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Muscles extending the elbow joint

Triceps brachii

Anconeus

Anconeus

Anconeus is a small triangular muscle situated immediately behind the elbow joint, appearing almost to be part of triceps brachii. It arises from the posterior surface of the lateral epicondyle of the humerus and the adjacent part of the elbow joint capsule. The fibres pass medially and distally to attach to the lateral surface of the olecranon and upper quarter of the posterior surface of the ulna and to the fascia which covers it. 

Nerve supply

Anconeus is supplied by a branch of the radial nerve to the medial head of triceps, root value C7 and 8. The skin over anconeus is supplied by root T1.

Action

Anconeus assists in extension of the elbow joint.

Functional activity

By virtue of its long attachment on the ulna, it is thought that anconeus produces lateral movement(abduction of the ulna) and extension of the bone at its distal end. These movements occur during pronation and are essential if a tool, such as a screwdriver, is being used. Movement of the ulna with respect to the radius allows the axis of pronation and supination to be altered so that the forearm rotates about a single axis and so does not describe an arc. This can be seen on an articulated skeleton. This action allows the rotatory movement of the forearm to be transmitted along the screwdriver into the head of the screw.

Palpation

Anconeus can be palpated between the lateral epicondyle of the humerus and the upper part of the ulna during pronation and supination, particularly if the axis of rotation is maintained through the extended index finger. As a practical exercise, it can be demonstrated that anconeus alters the axis of pronation and supination by making each of the fingers, in turn, the axis of rotation.

Muscles flexing the elbow joint

Biceps brachii

Brachialis

Brachioradialis

Pronator teres

Brachialis

Brachialis lies under cover of biceps brachii in the lower half of the anterior aspect of the arm. It arises from the distal two-thirds of the anterior surface of the shaft of the humerus extending outwards onto the medial and lateral intermuscular septa. The muscle fibers are separated from the lower part of the lateral intermuscular septum by brachioradialis, with which it may be partly fused, and extensor carpi radialis longus. The fibres converge to a thick tendon which forms the floor of the cubital fossa and attaches to the rough triangular brachialis impression on the inferior part of the coronoid process and tuberosity of the ulna. Some deeper fibres of brachialis insert into the capsule of the elbow joint and serve to pull it away from the moving bones during flexion and prevent them from becoming trapped.

Nerve supply

Brachialis is supplied mainly by the musculocutaneous nerve, root value C5 and 6; but also receives a branch from the radial nerve; again root value C5 and 6, as it runs along the lateral border of the muscle. However, this latter branch is thought to be almost entirely sensory.

Action

Brachialis is the main flexor of the elbow joint.

Functional activity

Although brachialis flexes the elbow, it is important in controlling extension produced by gravity. In this situation, the flexors of the elbow control the movement by an eccentric contraction.

Palpation

When biceps brachii has been identified, brachialis can be felt extending either side of its belly with the elbow flexed. The tendon can be palpated by applying deep pressure just above the coronoid process of the ulna.

Brachioradialis

Brachioradialis is a superficial muscle found on the lateral side of the forearm extending almost as far as the wrist. It forms the lateral border of the cubital fossa, and is covered in its upper part by brachialis, with which it may be partly fused. The proximal attachment of brachioradialis is to the upper two-thirds of the front of the lateral supracondylar ridge of the humerus and the adjacent part of the lateral intermuscular septum. From here, the fibres run downwards forming a long, narrow, flat tendon in the middle of the forearm. The tendon is crossed by those of abductor pollicis longus and extensor pollicis brevis before it attaches to the lateral surface of the radius just above the styloid process.

Nerve supply

Brachioradialis is supplied by a branch from the radial nerve, root value C5 and 6, which enters its medial side above the elbow. The skin over the muscle is also supplied by roots C5 and 6.

Action

Brachioradialis flexes the elbow joint particularly when the forearm is midway between pronation and supination. It also helps to return the forearm to this mid position from the extremes of either pronation or supination; this can be confirmed by palpation.

Functional activity

Brachioradialis acts primarily to maintain the integrity of the elbow joint since its fibres run more or less parallel to the radius. It also works eccentrically as an extensor of the elbow joint in activities such as hammering.

Palpation

With the elbow flexed to 90° and forearm in a mid-pronated position, the brachioradialis can be felt along the top of the forearm when the position is maintained against resistance. Using firm pressure, the tendon can be palpated proximal to the radial styloid process. The brachioradialis reflex can be elicited by firmly tapping its tendon just above the wrist.

Pronator teres

Pronator teres forms the medial border of the cubital fossa at the elbow, and as such is the most lateral of the superficial muscles in the flexor compartment of the forearm. It arises by two heads: the humeral head and the ulnar head. The humeral head arises from the lower part of the medial supracondylar ridge and adjacent intermuscular septum. It also comes from the common flexor origin on the medial epicondyle and the covering fascia. The ulnar head arises from the pronator ridge, which runs downwards from the medial part of the coronoid process, to join with the humeral head on its deep surface. Between these two heads passes the median nerve. The muscle fibres pass downwards and laterally to attach via a flattened tendon into a roughened oval area on the middle of the lateral surface of the radius.

Nerve supply

Pronator teres is supplied by the median nerve, root values C6, 7. The overlying skin is supplied by roots C6 and T1.

Action

Pronator teres pronates the forearm by producing an anteromedial swing  of the lower end of the radius across the ulna. This movement of the radius carries the hand with it. Pronator teres is also a weak flexor of the elbow.

Palpation

The muscle can be palpated running along the medial border of the cubital fossa between the medial epicondyle of the humerus and the middle of the radius. Pronator teres can be most easily felt, and occasionally seen, when resisting pronation of the forearm.

Muscles laterally rotating the arm at the shoulder joint

Teres minor

Infraspinatus

Deltoid(posterior fibres)

Teres minor

When seen from the back, teres minor forms the upper boundary of both the upper triangular and quadrilateral spaces. It is a thin muscle which arises by two heads, separated by a groove for the circumflex scapular artery, from the upper two-thirds of the lateral border of the scapula, and the fascia between it and teres major(below) and infraspinatus(above). The fibres run upwards and laterally forming a narrow tendon which attaches to the lowest of the facets on the greater tubercle of the humerus and to the bone immediately below. The tendon reinforces and blends with the lower posterior part of the capsule of the shoulder joint.

Nerve supply

Teres minor is supplied by the axillary nerve, root value C5 and 6. The skin over the muscle is supplied by roots T1, 2 and 3.

Action

In the anatomical position teres minor is a lateral rotator, but when the arm is abducted it laterally rotates and adducts.

Palpation

Teres minor can be felt contracting if the examiner’s fingers are placed half way up the lateral border of the scapula and the arm is then actively laterally rotated. The tendon is found just below that of infraspinatus as determined above. 

Infraspinatus

Infraspinatus is a thick, triangular muscle which arises from the medial two-thirds of the infraspinous fossa of the scapula, tendinous intersections attached to ridges in this fossa, and the thick fascia covering the muscle. The fibres converge to a narrow tendon which inserts onto the middle facet on the greater tubercle of the humerus, and into the posterior part of the capsule of the shoulder joint. A bursa, which occasionally communicates with the shoulder joint, separates the muscle from the neck of the scapula. The upper part of the muscle lies deep to trapezius, deltoid and the acromion process; however, the lower part is superficial.

Nerve supply

Infraspinatus is supplied by the suprascapular nerve, root value C5 and 6. The skin over the muscle is supplied by the dorsal rami of T1 to T6.

Action

Infraspinatus is a lateral rotator of the arm at the shoulder joint.

When the arm is laterally rotated, contraction of infraspinatus can be felt in the medial part of the infraspinous fossa. Its tendon can be palpated if the greater tubercle is moved from below the acromion process. To accomplish this the subject lies prone supporting him or herself on the elbows and forearms. The arm is then laterally rotated some 25° and slightly adducted. The tendon can now be palpated just below the acromial angle. It is at this point that soft tissue techniques, such as transverse frictions or electrical treatments are applied if the tendon becomes inflamed.

Functional activity

Infraspinatus and teres minor are of importance during the sequence of movements which occur when the arm is fully abducted. During the latter part of this movement the humerus is laterally rotated so that the greater tubercle moves clear of the coracoacromial arch thereby enabling the remaining part of the humeral head to come into contact with the glenoid fossa, and full abduction to occur.

Teres minor, infraspinatus, supraspinatus and subscapularis, the musculotendinous “rotator cuff” of extensible ligaments around the shoulder joint, are all concerned with its stability; the proximity of their tendons to the joint enhances their effect. During movements of the head of the humerus on the glenoid fossa, interplay between these muscles reduces the sliding and shearing movements which tend to occur. When carrying a weight in the hand these same four muscles brace the head of the humerus against the glenoid fossa.

Muscles medially rotating the arm at the shoulder joint

Subscapularis

Teres major

Latissimus dorsi

Pectoralis major

Deltoid(anterior fibres)

Subscapularis

Subscapularis forms the greater part of the posterior wall of the axilla and as such lies in close proximity to teres major and latissimus dorsi. The anterior surface of the muscle lies on serratus anterior. When seen from the front it forms the upper boundary of the upper triangular and quadrilateral spaces.

Subscapularis is a multipennate muscle which arises from the medial two-thirds of the subscapular fossa and from tendinous septa, which reinforce the muscle, attached to bony ridges in the fossa. There is also an attachment to the fascia covering the muscle. The muscle fibres narrow and form a broad, thick tendon which attaches to the lesser tubercle of the humerus, the capsule of the shoulder joint and the front of the humerus below the tuberosity. A bursa, which communicates directly with the shoulder joint, separates the tendon from the neck of the scapula. 

Nerve supply

Subscapularis is supplied by the upper and lower subscapular nerves, root value C5, 6 and 7, from the posterior cord of the brachial plexus.

Action

Subscapularis is a strong medial rotator of the arm at the shoulder joint; it may also assist in adduction of the arm.

Functional activity

As part of the “rotator cuff”, subscapularis plays an important role in maintaining the integrity of the shoulder joint during movement, by keeping the head of the humerus within the glenoid fossa. It also resists upward displacement of the humeral head when deltoid, biceps and the long head of triceps are active.

Palpation

The muscle belly cannot be palpated as it lies deep to the scapula. However, careful deep palpation may allow the tendon to be felt just before its insertion onto the lesser tuberosity.

Muscles adducting the arm at the shoulder joint

Coracobrachialis

Pectoralis major

Latissimus dorsi

Teres major

Muscles extending the arm at the shoulder joint

Latissimus dorsi

Teres major

Pectoralis major

Deltoid(posterior fibres)

Triceps(long head)

Latissimus dorsi

Latissimus dorsi is a large flat triangular sheet of muscle running between the trunk, via an extensive attachment, and the humerus by a narrow tendon. Consequently, it acts on the shoulder joint. The superior surface of the muscle forms the lower border of the triangle of auscultation, while its lateral border forms the medial border of the lumbar triangle.

Latissimus dorsi arises from the posterior layer of the thoracolumbar fascia, which attaches to the spinous processes of the lower six thoracic and all of the lumbar and sacral vertebrae, as well as to the intervening supraspinous and interspinous ligaments.

That part arising from the lower six thoracic vertebrae is covered by trapezius. In addition to this vertebral attachment, latissimus dorsi arises from the posterior part of the outer lip of the iliac crest, most laterally by direct muscular slips. As the muscle fibres sweep upwards and laterally across the lower part of the thorax, they attach to the outer surfaces of the lower three or four ribs and via fascia to the inferior angle of the scapula. From this widespread origin the fibres converge as they pass to the humerus and form a thin flattened tendon. The tendon winds around and adheres to the lower border of teres major, and inserts into the floor of the intertubercular groove anterior to the tendon of teres major, being separated from it by a bursa. The effect of twisting the muscle through 180° means that the anterior surface of the tendon is continuous with the posterior surface of the rest of the muscle. Consequently, the fibres with the lowest origin on the trunk gain the highest attachment on the humerus.

Nerve supply

Latissimus dorsi is supplied by the thoracodorsal nerve, root value C6, 7, 8, which enters the muscle on its deep surface. The skin covering the muscle is supplied by roots T4 to T12 inclusive, by both ventral and dorsal rami, and L1 to L3 by the dorsal rami.

Action

Latissimus dorsi is a strong extensor of the flexed arm; however, if the humerus is fixed relative to the scapula it retracts the pectoral girdle. It is also a strong adductor and medial rotator of the humerus at the shoulder joint.

Functional activity

Functionally, latissimus dorsi is a climbing muscle, and with the arms fixed above the head it can raise the trunk upwards, in conjuction with pectoralis major. Latissimus dorsi has an important function in rowing and during the downstroke in swimming. Attachment of the muscle to the ribs means that it is active in violent expiration, and can be felt pressing forcibly inwards during a cough or sneeze, as it acts to compress the thorax and abdomen.

The attachment to the inferior angle of the scapula allows latissimus dorsi to assist in holding it against the thorax during movements of the upper limb.

If the humerus becomes fixed point when standing, as for example when using crutches, latissimus dorsi is able to pull the trunk forwards relative to the arms; associated with this is a lifting of the pelvis. In patients with paralysis of the lower half of the body, the fact that latissimus dorsi attaches to the pelvis and is still innervated allows it to be used to produce movement of the pelvis and trunk. Consequently, patients wearing calipers and using crutches can produce a modified gait by fixing the arms and hitching the hips by the alternate contraction of each latissimus dorsi.

Palpation

In a lean subject, latissimus dorsi can be made to stand out relative to the thorax by asking the subject to raise his or her arm to 90° flexion and to hold it steady against an upwardly directed pressure. The muscle can be felt contracting if the posterior axillary fold is held between the finger and thumb while the subject coughs. Adduction of the abducted arm against resistance also enables latissimus dorsi to be seen and felt.

Teres major

In the posterior part of the axilla, teres major forms the lower boundary of both the upper triangular and quadrangular spaces. It is a thick, chunky muscle, forming, with latissimus dorsi, the posterior fold of the axilla. It arises from an oval area on the dorsal surface of the scapula near the inferior angle, and from the fascia between it and adjacent muscles. The muscle fibers, which adhere to those of latissimus dorsi, run upwards and laterally to form a broad, flat tendon which attaches along the medial lip of the intertubercular groove. The tendon is separated from that of latissimus dorsi by a bursa, with the latter muscle virtually covering the whole of teres major.

Nerve supply

Teres major is supplied by the lower subscapular nerve, root value C6 and 7.

Action

Teres major adducts and medially rotates the humerus at the shoulder joint. In addition it can help to extend the flexed arm.

Functional activity

Teres major, like latissimus dorsi, is a climbing muscle and works with the latter and pectoralis major to pull the trunk upwards when the arms are fixed. In conjunction with latissimus dorsi and pectoralis major, teres major is important in stabilizing the shoulder joint.

Palpation

Teres major is covered by latissimus dorsi, and as these two muscles have similar actions, considerable care must be exercised when it is tested. The inferior angle of the scapula must first be found, the fingers are then moved upwards and laterally into the posterior wall of the axilla. The subject should abduct the arm to 90° and then adduct against an upwardly directed resistance. The rounded contour of teres major should now be palpable. During this same manoeuvre the flattened tendon of latissimus dorsi, as it twists around teres major, may also be felt.

Triceps brachii

Triceps brachii is situated on the back of the arm and, as suggested by its name, arises by three heads. Two of the heads arise from the humerus, being separated by the spiral groove, and the third comes from the scapula. The three heads are reffered to as: the long head, lateral head and medial head. The muscle attaches via a tendon of the ulna.

Long head. The tendinous long head comes from the infraglenoid tubercle of the scapula and the adjacent glenoid labrum, where it blends with the lower part of the shoulder joint capsule. Named after its length, the long head is also the most medial of the three, the fibres running downwards superficial to the medial head before joining the tendon of insertion. As the long head descends from the infraglenoid tubercle, it passes between teres minor, to which it is anterior, and teres major, to which it is posterior. In its course it forms the medial border of the quadrilateral and lower triangular spaces, and the lateral border of the upper triangular space.

Lateral head. The fleshy lateral head arises above and lateral to the spinal groove on the posterior surface of the humerus between the attachments of teres minor and deltoid. As the fibres pass to join with those of the medial head, they cover the spiral groove.

Medial head. The large, fleshy medial head lies deep of the other two, and arises from the posterior surface of the humerus, below and medial to the spiral groove as far distally as the olecranon fossa. It has an additional attachment to the posterior aspect of the medial and lateral intermuscular septa.

The three heads of triceps come together to form a broad, laminated tendon; the superficial part of which covers the posterior aspect of the lower third of the muscle, while the deeper part arises from within the substance of the muscle. Such an arrangement creates a larger surface area for the attachment of the muscle fibres. Both laminae blend to form a single tendon which attaches to the posterior part of the proximal surface of the olecranon of the ulna, and to the deep fascia of the forearm on either side. Some muscle fibers from the medial head attach to the posterior part of the capsule of the elbow joint and serve to pull it clear of the moving bones and prevent it becoming trapped during extension of the joint.

Nerve supply

All three parts of the muscle are supplied separately by branches from the radial nerve. The branch to the lateral head is derived from C6, 7 and 8, while those to the long and medial heads come from C7 and 8. Of these, the medial head receives two branches, one of which accompanies the ulnar nerve for a considerable distance before entering the distal part of the muscle. The other branch enters more proximally, continuing through the substance of the muscle to end in, and supply, anconeus. The skin over the muscle is supplied by roots C5, 7, T1 and T2.

Action

Triceps brachii is the extensor of the elbow joint. The long head can also adduct the arm and extend it from a flexed position.

Functional activity

Once the elbow has been flexed, gravity often provides the necessary force for extension, with the elbow flexors working eccentrically to control the movement. Triceps only becomes active in this form of extension when the speed of the movement becomes important as in executing a karate chop. Triceps works strongly in pushing and punching activities, and when performing “press-ups”. In the latter it is working concentrically in the upward movement, and eccentrically in the downward movement. It works in a similar manner when using the arms to get out of, or to lower oneself into, a chair with arms, or when using crutches or parallel bars to relieve body-weight from the legs during walking. When using a wheelchair, triceps brachii works strongly to push the wheel round and so propel the chair forwards.

Triceps brachii is also an important extensile ligament on the under surface of the shoulder joint capsule during abduction of the arm.

Palpation

The bulk of triceps is easy to see and feel on the posterior aspect of the arm. All three heads can be felt contracting if the subject flexes the elbow to 90° with the hand resting on a table, and then alternately presses downwards and relaxes. The long head can be felt high up on the back of the arm almost at the axilla; careful palpation enables it to be traced almost to its insertion on the scapula. The lateral head can be felt on the upper lateral part of the arm, extending as far round as the biceps brachii, while the medial head, covered by the other two heads, can be felt contracting just above the olecranon.

The thick tendon of triceps can be easily gripped between the thumb and index finger of the examiner’s hand, just above the olecranon of the ulna. The triceps reflex is elicited by tapping the tendon just above its insertion, with the elbow slightly flexed.