272
UNIT TWO
Elbow Joint
The
elbow joint
is a complex structure that includes two
articulations—a hinge joint between the trochlea of the
humerus and the trochlear notch of the ulna and a plane joint
between the capitulum of the humerus and a shallow depres-
sion (fovea) on the head of the radius. A joint capsule com-
pletely encloses and holds together these unions
(f g. 8.15)
.
Ulnar and radial collateral ligaments thicken the two joints,
and F bers from a muscle (brachialis) in the arm reinforce its
anterior surface.
The
ulnar collateral ligament,
a thick band of dense
connective tissue, is located in the medial wall of the capsule.
The anterior portion of this ligament connects the medial
epicondyle of the humerus to the medial margin of the coro-
noid process of the ulna. Its posterior part is attached to the
medial epicondyle of the humerus and to the olecranon pro-
cess of the ulna
(f
g. 8.16
a
)
.
The
radial collateral ligament,
which strengthens the
lateral wall of the joint capsule, is a F brous band extend-
ing between the lateral epicondyle of the humerus and the
anular ligament of the radius.
The anular ligament, in turn,
attaches to the margin of the trochlear notch of the ulna, and
it encircles the head of the radius, keeping the head in con-
tact with the radial notch of the ulna (F g. 8.16
b
). The elbow
joint capsule encloses the resulting radioulnar joint so that
its function is closely associated with the elbow.
of the deltoid muscle, the
subacromial bursa
between the
joint capsule and the undersurface of the acromion process
of the scapula, and the
subcoracoid bursa
between the joint
capsule and the coracoid process of the scapula. Of these,
the subscapular bursa is usually continuous with the syn-
ovial cavity of the joint cavity, and although the others do
not communicate with the joint cavity, they may be con-
nected to each other (see F
gs. 8.13 and 8.14).
The shoulder joint is capable of a wide range of move-
ment, due to the looseness of its attachments and the large
articular surface of the humerus compared to the shal-
low depth of the glenoid cavity. These movements include
fl exion, extension, adduction, abduction, rotation, and cir-
cumduction. Motion occurring simultaneously in the joint
formed between the scapula and the clavicle may also aid
such movements.
The shoulder joint is somewhat weak because the bones are mainly
held together by supporting muscles rather than by bony structures
and strong ligaments. Consequently, the articulating surfaces may
become displaced or dislocated easily. Such a
dislocation
can occur
with a forceful impact during abduction, as when a person falls on an
outstretched arm. This movement may press the head of the humerus
against the lower part of the joint capsule where its wall is thin and
poorly supported by ligaments. Dislocations most commonly aF
ect
joints of the shoulders, knees, ±
ngers, and jaw.
Coracohumeral
ligament
Transverse
humeral
ligament
Tendon of
biceps
brachii
(long head)
Acromion process
Clavicle
Coracoid
process
Acromion
process
Subscapular
bursa
Joint
capsule
Coracoid
process
Clavicle
Glenohumeral
ligaments
Glenoid cavity
Triceps
brachii
(long head)
Glenoid
labrum
Scapula
Humerus
Scapula
Articular capsule
(glenohumeral
ligaments hidden)
(a)
(b)
FIGURE 8.14
Ligaments associated with the shoulder joint. (
a
) Ligaments hold together the articulating surfaces of the shoulder. (
b
) The glenoid
labrum is composed of ±
brocartilage.
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