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BIOLOGY 03048, ANATOMY, WEEK 14: UPPER EXTREMITY 11/29/99

W. Crone (303 FTZ, 629-7439, cronewil@hvcc.edu, http://www.hvcc.edu/academ/faculty/crone/index.html)

Moore and Dalley, Ch. 6

possible web site: http://www.vesalius.com/graphics/cf_storyboards/hand/cfsb_hand_palm1.asp

(palmar view of hand--shows layers)

The upper limb girdle consists of the clavicle and scapula. The clavicle holds the scapula out at a fixed distance (articulates with acromion), but strong coracoclavicular ligaments are less likely to tear than the clavicle is to break.2 The clavicle is frequently fractured. The scapula, with its aspects of glenoid cavity, coracoid process, spine elaborating into acromion.

The humerus has a ball-faced head, with nearby greater and lesser tubercles separated by the bicipital groove. The glenohumeral joint capsule between scapula and humerus has a lot of slack in it and so offers little resistance to dislocation. Ligaments do assist in preventing dislocation, and the acromion assists in preventing posterior dislocation. The muscles around the shoulder joint (rotator cuff) are primary protection against dislocation, though.

Continuing with the humerus: At the distal end of the humerus there are two rounded condyloid surfaces: 1) capitulum, a lateral rounded condyle for articulation with the radius; 2) trochlea, a bit more pulley-like condyle for articulation with the ulna. Epicondyles flank the condyles: lateral epicondyle--wrist finger extensor attachment, and medial epicondyle--wrist/finger flexor attachment.

Fractures of the humerus are common and have different effects depending on the site of fracture. A fracture in the surgical neck of a humerus may damage the nearby axillary nerve and limit abduction of the arm. In contrast, a fracture in the middle third of the humeral shaft may damage the radial nerve, paralyzing the extensor muscles of the hand (wrist drop).2

MUSCLES THAT AFFECT THE SCAPULA: Seven muscles move/stabilize the scapula. Motions of the scapula include retraction, protraction, elevation, depression, and rotation.

1) trapezius m.: depending on what fibers involved, many possibilities of scapular motion. CN XI (accessory nerve) innervation, as trapezius originally derived from gill-raising muscles.

2) serratus anterior m.: most powerful protractor of the scapula, also keeping the scapula applied to the chest wall at all times. In fact, damage to the long thoracic nerve and paralysis of the serratus anterior leads to"winged scapula," where the scapula projects posteriorly as the arm is abducted.2

3) levator scapulae m.: elevates the scapula.

4,5) rhomboid major and rhomboid minor mm.: They are forceful retractors, lowering the raised arm (woodsman with ax), as well as for keeping the scapula applied to the chest wall.2

6) pectoralis minor m.: its action is to assist in stretching the arm to reach for something out of reach by stabilizing the scapula; also, axillary vessels are underneath it.2

7) subclavius muscle: this small muscle restrains excessive elevation of the clavicle and can protect the subclavian vessels if the clavicle is broken.

ROTATOR CUFF:

1) The supraspinatus muscle: abduction

2) The infraspinatus muscle: lateral (external) rotation

3) The teres minor muscle: lateral (external) rotation

4) The subscapularis muscle: medial (internal) rotation

The support of the musculotendinous (rotator) cuff is such that there is inferior instability, so that many dislocations (subluxations or partial dislocations) of the shoulder initiate that way, e.g., when the joint is abducted or when in athletics, with extension and lateral rotation. The dislocated humeral head is pulled into a subcoracoid position.2 The subacromial bursa lubricates the supra/infraspinatus tendons, so possibilities of tendinitis with insufficient lubrication or bursitis with inflammation. The supraspinatus tendon is often worn with age and so the most likely to rupture of the rotator cuff.2

OTHER MUSCLES SPANNING THE SHOULDER JOINT TO INSERT ON THE HUMERUS:

1) Pectoralis major m., a large chest muscle that binds the humerus to the anterior rib cage, and is a primary flexor of the arm, while also adducting and medially rotating.

2) Latissimus dorsi m., antagonistic to the pectoralis major, so a powerful extensor (e.g., swimmers), while also adducting and medially rotating.

Axilla (armpit): clinically important because of the subcutaneous position of vessels, nerves, and lymph nodes. Anterior axillary fold is produced by the pectoralis major m. and the posterior fold is produced from the latissimus dorsi m.

3) Deltoid m., capping the shoulder joint, is the principle abductor of the arm at the shoulder. Possible injection site for intramuscular (IM) injections. Axillary n.

4) Teres major m., similar actions to latissimus dorsi. m.

THE BRACHIAL PLEXUS: The brachial plexus is formed from the ventral rami of C5-T1 (with occasional help from C4 and T2). It extends downward and laterally, passing over the first rib underneath the clavicle, and enters the axilla. Structurally, the brachial plexus is divided into: roots, trunks, divisions, cords, and nerves (RTDCN).

Roots: ventral rami (after all, these are all hypaxial muscles).

Trunks: fusions of the roots or ventral rami:

a) superior (upper) trunk: fusion of the ventral rami of C5 and C6.

b) middle trunk: ventral ramus of C7.

c) inferior (lower) trunk: fusion of the ventral rami of C8 and T1.

 

Each of the trunks then immediately divide into anterior and posterior divisions, which fuse together to form three cords:

Cords: fusions off of the divisions off of the trunks:

a) posterior cord: fusion of the entire posterior division off of the superior, middle, and inferior trunks.

b) medial cord: a continuation of the anterior division of the inferior trunk.

c) lateral cord: fusion of the anterior divisions of the superior and middle trunks.

These cords derive their name from their relationship to the axillary artery (continuation of the subclavian artery), which runs through the middle of the plexus.

The nerves of the upper extremity arise from the cords. Five major ones:

1) axillary nerve: arises from the posterior cord and provides sensory innervation to the lateral shoulder region, and motor innervation to deltoid m. and teres minor m.

2) radial nerve: the main derivation from the posterior cord. It extends posteriorly along the upper extremity to the radial side of the forearm. The radial nerve supplies motor innervation to extensor muscles of the upper extremity. Injuries that might occur to the radial nerve include crutch paralysis where the person has let the crutch dig into the axilla and compress the radial nerve. The symptom that would result would be wrist drop.2

3) musculocutaneous nerve: arises from the lateral cord and provides motor innervation to the anterior muscles of the forearm (biceps brachii, etc.). Hence, damage to the musculocutaneous nerve would greatly weaken elbow flexion and forearm supination.

4) median nerve: arises from the medial and lateral cords and provides motor innervation to most of the flexor muscles (e.g., lateral ½ of FDP) of the forearm and most of the thenar muscles. Or another way to think about it: LOAF muscles (first two lumbricals, index and middle fingers; thumb opposition, abduction, and flexion). When the median nerve is involved (e.g., carpal tunnel syndrome), think of thumb and thenar eminence (palpable bulge of muscle proximal to thumb).

5) ulnar nerve: arises from the medial cord and provides sensory innervation to the skin on the medial (ulnar side) aspect of the hand. Motor innervation is to flexor carpi ulnaris and medial ½ of flexor digitorum profundus and to all of the intrinsic muscles of the hand except of the thumb ones taken care of by the median nerve, e.g., the hypothenar eminence. Often"stimulated" at the elbow ("funny bone").

In a difficult delivery, one can pull on the head of the baby and injure the superior part of the brachial plexus, or upper arm birth palsy (Erb-Duchenne palsy). Paralysis of the abductors and lateral rotators of the shoulder, and flexors of the elbow, occurs so that the arm hangs in medial rotation, pronation, and wrist/finger flexion (waiter's tip position).2

BONES: The radius and ulna are the bones of the forearm. Distally, at the wrist, the radius predominates, but both ulna and radius have a styloid process for wrist articulation stability. Colles' fracture is a common fracture of the radius at the distal end. Most common type of wrist fracture in those > 50 yo, as in falling with outstretched arms."Dinner fork" deformity with superior, posterior displacement of fragment(s).5

wrist (carpus): there are 8 bones in two rows of 4. From lateral to medial:

proximal row: scaphoid (navicular), lunate, triquetrum, and pisiform bones

distal row: trapezium, trapezoid, capitate, and hamate bones

Most common carpal fracture is to the scaphoid, e.g., fall on outstretched hands.2 The scaphoid b. is in the floor of the anatomical snuffbox, as defined by the tendons of extensor pollicis longus vs. abductor pollicis longus and extensor pollicis brevis mm. Concern about avascular necrosis in proximal fragment after scaphoid fracture.

Metacarpals make up the palm of the hand, with their heads forming the knuckles.

Phalanges are proximal, middle, distal in each finger, but the thumb (pollex) has only two. The interphalangeal joints are hinge joints. Osteoarthritis is a common"wear 'n tear" arthritis affecting the distal interphalangeal (DIP) joints ("Heberden nodes") more than the proximal (PIP) joints ("Bouchard nodes"), and with (reasonably) painless bone enlargement. In contrast, rheumatoid arthritis (RA) will tend to be more inflammatory, more polyarticular, and more in the metacarpophalangeal (MCP) joints and PIP joints.1

THE ELBOW JOINT: The elbow is a hinge joint formed by humerus, radius, and ulna. These are combined in one joint capsule, with the support of collateral ligaments, as well as an anular ligament to hold the radial head against a corresponding ulnar notch. Subluxation of radial head ("pulled elbow"): when a child is lifted up and this anular ligament is torn.2 With the large olecranon process, a superficial bursa can't be far away: olecranon bursitis-"draftman's elbow."1,2

Tennis elbow: lateral epicondylitis (inflammation). Extensor muscles originate from the lateral epicondyle and repeated use, as with a backhand stroke with a tennis racket, may cause a strain on the periosteum and tendinous muscle attachments.2

Those muscles that flex the elbow joint are members of the brachial group, and are innervated by the musculocutaneous nerve, e.g., biceps brachii muscle and brachialis muscle.

Those muscles that extend the elbow joint are innervated by the radial nerve: triceps brachii m..

Muscles in the forearm move the wrist, hand, and fingers. There are four primary actions: supination, pronation, flexion, and extension. The supinator muscle (radial nerve) is positioned proximally, so that it supinates, along with biceps brachii if more force is needed. In contrast, the pronator teres and the pronator quadratus muscles (both median nerve) pronate. Pronator teres is proximal and is used for additional force in pronation, e.g., with screwdriving, and the pronator quadratus is distal, and used for most pronation.

The superficial flexors of the hand, wrist, and fingers arise from the medial epicondyle of the humerus:

Median nerve: flexor carpi radialis, palmaris longus, flexor digitorum superficialis, lateral ½ of flexor digitorum profundus, flexor pollicis longus mm..

Ulnar nerve: flexor carpi ulnaris, medial ½ of flexor digitorum profundus mm..

Extensors are innervated by the radial nerve.

Superficial extensors arise from the lateral epicondyle: extensor carpi radialis longus and brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris. Note that extensor digitorum inserts via an extensor expansion across the MCP joint (so needs assistance to extend the PIP and DIP joints with the lumbricals).

Deep extensors (still radial nerve territory) include: extensor pollicis longus, abductor pollicis longus, and extensor pollicis brevis.

Intrinsic muscles of the hand are muscles are designed to coordinate adduction, abduction, opposition, with flexion and extension, for fine finger movements.

Thumb use, especially opposition, are essential to hand function. The thenar eminence is the fleshy base of the thumb, and so is all median nerve (in particular, worry about a small recurrent branch of median nerve that can be easily damaged with penetrating injury):

abductor pollicis brevis, flexor pollicis brevis, opponens pollicis

Muscles of the intermediate group are positioned between thenar and hypothenar eminences: 1) adductor pollicis (medially, so ulnar nerve), 2) lumbricals: 4 total, one for each digit besides pollex, originate from the tendons of flexor digitorum profundus and insert on the lateral sides of the extensor expansions of digits 2-5, and help to flex at the MCP joints and extend the PIP, DIP joints (writing position). 1st two are median nerve, 2nd two are ulnar nerve. 3) The interossei, all ulnar nerve: palmar interossei adduct, dorsal interossei abduct fingers, and both assist the lumbricals.

Hence, to think more about ulnar nerve injury: loss of adduction/abduction of fingers. Sensory deficits on ulnar side of hand. Hypothenar muscle weakness/wasting. With the interossei and the medial half of the lumbricals weakened or nonfunctional, can see the following: if extensor digitorum is extending the MCP joints, PIP and DIP joints in the affected digits can't be extended, hence a"clawhand."2

Common median nerve injury: carpal tunnel syndrome is caused by compression of the median nerve within the carpal tunnel formed by the carpal bones and the flexor retinaculum. Tendons of flexor digitorum superficialis, flexor digitorum profundus, and flexor pollicis longus mm. run in the tunnel along with the median nerve.

A dorsal ganglion is an abnormal collection of tenosynovial fluid. Tenosynovitis is an infection of the synovial tendon sheath in the wrist or hand, with digital sheath infections that can follow a puncture injury into the synovial sheath. The palmar aponeurosis superficial to these tendons can become locally thickened in a progressive condition called Dupuytren's contracture.2

BLOOD SUPPLY OF THE UPPER EXTREMITY: The subclavian/axillary/brachial artery, with a deep brachial artery to supply triceps brachii m. If there is damage to the brachial artery, concern with ischemic damage to forearm and hand muscles: Volkmann's ischemic contracture.2 In the inferior cubital fossa, the brachial artery divides into the radial and ulnar arteries. The radial artery runs down the lateral (radial) side of the arm, and the ulnar artery is down the medial (ulnar) side of the arm. Arterial pulses are palpable when an artery lies close to a body surface, e.g., radial pulse on distal radius. Deep (radial and ulnar veins leading to brachial vein) and superficial venous drainage (cephalic, basilic veins and their connection with the median cubital vein) are seen in the upper extremity.

 

  1. BC Anderson, Office Orthopedics for Primary Care (WB Saunders, Philadelphia, 1995), pp. 31, 49-53.
  2. KL Moore, AF Dalley, Clinically Oriented Anatomy, 4th ed. (Lippincott Williams & Wilkins, Philadelphia, 1999), pp. 667, 670, 674, 675, 689, 695, 699, 716, 719, 728, 729, 746, 761, 766, 793, 794, 798, 801, 802, 821, 826.

 


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This page updated on November 22, 1999