Superficial flexors of the forearm
The superficial flexors of the forearm are a group of five muscles located in the anterior (flexor) compartment of the forearm. These muscles include the pronator teres, flexor carpi radialis, flexor carpi ulnaris, palmaris longus and flexor digitorum superficialis.
The superficial flexors of the forearm share a common origin on the common flexor tendon that arises from the medial epicondyle of humerus. The majority of muscles from this group are innervated by the median nerve (C6-C7), except for the flexor carpi ulnaris muscle that receives its innervation via the ulnar nerve (C7-T1).
All of the muscles in this compartment work in synergy to produce movements of the hand and digits. More specifically, the superficial flexors are in charge of flexion, adduction and abduction of the hand in the wrist joint, as well as flexion of the fingers at the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints. Only the pronator teres muscle acts specifically on the proximal radioulnar joint, producing pronation of the forearm.
This article will introduce you to the anatomy and function of the superficial flexors of the forearm.
|Definition and function||The flexors of the forearm are a group of five muscles mainly in charge of movements of forearm, hand and fingers|
|Muscles||Pronator teres, flexor carpi radialis, flexor carpi ulnaris, palmaris longus and flexor digitorum superficialis|
|Innervation||All supplied by the median nerve, except for flexor carpi ulnaris that is supplied by the ulnar nerve|
|Blood supply||Ulnar artery, radial artery, brachial artery|
- Pronator teres muscle
- Flexor carpi radialis muscle
- Flexor carpi ulnaris muscle
- Palmaris longus muscle
- Flexor digitorum superficialis muscle
- Clinical note
Pronator teres muscle
The pronator teres is the most laterally placed muscle of the superficial flexors of the forearm. It consists of two heads (humeral and ulnar) each of which originates from a separate site. The humeral head originates from the medial supracondylar ridge of humerus, while the ulnar head arises from the coronoid process of ulna. The fibers from both muscle heads converge onto a single tendon that inserts on the pronator tuberosity on the lateral surface of the radius.
The pronator teres muscle receives its innervation via the median nerve (C6, C7) and its blood supply via brachial, radial and ulnar arteries. The main action of pronator teres is pronation of the forearm at the proximal radioulnar joint, while it also contributes to the flexion of the forearm at the elbow joint.
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Flexor carpi radialis muscle
The flexor carpi radialis is a fusiform muscle of the forearm situated medially to the pronator teres muscle. It originates from the medial epicondyle of humerus and descends inferomedially to the midpoint of the forearm, where it extends into a long tendon. The tendon passes beneath the flexor retinaculum and goes on to insert onto the bases of the metacarpal bones 2-3.
Like the majority of the muscles in this compartment, it is innervated by the median nerve (C6, C7) and vascularized by the branches of the recurrent ulnar and radial arteries. The contraction of flexor carpi radialis produces movements of the hand at the wrist joint. Its main actions include wrist flexion and wrist abduction (radial deviation). To a lesser extent, the muscle contributes to the pronation of the forearm.
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Flexor carpi ulnaris muscle
The flexor carpi ulnaris is the most medial muscle of this group. It originates by two heads; humeral and ulnar. The humeral head arises from the medial epicondyle of humerus, while the ulnar head arises from the olecranon and proximal two-thirds of the posterior surface of the ulna. The heads converge into a thick tendon which goes on to insert onto the pisiform and hamate bones and the base of metacarpal bone 5.
It is the only muscle from this group that receives its innervation via the ulnar nerve (C7-T1). The blood supply for this muscle comes from the posterior ulnar recurrent artery.
Flexor carpi ulnaris contributes to the flexion of the hand at the wrist joint. Moreover, it is also involved in the adduction (ulnar deviation) of the hand.
Palmaris longus muscle
The palmaris longus is the most superficial muscle of the superficial forearm flexors. It originates from the medial epicondyle of humerus and descends to the midpoint of the forearm, where it becomes tendinous. The tendon continues towards the wrist and passes superficial to the flexor retinaculum and goes on to insert onto the palmar aponeurosis.
Palmaris longus is innervated by the median nerve (C7, C8) and vascularized by the anterior ulnar recurrent artery.
The palmaris longus primarily acts with other superficial flexors and contributes to the balanced flexion of the hand on the wrist joint. Additionally, it stabilizes the elbow joint and produces a weak flexion of 2nd to 5th metacarpophalangeal joints by pulling on the palmar aponeurosis.
Flexor digitorum superficialis muscle
The flexor digitorum superficialis is the largest muscle of the superficial flexors. It consists of two heads that are named according to their origins. The humeroulnar head originates from the medial epicondyle of humerus and the coronoid process of ulna, while the radial head originates from the shaft of radius. The muscle splits into four tendons that pass behind the flexor retinaculum and go on to insert onto the middle phalanges of digits 2-5.
Flexor digitorum superficialis is innervated by the median nerve (C8-T1) and vascularized by the ulnar and radial arteries.
The prime function of flexor digitorum superficialis is flexion of the digits 2-5 at the PIP and MCP joints. In addition, it contributes to the flexion of the hand at the wrist joint.
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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.