Forearm Muscles

Anastomoses - Complete your study of the recurrent arterial branches around the elbow during today's dissection. Some of these may have been difficult to find during our last dissection because they are in the anterior forearm at their branch point. The interosseous recurrent artery is still out of the dissection field and will not be seen until the posterior forearm is dissected.
Here are some clues to finding the anastomotic branches of arteries around the elbow:
- The superior ulnar collateral artery accompanies the ulnar nerve posterior to the medial intermuscular septum in contact with the medial head of the triceps brachii muscle; it courses posterior to the medial epicondyle of the humerus.
- The inferior ulnar collateral artery branches off the brachial artery close to the level of the elbow joint; its anterior branch is found in the interval between the brachialis and pronator teres muscles of the cubital region.
- Follow the ulnar collateral arteries until they join the ulnar artery and you have found the anterior and posterior ulnar recurrent arteries.
- To find the middle and radial collateral arteries, follow the profunda brachii artery distally.
  - The middle collateral artery is the hardest to find because it plunges into the medial head of the triceps and cannot be followed distally unless it is very large in your specimen.
  - The radial collateral artery is the continuation of the profunda brachii artery and it accompanies the radial nerve. Look for it in the interval between the brachialis muscle and the brachioradialis muscle in the cubital region.
- Follow the radial collateral artery until you come to the radial artery and you have found the radial recurrent artery.
- The interosseous recurrent artery (which anastomoses with the middle collateral artery) lies posterior to the interosseous membrane and is best left to a later dissection.
- All of these anastomotic branches supply muscles as their primary function and they may be small or get lost in the muscles that they supply. The two easiest pairs of arteries to find are the radial recurrent/radial collateral pair and the anterior ulnar recurrent/inferior ulnar collateral pair.
Tendon patterns - Use tendon patterns to learn muscles in the forearm. Insertion points and tendon positions are very helpful. Since most muscles arise from common tendons of origin, origins are not very helpful identification aids in the forearm.
Cut the superficial head of pronator teres - The superficial head of the pronator teres m. (the part that takes origin from the common flexor tendon) should be cut to broaden the dissection field when following the median nerve. To do this, insert a probe along the median nerve on its superficial surface and use a scalpel to cut down to the probe. The two ends of the superficial head can then be reflected (folded back out of the way).
Variable transection planes - Today's dissection instructions (Grant's Dissector pg. 206) tell you to detach the radial origin of the flexor digitorum superficialis muscle. You then turn the muscle medially, leaving it attached to its ulnar origin. Later you will need to cut the flexor digitorum superficialis muscle tendons to permit you to pull the tendons distally through the carpal tunnel. You will also need to transect some of the other forearm muscles in the distal forearm. When you do this, make your transections of the muscles at different proximodistal levels to make reassembly for review easy. Do not cut too close to the wrist; 1.5-2.5 inches proximal to the wrist is about right.
Definition - reflection - Reflection in these dissection instructions means fold it back, not cut it off.

WHEN YOU FINISH THIS SECTION, YOU SHOULD BE ABLE TO PERFORM THE FOLLOWING TASKS AND ANSWER THESE QUESTIONS

What large muscle mass originates from the medial epicondyle of the humerus?
The flexor digitorum superficialis m. inserts on which phalanx in which digits? Where does the flexor digitorum profundus m. insert?
The two pronator muscles of the forearm are innervated by which nerve?
Diagram the anastomoses around the elbow joint.
When the forearm and hand are pronated, what is the relationship of the radius to the ulna?
Which muscles in the flexor-pronator group adduct the hand? Which muscles in this group abduct the hand?

FLEXOR COMPARTMENT OF THE FOREARM

Cutaneous nerves and vessels (review)

Antebrachial fascia

Palmar carpal ligament (a thickening of the antebrachial fascia)

Palmar aponeurosis of the hand

Tendon of palmaris longus m. attaches to it

Flexor retinaculum (deep to the palmar aponeurosis)

Carpal tunnel is formed by the carpal bones and the flexor retinaculum

OSTEOLOGY

Humerus (review this topic using the tables below)

Ulna (review this topic using the tables below)

Radius (review this topic using the tables below)

Interosseous membrane

Carpal bones

Proximal Row
- Scaphoid
- Lunate
- Triquetrum
- Pisiform
Distal Row
- Trapezium
- Trapezoid
- Capitate
- Hamate

Metacarpal bones

Phalanges

RADIOULNAR ARTICULATION

Interosseous membrane

WRIST JOINT

Distal radioulnar articulation

Articular disc

Radiocarpal joint

Ulnar collateral ligament
Radial collateral ligament

FLEXOR-PRONATOR MUSCLES OF THE FOREARM

In addition to being able to identify them, learn the origin, insertion, action, innervation and blood supply of each member of the following two groups of muscles:

Superficial group

Pronator teres m.
Flexor carpi radialis m.
Palmaris longus m.
Flexor digitorum superficialis m.
Flexor carpi ulnaris m.

Deep group

Flexor digitorum profundus m.
Flexor pollicis longus m.
Pronator quadratus m.

VESSELS OF THE FLEXOR REGION OF THE FOREARM

Brachial a.

Radial a.
- Radial recurrent a.
Ulnar a.
- Anterior ulnar recurrent a.
- Posterior ulnar recurrent a.
- Common interosseous a.
  - Anterior interosseous a.
  - Posterior interosseous a.
    - Interosseous recurrent a.

NERVES OF THE FLEXOR REGION OF THE FOREARM

Radial n.

Superficial br.
Deep br.

Ulnar n.
Median n.

Anterior interosseous n.

ANATOMY TABLES FOR TODAY'S TOPIC

Osteology of the Flexor Forearm and Elbow Regions
Bone	Structure	Description	Notes
humerus		the bone of the arm (brachium)	the humerus articulates proximally with the scapula at the glenoid fossa; it articulates distally with the radius and ulna at the elbow joint
	head	the smooth, rounded proximal end of the humerus	it articulates with the glenoid cavity of the scapula to form the shoulder joint
	anatomical neck	the constricted region located adjacent to the head	it is located at the circumference of the smooth articular surface of the head
	surgical neck	the proximal part of the shaft of the humerus	it is located inferior to the greater and lesser tubercles; it is a site of frequent fracture; fractures of the surgical neck of the humerus endanger the axillary n. and the posterior circumflex humeral vessels
	greater tubercle	the large projection located lateral to the head of the humerus	it is the attachment site of the supraspinatus, infraspinatus & teres minor mm. which are three members of the rotator cuff group
	lesser tubercle	the projection located on the anterior surface of the proximal end of the humerus	it is the insertion site of the subscapularis m., a member of the rotator cuff group
	crest of the greater tubercle	the ridge of bone on the anterior surface of the humerus extending inferiorly from the greater tubercle	it forms the lateral lip of the intertubercular groove; it is the attachment site for the transverse humeral ligament and the pectoralis major m.
	crest of the lesser tubercle	the ridge of bone on the anterior surface of the humerus extending inferiorly from the lesser tubercle	it forms the medial lip of the intertubercular groove; it is the attachment site for the transverse humeral ligament and the teres major m.
	intertubercular groove	the groove on the anterior surface of the humerus that is located between the crest of the greater tubercle and the crest of the lesser tubercle	it is occupied by the tendon of the long head of the biceps brachii m.; the transverse humeral ligament spans the intertubercular groove and holds the tendon of the long head of the biceps in place; it is the attachment site for the tendon of the pectoralis major (lateral lip), teres major (medial lip), and latissimus dorsi (floor)
	deltoid tuberosity	the roughened process on the lateral surface of the mid-shaft of the humerus	it is the insertion site of the deltoid m.
	radial groove	the groove that spirals around the posterior surface of the shaft of the humerus	it is a depression for the radial n. and the deep brachial vessels; fracture of the humerus at mid-shaft can injure the radial nerve and deep brachial vessels because they are in contact with bone at this location
	lateral epicondyle	a knob-like projection on the lateral side of the humerus proximal to the capitulum	it is the site of attachment of the common extensor tendon which is the origin of several forearm extensor muscles (extensor carpi radialis brevis m., extensor digitorum m., extensor digiti minimi m. and extensor carpi ulnaris m.); inflammation of the attachment of the common extensor tendon is called lateral epicondylitis which is also known as "tennis elbow"
	medial epicondyle	a knob-like projection on the medial side of the humerus proximal to the trochlea	it is the attachment site of the common flexor tendon which is the origin for the superficial group of forearm flexor muscles (pronator teres m., flexor carpi radialis m., palmaris longus m., flexor carpi ulnaris m. and flexor digitorum superficialis m.); inflammation of the attachment of the common flexor tendon is called medial epicondylitis; the ulnar nerve is in contact with bone as it courses posterior to the medial epicondyle where it is susceptible to injury from blunt trauma or fracture
	medial supracondylar ridge	a narrow ridge running proximally from the medial epicondyle of the humerus	the pronator teres m. takes origin from the common flexor tendon near the most inferior part of the medial supracondylar ridge
	lateral supracondylar ridge	a narrow ridge running proximally from the lateral epicondyle of the humerus	it is the site of origin of the brachioradialis m. and the extensor carpi radialis longus m.
	coronoid fossa	the depression on the anterior surface of the humerus located proximal to the trochlea near the elbow	it accommodates the coronoid process of ulna when the elbow is flexed
	radial fossa	the depression on the anterior surface of the humerus located proximal to the capitulum near the elbow	it accommodates the head of the radius when the elbow is flexed
	olecranon fossa	the depression on the posterior surface of the humerus located just proximal to the elbow	it accommodates the olecranon process of the ulna when the elbow is extended
	capitulum	the rounded process that caps the distal end of the lateral condyle of the humerus	it articulates with the head of the radius; capitulum means "little head"
	trochlea	the grooved process that caps the distal end of the medial condyle of the humerus	it articulates with the trochlear notch of the ulna; the shape of the trochlea and the trochlear notch limits side-to-side movement and guarantees a hinge action; trochlea means "pulley"
ulna		the bone on the medial side of the forearm (antebrachium)	the ulna articulates proximally with the trochlea of the humerus and the head of the radius; it articulates distally with the ulnar notch of the radius
	olecranon	the proximal end of the ulna	it is the insertion site of the tendon of the triceps brachii m.; when the elbow is extended, the olecranon of the ulna engages the olecranon fossa of the humerus
	trochlear notch	the crescent shaped notch on the anterior surface of the proximal end of the ulna	it is located between the olecranon and the coronoid process; it articulates with the trochlea of the humerus; a ridge within the trochlear notch fits into the groove in the trochlea of the humerus which limits side-to-side movement and guarantees a hinge action
	coronoid process	the anterior projection of bone located distal to the trochlear notch	it is the insertion site of the brachialis m.
	radial notch	the notch on the lateral surface of the ulna located just distal to the trochlear notch	it accommodates the head of the radius; the ends of the annular ligament attach to the anterior and posterior edges of the radial notch of the ulna to encircle the head of the radius
	body	the long slender midportion of the ulna	it is also called the shaft or diaphysis; the interosseous membrane attaches to the entire length of the interosseous border of the body of the ulna
	head	the distal end of the ulna	it is small and rounded for articulation with the radius
	styloid process	a small projection from the distal surface of the head of the ulna	it is the site of attachment of the articular disk of the distal radioulnar joint
radius		the bone on the lateral side of the forearm (antebrachium)	the radius pivots on its long axis and crosses the ulna during pronation
	head	the rounded proximal end of the radius	it has a smooth, rounded surface for articulation with the ulna; the head of the radius is encircled by the annular ligament (4/5 of a circle) and the radial notch of the ulna (1/5 of a circle)
	neck	the constricted area of the radius located distal to the head	the annular ligament of the radius surrounds the head of the radius, not the neck of the radius
	radial tuberosity	a roughened area on the anteromedial surface of the radius located just distal to the neck	it is the insertion site of the tendon of the biceps brachii m.
	body	the long, slender midportion of the radius	it is also known as the shaft or diaphysis; the interosseous membrane attaches to the entire length of the body of the radius along its interosseous border; a fracture of the distal end of the body of the radius with a dorsal displacement of the distal fragment is quite common and is called a Colles' fracture
	ulnar notch	a shallow notch located on the medial surface of the distal end of the radius	it articulates with the head of the ulna
	styloid process	the distal-most projection from the lateral side of the radius	the radial styloid process projects lateral to the proximal row of carpal bones

ANATOMY TABLES FOR TODAY'S TOPIC

Osteology of the Flexor Forearm and Elbow Regions