Muscles of the Wrist and Hand: Origin, Insertion, Action, Innervation

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Flexor Carpi Radialis

Proximal attachments
Medial epicondyle of the humerus via the common flexor tendon.

Distal attachments
Palmar aspect of the base of the second metacarpal (with a slip to the third).

Nerve supply
Median nerve (C6, 7).

Actions
Flexes the wrist by acting with other flexors (flexor carpi ulnaris +/- flexor digitorum superficialis).

Radially deviates the wrist by acting with extensor carpi radialis longus and brevis.

Palmaris Longus

Proximal attachments
Common flexor origin and tendon.

Distal attachments
Passes superficial to the flexor retinaculum at the wrist sending a few fibers to intermingle with the retinaculum but mostly passing distally, separating into 5 bundles for the five digital rays and passing to various insertions in the distal palm and digits via a palmar fascial continuum.

Nerve supply
Median nerve (C7, 8).

Actions
This muscle tenses the palmar fascia, anchoring the skin of the palm during gripping. It can assist in wrist flexion but is a weaker wrist flexor

Flexor carpi ulnaris

Proximal attachments
Humeral head: from the common flexor tendon.

Ulnar head: from medial border of olecranon and the upper two thirds of the subcutaneous border of the ulna via an aponeurosis.

Distal attachments
Pisiform, hook of the hamate and the fifth metacarpal.

The pisiform is a sesamoid bone in the tendon on flexor carpi ulnaris. Fibers from the tendon continue distal to the pisiform to insert into the hamate (pisohamate ligament) and the fifth metacarpal (the pisometacarpal ligament).

Nerve supply
Ulnar nerve (C7, 8).

Actions
Flexes the wrist by acting with other flexors (flexor carpi radialis +/- flexor digitorum superficialis).

Ulnar deviation of the wrist by acting with extensor carpi ulnaris.

Flexor Digitorum Superficialis

Proximal attachments
Humeroulnar head: Common flexor tendon; anterior part of ulnar collateral ligament; adjacent intermuscular septa and medial aspect of the coronoid process.

Radial head: A fibrous arch continues to the radial tuberosity and anterior oblique line to which the muscle is attached as a thin sheet.

Flexor digitorum superficialis arises from its proximal attachments, courses distally, and forms, within its substance, an intermediate tendon from which distal fibers of the muscle arise. These are the fibers of the deeper part of the muscle which give rise to deep tendons for the index and little fingers. The fibers for the middle finger arise mostly from the radius with a small contribution from the common flexor origin. The fibers from the ring finger arise from the common flexor origin. The muscle fibers, and therefore the tendons, of the middle and ring fingers lie superficial to the index and little.

These tendons pass in this relationship within a common synovial flexor sheath beneath the flexor retinaculum, and then diverge towards the individual digital rays.

Distal attachments
At the base of the respective proximal phalanx each superficialis tendon divides into two slips (bifurcation) which pass around the tendon of the flexor digitorum profundus. The tendon slips cross over dorsal to the profundus tendon, at the chiasm of Camper thus forming a fibrous tunnel before inserting into the palmar aspects of the shafts of the middle phalanges within the A4 annular flexor tendon pulley.

The tendon blood supply within the digital fibrous sheaths is by vincula; the vinculum longum superficialis and vinculum brevis.

Nerve supply
Median nerve (C 7, 8and T1).

Actions
Flexion of all of the joints crossed; primarily the proximal interphalangeal (PIP), and secondarily the metacarpophalangeal (MCP) and the wrist joint

Flexor Digitorum Profundus

Proximal attachments
Flexor digitorum profundus is a deep flexor and arises from the upper three quarters of the medial and anterior aspects of the ulna and from the anterior aspect of the interosseous membrane.

Distal attachments
To the palmar aspects of the bases of the distal phalanges of the index, middle, ring and little fingers.

The tendon to the index finger is separate whereas the remaining three to the middle, ring and little fingers have a common tendon which only becomes completely separate in the palm.

The lumbrical muscles arise in the palm from the tendons of flexor digitorum profundus.

The tendons of flexor digitorum profundus reach the distal phalanx by passing through the fibrous tunnels formed by flexor digitorum superficialis.

Nerve supply
Ulnar half (little, ring): ulnar nerve.

Radial half (index, middle): Anterior interosseous branch of the median nerve (C8and T1).

Extent of innervation by each nerve varies.

Actions
Flexion of all joints crossed. The sole flexor of the distal interphalangeal joints. Acts with flexor digitorum superficialis to flex the PIP and MP joints of the fingers and secondarily the wrist

Flexor Pollicis Longus

Proximal attachments
Anterior surface of the middle third of the radius distal to the radial tuberosity and the adjacent interosseous membrane.

Distal attachments
Base of the distal phalanx of the thumb.

Its tendon passes through the flexor retinaculum at the wrist in its own synovial sheath.

Nerve supply
Anterior interosseous branch of the median nerve (C8, T1).

Actions
Flexion of all joints over which the tendon passes; the thumb interphalangeal, metacarpophalangeal and weak flexion at the wrist (Anim). Isometric contraction is important in pinch and grip

Extensor Carpi Ulnaris

Proximal attachments
The common extensor tendon and by an aponeurotic sheet from the mediodorsal ulnar border which is common to this muscle, flexor carpi ulnaris and flexor digitorum profundus.

The extensor carpi ulnaris is part of the group of four superficial extensor muscles in the forearm (extensor carpi ulnaris, extensor digiti minimi, extensor digitorum and extensor carpi radialis brevis) which share a common tendinous attachment to the lateral epicondyle of the humerus.

Distal attachments
Dorsoulnar aspect of fifth metacarpal base.

The tendon of extensor carpi ulnaris passes in a groove just ulnar to the ulnar styloid and is inserted symmetrically with flexor carpi ulnaris (via the pisometacarpal ligament) to the base of the fifth metacarpal

Nerve supply
The posterior interosseous nerve (deep motor branch of the radial nerve) from the radial nerve (C7, 8).

Actions
Extensionand ulnar deviation of the wrist. Together the flexor and extensor carpi ulnaris act to ulnarly deviate the wrist

Extensor Carpi Radialis Brevis

Proximal attachments
The lateral epicondyle of the humerus via the common extensor tendon. Radial collateral ligament, adjacent intermuscular septa.

The extensor carpi radialis brevis is one of a group of four superficial extensor muscles in the forearm (extensor carpi ulnaris, extensor digiti minimi, extensor digitorum and extensor carpi radialis brevis) which share a common tendinous attachment to the lateral epicondyle of the humerus.

Distal attachments
The dorsal aspect of the base of the third metacarpal.

The tendon of extensor carpi radialis brevis may send an accessory slip to attach to the second metacarpal.

Nerve supply
The posterior interosseous nerve, a branch of the radial nerve (C7, 8).

Occasionally the nerve supply to the extensor carpi radialis brevis may come from the superficial branch of the radial nerve.

Actions
Extension and (when acting together with flexor carpi radialis and extensor carpi radialis longus) radial deviation of the wrist

Extensor Carpi Radialis Longus

Proximal attachments
Distal third of the lateral supracondylar ridge of the humerus and the lateral intermuscular septum.

Distal attachments
Through a flattened tendon into the posterior aspect of the base of the second metacarpal.

Its tendon may send accessory slips to attach to the first or third metacarpals.

Nerve supply
Radial nerve (C6, 7).

Actions
Extension and, (particularly when acting together with flexor carpi radialis), radial deviation of the wrist

Extensor digitorum

Proximal attachments
The lateral epicondyle of the humerus via the common extensor tendon and adjacent intermuscular septum.

The extensor digitorum is part of the group of four superficial extensor muscles in the forearm (extensor carpi ulnaris, extensor digiti minimi, extensor digitorum and extensor carpi radialis brevis) which share a common tendinous attachment to the lateral epicondyle of the humerus.

Distal attachments
Through separate tendons to the extensor apparatuses of the four fingers.

Nerve supply
From the posterior interosseous nerve, the deep motor branch of the radial nerve (C7, 8).

Actions
Extension of all joints crossed by the tendons. They primarily extend the MP joints and secondarily extend the wrist (together with the wrist extensors)

The extensor digitorum and the intrinsic muscles (especially the lumbricals) insert into the blended fibers of the extensor apparatus, to extend the interphalangeal joints.

Extensor Indicis

Proximal attachments
The junction of the middle and distal thirds of the ulna and the interosseous membrane.

Distal attachments
The extensor apparatus of the index finger medial (ulnar) to the tendon of extensor digitorum.

Nerve supply
Posterior interosseous nerve (deep motor branch of the radial nerve) (C7, 8).

Actions
Extension of the MP joint of the index finger and in conjunction with the lumbricals and interossei, extension of the IP joints

It also assits with adduction of the index finger at the carpometacarpal joint.

Extensor Digiti Minimi

Proximal attachments
Common extensor tendon, adjacent intermuscular septum.

The extensor digiti minimi is part of the group of four superficial extensor muscles in the forearm (extensor carpi ulnaris, extensor digiti minimi, extensor digitorum and extensor carpi radialis brevis) which share a common tendinous attachment to the lateral epicondyle of the humerus.

The muscle belly and tendon lie ulnarly to the extensor digitorum.

Distal attachments
Extensor apparatus of the little finger.

As the tendon passes over the distal radioulnar joint it may split into two. The more radial tendon is joined by the extensor digitorum tendon to the little finger just proximal to the metacarpophalangeal joint.

Nerve supply
The posterior interosseous nerve from the radial nerve (C7, 8).

Actions
Extends the little finger and assists in extension of the wrist. Primarilary it extends the metacarpophalangeal joint and secondarily extends the interphalangeal joint through the extensor apparatus as well as assisting to extend the wrist

It also assist with abduction of the fifth digit at the carpometacarpal joint.

Extensor Pollicis Longus

Proximal attachments
Posterolateral aspect of the middle third of the ulna and interosseous membrane.

Distal attachments
Base of the distal phalanx of the thumb.

At its distal attachment the tendon is joined radially by an expansion from the tendon of abductor pollicis brevis and ulnarly from the tendon of adductor pollicis.

Nerve supply
Posterior interosseous nerve (deep motor branch of the radial nerve)(C7, 8).

Actions
Extension of the thumb distal interphalangeal joint and assistance with extension of the MP and CMC joints of the thumb

Extensor Pollicis Brevis

Proximal attachments
Radius and interosseous membrane below abductor pollicis longus.

Distal attachments
Dorsal aspect of the base of the proximal phalanx of the thumb.

Nerve supply
Posterior interosseous nerve (deep motor branch of the radial nerve) (C7, 8).

Actions
Extension of the proximal phalanx of the thumb. Assists in extension (and abduction) of the carpometacarpal joint of the thumb

It also assists in wrist deviation

Abductor Pollicis Longus

Proximal attachments
From an oblique area over the posterior aspects of the radius, ulna and interosseous membrane. The ulnar attachment is more proximal than the radial.

Distal attachments
Radial aspect of the base of the first metacarpal.

Nerve supply
Posterior interosseous nerve (deep motor branch of the radial nerve) (C7, 8).

Actions
Abduction and extension of the thumb (Movie) at the first carpometacarpal joint

Can assist in radial abduction and flexion of the wrist.

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