The spoke is one of the two forearm bones. More about her anatomy and possible diseases, read here!


The spoke (Radius) is one of the two bones of the forearm. Together with the ulna, the ulna, it connects the humerus with the carpal bones. With numerous muscles and tendons, the spokes are involved in the movements of the forearm against the upper arm and the hand against the forearm. Read everything important about the spoke!

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  • What is the spoke?

  • What is the function of the spoke?

  • Where is the spoke?

  • What problems can the spoke cause?

What is the spoke?

The spine is a tubular bone, which lies parallel next to the Ulna (Elle) and is connected to this by a strong membrane of tight connective tissue. Like the ulna, the radius is divided into three areas: the Shank (Corpus) as well as one upper (proximal) and lower (distal) end.

In the middle area, the shaft, the spoke is about the same thickness as the ellipse and triangular. At the upper (proximal) end, it is slender and round with a flattened head (caput radii). This carries above a dentation for the head of the humerus (Capitulum humeri). In addition, there is still a hinged connection with the ulna, which in turn is also articulated to the humerus. All three partial joints together form the elbow joint.

Downwards, towards the wrist, the spine becomes wider and thicker and ends in a concave articular surface, articulated with the two carpal bones of the scaphoid and lunate. On the outer side (small finger side), the radius is hinged to the ulna. On the inner side (thumb side) the spoke has a short bony protrusion (styloid process), to which the upper arm spinal muscle (brachial dia- talis) attaches. This flexes the forearm in the elbow joint when the palm is facing down and turns the forearm to a central position until the palm is vertical.

Many other muscles include the spoke. They are divided into two groups: a superficial and a deep layer. The first group includes the common extensor digitorum, which stretches the 2nd to 5th fingers and the whole hand, as well as the miniature extensor (Extensor digiti minimi), which stretches the little finger and slightly the whole hand.

The second group includes the supinator, which rises from the back of the cubit but then covers the top end of the spoke and turns the arm and hand outward. The long thumb puller (abductor pollicis longus) attaches to the base of the metacarpal bone of the thumb, spreads the thumb and gently turns the palm upwards. The short and the long thumb extensor (Extensor pollicis brevis and longus) stretch the thumb and help with the lateral movement of the hand. The forefinger extensor (Extensor indicis) stretches the forefinger and the hand and turns the palm slightly upwards.

The long radial extensor (extensor carpi radialis longus) extends from the humerus to the lateral epicondyle of the humerus and continues in a long tendon to the second metacarpal bone. He draws his hand up and to the side of the thumb - as does the short radial handgrip, which starts at the humerus and attaches to the third metacarpal bone.

What is the function of the spoke?

The spoke joins together with the ulna the humerus with the carpal bones and thus with the hand. In the elbow joint, it contributes to a small part of the flexion - the largest part is done by the ulna-humeral joint, the joint between the ulna and humerus. At the wrist, the spoke carries the greater part of the articulated connection with two of the carpal bones (the moon and navicular bones).

Where is the spoke?

It lies parallel to the ulna and forms with it the forearm. At the upper end, she is involved in the construction of the elbow joint together with the ulna and at the lower end - also together with the Elle - at the construction of the wrist.

What problems can the spoke cause?

A distal radius fracture - ie a fracture of the spine in the lowest area - represents about a quarter of all fractures. In the majority of cases, the cause is a fall that you try to catch with the extended wrist (for example, when snowboarding, inline skating, etc.). Rarely, the hand is flexed on impact, so that one lands first with the back of the hand. In children, the spoke fracture is often a so-called Grünholzfraktur, in which, although the bone is broken, the periosteum is still intact.

The spoke can also break in the middle to upper range. Less common is a radial head fracture, ie a fracture of the radial head in the elbow area.

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