Superficial flexors of the forearm
The superficial flexors of the forearm are a group of five muscles found at the anterior/ventral forearm. They form the surface of the ulnar side of the forearm where they can also be easily palpated. These muscles include:
- Pronator teres muscle
- Flexor carpi radialis muscle
- Flexor carpi ulnaris muscle
- Palmaris longus muscle
- Flexor digitorum superficialis muscle
Their long tendons can be followed very well at the wrist joint, especially during flexion.
|Superficial flexors of the forearm||
Flexor carpi radialis
Flexor carpi ulnaris
Flexor digitorum superficialis
All supplied by the ulnar artery solely, except for the pronator teres which is supplied by both ulnar and radial arteries
All supplied by the median nerve, except for the flexor carpi ulnaris that is supplied by the ulnar nerve
Medial epicondylitis, golfer's elbow
This article will discuss the anatomy of the superficial flexors of the forearm.
Anatomy and supply
All five muscles arise from the common flexor tendon located at the medial epicondyle of the humerus; some of them have additional attachment points on the radius and ulna.
The following muscles described are known to be the superficial flexors.
Pronator teres muscle
The pronator teres muscle originates at the medial epicondyle of the humerus (humeral head) and coronoid process of the ulna (ulnar head). From there it courses under the brachioradialis and attaches to the lateral side of the radius, specifically at a roughening of the midshaft referred to as the pronator tuberosity. It is the most lateral of all the superficial flexors. (Innervation: median nerve (C6-C7))
|Origins||Humeral head (medial epicondyle of the humerus), ulnar head (coronoid process of the ulna)|
|Insertions||Lateral side of the radius|
|Function||Pronation of forearm, flexion of elbow|
Flexor carpi radialis muscle
This muscle runs from the common flexor tendon at the humerus to the bases of the second and third metacarpal bones.
(Innervation: median nerve (C6-C7))
|Origins||Medial epicondyle of the humerus (common flexor tendon)|
|Insertions||Bases of 2nd metacarpal bone|
|Function||Flexion and abduction of the hand at the wrist joint|
Flexor carpi ulnaris muscle
The flexor carpi ulnaris arises from the medial epicondyle of the humerus (humeral head) and the olecranon of the ulna (ulnar head).
The muscle has 3 insertion points: first, its tendon inserts into the pisiform bone, where the pisiform bone functions as a sesamoid bone; from there, it relays towards its other 2 insertion points at the hook of the hamate and the base of the 5th metacarpal bone. This muscle is the most medial of all superficial flexors and is mainly responsible for the contour of the ulnar side of the forearm.
(Innervation: ulnar nerve (C7-Th1))
|Origins||Humeral head (medial epicondyle of the humerus), ulnar head (olecranon and posterior border of the ulna)|
|Insertions||Pisiform bone, hook of hamate bone, base of the 5th metacarpal bone|
|Function||Flexion and adduction of the hand at the wrist|
Palmaris longus muscle
The palmaris longus is a very slender muscle originating from the common flexor tendon and inserting at the flexor retinaculum and palmar aponeurosis. This muscle is variable and can be, in some cases, missing on one or both arms or have an alternative course.
(Innervation: median nerve (C7-Th1))
|Origins||Medial epicondyle of the humerus (common flexor tendon)|
|Insertions||Flexor retinaculum and palmar aponeurosis|
|Function||Flexion of the hand at the wrist joint|
Flexor digitorum superficialis muscle
The FDS has a large origin point attached to the medial epicondyle of the humerus (humeral head), the coronoid process of the ulna (ulnar head) and distally from the radial tuberosity (radial head).
|Origins||Humero-ulnar head (medial epicondyle of the humerus and coronoid process of the ulna), ulnar head (superior half of anterior border)|
|Insertions||Shafts of middle phalanges of medial four digits|
|Function||Flexion of middle phalanges at proximal interphalangeal joints and flexion of the proximal phalanges at the metacarpophalangeal joints of the middle four digits|
Its four insertion tendons split into two smaller end tendons each of which then insert on both sides of the middle phalanges of the second to fifth fingers. This is the deepest muscle of all superficial flexors. Innervation: median nerve (C7-Th1).
Innervation of the superficial flexors
All superficial flexors of the forearm are supplied by the median nerve except the flexor carpi ulnaris. In the elbow this nerve runs underneath the bicipital aponeurosis and between the two heads of the pronator teres.
From there, it courses under the flexor digitorum superficialis between the superficial and deep flexors and through the carpal tunnel at the wrist joint, and finally branches off into sensory and motor branches at the palm of the hand.
The carpal tunnel is a passage formed by the carpal bones and a densification of the antebrachial fascia (flexor retinaculum). In addition to the median nerve, the carpal tunnel also contains the tendons of the flexor digitorum superficialis, flexor digitorum profundus and flexor pollicis longus.
The superficial flexors support various movements of the antebrachial and hand joints. As the name reveals, (almost) all of them do flexion of the wrist joint (except the pronator teres). Another thing these muscles have in common is that they are weak flexors of the elbow joint.
- Furthermore, the pronator teres rotates the radius medially (pronation).
- The contraction of the flexor carpi radialis moves the hand radially (radial abduction) whereas the flexor carpi ulnaris moves the hand ulnarly (ulnar abduction).
- The flexor digitorum superficialis is involved in flexion of the metacarpophalangeal (MCP) and proximal interphalangeal joints (PIP) of the second to fifth finger.
- The palmaris longus' major function is to support the palmar aponeurosis.
A chronic false strain of the superficial flexors often leads to inflammation and increased connective tissue in the common flexor tendon at the medial epicondyle of the humerus (medial epicondylitis).
Particularly golfers are affected by this condition as they permanently have to flex their hand wrist for the swing. For that reason, this condition is also referred to as the golfer’s elbow.
Classic symptoms are pain which increases during hand movements and trouble performing day-to-day tasks (e.g. pressing the door handle, hand shaking). Noticeably, adolescent baseball players often suffer from the medial epicondylitis as well (“little league elbow”). The reason is that children’s bones have ossification centers as they are still growing. When these experience massive false strain, the pressure is carried forward to the apophysis causing inflammation (apophysitis) or even deformation.