Download Glenohumeral Articulation

The Shoulder Joint
(Glenohumeral Articulation)
By
Prof. Dr. Muhammad Imran Qureshi
Type Of the Joint:
Simple Synovial
Variety Of the Joint:
Multiaxial
Ball and Socket Variety
Articular Surfaces:
Head Of the Humerus
Glenoid Fossa of The Scapula
Disproportion between the large rounded head of Humerus and
small shallow Glenoid cavity
Fibrous Capsule:
On the Scapula, it is attached beyond the supraglenoid tubercle and
margins of the Labrum.
On the Humerus, it is attached around the articular margins of the Head
(anatomical Neck) except inferiorly, where it is attached to the surgical neck
(which lies about 1.5 cm below the articular margin). The capsule bridges
the gap between the greater and lesser tuberosities i.e. the intertubercular
groove, forming the Transverse ligament.
A gap is always present in the anterior part of the capsule, through which,
the cavity of the joint communicates with the subscapularis bursa.A similar
gap may sometimes be present posteriorly, communicating the joint
cavity with the Infraspinatus bursa. The fibers of the capsule run
HORIZONTALLY between the scapula and the humerus.It is THICK
and STRONG but very LAX.Near the humerus, it is greatly
thickened by fusion of the tendons of short scapular muscles (Rotator
Cuff).The tendon of the long head of biceps is Intracapsular.
Synovial Capsule / Membrane:
On the Scapula, It is attached around the glenoid labrum and lines
the capsule.
On the Humerus, it is attached to the articular margins of the head,
and covers the bare area of the surgical neck that lies within the
capsule on the upper end of the shaft medially.
It herniates through the gap in the anterior part of the capsule, to
communicate with the subscapularis bursa.
It invests the tendon of long head of biceps in a tubular sleeve that is
reflected back on the tendon to the transverse ligament and adjoining
floor of the intertubercular sulcus. This sleeve of synovial membrane
glides to and fro with the tendon of the long head of biceps during the
movements of abduction and adduction.
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Ligaments of the joint:
Extracapsular Ligaments:
Coracohumeral Ligament: Passes laterally across the
capsule, from the under surface of the coracoid process to the
margins of the greater tuberosity and along the transverse
ligament.
Coracoacromial Ligament: Passes from the medial border
of acromion, in front of the acromioclavicular joint and fans
out in the form of a strong flat triangular band, to the
coracoid Process. It lies above the head of the
humerus and serves to increase the surface upon
which, the head of the humerus is supported. It is
separated from the ‘rotator cuff’ by the sub acromial
bursa.
Transverse Humeral Ligament
Intracapsular Ligaments:
Glenohumeral Ligaments: These are thickenings above and
below the opening into the subscapular bursa in the anterior
part of the capsule. They are three in number.
Superior glenohumeral ligament: Is a thickened
transverse part that spans between the upper ends of
the glenoid rim and anatomical neck of the humerus.
Inferior glenohumeral ligament: Is a thickened
transverse part that spans between the lower parts
of the glenoid rim to the lower part of the
anatomical neck of the humerus.
Middle glenohumeral ligament: Is a thickened
oblique part that spans between the upper part of the
glenoid rim to the lower part of the anatomical neck
of the humerus.
Blood Supply of the joint:
Branches from the following arteries supply the
joint:
Anterior Circumflex Humeral Artery
Posterior Circumflex Humeral Artery
Suprascapular Artery
Circumflex Scapular artery.
Nerve Supply of the joint:
It follows the Hilton’s Law.
It is innervated predominantly from the posterior cord of the
brachial plexus via the Axillary and Radial nerves.The capsule
is also supplied by the Suprascapular Nerve, the Lateral
Pectoral nerve and the Musculocutaneous nerve.
Movements of the joint:
Due to 1:4 disproportion between the head of Humeral and the
Glenoid fossa, there is a substantial freedom for a variety of
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movements at this joint. Three basic movements take place at
this joint:
Flexion and Extension,
Abduction and Adduction, and
Rotation.
Circumduction is merely a combination of the first two
movements in a specific sequence.
Movements at the shoulder joint are accompanied by
movements of the scapula on the thoracic wall and by
subsequent movements of the Clavicle. (Thoracohumeral
articulation)
Analysis of the movements:
Abduction: It takes place in the coronal plane along an
anteroposterior axis, and is produced by the Supraspinatus and
the Deltoid (but only for the initial 90o). The Supraspinatus
(attached to the greater tuberosity) tends to pull it upwards. It
initiates the movement. This appears to cause the head of the
humerus to move down slightly as the greater tuberosity is
pulled upwards and medially. At the same time, the
subscapularis, teres minor and major and infraspinatus exert a
downward pull on the head of the humerus and act as a
stabilizing couple against the upward pull of the deltoid.
Movement beyond 90o is produced by subsequent scapular
rotation, which is achieved by the simultaneous contraction of
the upper and lower fibers of the Trapezius and the lowest four
digitations of the Serratus anterior.
Range is 180o. 120o of this movement takes place at the
shoulder joint while the remaining 60o is provided by scapular
rotation. In other words, over the whole range, the ratio of
shoulder joint to scapular movement is 2:1. For the First 30o,
the scapular movement is negligible.
Adduction:
It is produced by the short scapular muscles (except
supraspinatus) when the deltoid relaxes. This movement is
aided by the contraction of the great muscles of the axillary
fold (Pectoralis Major and Latissimus Dorsi)
Flexion:
It is produced by the clavicular head of Pectoralis Major and
anterior fibers of the deltoid.
Extension:
It is produced by the Latissimus dorsi, Posterior fibers of
deltoid and long head of triceps.
Lateral Rotation:
It is produced by Infraspinatus and Teres Minor
Medial Rotation:
It is produced by the Subscapularis and Teres Major.
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Stability Of the joint:
It depends upon THREE factors:
Bony Factors
Ligamentous Factors, and
Muscular Factors
Bony Factors:
There is 1:4 disproportion between the head of the
Humerus and the Glenoid fossa. The Glenoid fossa is very
shallow. Some stability is contributed to the joint by the
Glenoid Labrum. The Capsule, though strong but is lax.
So if the labrum is fractured, the dislocation becomes
inevitable. So, the bony factors are the least important as
far as the stability of the joint is concerned.
Ligamentous Factors:
This plays a relatively more important role in the
stability of the joint. In this respect, the coracoacromial
ligament (along with the under surfaces of the respective
bones) plays a vital role. The whole structure is called
the coracoacromial arch. The sub acromial bursa located
below the arch functions mechanically as an ‘articular surface’
Muscular Factors:
These play the MOST IMPORTANT role in the
stability of the joint.
Of the muscles, the most important role is played by
the ROTATOR CUFF, which alone is an
indispensable factor regarding the stability of the
joint. The pull of the rotator cuff not only holds the
head of the humerus against the glenoid fossa, but it
also prevents the lax capsule of the joint from being
nipped. Since there is no rotator cuff inferiorly, the
capsule here is attached well below the articular
margins.
Muscles attaching Humerus to the Pectoral
Girdle: All these muscles assist the joint by
maintaining their TONE. The Long heads of
Biceps and Triceps play a vital role in this
respect. The tendon of the Long head of
Biceps is intracapsular and passes above the
head of the humerus, preventing upward
displacement, while the tendon of long head
of Triceps passes below the joint when it is
abducted. In fact, during abduction, the tendon of long head of triceps is the only structure that
supports the head from below (which is the weakest part of the capsule)
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Clinical Considerations
If the capsule of the joint becomes inflamed, it
may thicken and fibrose.
This is accompanied by synovitis, which results in
contracture and adhesions, giving rise to a
condition called the “Adhesive Capsulitis” or
“Frozen Shoulder”.
The laxity of the capsule, which is an asset for the
movement, now becomes a liability by providing a
greater surface area for adhesions.
Dislocation of the shoulder joint will occur if a
strong downward force is applied to the semi
abducted shoulder.
This may occur in contact sports when a tackle
is being discouraged by an outstretched arm.
The problem may become recurrent if the
capsule and ligaments are weakened, and in
this context the strength of the rotator cuff
muscles assumes paramount importance.
The sub acromial surface forms a tunnel
occupied by the tendon of supraspinatus and
the overlying sub acromial bursa, which
protects the tendon from the coracoacromial
arch.
If either the tendon or the bursa (or both) get
inflamed, abduction becomes painful in an arc of movement classically between about 450 and
1600 as the greater tuberosity compresses the inflamed sub acromial structures.
This is known as the “Painful arc”and is a useful sign in clinical diagnosis
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