Notes on Shoulder Anatomy
Rahul's Noteblog
Notes on Anatomy
Notes on Shoulder Anatomy
Osteology: (described earlier in Chest Wall lesson)
1. Clavicle:
2. Scapula:
3. Humerus:
4. Ulna:
5. Radius:
6. Carpus, Metacarpus and Phalanges:
7. Movements:
Clinical:
Fracture of the clavicle:
The clavicle is often fractured as a result of a forceful blow to the point of the shoulder. It may also result from a fall on outstretched hands, the force of the fall being transmitted from hand to radius to humerus and then to the shoulder girdle. The fractures usually occur in the middle third of the shaft, medial to the attachment of the coracoclavicular ligament. The coracoclavicular ligament is made up of the trapezoid and conoid ligaments. The medial clavicular segment of the clavicle is displaced upward due to the pull of the sternocleidomastoid muscle (head and neck course) and the lateral segment pulled downward by gravity, with inability of the trapezius to elevate it.
Mid shaft fracture of the humerus:
The radial nerve runs a spiral course around the posterior surface of the humerus as it descends toward the elbow. A mid-shaft fracture may injure the radial nerve. Such an injury would be expected to produce a weakness in the extensor muscles of the forearm and a “wrist drop” or inability to maintain the wrist in a position midway between true flexion and extension. In addition with sensory loss on the dorsum of the forearm and the dorsal side of the lateral 3 1/2 digits of the hand.
Fracture of the humeral head:
Common in young adults or children where a humerus fracture will displace the head of the humerus along its Epiphyseal line. In severe cases the humeral head slides anteriorly, and the examiner can palpate the edge of the humeral shaft posteriorly along the proximal end of the humerus. The surgical neck is crossed anteriorly by the radial nerve which may be torn or stretched by a surgical neck fracture. The axillary nerve may be injured during surgical neck fracture which results in weakness of the deltoid and teres minor muscles and loss of sensation on the lateral surface of the skin over the shoulder.
The shoulder girdle consists of two bones which attach the upper limb to the thoracic wall (scapula and clavicle).
Joints of the shoulder Girdle:
Sternoclavicular joint (see Snell Fig. 9-22):
Bony attachment
• Medial end of the clavicle, part of costal cartilage of first rib and lateral surface of manubrium.
Supporting ligaments
• Anterior and posterior sternoclavicular ligament. Costoclavicular ligament. Intra-articular disc resists superior and medial displacement of joint.
Movements
• Elevation and flexion of the lateral clavicle.
Type of joint:
Acromioclavicular joint (see Snell Fig. 9-22 ):
Bony attachment
• Lateral end of clavicle to the scapular acromion.
Supporting ligaments
• Coracoclavicular ligament (coracoid process of scapula to trapezoid line and conoid tubercle of clavicle). Coracoacromial ligament.
Movements
• Around the vertical axis making the glenoid face further anteriorly. Around the horizontal axis making the glenoid face upward and laterally.
Type of joint:
Glenohumeral joint (see Snell Fig. 9-24):
Bony attachment
• Humeral head and the glenoid fossa.
Supporting ligaments
• Glenohumeral ligament (superior, middle and inferior). Coracohumeral ligament. Transverse humeral ligament. Strong fibrous capsule (highly innervated). Small apertures through capsule for muscle tendons.
Movements
• All directions.
Type of joint
• A ball and socket joint.
Bursae:
Flattened sacs lined by synovial membrane. The synovial membrane produces lubricating fluid. Bursae serve to prevent friction between muscles and tendons. There are three bursae in the pectoral girdle:
• The subscapular bursa is beneath the subscapularis tendon (between the tendons of the subscapularis muscle and the scapular neck).
• The subacromial bursa is the largest pectoral bursa. It is important in deltoid muscle movement.
• The sub-deltoid bursa communicates with the subacromial bursa.
Clinical:
• Bursitis is an inflammation of the bursal membrane.
Shoulder dislocation commonly occurs in the inferior glenohumeral portion. It is due to the opening in the inferior capsule by the muscle tendon and weakness of the ligament itself at this point.
Muscles: (refer to Snell for origins, insertions, innervation and actions)
• Extrinsic muscles: attach upper limb to trunk.
• Trapezius, rhomboid major and minor, levator scapulae, latissimus dorsi, serratus anterior.
Scapulohumeral muscles:
• Deltoid, supraspinatus, infraspinatus, teres major, teres minor, subscapularis and long head of triceps. The rotator cuff muscles (S.I.T.S.) include the supraspinatus, infraspinatus, teres minor and subscapularis muscles. The rotator cuff muscles initiate abduction. The deltoid muscle then takes over abduction.
Clinical:
1. Rotator cuff injuries. There is a mantle of tendons of four muscles (S.I.T.S.) which enclose the Glenohumeral joint on its posterior, superior and anterior aspects. It is the strongest element engaged in reinforcing the shoulder joint. The muscles of the rotator cuff, especially the supraspinatus are frequently torn during forceful exercise (throwing a ball, lifting a heavy weight or direct trauma). The degenerative inflammatory changes will also predispose tendons to rupture. Patients present with painful arm abduction.
2. Winging of the scapula. One of the most important motions of the scapula is its ability to “slide” anteriorly and posteriorly along the posterolateral surface of the chest wall (protraction and retraction). The major muscle of protraction is the serratus anterior muscle. When this muscle is not functioning (due to loss of innervation by the long thoracic nerve) the scapula is not held tightly against the chest wall and will protrude outward, “wings”, when protraction is attempted. This problem is usually unilateral (only one side is affected).
Muscular Triangular Space: see slide # 7
There are three boundaries of the muscular triangular space:
• Teres minor (superior border).
• Teres major (inferior border).
• Long head of the triceps (lateral border).
The muscular triangular space has as its contents the circumflex scapular artery.
Muscular Quadrangular Space: See slide # 8 and 9
There are four boundaries of the muscular quadrangular space:
1. Teres minor and subscapularis tendon (superior border).
2. Teres major (inferior border).
3. Long head of triceps (medial border).
4. Surgical neck of humerus (lateral border).
The muscular quadrangular space has as its contents the axillary nerve and the posterior humeral circumflex artery.
Scapular anastomoses: see Slide # 10
The clinical importance of collateral circulation in the arm is only apparent when the main arterial pathway to the arm is interrupted. For example, if the axillary artery is obstructed between the thyrocervical trunk and subscapular artery, the direction of blood flow in the subscapular artery is reversed, enabling blood to reach the distal part of the axillary artery. Slow occlusion of an artery will often allow sufficient collateral circulation to develop. Sudden occlusion of an artery does not permit this development of the collateral circulation to prevent ischemia.
1. Suprascapular artery:
Comes off the thyrocervical trunk (first branch of subclavian artery). May also originate at the 3rd part of the subclavian instead. Travels anteriorly to the scalenus anterior muscle and the root of the brachial plexus then above to the transverse ligament to enter and supply the infraspinatus and supraspinatus fossa containing muscles.
2. Transcervical artery:
Comes off the thyrocervical trunk (first branch of the subclavian artery). Follows the posterior belly of omohyoid muscle and supplies the trapezius and levator scapulae muscles. Eventually becomes the dorsal scapular artery.
3. Dorsal scapular artery:
70% off 2nd or 3rd part of subclavian artery and 30% off transverse cervical. Descends deep to the rhomboid muscle. Supplies the rhomboid, levator scapulae and serratus anterior muscle. The dorsal scapular artery is a continuation of the transverse cervical artery distal to the levator scapulae.
4. Subscapular artery:
Comes off the 3rd part of the axillary artery to the subscapularis muscle.
5. Circumflex scapular artery:
Comes off the subscapular artery. Feeds the lateral border of the scapula.
6. Some intercostal arteries:
Form anastomoses with the dorsal scapular artery.
Clinical:
The anastomoses around the scapula play a major surgical role during ligation of an injured axillary or subclavian artery (the axillary artery is a continuation of the subclavian artery into the upper limb). So the axillary artery can be ligated between the thyrocervical and the subscapular artery which result in directing blood flow from the anastomoses sites to the axillary artery distal to the ligation (i.e. the subscapular artery will receive blood via the suprascapular, transverse cervical, dorsal scapular and intercostal arteries), but unfortunately, axillary artery ligation distal to the subscapular artery will result in severe reduction in blood flow to the arm.
Clinical:
Subclavian steal syndrome. This is a rare condition caused by a narrowing of the left subclavian artery near its origin. In order to compensate for the reduction in blood flow to the arm, blood will flow from the right vertebral artery into the left vertebral artery and then into the left subclavian artery. This results in reduction of blood flow to the brain, causing giddiness, fainting attacks and problems with ischemia of the left arm.
Clinical:
Axillary artery aneurysm. Ballooning of the axillary artery is not uncommon. Because the axillary artery and the major branches of the brachial plexus are contained within the axillary sheath, a progressive dilatation (aneurysm) of the axillary artery will compress the nerves of the brachial plexus and produce neurological deficits. This is a good example of how symptoms involving one system of the body may point to pathology elsewhere.
Clinical Case:
A 26 year old male computer worker was referred to the orthopeadic clinic with a two-week history of weakness at the right shoulder and difficulty raising his arm. He decided to seek medical advice when his wife noticed that his shoulder blade was stuck out, particularly when he moved his arm forwards. The patient was otherwise healthy, but he reported having had influenza a week previously. The surgeon examined the shoulder and asked him to push against the consulting room wall where he confirmed the bulging out of his shoulder blade. The surgeon sent the patient for nerve conduction studies and electromyography.
• Paralysis of which muscle(s) was suggested by the shoulder blade movement which necessitate the electromyography?
• Why does the patient have difficulty raising his arm?
• What movement of the blade bone was being tested by asking the patient to push forward against the wall?
• What is the clinical diagnostic name for this condition?
• Paralysis of which nerve(s) was suggested by the shoulder blade movement for which nerve conduction studies were recommended?
The Axilla
The axilla is a space surrounded by four walls in the shape of a pyramid. It has six boundaries:
The Boundaries of the Axilla
Apex
• The apex is located at the first rib between the clavicle (anteriorly) and the acromion of the scapula (posteriorly).
Base
• Skin and fascia of the armpit.
Medial wall
• The rib cage (ribs 1-4), and the serratus anterior.
Lateral wall
• The intertubercular groove of the humerus.
Anterior wall
• Pectoralis major and minor muscles.
Posterior wall
• The scapula, teres major, latissimus dorsi, and subscapularis.
Contents of the Axilla: (muscles, nerves, arteries and lymphatics).
Muscles: see slide # 1
The Pectoral Muscles
Muscle
• Pectoralis Major
• Pectoralis Minor
Origin
• Clavicular head: anterior surface of medial half of clavicle. Sternocostal head: anterior surface of sternum, superior six costal cartilages.
• 3rd to 5th ribs near their costal cartilages.
Insertion
• Lateral lip of intertubercular groove of humerus.
• Medial border of superior surface of coracoid process of scapula.
Innervation
• Lateral and medial pectoral nerves. Clavicular head (C5 and C6). Sternocostal head (C7, C8, T1).
• Medial pectoral nerve (C8 and T1).
Action
• Adducts and medially rotates humerus. Draws scapula anteriorly and inferiorly. When acting alone, the clavicular head flexes humerus and the sternocostal head extends it.
• Stabilizes scapula by drawing it inferiorly and anteriorly against the thoracic wall.
Muscle
• Subclavius
• Serratus Anterior
Origin
• Junction of 1st rib and its costal cartilage.
• External surfaces of lateral parts of 1st to 8th ribs.
Insertion
• Inferior surface of middle third of clavicle.
• Anterior surface of medial border of scapula.
Innervation
• Nerve to subclavius (C5 and C6).
• Long thoracic nerve (C5, C6 and C7).
Action
• Anchors and depresses clavicle.
• Protracts scapula and holds it against the thoracic wall. Rotates the scapula.
The axillary artery: (three parts)
• Part of axillary artery
Arterial branches
First
• Superior to pectoralis minor muscle (up to first rib).
• The superior thoracic artery
Second
• Posterior (deep) to pectoralis minor muscle
• The thoraco-acromial and lateral thoracic arteries
Third
• Inferior to pectoralis minor muscle
• Subscapular, anterior and posterior circumflex humeral.
Notice that the first part of the axillary artery gives off one branch. The second part gives off two branches and the third part gives off three branches. There is an alternate way of specifying the sub-parts of the axillary artery. The results are the same.
Part of artery:
First
• From lateral border of first rib to superior border of pectoralis minor.
Second
• Deep to the pectoralis minor.
Third
• Inferolateral to pectoralis minor.
The axillary vein: see slide # 2 and 3
The proximal continuation of the brachial vein. Continues as the subclavian vein medial to the lateral border of the first rib.
Minor tributaries of the axillary vein:
• Tributaries correspond to the axillary artery branches.
• The basilic vein drains the ulnar (medial) side.
• The cephalic vein drains the radial (lateral) side.
• Venae comitants are deep veins which accompany the deep arteries (e.g. branches of the brachial artery).
The pulsations in the artery improve blood flow through the veins due to the presence of a connective tissue sheath.
The axillary lymph nodes: (5 important groups), see slide # 4
Area Serviced by this Group:
Pectoral (aka anterior)
• The pectoral (anterior) axillary lymph node drains the anterior medial wall of the axilla. It drains the breast and anterior upper 1/2 of trunk.
Subscapular (aka posterior)
• The subscapular (posterior) axillary lymph node drains the posterior medial wall of the axilla. It drains the posterior upper 1/2 of trunk.
Lateral
• The lateral lymph node is located along the medial part of the axillary vein. It runs with the lateral thoracic artery. It drains the upper limb.
Central
• The central lymph node is the largest of the axillary lymph nodes. It is located in the fat of the axilla. It is enlarged in male patients. It drains the pectoral, subscapular and lateral lymph nodes.
Apical
• Located in the apex of the axilla. It forms a small trunk that receives lymphatic duct from central. It is the last station before the subclavian lymphatic trunk.
The Subclavian lymphatic Trunk:
Drains the supra clavicular lymph node which lies in the lower part of the posterior triangle of the neck. The trunk eventually drains into the thoracic duct (on the left side) or the right lymphatic duct (right side).
Clinical:
Axillary lymph node dissection. This is an important part of many cancer operations, especially those involved in removal of the breast. This is necessary since breast cancers frequently spread to the axillary lymph nodes. A complete axillary dissection involves exposure and risk to many important structures. In addition, most of these operations will sacrifice some or all of the following:
• Pectoralis major and minor muscles with their nerve supply.
• Axillary tail of the breast.
• Thoraco-acromial vessels of the axilla.
• Many tributaries of the axillary vein.
• Many smaller branches of the axillary artery.
However, surgeons make every effort to preserve the following:
• Brachial plexus.
• Axillary vein and artery.
• Thoraco-dorsal nerve (to latissimus dorsi muscle).
• Long thoracic nerve (to serratus anterior muscle).
Axillary fat and fascia:
Axillary fascia
• Located between pectoralis major muscle and latissimus dorsi muscles. Protection of lymph nodes, blood vessels and nerves.
Clavi-pectoral fascia
• Fascia between upper pectoralis major and pectoralis minor and subclavius. An extension of axillary fascia which covers pectoralis minor, subclavius and attaches superiorly to the clavicle.
Axillary sheath
• An extension of deep fascia starting at the neck and continuing down to the axilla. Attaches to the first rib. Covers the axillary artery/vein and proximal upper portion of brachial plexus.
Axillary tail fascia
• Fascia that covers the axillary tail. The axillary tail is the prolongation of breast tissue which extends up into the axilla from the superolateral side. The axillary tail fascia also covers the inferolateral margin of pectoralis major.
The Brachial Plexus:
The upper brachial plexus lies in the neck, the lower part lies in the axilla. Refer to Snell Fig 9-14 and slide # 5
Roots of the brachial plexus:
• C5, C6, C7, C8, T1
Trunks of the brachial plexus:
• Upper (C5 and C6), Middle (C7) and Lower (C8 and T1) Divisions
• Anterior and posterior Cords
• Lateral, posterior and medial
Clinical:
1. Axillary nerve block. Anesthetic block of the brachial plexus is achieved by infusing local anesthetic into the axillary sheath (an extension of the pre vertebral fascia of the neck, which encloses the major branches of the brachial plexus, the axillary artery and vein). This anesthetic block combined with block of the blood flow to the upper limb (by tourniquet) allows surgeons to operate on the upper limb without having to place the patient under general anesthesia. It is interesting to note that the upper limb can tolerate 1 to 2 hours without blood flow and still be entirely normal when the tourniquet is relaxed and the blood flow is reestablished at the end of the operation. This capacity to tolerate extended periods without blood flow makes possible the reattachment of traumatically severed fingers or indeed the entire upper limb).
2. Axillary artery aneurysm. Ballooning of the axillary artery is not an uncommon occurrence. Because the axillary artery and the major branches of the brachial plexus are contained within the axillary sheath, a progressive dilatation (aneurysm) of the axillary artery will compress the nerves of the brachial plexus and produce neurological deficits. This is a good example of how symptoms involving one system of the body may point to pathology elsewhere.
3. Variation of brachial plexus structure. The contribution of the segmental nerves and T2 to the brachial plexus vary. When C4 provides a significant input, the plexus is said to be prefixed. When T2 contributes axons, the brachial plexus is said to be post fixed.
4. Erb-Duchenne palsy. This is a tearing or traction injury involving the upper roots of the brachial plexus (C5 and C6). It results from the application of stretching forces to the shoulder that pull the head away from the shoulder. For example, exaggerated lateral flexion of the shoulder. This can occur as a result of a forceful fall onto the shoulder or during childbirth. During childbirth, it is possible for the obstetrician to apply force to the baby’s head while the shoulder has yet to be delivered. The result is dysfunction of those muscles innervated by segments C5 and C6. The usual clinical presentation is an upper limb with an adducted shoulder, medially rotated arm, extended elbow and flexed wrist.
• Erb-Duchenne palsy is an injury of the upper brachial plexus (C5 and C6).
• It affects the shoulder and arm.
5. Klumpke’s paralysis. This is the result of injury to the lower roots of the brachial plexus (C8 and T1). Such an injury can occur when the shoulder joint is forcefully abducted. This can be the case during childbirth (breech presentation when the obstetrician pulls forcefully on the trunk while the upper limb remains inside the birth canal). This will affect mainly intrinsic muscles of the hand. The clinical presentation of Klumpke’s paralysis is a “claw hand”.
• Klumpke’s paralysis is an injury of the lower brachial plexus (C8 and T1).
• It affects the forearm and hand.
6. Transient paralysis. This results from pressure on the axilla, either from use of a crutch or from a heavy sleep. Transient paralysis can occur if one sleeps with an arm over the back of a chair (possibly while drunken). The radial and ulnar nerves are most frequently involved.
Additional Reading:
Histology and Cytology
1. Cell Components
2. Nervous Tissue
3. Muscle Tissue
4. Lymphoid Tissue
5. Integument
6. Respiratory System
7. Gastrointestinal System
8. Renal/Urinary System
9. Male Reproductive System
10. Female Reproductive System
Gross Anatomy
1. Back and Nervous System
2. Thorax
3. Abdomen, Pelvis, and Perineum
4. Upper Limb
5. Lower Limb
6. Head and Neck
7. Chest Wall
8. Shoulder
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