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Joints and Ligaments

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The elbow-joint is a ginglymus or hinge-joint. The trochlea of the 
humerus is received into the semilunar notch of the ulna, and the 
capitulum of the humerus articulates with the fovea on the head of 
the radius. The articular surfaces are connected together by a capsule, 
which is thickened medially and laterally, and, to a less extent, in front 
and behind. 
Synovial Membrane 
The synovial membrane is very extensive. It extends from the margin of 
the articular surface of the humerus, and lines the coronoid, radial and 
olecranon fossæ on that bone; it is reflected over the deep surface of the 
capsule and forms a pouch between the radial notch, the deep surface of 
the annular ligament, and the circumference of the head of the radius. 
Projecting between the radius and ulna into the cavity is a crescentic 
fold of synovial membrane, suggesting the division of the joint into two; 
one the humeroradial, the other the humeroulnar.    
Between the capsule and the synovial membrane are three masses of fat: 
the largest, over the olecranon fossa, is pressed into the fossa by the 
Triceps brachii during the flexion; the second, over the coronoid fossa, 
and the third, over the radial fossa, are pressed by the Brachialis into 
their respective fossæ during extension.    

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The muscles in relation with the joint are, in front, the Brachialis; 
behind, the Triceps brachii and Anconæus; laterally, the Supinator, and 
the common tendon of origin of the Extensor muscles; medially, the common 
tendon of origin of the Flexor muscles, and the Flexor carpi ulnaris.     
The arteries supplying the joint are derived from the anastomosis between 
the profunda and the superior and inferior ulnar collateral branches of 
the brachial, with the anterior, posterior, and interosseous recurrent 
branches of the ulnar, and the recurrent branch of the radial. These 
vessels form a complete anastomotic network around the joint.   
  The nerves of the joint are a twig from the ulnar, as it passes between 
the medial condyle and the olecranon; a filament from the musculocutaneous,
and two from the median.    
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Anterior Ligament 
 The anterior ligament is a broad and thin fibrous layer covering 
the anterior surface of the joint. It is attached to the front of the 
medial epicondyle and to the front of the humerus immediately above the 
coronoid and radial fossæ below, to the anterior surface of the coronoid 
process of the ulna and to the annular ligament, being continuous on either
side with the collateral ligaments. Its superficial fibers pass obliquely 
from the medial epicondyle of the humerus to the annular ligament. The 
middle fibers, vertical in direction, pass from the upper part of the 
coronoid depression and become partly blended with the preceding, but are 
inserted mainly into the anterior surface of the coronoid process. The 
deep or transverse set intersects these at right angles. This ligament is 
in relation, in front, with the Brachialis, except at its most lateral 
Posterior Ligament 
 This posterior ligament is thin and membranous, and consists of 
transverse and oblique fibers. Above, it is attached to the humerus 
immediately behind the capitulum and close to the medial margin of the 
trochlea, to the margins of the olecranon fossa, and to the back of the 
lateral epicondyle some little distance from the trochlea. Below, it is 
fixed to the upper and lateral margins of the olecranon, to the posterior 
part of the annular ligament, and to the ulna behind the radial notch. The
transverse fibers form a strong band which bridges across the olecranon 
fossa; under cover of this band a pouch of synovial membrane and a pad of 
fat project into the upper part of the fossa when the joint is extended. 
In the fat are a few scattered fibrous bundles, which pass from the deep 
surface of the transverse band to the upper part of the fossa. This 
ligament is in relation, behind, with the tendon of the Triceps brachii 
and the Anconæus.    
Ulnar Collateral Ligament  
This ligament is a thick triangular band consisting of two portions, an 
anterior and posterior united by a thinner intermediate portion. The 
anterior portion, directed obliquely forward, is attached, above, by its
apex, to the front part of the medial epicondyle of the humerus; and, 
below, by its broad base to the medial margin of the coronoid process. The 
posterior portion, also of triangular form, is attached, above, by its 
apex, to the lower and back part of the medial epicondyle; below, to the 
medial margin of the olecranon. Between these two bands a few intermediate 
fibers descend from the medial epicondyle to blend with a transverse band 
which bridges across the notch between the olecranon and the coronoid 
process. This ligament is in relation with the Triceps brachii and Flexor 
carpi ulnaris and the ulnar nerve, and gives origin to part of the Flexor 
digitorum sublimis.   
Radial Collateral Ligament 
This ligament is a short and narrow fibrous band, less distinct than the 
ulnar collateral, attached, above, to a depression below the lateral 
epicondyle of the humerus; below, to the annular ligament, some of its 
most posterior fibers passing over that ligament, to be inserted into 
the lateral margin of the ulna. It is intimately blended with the tendon 
of origin of the Supinator.    
Proximal Radioulnar Articulation 
  Annular Ligament
 - This ligament is a strong band of fibers, which encircles the head of 
the radius, and retains it in contact with the radial notch of the ulna. 
It forms about four-fifths of the osseo-fibrous ring, and is attached to 
the anterior and posterior margins of the radial notch; a few of its lower 
fibers are continued around below the cavity and form at this level a 
complete fibrous ring. Its upper border blends with the anterior and 
posterior ligaments of the elbow, while from its lower border a thin 
loose membrane passes to be attached to the neck of the radius; a 
thickened band which extends from the inferior border of the annular 
ligament below the radial notch to the neck of the radius is known as 
the quadrate ligament. The superficial surface of the annular ligament 
is strengthened by the radial collateral ligament of the elbow, and 
affords origin to part of the Supinator. Its deep surface is smooth, 
and lined by synovial membrane, which is continuous with that of the 

Middle Radioulnar Union
The shafts of the radius and ulna are connected by the Oblique Cord and 
the Interosseous Membrane.    
  Oblique Cord 
  - The oblique cord is a small, flattened band, extending downward and 
lateralward, from the lateral side of the tubercle of the ulna at the 
base of the coronoid process to the radius a little below the radial 
tuberosity. Its fibers run in the opposite direction to those of the 
interosseous membrane. It is sometimes wanting.   
  Interosseous Membrane 
  - The interosseous membrane is a broad and thin plane of fibrous tissue 
descending obliquely downward and medialward, from the interosseous crest 
of the radius to that of the ulna; the lower part of the membrane is 
attached to the posterior of the two lines into which the interosseous 
crest of the radius divides. It is deficient above, commencing about 
2.5 cm. beneath the tuberosity of the radius; is broader in the middle 
than at either end; and presents an oval aperture a little above its 
lower margin for the passage of the volar interosseous vessels to the 
back of the forearm. This membrane serves to connect the bones, and to 
increase the extent of surface for the attachment of the deep muscles. 
Between its upper border and the oblique cord is a gap, through which the 
dorsal interosseous vessels pass. Two or three fibrous bands are 
occasionally found on the dorsal surface of this membrane; they descend 
obliquely from the ulna toward the radius, and have consequently a 
direction contrary to that of the other fibers. The membrane is in 
relation, in front, by its upper three-fourths, with the Flexor pollicis 
longus on the radial side, and with the Flexor digitorum profundus on the 
ulnar, lying in the interval between which are the volar interosseous 
vessels and nerve; by its lower fourth with the Pronator quadratus; 
behind, with the Supinator, Abductor pollicis longus, Extensor pollicis 
brevis, Extensor pollicis longus, Extensor indicis proprius; and, near 
the wrist, with the volar interosseous artery and dorsal interosseous 
 Synovial Membrane 
  - The synovial membrane of this articulation is extremely loose, and 
extends upward as a recess (recessus sacciformis) between the radius 
and the ulna.    

Distal Radioulnar Articulation 

  Volar Radioulnar Ligament 
 - This ligament is a narrow band of fibers extending from the anterior 
margin of the ulnar notch of the radius to the front of the head of the 
  Dorsal Radioulnar Ligament 
 - This ligament extends between corresponding surfaces on the dorsal 
aspect of the articulation.    
  Articular Disk 
 - The articular disk is triangular in shape, and is placed transversely 
beneath the head of the ulna, binding the lower ends of the ulna and
radius firmly together. Its periphery is thicker than its center, which 
is occasionally perforated. It is attached by its apex to a depression 
between the styloid process and the head of the ulna; and by its base, 
which is thin, to the prominent edge of the radius, which separates the 
ulnar notch from the carpal articular surface. Its margins are united to 
the ligaments of the wrist-joint. Its upper surface, smooth and 
concave, articulates with the head of the ulna, forming an arthrodial 
joint; its under surface, also concave and smooth, forms part of the 
wrist-joint and articulates with the triangular bone and medial part 
of the lunate. Both surfaces are clothed by synovial membrane; the 
upper, by that of the distal radioulnar articulation, the under, by 
that of the wrist. 
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  - The elbow-joint comprises three different portions-viz., the 
joint between the ulna and humerus, that between the head of the radius 
and the humerus, and the proximal radioulnar articulation, described
below. All these articular surfaces are enveloped by a common synovial 
membrane, and the movements of the whole joint should be studied together. 
The combination of the movements of flexion and extension of the forearm 
with those of pronation and supination of the hand, which is ensured by 
the two being performed at the same joint, is essential to the accuracy 
of the various minute movements of the hand.    
  The portion of the joint between the ulna and humerus is a simple 
hinge-joint, and allows of movements of flexion and extension only. 
Owing to the obliquity of the trochlea of the humerus, this movement 
does not take place in the antero-posterior plane of the body of the 
humerus. When the forearm is extended and supinated, the axes of the 
arm and forearm are not in the same line; the arm forms an obtuse angle 
with the forearm, the hand and forearm being directed lateral-ward. 
During flexion, however, the forearm and the hand tend to approach the 
middle line of the body, and thus enable the hand to be easily carried 
to the face. The accurate adaptation of the trochlea of the humerus, 
with its prominences and depressions, to the semilunar notch of the ulna,
prevents any lateral movement. Flexion is produced by the action of the 
Biceps brachii and Brachialis, assisted by the Brachioradialis and the 
muscles arising from the medial condyle of the humerus; extension, by 
the Triceps brachii and Anconæus, assisted by the Extensors of the wrist, 
the Extensor digitorum communis, and the Extensor digiti quinti proprius. 
proximal radioulnar articulation 
The movements allowed in this articulation are limited to rotatory 
movements of the head of the radius within the ring formed by the 
annular ligament and the radial notch of the ulna; rotation forward 
being called pronation; rotation backward, supination. Supination is 
performed by the Biceps brachii and Supinator, assisted to a slight 
extent by the Extensor muscles of the thumb. Pronation is performed 
by the Pronator teres and Pronator quadratus.    
distal radioulnar articulation 
The movements in the distal radioulnar articulation consist of rotation 
of the lower end of the radius around an axis which passes through the 
center of the head of the ulna. When the radius rotates forward, 
pronation of the forearm and hand is the result; and when backward, 
supination. It will thus be seen that in pronation and supination the 
radius describes the segment of a cone, the axis of which extends from 
the center of the head of the radius to the middle of the head of the 
ulna. In this movement the head of the ulna is not stationary, but 
describes a curve in a direction opposite to that taken by the head of 
the radius. This, however, is not to be regarded as a rotation of the 
ulna the curve which the head of this bone describes is due to a combined 
antero-posterior and rotatory movement, the former taking place almost 
entirely at the elbow-joint, the latter at the shoulder-joint.  

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