What is the humerus?
The humerus is the upper arm bone – a long, straight tubular bone that is divided into an upper (proximal) end, a middle section (humeral shaft, corpus humeri) and a lower (distal) end.
At the upper, proximal end – towards the shoulder – there is a spherical head (caput humeri), which is covered by a thick layer of cartilage. The surface area of the humeral head is about four times as large as that of the glenoid cavity of the shoulder. This disproportion and the fact that the glenoid cavity is relatively flat enable the shoulder joint to be very mobile: it has the largest circumference of all joints and allows the arm to move in all directions.
Directly under the humeral head, the humerus is separated from the neck (collum anatomicum) by a retraction, under which there are two strong tubercles (tuberculum majus and tuberculum minus) – attachment points for various muscles.
The lower, distal end of the humerus has a triangular shape in cross-section. The sharp lateral edges end in two cusps (medial and lateral epicondyle), which can be clearly felt on the inside and outside of the elbow joint. The muscles that flex the forearm originate from the anterior surface. A groove for the ulnar nerve runs along the back. An impact or blow at this point triggers an electric shock-like pain that radiates into the little finger.
What is the function of the humerus?
The upper end of the humerus forms the joint head of the shoulder joint. The lower end of the humerus, together with the two forearm bones, the radius and ulna, is involved in the structure of the elbow joint.
Various muscles that attach to the humerus are responsible for the various movements in the shoulder joint, such as the deltoid muscle, which is part of the shoulder musculature. There are also other muscles in the upper arm that are responsible for movements in the shoulder joint as well as the elbow joint. These include, for example, the two-headed arm muscle (biceps brachii muscle), the arm flexor (brachialis muscle) and the three-headed arm muscle (triceps brachii muscle).
Where is the humerus located?
What problems can the humerus cause?
The head of the humerus is involved in the construction of the shoulder joint – the most mobile, but also the least secure joint in the body. As the joint capsule is shaped like a long, wide sac, it allows the humeral head to slide up to 1.5 centimeters out of the joint socket when air enters. The joint capsule is also very thin in the anterior region. Overall, this easily leads to dislocations (luxations) of the joint towards the front.
Painful tennis elbow (epicondylitis humeri radialis) is caused by overloading the tendon that attaches to the outside of the elbow at the lower end of the humerus and is responsible for extending the wrist. If, on the other hand, the flexor muscles of the wrist are overloaded, the inside of the elbow is affected and is referred to as golfer’s elbow (epicondylitis humeri ulnaris).
Older people with osteoporosis in particular can easily break the head of the humerus in a fall (humeral head fracture, subcapital humeral fracture). The humerus can also break in other places, for example in the shaft area.
In impingement syndrome, soft parts of the capsule (such as tendons) become trapped in the joint space between the acromion and the humeral head, which is quite painful.
