Shoulder

Question 1

Subscapularis:
* Origin
* Insertion
* Nerve supply
* Action

Answer 1

• Origin - medial 2/3rds of the costal surface of the scapula (subscapular fossa).
• Insertion - lesser tubercle of humerus.
• Nerve supply - Upper and lower subscapular nerves (C5, 6) from the posterior cord of the brachial plexus.
• Action - shoulder IR.

Question 2

Supraspinatus:
* Origin
* Insertion
* Nerve supply
* Action

Answer 2

• Origin - medial 2/3rds of the supraspinous fossa of the scapula.
• Insertion - upper part of the greater tubercle of the humerus.
• Nerve supply - Suprascapular nerve (C5, 6)
• Action - shoulder abduction.

Question 3

Infraspinatus:
* Origin
* Insertion
* Nerve supply
* Action

Answer 3

• Origin - medial 2/3rds of the infraspinous fossa and from the deep surface of the infraspinatus fascia.
• Insertion - greater tubercle of the humerus between supraspinatus above and teres minor below.
• Nerve supply - suprascapular nerve (C5, 6)
• Action - shoulder ER.

Question 4

Teres minor:
* Origin
* Insertion
* Nerve supply
* Action

Answer 4

• Origin - upper 2/3rds of the lateral border of the posterior surface of the scapula
• Insertion - attaches to the lowest facet on the greater tubercle of the humerus.
• Nerve supply - posterior branch of axillary nerve (C5, 6)
• Action - shoulder ER. Weak adductor of humerus.

Question 5

Teres major:
* Origin
* Insertion
* Nerve supply
* Action

Answer 5

• Origin - dorsal surface of the inferior angle of the scapula.
• Insertion - medial lip of the intertubercular sulcus of the humerus.
• Nerve supply - lower subscapular nerve (C5, 6).
• Action - shoulder adduction/IR.

Question 6

Deltoid:
* Origin
* Insertion
* Nerve supply
* Action

Answer 6

• Origin - anterior - anterior border and upper surface of the lateral 1/3rd of clavicle.
  Central/lateral - lateral border of acromion.
  Posterior - inferior lip of the crest of the scapular spine.
• Insertion - anterior - anterior margins of deltoid tuberosity.
  Central/lateral - deltoid tuberosity.
  Posterior - posterior margins of deltoid tuberosity.
• Nerve supply - axillary nerve (C5, 6).
• Action - Working with supraspinatus, deltoid abducts the arm by the multipennate acromial fibres. The anterior fibres assist pec major in flexing and medially rotating the arm. The posterior fibres assist latissimus dorsi in extending the arm and act as a lateral rotator.

Question 7

Describe the shoulder joint.

Answer 7

• The shoulder (glenohumeral) joint is a multiaxial ball- and-socket synovial joint.
• There is an approximately 4 to 1 disproportion between the large round head of the humerus and the small shallow glenoid cavity of the scapula.
• The glenoid labrum, a ring of fibrocartilage attached to the margins of the glenoid cavity, deepens slightly but effectively the depression of the glenoid ‘fossa.’
• The capsule of the joint is attached to the scapula beyond the supraglenoid tubercle and the margins of the labrum. It is attached to the humerus around the articular margins of the head (i.e. the anatomical neck) except inferiorly, where its attachment is to the surgical neck of the humerus a finger’s breadth below the articular margin.
• At the upper end of the intertubercular sulcus, the capsule bridges the gap between the greater and lesser tubercles, being here named the transverse humeral ligament.
• A gap in the anterior part of the capsule allows communication between the synovial membrane and the subscapularis bursa.
• A similar gap is sometimes present posteriorly, allowing communication with the infraspinatus bursa.
• The fibres of the capsule all run horizontally between scapula and humerus.
• The capsule is thick and strong but it is very lax, a necessity in a joint so mobile as this.
• Near the humerus the capsule is greatly thickened by fusion of the tendons of the short scapular muscles. * The long tendon of biceps is intracapsular and blends with the glenoid labrum at its attachment to the supraglenoid tubercle of the scapula.
• The synovial membrane is attached around the glenoid labrum and lines the capsule. It is attached to the articular margin of the head of the humerus and covers the bare area of the surgical neck that lies within the capsule at the upper end of the shaft.
• It ‘herniates’ through the hole in the front of the capsule to communicate with the subscapularis bursa and sometimes it communicates with the infraspinatus bursa.
• It invests the long head of biceps in a tubular sleeve that is reflected back along the tendon to the transverse ligament and adjoining floor of the intertubercular sulcus.
• The synovial sleeve glides to and fro with the long tendon of biceps during abduction–adduction of the shoulder.

Question 8

Outline the ligaments of the shoulder joint.

Answer 8

• The glenohumeral ligaments are three thickened bands between the glenoid labrum and humerus which reinforce the anterior part of the capsule.
• They are visible only from within the joint cavity, which communicates with the subscapularis bursa through an aperture between the superior and middle glenohumeral ligaments.
• The coracohumeral ligament is quite strong. It runs from the base of the coracoid process to the front of the greater tubercle, blending with the capsule as it does so.
• From the medial border of the acromion, in front of the acromioclavicular articulation, a strong flat triangular band, the coracoacromial ligament, fans out to the lateral border of the coracoid process.
• It lies above the head of the humerus and provides support to the head of the humerus. It is separated from the ‘rotator cuff’ by the subacromial bursa.

Question 9

Describe the subacromial bursa.

Answer 9

• The subacromial (subdeltoid) bursa is a large bursa which lies under the coracoacromial ligament, to which its upper layer is attached.
• Its lower layer is attached to the tendon of supraspinatus.
• It extends beyond the lateral border of the acromion under the deltoid with the arm at the side, but is rolled inwards under the acromion when the arm is abducted.
• Tenderness over the greater tuberosity of the humerus beneath the deltoid muscle which disappears when the arm is abducted is a feature of subacromial bursitis.
• Tearing the supraspinatus tendon brings the bursa into communication with the shoulder joint cavity, but in the normal shoulder the bursa does not communicate with the joint.

Question 10

Outline the stability of the shoulder joint.

Answer 10

• The head of the humerus is much larger than the glenoid cavity, and the joint capsule, though strong, is very lax. These factors suggest that the shoulder joint is an unstable articulation.
• The factors, however, that contribute to stability are:
• Strengthening of the capsule by fusion with it of the tendons of scapular muscles.
• The glenohumeral and coracohumeral ligaments.
• The suprahumeral support provided by the coracoacromial arch.
• The deepening of the glenoid cavity by the labrum.
• The splinting effect of the tendons of the long heads of biceps and triceps above and below the humeral head.
• Upward displacement of the head of the humerus is prevented by the overhanging coracoid and acromion processes and the coracoacromial ligament that bridges them. * The whole constitutes the coracoacromial arch and the subacromial bursa lies between the arch and the underlying supraspinatus tendon and joint capsule.
• The arch is very strong. Upward thrust on the humerus will not fracture the arch; the clavicle or the humerus itself will fracture first.
• The tendons of subscapularis, supraspinatus, infraspinatus and teres minor fuse with the lateral part of the capsule and are attached to the humerus very near the joint. They are known as the rotator cuff, although the supraspinatus is not a rotator of the humerus. There is no cuff inferiorly and here the capsule is least supported.