Shoulder Joint

Learning Objectives:

After reading this post you will the following about shoulder joint:

  • Type of joint.
  •  Bones participating in formation of shoulder joint and the articular surface.
  • Attachment of capsule of joint.
  • Ligaments supporting the joint.
  • Factors providing stability to the joint.
  • Muscles reponsible for producing various movements.
  • Applied aspect of shoulder joint.

Q. Describe shoulder joint under the following headings:

     a. Type      b. Articular surfaces      c. Capsule  d. ligaments    e.Factors providing stability  f. Movements  g. Relations  h. Applied aspect

  A. Shoulder joint is the most movable joint and is also  more prone to dislocation than any other  joint

a.Type : Ball and socket type of synovial joint.

       b. Articular surfaces:

  • Large round head of the humerus and
  • Small and shallow glenoid cavity.

The fibrocartilagenous ring called glenoid labrum deepens the glenoid cavity.

shoulder joint

c. Capsule: The capsule is thick and strong but lax.

  • The fibrous capsule surrounds the joint .
  • It is attached medially to the margins of the glenoid cavity beyond the glenoid labrum.
  • Laterally it attached to the anatomical neck of the humerus except
    • Inferiorly where it is attached to the surgical neck of the humerus a finger’s breadth below the articular margin.
    • Superiorly at the upper end of the intertubercular groove, it is deficient to allow the passage of the long head of biceps brachii.

attachment of capsule of shoulder joint

dLigaments:

  • Glenohumeral ligaments: Superior , middle & inferior glenohumeral ligaments in the anterior part of the capsule .
  • Coracohumeral ligament : extends from the base of the coracoids process to the greater tubercle of the humerus.
  • Transverse humeral ligsment : bridges the upper end of the intertubercular sulcus.

ligaments of shouldr joint

      e. Factors providing the stability:

  1. Muscultendinous cuff/rotator cuff: is formed by the flattened tendons of the
  • Subscapularis anteriorly
  • Supraspinatus superiorly
  • Infraspinatus and teres minor posteriorly

(rotator cuff muscles dos not support the joint inferiorly)

2. Coracoacromial arch: prevents the upward dislocation of the head of the humerus.

3. Glenoid labrum: deepens the glenoid cavity

4. Long head of biceps brachii: prevents the upward dislocation of the head of the humerus.

f. Movements:

MovementMuscles Responsible for the Movement
FlexionPectoralis major ( clavicular part)
Deltoid ( clavicular part )
Coracobrachialis
Biceps brachii(short head)
ExtensionDeltoid (posterior fibers)
Latissimus dorsi
Teres major
Long head of triceps
Abduction 0-15°- Spraspinatus
15-90°- Deltoid (middle fibers)
Overhead abduction:
Serratus anterior
Trapezius
Adduction Pectoralis major
Latissimus dorsi
Teres major
Medial rotationSubscpularis
Deltoid (anterior fibers)
Pectoralis major
Teres major
Latissimus dorsi
Lateral rotationInfraspinatus
Teres minor
Deltoid (posterior fibers)

Abduction at shoulder joint:

  • The first 15 degree of abduction is   done by supraspinatus muscle.
  • 15-90 degrees is done by deltoid muscle.
  • For overhead abduction , the scapula has to be rotated laterally so that the glenoid cavity gradually faces upwards.  This is done by upper fibers of trapezius and  serratus anterior muscle  Every 2 dgrees of movement at shoulder joint is accompanied by 1 degree of rotation of scapula ( called scapulo-humeral rhythm).

g. Relations: the following diagram shows the structures related to shoulder joint.

relations of shoulder joint

h. Applied:

1.Write anatomical basis for the following:
a. 
Inferior dislocation of shoulder joint is common. :

Inferior dislocation of shoulder joint is common because:

  • The capsule descends downwards on the surgical neck inferiorly.
  • The capsule is not supported by the muscultendinous cuff inferiorly.

  b.  Following inferior dislocation of shoulder joint, the  rounded contour of shoulder is lost  and weakness of abduction of arm.

          The axillary nerve is likely to be injured in the inferior dislocation as it is related to the surgical neck of humerus. As the axillary nerve supplies deltoid muscle, paralysis of deltoid muscle results in loss of abduction ( between 15-90  degrees)  and rounded contour of shoulder.. Axillary nerve also supplies skin over lower half of deltoid (regimental badge area), therfore sensory loss over regimental badge area is also observed.

 c.Frozen shoulder.

Frozen shoulder occurs due to  adhesive capsulitis, a disorder in which the capsule and the connective tissue surrounding the  shoulder joint becomes inflamed and stiff, greatly restricting movement of shoulder joint and causing chronic pain.

 d. Painful arc syndrome.

Thickening or calcium deposits in the supraspinatus tendon or subacromial bursitis results in pain during abduction of shoulder joint from 60° to 120°. This is known as ‘painful arc syndrome‘.

Q. name the arteries and nerves that supply shoulder joint.

A. Arteries supplying shoulder joint

  • Suprascapular artery
  • Anterior and posterior circumflex humeral arteries
  • Subscapular artery

   Nerves supplying shoulder joint

  • Suprascapular nerve
  • Axillary nerve
  • Musculocutaneous nerve

 

 

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