The teres minor takes origin from the superior two- thirds of the inferior margin of the scapula and is inserted into the posterior facet on the greater tu- bercle of the humerus [see Figs. 4.6, 6.1]. Nerve supply: axillary nerve. Actions: lateral rotation and stabilization of the shoulder joint.
Fig. 6.2 Anterior aspect of the humerus to show muscle attachments.
Supraspinatus Subscapularis
Pectoralis major Latissimus dorsi
Teres major
Deltoid
Coracobrachialis
Brachialis
Brachioradialis
Extensor carpi radialis longus Common extensor origin Common flexor origin
Fig. 6.3 Deltoid muscle and lateral aspect of the arm.
Lateral end of clavicle Cephalic V.
Deltoid
Cutaneous branches of axillary N.
Upper lateral cutaneous N. of arm
Lateral head of triceps
Brachialis Lower lateral cutaneous N. of arm Posterior cutaneous N. of forearm
Brachioradialis
Tendon of triceps
Olecranon Extensor carpi radialis longus
Fig. 6.4 MR axial image of the shoulder.
Head of humerus
Deltoid
Scapula Labrum
Labrum
Subscapularis Subscapularis tendon
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The shoulder
DISSECTION 6.1 Shoulder region-1 Objectives
I. To study the deltoid, infraspinatus, teres minor, and long head of the triceps, and to identify the boundaries of the quadrangular and triangular spaces. II. To iden- tify and trace the axillary and radial nerves.
Instructions
1. Remove the fascia from the surface of the deltoid muscle, and study its attachments. It has a V-shaped origin from the lateral third of the clavicle, the acro- mion, and the crest of the spine of the scapula. It is inserted into the deltoid tuberosity of the humerus.
Note that the long anterior and posterior fibres run parallel to each other on the corresponding surfaces of the shoulder joint. The lateral fibres are short and multipennate to increase the power of this part.
2. Separate the muscle from the spine of the scapula, and turn this part downwards to expose the underly- ing infraspinatus muscle. Remove the dense deep fascia from the surface of the infraspinatus. Define its attachments to the infraspinous fossa and the greater tubercle of the humerus.
3. Find the inferior border of the infraspinatus, and separate it from the teres major and the minor
muscles which arise from the lateral margin of the scapula.
4. Turn the detached part of the deltoid forwards; iden- tify the axillary nerve (from which the upper lateral cutaneous nerve of the arm arises) and the posterior humeral circumflex vessels supplying its deep surface.
5. Trace these on the surgical neck of the humerus through the quadrangular space [Fig. 6.5], inferior to the teres minor and the articular capsule of the shoul- der joint.
6. Expose the long head of the triceps medial to the quadrangular space. It descends from the infragle- noid tubercle of the scapula and passes between the teres minor and the major muscles close to the humerus.
7. Find the branch of the axillary nerve to the teres minor, and follow this muscle to its attachments separating it from the teres major.
8. Divide the remainder of the deltoid from the acro- mion and clavicle, and turn it downwards. It lies on the proximal end and surgical neck of the humerus, superficial to the anastomosis of the circumflex humeral vessels [Fig. 6.6].
Deltoid-reflected
Infraspinatus
Capsule of shoulder joint N. to teres minor
Deltoid
Anterior branch of axillary N.
Posterior branch
Upper lateral cutaneous N. of arm
Lateral head of triceps
Radial N.
Profunda brachii A.
N. to medial head of triceps Lateral head of triceps Brachial A.
Long head of triceps Quadrangular space Triangular space Teres major Teres minor Circumflex scapular A.
Suprascapular A.
Infraspinatus Supraspinatus
Spine of scapula
Fig. 6.5 Dissection of the scapular region and back of the arm showing the quadrangular and triangular spaces. The lateral head of the triceps has been divided and turned aside to expose the spiral groove on the humerus.
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Muscles attaching the humerus to the scapula
Dissection 6.1 explores the shoulder region.
8
8
Deltoid
8 7
3
1 2
5 4 6
Fig. 6.6 Diagram of the circumflex humeral arteries and axillary nerve. 1. Axillary artery. 2. Anterior circumflex humeral artery. 3. Posterior circumflex humeral artery. 4. Axillary nerve. 5. Articular branch. 6. Humerus. 7. Branch to teres minor. 8. Cutaneous branches.
DISSECTION 6.2 Shoulder region-2 Objectives
I. To study the teres major, coracobrachialis, short head of biceps and subscapularis. II. To identify and trace the axillary and radial nerve. III. To explore the subacromial and subscapular bursa.
Instructions
1. On the anterior surface of the scapula, follow the sub- scapularis muscle from the subscapular fossa to the lesser tubercle [Fig. 6.7].
2. Separate it inferiorly from the teres major, and trace that muscle to its insertion on the medial lip of the intertubercular crest of the humerus immediately behind the insertion of the latissimus dorsi. Both these insertions are lateral to the coracobrachialis and the short head of the biceps which descend in front of them from the coracoid process.
3. Find the axillary nerve arising from the posterior cord of the brachial plexus, and follow it to the quad- rangular space which, when seen from the front, is between the subscapularis and teres major.
4. Identify the radial nerve as it arises from the poste- rior cord. It descends between the parts of the triceps muscle, after giving branches to the long and medial heads [Fig. 6.5].
5. Remove the fascia covering the coracobrachialis and the short head of the biceps from the coracoid process to the insertion of the coracobrachialis on the medial aspect of the body of the humerus.
6. Follow the musculocutaneous nerve from the lat- eral cord of the brachial plexus into the medial aspect of the coracobrachialis, and find the branch which it gives to that muscle.
7. Pull these muscles medially, and identify the tendon of the long head of the biceps. It lies in the intertu- bercular sulcus posterolateral to the short head. Fol- low the long head upwards to the lower border of the lesser tubercle where it disappears deep to the articu- lar capsule of the shoulder joint.
8. Move the fascia covering the superior surface of the greater tubercle of the humerus. It slides easily on the tubercle because of the subacromial bursa deep to the fascia.
9. Make a small incision into the bursa, and explore its limits with a blunt seeker. Then open it widely. The bursa separates the superior surface of the humerus and the capsule of the shoulder joint from the ac- romion and coracoacromial ligament, and makes a secondary synovial socket for the humerus with the coracoacromial arch.
Dissection 6.2 continues to explore the shoulder region.
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The shoulder