Shoulder and Scapular Region

Shoulder and Scapular Region

Learning Objectives

After reading this post you will know:

  • Origin insertion, action and nerve supply of deltoid muscle.
  • Muscles forming rotator cuff/musculotendinous cuff.
  • Location and clinical significance of subacromial bursa.
  • Boundaries and contents of intermuscular spaces ( quadrangular, upper triangular and lower triangular ) in scapular region.
  • Anastomosis around scapula and its clinical significance.
  • Origin, insertion, action and nerve supply of muscles of scapular region. 

Q1. Write short notes on the following:

  1. Deltoid muscle
  2. Musculotendinous or rotator cuff
  3. Subacromial bursa

 A. a. Deltoid muscle: It is a triangular (inverted delta) shaped muscle that forms the  rounded contour of  the shoulder. It is divided into three parts anterior, middle and posterior.

Origin:deltoid muscle origin and insertion

  • Anterior part: Anterior border of lateral 1/3rd of  clavicle.
  • Middle (acromial) part: Lateral border of the acromion process of scapula.
  • Posterior part : Lower lip of the crest of spine of scapula

Insertion:  ‘V’ shaped deltoid tuberosity  on anterolateral surface of humerus.

 Action:

  • Anterior fibers: Flexion and medial rotation of arm.
  • Middle fibers: Abduction of arm from 15 to 90.
  •  Posterior fibers : Extension and lateral rotation of the arm.

Nerve supply : Axillary nerve (C5,C6) from  posterior cord of brachial plexus.

Applied:

  • Deltoid muscle is often used to  administer intramuscular injection  It  should be  given in the middle of the  muscle to avoid injury to axillary  nerve. 
  • If deltoid is paralysed , rounded contour of the shoulder is lost and there is  loss of power of abduction of arm from 15 to 90ο.

Q. Write the origin, insertion , action and nerve supply of muscles of scapular region in a tabulated form.

muscles of scapular region - origin,insertion,action and nerve supply

 

2. Musculotendinous or rotator cuff: Rotator cuff is formed by a group of four muscles that  surround the   shoulder joint . As a group, they are  responsible for stabilizing the shoulder  joint. Individually, they rotate the shoulder joint. The  muscles that form rotator cuff are:

  1. Supraspinatusrotator cuff/musculotendinous cuff muscles
  2. Infraspinatus
  3. Teres minor
  4. Subscapularis
  • The muscles take origin from scapula and are inserted on lesser and greater tubercles of humerus.
  • Their flattened tendons while crossing the shoulder joint blend with each other and with the capsule of the joint.
  • Musculotendinous cuff provides support to  the capsule of the shoulder joint all around except  The joint is supported anteriorly by subscapularis, superiorly by supraspinatus and  posteriorly by infraspinatus and teres minor.As the joint is not protected inferiorly , the head of the humerus  is usually  dislocated inferiorly. The axillary nerve related to the surgical neck of humerus may get injured.
  • Details of the muscles forming ‘Rotator cuff’ are as follows:

     

Muscle Action Nerve supply
Supraspinatus Abduction of arm - Initial 15 degrees Suprascapular nerve
Infraspinatus Lateral rotation of arm Suprascapular nerve
Teres minor Lateral rotation of arm Axillary nerve
Subscapularis Medial rotation of arm Upper & lower subscapular nerves

                                          *  The rotator cuff muscles can be easily remembered using the acronym SITS

 3. Subacromial bursa:

  • Is the largest bursa in the body. It is located inferior to the acromion arch and above the tendon of supraspinatus and greater tubercle of humerus.
  • It is continuous with the subdeltoid bursa present beneath the deltoid muscle.
  • It protects the supraspinatus tendon from friction against acromion during abduction of arm.
  • Subacromial bursitis is a condition caused by inflammation of the bursa.

subacromial bursa

Q2. Name the intermuscular spaces in the scapular region , give their boundaries and  contents.

A. Three intermuscular spaces are present in the  scapular region:

Quadrangular space:

    Boundaries 

  • Superiorly – Subscapularis, capsule of shoulder joint, teres minor ( from front to back)
  • Inferiorly – Teres major
  • Laterally – surgical neck of humerus
  • Medially – long head of triceps

   Contentsquadrangular, upper and lower triangular spaces of scapular region

  • Axillary nerve
  • Posterior circumflex humeral vessels

Upper triangular space

    Boundaries

  • Laterally – Long head of triceps
  • Medially – Teres minor
  • Inferiorly – Teres major

Contents

  • Cirumflex scapular artery

Lower triangular space

   Boundaries

  • Superiorly – Teres major
  • Laterally – Shaft of humerus
  • Medially – Long head of triceps

  Contents

  • Radial nerve and profunda brachii vessels

 

Q. Draw a labeled diagram to show the anastomosis around scapula.

A. Anastomosis around scapula  is between branches of first part of subclavian artery and branches of third part of axillary artery. It provides collateral circulation in case distal part of subclavian artery or proximal part of axillary artery is blocked.

Arterial anastomosis around scapula

 

Q. Enumerate the movements possible at scapulothoracic joint (movement of scapula) and the muscles responsible for them.

A. 

MovementMuscles responsible
ElevationLevator scapulae
Trapezius (upper fibres)
DepressionTrapezius (lower fibres)
Pectoralis major and minor
Latissimus dorsi
Gravity
ProtractionSerratus anterior
Pectoralis minor
RetractionRhomboids
Trapezius (middle part)
Upward rotation - makes the glenoid cavity face upwardsSerratus anterior (lower part)
Trapezius (upper and lower parts)
Downward rotation - makes the glenoid cavity face downwardsPectoralis major
Latissimus dorsi
Rhomboideus major and rhomboideus minor
Gravity

Q. What are the boundaries of “Triangle of Auscultation”?

A.  The “Triangle of Auscultation” is bounded:

  • Medially by lateral border of trapezius muscle.
  • Laterally by medial border of scapula.
  • Inferiorly by upper border of latissimus dorsi muscle.

Respiratory sounds of inferior lobe of lung are heard better ( using stethoscope) over triangle of auscultation as no large muscle covers this area.

Triangle of Auscultation

 

 

 

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