Hand nerve injuries
The N. medianus originates from the nerve plexus from the so-called medianus fork. After it has passed the upper arm, this hand nerve pulls on the flexion side of the arm towards the thumb. It runs under the retinaculum musculorum flexorum in the carpal tunnel between the deep and superficial tendons of the flexor muscles to the palm.
In the palm it finally branches out into its motor and sensitive branches. The motor nerve fibers supply the musculature of the thumb (thenar muscles). There they cause abduction, flexion and the juxtaposition of the thumb and the little finger.
In addition, the median nerve innervates the deep flexor muscles of the index finger and middle finger. The inner surface of the hand on the side of the thumb, the thumb itself and the index and middle finger are sensitively supplied by the hand nerve. This is where the transmission of sensitivity such as touch and tactile sensation takes place.
The nerve at the tips of the index and middle finger has its own and sole sensitive supply area, which is called an autonomous area. Various causes can lead to a chronic increase in pressure in the carpal tunnel. These causes can include space-consuming processes, fractures, dislocations of the carpal bones, inflammatory processes of the tendons, but also edema caused by pregnancy.
The traversing median nerve is compressed by the existing constriction and its function is restricted. In the following, loss of sensitivity occurs especially in the fingertips. If the increase in pressure in the carpal tunnel persists for a longer period of time, additional motor failures occur as the process progresses.
One speaks of a positive bottle sign, since the patient is no longer able to completely enclose a bottle with his thumb. In the area of the elbow, traumatic damage such as fractures and luxation can also occur. Due to the close proximity to the hand nerve, it can also be injured quickly.
The clinical picture then shows the typical swearing hand for such an injury. If the affected person tries to close his restricted hand to the fist, thumb, index and middle finger are not bent properly. The muscles are no longer innervated by the hand nerve and are no longer able to perform their actual movement. In addition, other symptoms such as numbness and muscle atrophy in the thumb area can occur.
