HUMERUS ANATOMY

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The humerus is a long bone. 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 3 sections – the humeral upper extremity, body, and lower extremity. The upper extremity has a rounded head, a narrow neck, and 2 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 2 epicondyles, 2 processes (trochlea and capitulum, and 3 fossae (radial fossa, coronoid fossa, and olecranon fossa). • The Upper Extremity: 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/intertubercular groove/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 3 borders and 3 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. • The 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. • Model from: https://www.turbosquid.com/FullPrevie...

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