Corpus: Flexor digitorum superficialis muscle
1. Definition
The flexor digitorum superficialis muscle, abbreviated as FDS, belongs to the superficial layer of the flexors of the forearm. It is a two-headed muscle, which can be differentiated into a humeroulnar head and a radial head.
2. Anatomy
2.1. Origin
The humeroulnar head originates from the medial epicondyle of the humerus, the coronoid process of the ulna, and the antebrachial fascia. The radial head originates from the anterior surface of the radius.
2.2. Insertion
The tendon passes under the flexor retinaculum through the carpal tunnel and divides before insertion into four tendons, which attach laterally to the middle phalanges (middle phalanges) of the 2nd to 5th fingers. Just before their attachments, the tendons split again into two separate strands. The tendons of the flexor digitorum profundus muscle run through the gaps between these two strands, a configuration known as the tendinous chiasm.
3. Innervation
The innervation of the flexor digitorum superficialis muscle is provided by the median nerve with fibers from segments C7 and C8.
4. Function
As indicated by the name "flexor digitorum superficialis," the muscle facilitates flexion (bending) of the wrist and the 2nd to 5th fingers up to the middle phalanx. It is thus one of the most important finger flexors.
5. Clinic
For functional testing, the examiner first fixes the fingers not being tested in an extended position, which inactivates the flexor digitorum profundus muscle. In this position, the patient is asked to flex the finger at the middle joint. If flexion is not possible, an injury to the tendon of the flexor digitorum superficialis muscle can be assumed. If the patient reports pain during finger flexion, this is an indication of tendosynovitis of the tendon.