In this lesson, you will learn about the humerus bones in the human body. You’ll also explore the anatomy of this prominent arm bone and how it can be fractured.
Definition of Humerus
The humerus is the long bone of your upper arm. It’s attached to several other bones. At the elbow, the humerus helps to form the elbow joint.
At the shoulder joint, the top of the humerus is the ball part of the joint. The humerus also connects to the clavicle (the long curved bone just above the first rib), and the scapula (the triangular bone just below the shoulder which angles toward the back).
The anatomical (physical and structural) features of the humerus include:1. The head, which is the top of the bone that fits into the shoulder joint.
In the back, the head looks very round – like a ball. In the front, the head flattens a bit where it attaches to the scapula and clavicle. The three bones that form part of the shoulder joint are the humerus, the scapula, and the clavicle.2. The neck lies just below the head of the humerus. There is a portion called the anatomical neck and one called the surgical neck. The anatomical neck is the portion that lies just below the head.
As the neck continues along the humerus body, it is called the surgical neck (so named because this is the location of many fractures that require surgery).3. The greater tubercle (a round projection, also called a nodule), is where muscles and ligaments attach. It is located on the upper most part of the head where it flattens and has a front and back face. This is where three of the muscles that form the rotator cuff – which provides mobility and strength to the shoulder joint – attach.4. The lesser tubercle is located on the opposite side of the greater tubercle and is where the last rotator cuff muscle attaches.
As the name implies, it’s much smaller than the greater tubercle.5. The intertubercular groove, also called sulcus, is located between the greater and lesser tubercles. It’s a deep indentation and the outer edges are called ‘lips’. Many ligaments are attached to this grove.
6. The body (also called the shaft), is the long straight cylinder like section of the bone with a rough surface. There are many muscles and ligaments that attach to the humerus – the rough surfaces are due to these attachments.
7. The deltoid tuberosity is on the side of the shaft where the deltoid muscle attaches to the humerus.8. The radial groove runs down the back surface of the shaft and is parallel to the deltoid tuberosity. The radial nerve and profunda brachii artery are attached to this groove.9.
The medial and lateral supraepicondylar ridges – a condyle – form the knuckle projection of a bone. This is the location of muscle attachments of the back forearm bones (the ulna and radius).10. The lateral and medial epicondyles are where the ulnar nerve resides.11.
The trochlea is located in the front and goes around to the back of the humerus. The ulna bone is attached here.12. The capitulum is beside the trochlea and it’s where the radius bone attaches.13.
Finally, there are 3 depressions on the humerus located at the end of the bone. They are the coronoid, radial and olecrannon fossae. These areas are very important because without them there would be no place for the forearm bones when the elbow is bent. They accommodate the forearm bones during bending of the elbow.
Imagine this scenario: your friend Susie loves to climb trees.
The other day, she was climbing down a tree when a bee landed on her nose. When Susie was swatting at the bee, she lost her balance and down she went. When Susie fell, she landed on her left arm, which was pointing straight down and she heard a bone snap.
The fracture (or broken bone) occurred at Susie’s surgical neck of the left arm. Luckily, she did not cut an artery or any nerves but she still needed to have surgery and her arm will need to be in a cast for about 6 weeks, which means no more tree climbing for awhile.Whenever there is a fracture of the surgical neck, doctors are very concerned because of the arteries and nerves that are located in that area.
Let’s talk about this a little. Any cutting of an artery is a medical emergency because blood can be lost at such a rate that the person can easily die. But the artery of most concern in a situation like this is the posterior circumflex artery.The axillary nerve is also located in this area and when that nerve is cut, the arm muscles will become paralyzed (or unable to move). As a result, a person whose axillary nerve has been cut cannot raise his or her arm and will be unable to feel sensation below the cut.
Now let’s talk about other fractures that may occur and the resulting defects, including a mid shaft fracture and distal humerus fractures:1. A mid shaft fracture can damage the radial nerve causing the wrist to drop and loss of sensation to parts of the hand and fingers.2. A distal humerus fractures include two types: supraepicondylar fractures and medial epicondyle fractures. The first type happens when a person falls on an open arm but it fractures at the elbow. The deformity caused by this type of fracture is called Volkmann’s ischaemic contracture where the whole hand cannot close. In a medial epicondyle fracture, the ulnar nerve is affected and the index and middle fingers cannot bend.
This is referred to as the ulnar claw.
The humerus bone is one of the major bones in the upper arm that provides structure and function for an individual. Some specifics of structure include the formation of the joints and the support for muscles and ligaments.
Functions of the humerus include the stability to move the upper arm and the location for attachment of the muscles and ligaments to other bones.The major anatomical features of the humerus include the head, the two necks, the body or shaft, and the condyles. The minor features include the tubicles, groves, tuberosity, trochlea, capitulum, and the three depressions.Fractures usually occur at the surgical neck. Other fractures can occur at the mid-shaft area and in the distal area of the humerus.
The two distal fracture areas are located at the supraepicondylar and medial epicondyle areas.