesser tubercle forms the
medial lip of the bicipital groove. The bicipital groove begins between the two tubercles and
extends longitudinally down the shaft of the humerus.
The shaft of the humerus has three borders and three surfaces. The borders are anterior,
medial, and lateral. The surfaces are antero-medial, antero-lateral, and posterior.
The anterior border runs from the greater tubercle to just above the coronoid fossa.
The medial border runs from the lesser tubercle to the medial epicondyle. Finally, the lateral
border extends from the back of the greater tubercle to the lateral epicondyle.
Now onto the surfaces. The anteromedial surface is between the medial border of the humerus
to continuation of crest of greater tubercle. It is found between the anterior and medial
borders. Its upper part is narrow, and its base is smooth and wide.
The anterolateral surface is the area between the lateral border to the anterior border.
In the middle of this surface, the deltoid tuberosity is featured.
The posterior surface is between the medial and lateral borders and appears kind of twisted.
The upper portion is twisted medially, and the lower portion is twisted laterally.
The deltoid tuberosity is a roughened, triangular area on the lateral surface of the humerus’
shaft and it is the site of insertion of the deltoid.
The radial sulcus also goes by several other names – the spiral groove, the musculospiral
groove, the radial groove. Whatever you want to call it, it is found here on the posterior
surface of shaft. It is shallow and broad and it found at the center of the lateral
border. It’s located posteroinferior to the deltoid tuberosity. The inferior boundary
of the spiral groove is continuous distally with the lateral border of the shaft.
The nutrient foramen is hard to see on this model. It’s located in the anteromedial
surface of the humerus and allows the nutrient arteries to enter the humerus. Inside the
humerus, they send branches both upward and downward to the bone marrow.
Now let’s cover the humeral lower extremity. The olecranon fossa is a hollow found on the
posterior of the humerus. When you extend your elbow, it accommodates the olecranon
process. The coronoid fossa is a medial hollow on the anterior surface of distal humerus.
When you flex your elbow to the max, it receives the coronoid process of the ulna. The radial
fossa is located laterally on the anterior surface of the distal forearm and this part
receives the head of the radius during max flexion of the elbow. The capitulum of the
humerus is a rounded eminence forming the lateral part of the distal humerus. It articulates
with the head of the radius. The trochlea is found on the medial portion of the distal
humerus and articulates with the ulna. The lateral epicondyle is a bulge of bone
located superior and lateral to the capitulum, while the more prominent medial epicondyle
is a bulge of bone located superior and medial to the trochlea. The medial supracondylar
ridge is the sharp medial border of the distal humerus. The lateral supracondylar ridge is
the sharp lateral border of the distal humerus.