Download (ArticulatioCubiti) By Prof. Dr. Muhammad Imran Qureshi

The Elbow Joint
(ArticulatioCubiti)
By
Prof. Dr. Muhammad Imran Qureshi
Type Of the Joint:
Compound Synovial
Humeroulnar articulation
Humeroradial articulation
Superior Radioulnar articulation
Variety Of the Joint:
Uniaxial of Hinge Variety (Ginglymus)
The requisites of a hinge are that:
The capsule must be loose in front and behind to permit flexion and extension, and
Strong collateral ligaments must be present to prevent medial and lateral movements.
Articular Surfaces:
The articular surfaces are covered with Hyaline Cartilage. They are:
At the lower end of the Humerus,
there is a lateral “Capitulum” and
medial “Trochlea”. The trochlea is not
a simple pulley because its medial
flange exceeds the lateral one, thus
projecting at a lower level (0.6mm).
This means that the plane of the joint
is about 2cms distal to the inter
epicondylar line and is tilted
inferomedially. The Trochlea is also
widest posteriorly, and here its lateral
edge is sharp. The trochlea has an
asymmetrical saller surface, largely
concave transversely and convex
anteroposteriorly. The medial surface of the trochlea is NOT covered with hyaline
cartilage.
On the Upper end of the Radius is its disc shaped “Head”, which is covered with
hyaline cartilage that extends onto its circumference and thereby into the proximal
radioulnar joint. The rim of the radial head, which is more prominent medially, fits the
groove between the humeral capitulum and trochlea. The superior surface of the head
is shallowly concave.
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On the Upper end of the Ulna is its
“Trochlear Notch” (Semilunar notch), which
is formed by the Olecranon and coronoid
processes of the ulna. These two processes
of the ulnar notch are usually separated by
a rough strip devoid of articular cartilage
and covered by fibroadipose tissue and
synovial membrane.
On the lateral surface of the coronoid
process of the ulna, there is a concave facet
called Radial notch of the Ulna. It forms
about one fifth of a circle.
Fibrous Capsule:
On The Humerus: The capsule is
attached laterally to the articular
margins of the capitulum. Anteriorly, it
leaves the superior articular margin of
the capitulum and passes on above the
margins of the radial and coronoid
fossae. From here, it passes on to the
articular margins of the medial flange of
the trochlea and with it passes
posteriorly. Here, it leaves the superior
articular margin of the posterior aspect
of the trochlea and passes above the Olecranon fossa, from where it reaches the lateral
flange of the trochlea and thence to the articular
margin of the capitulum.
On The Ulna: From the humerus, the fibres of the
capsule pass to the ulna, where they are attached
to the articular margins of the Trochlear notch of
Ulna and the anterior and posterior margins of the
radial notch of ulna.
On The Radius: The capsule is NOT attached to
the radius. It is attached to the Annular Ligament
instead.
The anterior part of the capsule is irregularly
arranged, and some of the deeper fibres of
Brachialis are inserted into it.
The posterior part of the capsule is thin and may
be deficient medially. It is protected by the Triceps.
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Synovial Capsule / Membrane:
On the Humerus, It is attached to the articular margins of the capitulum and the
Trochlea and lines the two anterior and one posterior fossae. From here, it is reflected
to line the inner
aspect of the
fibrous capsule.
On the Ulna, it
follows the
articular margins
of the Olecranon
and Coronoid
processes, and
the anterior and
posterior lips of
the radial notch of
the ulna.
On the Radius, it is attached to the lower margin of its cylindrical articular surface of its
head.
From the articular margin of the head of radius, it hangs down between the annular
ligament and the neck of the radius (which it encircles like a sleeve and thus preventing
friction between the two).
Ligaments of the joint:
Only Extracapsular Ligaments are present in this joint. They are:
Ulnar (Medial) Collateral Ligament: It is
Triangular in shape and comprises of the
following THREE bands:
Anterior Band: It is the strongest of the
three. On the Humerus, it is attached to
the medial epicondyle and passes down to
be attached to a tubercle on the medial
border of coronoid process of the ulna.
Posterior Band: It passes from the same
tubercle on the medial border of the ulna
to the medial border of the olecranon
process.
Middle Band: It spans (bridges the gap) between the anterior and posterior bands.
(Forms carpet for the ulnar nerve on its way to the forearm)
Radial (Lateral) Collateral Ligament: It is a flat triangular band, one end of which is
attached to the lateral humeral epicondyle (below the common extensor origin), while
the other end fans out and its fibres blend with the fibres of the annular ligament. (It is
not attached to radius)
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Annular Ligament: It is attached to the anterior and
posterior lips of the radial notch of the ulna. Around
the radial head, it is wide, while around its neck, it is
narrow.
Quadrate Ligament: Though NOT a part of the joint,
it plays a vital role in preventing the herniation of the
synovial membrane between the anterior and
posterior edges of the annular ligament. It is attached
to the neck of the radius proximal to its tuberosity to
the upper part of the supinator fossa of the ulna just
distal to the radial notch. It prevents herniation of the
synovial membrane as it forms a sleeve around the
radial neck.
Blood Supply of the joint:
Branches from the arteries which anastomose around it.
Nerve Supply of the joint:
It follows the Hilton’s Law.
Musculocutaneous nerve.
Median nerve.
Ulnar nerve.
Radial nerve.
Movements of the joint:
Flexion: It is produced by the Brachialis and the Biceps brachii, assisted by all the
muscles that cross the joint whose line of pull passes in front of the axis of flexion and
extension. Approximation of the ventral surfaces of the arm and forearm limit it. The
range is about 140o.
Extension: Triceps brachii is the prime mover, assisted by all the muscles that cross
the joint whose line of pull passes behind the axis of flexion and extension.
Stability Of the joint:
It depends upon THREE factors:
Bony Factors
Ligamentous Factors, and
Muscular Factors
Bony Factors:
The joint is quite secure when
extended. In this position, the
Olecranon process of the ulna
fits into the Olecranon fossa of
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the humerus….. The joint is
said to be locked (Secure).
Only fracture of the Olecranon
process will make the joint
unstable.
However, when the joint is
flexed, the Olecranon process
is out of the Olecranon fossa
of the humerus.
So in this position, any force
applied in the direction of
Olecranon process may cause
it to dislocate posteriorly with
or without fracture of the
Coronoid process of the ulna.
Ligamentous Factors:
The anterior and posterior parts of the capsule arelax and weak,
making anterior or posterior dislocation possible (depending on the
circumstances)
The collateral Ligaments are very strong, securing the joint from both sides. Thus lateral
dislocation is not possible.
The Annular Ligament is cup
shaped, being wider above and
narrow below, so the head of
the radius is also secure within
this ligament. Since this
ligament acquires the cup
shape gradually during
development, avulsion of the
head of radius is a common
phenomenon in young children.
Muscular Factors:
The Brachialis passes just in front of the capsule of the joint and is inserted just below
the joint into the Ulnar tuberosity, so it gives anterior support.
On the Lateral and medial sides, the tendons of origin of the common extensors and
flexors reinforce the collateral ligaments.
Posteriorly, since the Triceps tendon is inserted on the Olecranon process of the ulna,
its support is negligible.
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