Hey there everyone! It’s Matt from Kenhub, and in this tutorial, we will discuss the dorsal interossei muscles of the hand. There is a series of these muscles found in both the foot and in the hand and though they have different locations, their function is similar. This image that you see on the screen shows the back of your hand, and you can see that the dorsal interossei muscles of the hand are four short muscles of the metacarpus. Each of them is attached to the adjacent sides of two metacarpal bones. For example, the first one between thumb and index fingers, the second between index and middle fingers, and so on. These muscles are bipennate and each muscle has two heads as you can see on the image.
The first dorsal interosseus – the largest and strongest among the four – can be easily felt in the web between thumb and index finger. Nevertheless, it is also possible to palpate the remaining three between the metacarpal bones and the tendon of the extensor digitorum muscle.
As I just mentioned, each of these muscles has two heads which have their origin from the adjacent sides of the metacarpal bones. For example, the first dorsal interosseus muscle has its origin on the ulnar side of the metacarpal of the thumb and on the radial side of the metacarpal of the index finger. In the same way, the second interosseus muscle also arises from two heads with the one head originating from the ulnar side of the metacarpal of the index finger and the other head originating from the radial side of the middle finger and the same pattern goes for the rest of the dorsal interossei muscles of the hand.
The four interossei muscle tendons insert at the dorsal aponeurosis and the base of the proximal phalanx of fingers 2, 3 and 4. They all run towards the middle finger which leads to the following insertion surfaces: dorsal interosseus muscle 1 – radial side of the index finger, dorsal interosseus muscle 2 – radial side of the middle finger, muscle 3 – ulnar side of the middle finger, and 4 – ulnar side of the ring finger.
The four interossei muscle tendons insert at the dorsal aponeurosis and the base of the proximal phalanx of fingers 2, 3 and 4. They all run towards the middle finger which leads to the following insertion surfaces. The first dorsal interosseus muscle seen on the far right of the image inserts at the radial side of the index finger, the second dorsal interosseus muscle inserts at the radial side of the middle finger, the third dorsal interosseus muscle at the ulnar side of the middle finger, and, finally, the fourth dorsal interosseus seen on the far left of the image insert at the ulnar side of the ring finger.
The innervation of all dorsal interossei of the hand is carried by the deep branch of the ulnar nerve. The dorsal interossei partially perform opposite actions in the fingers. While the first and second pull the index and the middle fingers laterally, the third and fourth move the middle and ring fingers medially. In other words, abduction of index, middle and ring fingers. Furthermore, their contraction leads to flexion in the metacarpophalangeal joints and extension in the proximal and distal interphalangeal joints.
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