THE UPPER EXTREMITIES.
The upper extremities include the shoulders, arms, forearms, wrists,
and hands and contain each thirty-two bones. The bones of the two
shoulders taken together are called the _shoulder girdle_ and consist
of the two clavicles or collar bones and the two scapulæ or shoulder
blades, which together make an almost complete girdle of the shoulders.
The =clavicle= is a long slender bone extending almost horizontally
from the sternum to the scapula and can be felt for its whole length
in the living. For the inner two-thirds it is convex anteriorly,
for the outer third concave. In woman it is generally less curved,
smoother, and more slender than in man, and as bone is rough when the
muscles attached are powerful, the right clavicle, being used more, is
generally rougher and thicker than the left. Among the muscles attached
are the large neck muscle, the _sterno-cleido-mastoid_, whose tendons
form the _presternal notch_, the _trapezius_, the _pectoralis major_,
and the _deltoid_.
Being slender and superficial the clavicle is most frequently _broken_
of any bone in the body, generally by indirect violence, as by falling
with the hand out, though old people in such a case are apt to get
_Colles’ fracture_ at the wrist. The bone generally gives way at the
juncture of the outer and middle thirds, with displacement of the
parts inward, so that the fracture is seldom compound. Since, however,
the main vessels of the upper arm, with their nerves, lie beneath the
clavicle, there is danger of their being punctured. Such serious injury
is guarded against by the presence of the _subclavius muscle_. The
clavicle is occasionally removed for _sarcoma_.
[Illustration: FIG. 68.--Bones of the upper extremity. (Toldt.)]
[Illustration: FIG. 69.--Left scapula, posterior surface (after Toldt).]
The =scapula= or =shoulder blade=, so called from its shape, is a
large, flat, triangular bone with a prominent ridge, the _spine_,
crossing its dorsum or posterior surface near its upper edge. It
extends from the second to the seventh rib, with its posterior margin
parallel to and about one inch from the dorsal vertebræ. The _head_,
in which is situated the _glenoid cavity_ for articulation with the
humerus or upper arm bone, is surrounded by a slight constriction,
the _neck_. Above it projects the _coracoid process_, so called from
its fancied resemblance to a crow’s beak. This can usually be felt
about one inch from the juncture of the outer and middle thirds of
the clavicle and from it arise the short head of the biceps and the
coraco-brachialis muscle. The _acromion process_ at the end of the
spine extends out beyond the glenoid cavity posteriorly and affords
attachment to the deltoid and trapezius muscles. It forms the summit
of the shoulder. Numerous other muscles are attached to the surface
of the scapula, the only parts which are truly subcutaneous being the
whole length of the spine and the acromion process, though the lower
angle and the coracoid process can generally be felt. The muscles bulge
so much that the spine in the living appears as a slight depression
extending back almost to the vertebræ. The large number of the muscles
on the shoulder and arm is due to the great flexibility and strength
required for the various uses to which the arms are put.
=Shoulder Muscles.=--The most important shoulder muscle is the
_deltoid_, a large triangular muscle, which surrounds and protects
the shoulder-joint and gives the shoulder its rounded form. It rises
from the outer third of the clavicle, from the acromion process, and
from the whole length of the spine of the scapula, and is inserted
by a tendon into a rough prominence on the middle of the outer side
of the humerus. It serves to raise the arm and to draw it somewhat
forward or back, according as the anterior or posterior fibers are
used. The _pectoralis major_ rises from the inner half of the clavicle,
the front of the sternum, and the cartilages of the true ribs and its
fibers converge to form a fan-shaped muscle, which is inserted by a
flat tendon into the edge of the bicipital groove on the humerus. It
draws the arm forward and inward and helps considerably in forced
inspiration. The _serratus magnus_ rises from the outer surface and
upper border of the eight upper ribs and from an aponeurosis covering
the upper intercostal spaces, and is inserted along the whole length of
the posterior border of the scapula. It carries the scapula forward and
is used in pushing.
The scapula is seldom _broken_ because it is quite movable and is
covered with large muscles and because it lies on the chest, which
serves as an elastic cushion. The acromion process is the part most
frequently broken and occasionally the neck is fractured. _Tumors_
occur and may necessitate the amputation of the whole upper extremity.
=The Humerus.=--The bone of the upper arm, the humerus, is the largest
bone in the upper extremity and articulates with the scapula above
and with the ulna and radius below. At its upper end are the _head_
and the _anatomical neck_, with the _greater tuberosity_ external to
and the _lesser tuberosity_ in front of them. The constriction of the
surgical neck is below the tuberosities, and extending from between
them downward and inward along the upper third of the bone is the
bicipital groove for the long head of the biceps. Though round above,
below the _shaft_ becomes flattened from before backward and curves
slightly forward, terminating in the internal and external _condyles_,
from the former of which the flexors and the round pronator arise and
from the latter the extensors and supinators. From the external condyle
also there projects in front the _radial head_ or _capitellum_ for
articulation with the radius. Internally to the capitellum in front and
in a corresponding position on the back of the bone are the trochlear
surfaces for articulation with the ulna, there being a depression in
front called the _coronoid fossa_ for the reception of the _coronoid
process_ of the ulna in flexion of the forearm, and another depression
behind, the _olecranon fossa_, to receive the tip of the olecranon
process during extension. On the lower half of the humerus at the back
is the spiral groove for the _musculo-spiral nerve_ and the _superior
profunda artery_, while the _ulnar nerve_ runs in a groove back of the
internal condyle.
The humerus is almost completely covered with muscles, the only
part that is subcutaneous being a small portion of the external and
internal condyles. The head can be felt under the muscles and the
greater tuberosity forms the point of the shoulder. When the arm is
at the side, the biceps appears at the front and inner side and the
brachialis anticus on either side below, while on the back of the arm,
with its largest swelling above, is the triceps.
[Illustration: FIG. 70.
FIG. 70.--Superficial muscles of shoulder and arm (from before): 1,
Pectoralis major; 2, deltoid; 3, biceps brachii; 4, brachialis anticus;
5, triceps; 6, pronator radii teres; 7, flexor carpi radialis; 8,
palmaris longus; 9, flexor carpi ulnaris; 10, supinator longus; 11,
extensor ossis metacarpi pollicis; 12, extensor brevis pollicis; 13,
flexor sublimis digitorum; 14, flexor longus pollicis; 15, flexor
profundus digitorum; 16, palmaris brevis; 17, abductor pollicis.
(Dorland’s Dictionary.)]
[Illustration: FIG. 71.
FIG. 71.--Superficial muscles of shoulder and arm (from behind): 1,
Trapezius; 2, deltoid; 3, rhomboideus major; 4, infraspinatus; 5,
teres minor; 6, teres major; 7, latissimus dorsi; 8, triceps; 9,
anconeus; 10, brachialis anticus; 11, supinator longus; 12, extensor
carpi radialis longior; 13, extensor carpi radialis brevior; 14,
extensor communis digitorum; 15, extensor carpi ulnaris; 16, flexor
carpi ulnaris; 17, extensor ossis metacarpi pollicis; 18, extensor
brevis pollicis; 19, tendon of extensor longus pollicis. (Dorland’s
Dictionary.)]
=Upper Arm Muscles.=--The _biceps_ is the most important arm muscle. It
rises by a short head from the coracoid process of the scapula and by
a long head from a tubercle on the upper margin of the glenoid cavity,
the tendon arching over the head of the humerus and descending in the
bicipital groove. It is inserted into the back of the tuberosity of
the radius and by a broad aponeurosis into the fascia of the forearm.
It flexes and supinates the forearm and renders the fascia tense. Its
inner border forms a guide in tying the _brachial artery_, as this
artery runs along its inner side.
The _brachialis anticus_ rises from the lower half of the outer and
inner surfaces of the humerus and is inserted into the coronoid process
of the ulna, thus covering and projecting the elbow-joint anteriorly.
It is a flexor of the forearm.
Another smaller muscle on the anterior arm, which also aids in flexion,
is the _coraco-brachialis_, which extends from the coracoid process of
the scapula to the middle of the inner surface of the humerus.
Extending the entire length of the posterior surface of the humerus
is the _triceps_, similar to the quadriceps extensor in the thigh and
direct antagonist to the biceps and brachialis anticus muscles. It
rises by a long head from below the glenoid fossa, by the external head
from the upper third of the posterior surface of the humerus, and by
the internal head from the middle and lower thirds of the posterior
surface. It is inserted in the olecranon process of the ulna and serves
to extend the forearm and arm.
The humerus is more often _fractured_ by muscular action than any
other bone. Usually the fracture occurs in the lower half of the
bone and sometimes the musculo-spiral nerve is involved. There is a
great tendency to non-union, probably due to interposition of soft
parts. Sometimes the break is across and down between the condyles,
_T-fracture_. Involvement of the elbow-joint is more serious than
fracture of the humerus alone. _Sarcoma_ of the humerus does occur and
may require the removal of the clavicle and scapula as well as of the
arm bone itself. In _amputation_ of the humerus in children a long skin
flap is left to allow for growth of the bone, as it is liable to grow
again.
=The Ulna.=--In the forearm there are two bones, the ulna and the
radius, of which the former is the longer. The ulna is on the inner
side of the forearm and its upper end forms the greater part of the
articulation with the humerus, as most of the articulation at the wrist
is formed by the radius and the inter-articular fibro-cartilage. The
head of the ulna is at the lower extremity of the bone and articulates
on the outer side with the radius and below with the triangular
fibro-cartilage. From its inner side projects the _styloid process_.
The olecranon process forms the upper extremity and presents anteriorly
an articular surface, the _greater sigmoid cavity_, for articulation
with the trochlea of the humerus, where it fits into the olecranon
fossa during extension. The same articulating surface also covers
the _coronoid process_, a smaller projection below and in front of
the olecranon, which fits into the coronoid fossa during flexion.
Continuous with the greater sigmoid cavity on the outer side is the
_lesser sigmoid cavity_ for articulation with the head of the radius.
Under the _triceps tendon_, which is inserted into the olecranon, is a
_bursa_ or sac of synovial membrane, such as occurs in parts where much
force is brought to bear.
=The Radius.=--The radius, or spoke of the wheel, is on the outer
side of the forearm and gets its name from the way it turns upon
the ulna in pronation. The _shaft_ is larger below than above and
is slightly curved longitudinally for greater strength. The upper
extremity or _head_ is small and has a slightly concave upper surface
for articulation with the radial head of the humerus. It articulates by
its sides with the lesser sigmoid cavity and is bound to the ulna by
the _orbicular ligament_, which runs over a smooth articular surface.
Below the head is the constriction of the _neck_ with the tuberosity
for the biceps tendon to the inner side below. The lower extremity is
large and forms the chief part of the wrist-joint, articulating with
the semilunar and scaphoid bones of the wrist. From the lower extremity
the strong conical _styloid process_ projects externally.
[Illustration: FIG. 72.--Bones of the right forearm in a position of
supination. (Toldt.)]
In the living the _olecranon process_ of the ulna is always felt at
the elbow and the posterior border of the ulna forms the prominent
ridge down the forearm, leading to the styloid process. The head of
the radius is felt just below the external condyle and often makes a
dimple in the muscles of the forearm. The rest of its upper half is
concealed with muscles, but the lower half is easily felt as there are
only tendons over it. The styloid process is felt externally. Normally
that of the radius is a little lower than that of the ulna, so that in
cases of fracture their relative position is of considerable importance
as showing the amount of deformity.
The two forearm bones are more frequently _broken_ together than
separately and generally by direct violence, the lower fragment being
usually drawn up by the action of the flexor and extensor muscles and
producing a swelling on the palmar surface of the forearm. Indirect
violence usually causes fracture of the radius only. In both cases, but
especially in fracture of both bones, there is a tendency for membrane
to get between the fragments, so the arm is put up in splints with the
hand midway between pronation and supination in order to separate the
bones as far as possible. Care must be taken not to have the bandage
too tight or gangrene of the fingers may result. In most fractures of
the arm it is put up bent, but in _fracture of the olecranon_ it is put
up fully extended, as the fragment is sure otherwise to be displaced by
the pull of the triceps. In fact, the olecranon is sometimes fractured
by the muscular force of the triceps, though usually its fracture,
which is frequent, is due to direct violence. The ulna is also often
fractured in the middle by direct violence or the styloid process may
be broken. Fracture of the neck or shaft of the radius is very common,
the most important arm fracture being that of the lower end of the
radius or _Colles’ fracture_. This and the corresponding fracture in
the leg, _Pott’s fracture_, are two of the commonest fractures. In
_dislocation of the wrist_ the normal relation of the two styloid
processes remains unchanged, but in Colles’ fracture the lower fragment
often projects on the back of the hand, making a typical deformity
called the _silver fork deformity_.
The bones of the wrist and hand had best be described before the
forearm muscles are taken up, as the muscles of the forearm are
distributed largely to the fingers.
=The Wrist.=--The wrist or _carpus_ is made up of eight bones arranged
in two rows of four each. In the first row are the _scaphoid_ and
_semilunar bones_, on the outer side, articulating with the radius, the
_cuneiform_ articulating with the fibro-cartilage of the wrist-joint,
and the _pisiform_. In the second row, in corresponding positions,
are the _trapezium_, _trapezoid_, _os magnum_, and _unciform_. The
eminence felt on the radial side of the wrist is the protuberance of
the scaphoid, while the pisiform is generally felt on the ulnar side.
[Illustration: FIG. 73.--Right carpal bones, dorsal surface. _T_,
trapezium; _T´_, trapezoid; _7_, os magnum; _U_, unciform; _S_,
scaphoid; _L_, semilunar; _C_, cuneiform; _P_, pisiform.]
=The Hand.=--The hand contains nineteen bones, five _metacarpal bones_,
one for each finger and the thumb, whose bases articulate with the
lower row of wrist bones, and fourteen _phalanges_, three for each
finger and two for the thumb, of which the first row articulate with
the metacarpal bones. They are all long bones and are slightly concave
anteriorly. When the hand is flexed it is the heads of the metacarpal
bones, not the bases of the phalanges, that are so prominent, the head
of the third metacarpal being most prominent.
The metacarpals are seldom _fractured_, though bad fractures
occasionally occur. In comminuted fracture nothing can be done but
remove the bone. If the periosteum is left the bone will grow again.
Two diseases sometimes affect the metacarpals and the phalanges,
_tuberculosis_ and _syphilis_. Both cause swelling of the bones.
=Muscles of the Forearm.=--The chief groups of muscles on the forearm
are the _flexors_ and _pronators_ on the anterior surface and the
_extensors_ and _supinators_ on the posterior surface. In general the
flexors and pronators take their origin from on or around the internal
condyle, while the extensors and supinators arise on or around the
external condyle. Where not otherwise stated it will be understood that
such is their origin. In a general way they may by grouped as follows:
ANTERIOR SURFACE.
{ flexor carpi radialis
Flexors of wrist { flexor carpi ulnaris
{ palmaris longus
Flexors of fingers { flexor sublimis digitorum
{ flexor profundus digitorum
Flexor of thumb flexor longus pollicis
Pronators of hand { pronator radii teres
{ pronator quadratus
POSTERIOR SURFACE.
Extensor of forearm anconeus
{ extensor carpi radialis longior
Extensors of wrist { extensor carpi radialis brevior
{ extensor carpi ulnaris
{ extensor ossis metacarpi pollicis
Extensors of thumb { extensor primi internodii pollicis
{ extensor secundi internodii pollicis
Extensor of fingers extensor communis digitorum
Extensor of index finger extensor indicis
Extensor of little finger extensor minimi digiti
Supinators of hand { supinator longus
{ supinator brevis
Of the _flexors of the wrist_ the _flexor carpi radialis_ is inserted
into the base of the index and usually of the third metacarpal bone,
the _flexor carpi ulnaris_ into the fifth metacarpal, the pisiform and
the unciform bones, while the _palmaris longus_ goes to the anterior
annular ligament of the wrist and the palmar fascia of the hand. The
_flexor sublimis digitorum_ is inserted by four tendons into the second
phalanges of the fingers, while the _flexor profundus digitorum_ arises
from the upper part of the ulna and is inserted into the last phalanges
of the fingers. The _flexor of the thumb_ arises from the middle of the
radius and is inserted into the last phalanx of the thumb. Which joint
is flexed by a muscle depends upon the origin and insertion of the
muscle, all those included between being affected. Thus, the _flexor
sublimis digitorum_, which has its origin in part at least from the
condyle and is inserted in the second phalanges of the fingers, flexes
the forearm, wrist, and all the finger-joints but the last, while the
_flexor profundus digitorum_, arising from the ulna, though it flexes
the wrist and fingers, has no power of flexing the forearm.
The _pronator radii teres_, besides arising from the supra-condylar
ridge, rises from the coronoid process of the ulna. It is inserted into
the middle of the outer surface of the radius and serves to pronate
the forearm. The other pronator, the _pronator quadratus_, is a small
quadrilateral muscle extending transversely across the radius and ulna
just above their carpal extremities. It rises from the anterior surface
of the ulna and is inserted into the anterior external border of the
radius.
On the back of the forearm the _anconeus_ serves to extend the forearm
only, being inserted into the upper part of the posterior surface of
the ulna. The _extensors of the wrist_ are inserted into the bases of
the various metacarpal bones and have some power to extend the forearm
as well as the wrist. The _extensors of the thumb_, as their names
imply, go one to the metacarpal bone and one to each of the phalanges,
the longest one extending the whole thumb, the others only a part. They
rise from the ulna and radius, not the condyle. The _extensor communis
digitorum_ goes to all the phalanges of all the fingers, the _extensor
minimi digiti_ to those of the little finger only, and the _extensor
indicis_ to those of the index finger, the last two arising short of
the condyle.
Of the _supinators_ the longer one is inserted into the styloid process
of the radius, while the shorter one, the _supinator brevis_, is
inserted into the upper part of the same bone, both thus serving to
turn the radius on the ulna.
Where the _tendons_ of the various muscles pass over the wrist, both
front and back, they are covered with a synovial sheath and are held
down by a broad ligament, which some of them perforate, the annular
ligament. The strong fibrous band of the _anterior annular ligament_
arches over the carpal bones in front. Beneath it pass the median nerve
and the tendons of the flexors of the fingers and thumb. The _posterior
annular ligament_ is of less importance.
The deep _palmar fascia_ forms a sheath for the muscles of the hand.
In carpenters there sometimes occurs _Dupuytren’s contraction_ of the
palmar fascia, which draws the fingers up. As operation is not always
successful, it is quite a serious matter.
The _muscles of the hand_ itself include various abductor, adductor,
and short flexor muscles of the thumb and little finger. There also
extend between the metacarpal bones the _lumbricales_, four small
muscles that aid the deep flexor muscles; likewise seven _interossei_,
of which four are dorsal and three palmar. The _dorsal interossei_
arise by two heads from the adjacent sides of the metacarpal bones and
are inserted into the bases of the first phalanges, thus abducting the
fingers; while the _palmar interossei_, arising from the palmar surface
of the second, fourth, and fifth metacarpals, are inserted into the
three corresponding first phalanges and adduct the fingers toward an
imaginary line drawn through the middle finger.
=Joints of the Upper Extremity.=--The joints of the upper extremity,
with the exception of the wrist-joint, are the most freely movable of
any in the body, probably because the hand has the finest work to do
and a greater number of motions are required. Even the wrist has much
greater freedom of motion than the corresponding joint in the lower
extremity.
The _shoulder-joint_ is rather a deep joint, to allow of the varied
motion required, and has a capsular ligament from the margin of the
glenoid fossa above to the neck of the humerus below. The _elbow_,
which is a hinge joint, has an anterior and a posterior ligament and
two lateral ligaments, as is practically the case in all such joints.
The _wrist_ has several ligaments which, taken together, are capsular
in nature.
=Blood Supply of the Upper Extremity.=--The blood supply of the upper
extremity comes through the _subclavian artery_, which, on the right,
springs from the innominate artery and on the left from the aortic
arch. It remains one trunk as far as the elbow, though different names
have been given to different parts. Thus, as it passes over the lower
border of the first rib, it becomes the _axillary_, and at the lower
border of the axilla, where it starts down the arm, the _brachial_. At
the elbow it divides into the _ulnar_ and _radial arteries_.
In its upper part the _brachial artery_ lies internal to the humerus
but below it is in front of the bone. The _radial_ runs in a line from
the middle of the elbow anteriorly to the inner side of the styloid
process of the radius and is much exposed to injury in the lower third
of its course, as when the hand is thrust through glass. On it at the
wrist the pulse is counted. It is much smaller than the ulnar and winds
around the outer side of the thumb to the palm, where, with the deep
branch from the ulnar, it forms the _deep palmar arch_. The _ulnar
artery_ passes obliquely inward to the middle of the forearm and thence
along its ulnar border to the palm of the hand, where it divides into
the deep branch and the _superficial palmar arch_ which supplies the
four _digital arteries_.
From the _axillary artery_ branches go to the chest wall and shoulder,
the most important being the two _circumflex arteries_ to the deltoid.
The brachial has only two branches of any importance, the _superior_
and _inferior profunda_, both on the upper arm, of course.
In case of _hemorrhage_ compression can frequently be applied with the
fingers where the subclavian crosses the rib or in the axilla, where
the artery can be pressed up against the humerus.
=Nerves.=--The nerve supply of the shoulder comes chiefly from the
anterior and posterior _thoracic_, the _suprascapular_, and the
_circumflex_, these last going to the deltoid. The biceps is supplied
by the _musculo-cutaneous_, the triceps by the _musculo-spiral_, and
the brachialis anticus by both. Most of the flexor and pronator muscles
are supplied by the _median_, while the _posterior interosseous_ and
the _musculo-spiral nerves_ go to the extensors and supinators. The
_ulnar nerve_ supplies the hand largely.