The Forearm
Cutaneous innervation of the forearm:
1) The lateral side of the forearm is supplied by the lateral cutaneous nerve of the forearm,
2) The medial side of the forearm is supplied by the medial cutaneous nerve of the forearm, and
3) The narrow strip on the middle of the back of the forearm is supplied by the posterior cutaneous nerve of the forearm.
The anterior compartment of the forearm, includes:
Muscles of the front of the forearm
The eight muscles of the front of the forearm are arranged in three layers the superficial, intermediate and deep.
The superficial group consists of four muscles, as follows:
1) Pronator teres,
2) Flexor carpi radialis,
3) Palmaris longus, and
4) Flexor carpi ulnaris.
The intermediate group consists of one muscle:
1) Flexor digitorum superficialis.
The deep group consists of three muscles, as follows, the:
1) Flexor pollicis longus,
2) Flexor digitorum profundus, and
3) Pronator quadratus.
1) The lateral side of the forearm is supplied by the lateral cutaneous nerve of the forearm,
2) The medial side of the forearm is supplied by the medial cutaneous nerve of the forearm, and
3) The narrow strip on the middle of the back of the forearm is supplied by the posterior cutaneous nerve of the forearm.
The anterior compartment of the forearm, includes:
Muscles of the front of the forearm
The eight muscles of the front of the forearm are arranged in three layers the superficial, intermediate and deep.
The superficial group consists of four muscles, as follows:
1) Pronator teres,
2) Flexor carpi radialis,
3) Palmaris longus, and
4) Flexor carpi ulnaris.
The intermediate group consists of one muscle:
1) Flexor digitorum superficialis.
The deep group consists of three muscles, as follows, the:
1) Flexor pollicis longus,
2) Flexor digitorum profundus, and
3) Pronator quadratus.
Figure1: Superficial branch of radial nerve.
Figure2: Pronator teres and flexor carpi radialis.
Figure3: Pronator teres and pronator quadratus.
Figure: Anterior compartment of the forearm.
Figure5: Anterior compartment of the forearm 2.
Flexor carpi radialis
Origin
Flexor carpi radialis originates from the medial epicondyle by the common flexor tendon.
Insertion
The palmar surface of the base of the second and the third metacarpal bones.
Nerve supply
Median nerve.
Actions
Flexion and abduction of the hand at the wrist joint.
Figure6:Flexor carpi radialis.
Figure7:Flexor digitorum superficialis.
Palmaris longus
Origin
Palmaris longus originates from the medial epicondyle by the common flexor tendon.
Insertion
In the palmar aponeurosis.
Nerve supply
Median nerve.
Action
Flexion of the hand.
Origin
Palmaris longus originates from the medial epicondyle by the common flexor tendon.
Insertion
In the palmar aponeurosis.
Nerve supply
Median nerve.
Action
Flexion of the hand.
Figure8: Palmaris longus.
Figure9: palmaris longus.
Flexor carpi ulnaris
Origin
Flexor carpi ulnaris arises by two heads:
1) The humeral head which originates from the medial epicondyle by the common flexor tendon, and
2) The ulnar head which originates from the medial border of the olecranon process and the posterior border of the ulna.
Insertion
Primarily into the pisiform, but through the pisohamate and pisometacarpal ligaments into the hook of the hamate and the base of the fifth metacarpal.
Nerve supply
Ulnar nerve.
Actions
Flexes and adducts the hand at the wrist joint.
Figure10: Flexor carpi ulnaris.
Figure11: Flexor carpi ulnaris.
The intermediate Muscles in the anterior compartment of the Forearm
Flexor digitorum superficialis
Origin
Flexor digitorum superficialis arises by two heads, as follows:
1) The humero-ulnar head which originates from the medial epicondyle by the common flexor tendon and the medial border of the coronoid process of the ulna, and
2) The radial head which originates from the anterior oblique line of the radius.
Insertion
By four tendons in the sides of the palmar surface of the middle phalanges of the medial four fingers.
Nerve supply
Median nerve.
Actions
Flexes the middle and proximal phalanges of the medial four fingers and flexes the hand at the wrist joints.
Flexor digitorum superficialis
Origin
Flexor digitorum superficialis arises by two heads, as follows:
1) The humero-ulnar head which originates from the medial epicondyle by the common flexor tendon and the medial border of the coronoid process of the ulna, and
2) The radial head which originates from the anterior oblique line of the radius.
Insertion
By four tendons in the sides of the palmar surface of the middle phalanges of the medial four fingers.
Nerve supply
Median nerve.
Actions
Flexes the middle and proximal phalanges of the medial four fingers and flexes the hand at the wrist joints.
Figure12: Flexor digitorum superficialis.
Figure13: Flexor digitorum profundus.
The Deep Muscles in the anterior compartment of the Forearm
Flexor digitorum profundus
Origin
1) From the upper 3/4 of the anterior and medial surfaces of the shaft of the ulna.
2) Medial part of interosseous membrane.
Insertion
By four tendons into the bases of distal phalanges of the medial four fingers.
Nerve supply
1) Medial half supplied by the ulnar nerve.
2) Lateral half supplied by the anterior interosseous nerve which is a branch of the median nerve.
Actions
Flexes the terminal phalanges of the medial four fingers and flexes the other joints of the fingers and the hand at the wrist joint.
Flexor digitorum profundus
Origin
1) From the upper 3/4 of the anterior and medial surfaces of the shaft of the ulna.
2) Medial part of interosseous membrane.
Insertion
By four tendons into the bases of distal phalanges of the medial four fingers.
Nerve supply
1) Medial half supplied by the ulnar nerve.
2) Lateral half supplied by the anterior interosseous nerve which is a branch of the median nerve.
Actions
Flexes the terminal phalanges of the medial four fingers and flexes the other joints of the fingers and the hand at the wrist joint.
Figure14: Brachioradialis and flexor digitorum profundus.
Flexor pollicis longus
Origin
From the upper 2/3 of the anterior surface of the radius, adjacent interosseous membrane.
Insertion
Palmar surface of the base of the terminal phalanx of the thumb.
Nerve supply
Anterior interosseous branch of the median nerve.
Actions
Flexes the distal phalanx of the thumb and flexes the other joints of the thumb.
Origin
From the upper 2/3 of the anterior surface of the radius, adjacent interosseous membrane.
Insertion
Palmar surface of the base of the terminal phalanx of the thumb.
Nerve supply
Anterior interosseous branch of the median nerve.
Actions
Flexes the distal phalanx of the thumb and flexes the other joints of the thumb.
Figure15: Flexor pollicis longus.
Pronator quadratus
Origin
From the distal 1/4 of the anterior surface of the shaft of the ulna.
Insertion
Distal 1/4 of the anterior surface of the radius.
Nerve supply
Anterior interosseous branch of the median nerve.
Action
Pronation of the forearm.
Origin
From the distal 1/4 of the anterior surface of the shaft of the ulna.
Insertion
Distal 1/4 of the anterior surface of the radius.
Nerve supply
Anterior interosseous branch of the median nerve.
Action
Pronation of the forearm.
Figure16: Pronator quadratus and anterior interosseous nerve & artery.
Arteries of the Front of the Forearm
Radial Artery
The radial artery is the smaller of the two terminal branches of the brachial artery. It begins in the cubital fossa at the level of the neck of the radius and runs in the cubital fossa before leaving it at its apex. The radial artery runs on the lateral side of the forearm but then it winds around the lateral aspect of the wrist joint to reach the dorsum of the hand.
Relations
1) In the upper part of the forearm radial artery is covered by brachioradialis, while in the lower part it only covered by the skin and fasciae,
2) The radial artery running superficially between flexor digitorum superficialis and flexor carpi ulnaris tendons,
3) The radial artery runs lateral to flexor carpi radialis tendon,
4) The brachioradialis and the superficial branch of radial nerve lie lateral to the radial artery, and
5) It runs superficial to pronator quadratus.
Branches
1) Muscular branches.
2) The radial recurrent:
The radial recurrent artery arises from the lateral wall of the radial artery in the cubital fossa. It runs upwards anterior to the lateral epicondyle to anastomose around the elbow joint.
3) The superficial palmar artery:
The superficial palmar artery arises proximal to the wrist and enters the palm by passing superficial to the thenar muscles. It joins the anastomoses with the ulnar artery to form the superficial palmar arch.
4) The palmar carpal artery:
The palmar carpal artery arises near the wrist. It anastomoses with the palmar carpal branch of the ulnar artery to form the anterior carpal arch.
Figure17: Radial and ulnar arteries.
Ulnar artery
The ulnar artery is the larger of the two terminal branches of the brachial artery. It begins in the cubital fossa at the level of the neck of the radius. It runs on the medial side of the forearm deep to pronator teres then between flexor digitorum profundus and the flexor carpi ulnaris. Finally, it enters the palm by passing superficial to the flexor retinaculum.
Relations
1)Superficial:
In its upper half it is deep and covered by the superficial muscles of the forearm, while in its lower half it lies superficial and is only covered by skin and fasciae.
2) Medially:
The ulnar nerve lies medial to the ulnar artery in the distal two-thirds of the forearm.
Branches
1) Muscular branches.
2) Anterior ulnar recurrent artery:
The anterior ulnar recurrent artery arises at the origin of the artery and runs upwards to anastomose with the anterior branch of the inferior ulnar collateral artery, in front of the medial epicondyle of the humerus.
3) Posterior ulnar recurrent artery:
The posterior ulnar recurrent artery arises at the origin of the artery anastomoses with the superior ulnar collateral and the posterior branch of the inferior ulanr collateral artery behind the medial epicondyle of the humerus.
4) Common interosseous artery:
The common interosseous artery arises from the proximal part of the ulnar artery, just after its origin it runs a short route before dividing into anterior and posterior branches.
5) Palmar carpal artery:
The palmar carpal artery arises just proximal to the wrist and anastomoses with the corresponding branches of radial artery to form the anterior carpal arch.
6) Dorsal carpal artery:
The dorsal carpal artery arises just above the wrist and anastomoses with the corresponding branch of the radial artery to form the posterior carpal arch.
The ulnar artery is the larger of the two terminal branches of the brachial artery. It begins in the cubital fossa at the level of the neck of the radius. It runs on the medial side of the forearm deep to pronator teres then between flexor digitorum profundus and the flexor carpi ulnaris. Finally, it enters the palm by passing superficial to the flexor retinaculum.
Relations
1)Superficial:
In its upper half it is deep and covered by the superficial muscles of the forearm, while in its lower half it lies superficial and is only covered by skin and fasciae.
2) Medially:
The ulnar nerve lies medial to the ulnar artery in the distal two-thirds of the forearm.
Branches
1) Muscular branches.
2) Anterior ulnar recurrent artery:
The anterior ulnar recurrent artery arises at the origin of the artery and runs upwards to anastomose with the anterior branch of the inferior ulnar collateral artery, in front of the medial epicondyle of the humerus.
3) Posterior ulnar recurrent artery:
The posterior ulnar recurrent artery arises at the origin of the artery anastomoses with the superior ulnar collateral and the posterior branch of the inferior ulanr collateral artery behind the medial epicondyle of the humerus.
4) Common interosseous artery:
The common interosseous artery arises from the proximal part of the ulnar artery, just after its origin it runs a short route before dividing into anterior and posterior branches.
5) Palmar carpal artery:
The palmar carpal artery arises just proximal to the wrist and anastomoses with the corresponding branches of radial artery to form the anterior carpal arch.
6) Dorsal carpal artery:
The dorsal carpal artery arises just above the wrist and anastomoses with the corresponding branch of the radial artery to form the posterior carpal arch.
Figure18: Deep muscles of the anterior compartment.
The common interosseous artery
The common interosseous artery is the shortest branch of the ulnar artery. It arises from the ulnar artery in the cubital fossa. It then passes backwards to reach the upper border of the interosseous membrane and after a short route it divides into anterior and posterior interosseous arteries.
1) The anterior interosseous artery
The anterior interosseous artery arises from the common interosseous artery at the upper border of the interosseous membrane. It accompanies the anterior interosseous nerve and descends in front of the interrosseous membrane. Finally, it pierces the interosseous membrane at the upper border of pronator quadratus to reach the back of the forearm and join the posterior interosseous artery.
2) The posterior interosseous artery
The posterior interosseous artery arises from the common interosseous artery at the upper border of the interosseous membrane and passes above the interosseous membrane to reach the posterior compartment of the forearm. It ends by anastomosing with the anterior interosseous artery and joining the dorsal carpal arch of the wrist joint.
Figure19: Common interosseous artery.
The Nerves of the Front of the Forearm
The median nerve
The median nerve is the main motor nerve of the anterior compartment of the forearm.
Course and relations:
1) In the cubital fossa:
It lies medial to the brachial artery then leaves the cubital fossa by passing between the two heads of pronator teres.
2) In the forearm:
It runs with the median artery between flexor digitorum superficialis and flexor digitorum profundus.
3) Above the wrist:
About 5cm above the wrist, it becomes superficial and lies between the tendon of palmaris longus and flexor carpi radialis. It then enters the palm by passing deep to the flexor retinaculum.
Branches:
1) Muscular branches:
It innervates pronator teres, flexor carpi radialis, palmaris longus, and flexor digitorum superficialis muscles.
2) Articular branches:
It innervates the elbow joint.
3) The anterior interosseous nerve:
The anterior interosseous nerve is the largest branch of the median nerve and arises between the two heads of pronator teres. It descends in front of the interosseous membrane and accompanies the anterior interosseous artery. It innervates flexor pollicis longus, the lateral half of flexor digitorum profundus and pronator quadratus.
4) The palmar cutaneous branch:
The palmar cutaneous branch arises from the distal part of the median nerve just before its passage under the flexor retinaculum. It runs in front of the flexor retinaculum to innervate the area of skin over the central part of the palm.
The median nerve
The median nerve is the main motor nerve of the anterior compartment of the forearm.
Course and relations:
1) In the cubital fossa:
It lies medial to the brachial artery then leaves the cubital fossa by passing between the two heads of pronator teres.
2) In the forearm:
It runs with the median artery between flexor digitorum superficialis and flexor digitorum profundus.
3) Above the wrist:
About 5cm above the wrist, it becomes superficial and lies between the tendon of palmaris longus and flexor carpi radialis. It then enters the palm by passing deep to the flexor retinaculum.
Branches:
1) Muscular branches:
It innervates pronator teres, flexor carpi radialis, palmaris longus, and flexor digitorum superficialis muscles.
2) Articular branches:
It innervates the elbow joint.
3) The anterior interosseous nerve:
The anterior interosseous nerve is the largest branch of the median nerve and arises between the two heads of pronator teres. It descends in front of the interosseous membrane and accompanies the anterior interosseous artery. It innervates flexor pollicis longus, the lateral half of flexor digitorum profundus and pronator quadratus.
4) The palmar cutaneous branch:
The palmar cutaneous branch arises from the distal part of the median nerve just before its passage under the flexor retinaculum. It runs in front of the flexor retinaculum to innervate the area of skin over the central part of the palm.
Figure20: Ulnar and median nerves.
Figure21: Deep layer of the anterior compartment of the forearm.
The ulnar nerve
Course and relations
1) In the elbow:
The ulnar nerve passes behind the medial epicondyle of the humerus and enters the anterior compartment of the forearm by passing between the two heads of flexor carpi ulnaris.
2) In the forearm:
In the anterior compartment of the arm it runs between flexor digitorum profundus and flexor carpi ulnaris. It lies medial to ulnar artery in the lower two-thirds of the forearm.
3) In the wrist:
It lies between flexor carpi ulnaris medially and flexor digitorum superficialis laterally.
4) In to the palm:
It enters the palm by passing superficial to the flexor retinaculum lateral to the pisiform and medial to the ulnar artery.
Branches
1) Muscular branches:
It innervates flexor carpi ulnaris and the medial half of flexor digitorum profundus.
2) The palmar cutaneous branch:
The palmar cutaneous branch is a small branch arising at the middle of the forearm, and supplies the skin of the medial third of the palmar aspect of the hand.
3) The dorsal posterior cutaneous branch:
The dorsal posterior cutaneous branch arises at the distal part of the forearm just proximal to the wrist. It winds backwards to reach the dorsum of the hand to supply the skin of the medial third of the back of the hand and the medial half of the fingers.
Radial Nerve in the Forearm
The radial nerve ends in front of the lateral epicondyle, under brachioradialis after piercing the lateral intermuscular septum by dividing into a superficial and a deep terminal branch.
1) The superficial terminal branch of radial nerve:
The superficial terminal branch of the radial nerve is the continuation of the radial nerve into the front of the forearm and the dorsum of the hand. It descends in the forearm deep into brachioradialis. In the middle third of the forearm it is related to the lateral side of the radial artery. At the distal part of the forearm it descends to the dorsum of the hand where it divides into the terminal dorsal digital nerves that supply the skin of the lateral two thirds of the dorsum of the hand and the lateral 3½ fingers.
2) The deep terminal branch of radial nerve:
Is called the posterior interosseous nerve. It pierces the supinator muscle to reach the back of the forearm.
