2.1 Pectoral Girdle

 

Pectoral Girdle

 

Pectoralis Major

Clavicular Head (from med. ½ of clavicle) ® ant. lamina of insertion into bicipital groove

Sternocostal Head  (from manubrium & body of sternum) ® intermediate lamina

Posterior fibres of S-C head ® posterior lamina inserting into capsule of shoulder jt.

Nerve supply

Med pectoral n pierces (and supplies) pec minor --> enters deep surface of pec major.

Lat pectoral nerve (C5,6,7) pierces clavipectoral fascia  medial to med pect nerve ® deep surface of PM

Only upper limb muscle supplied by all five segments of brachial plexus.

 

Pectoralis Minor

Arises from 3rd-5th ribs ® coracoid process

Impt landmark for axillary artery and brachial plexus

Nerve Supply

medial pectoral nerve C8,T1

 

Clavipectoral Fascia

Passing inwards: cephalic vein and lymphatics

Passing outwards: thoracoacromial vessels  and lateral  pectoral nerve.

 

Subclavius

Costochondral junct of 1st rib ® inf surface of clavicle. Enclosed by clavipectoral fascia.

Nerve Supply

Upper trunk of brachial plexus ® n to subclavius  C5, C6

 

Trapezius

Not derived from limb bud myotomes so not supplied by brachial plexus. 
Origin from sup nuchal line ® all cervical and thoracic vertebrae.  Insertion: lat 1/3 of clavicle, acromion and spine of scapula. 

Nerve supply

Spinal part of CN XI, = C1-5, + branches of cervical plexus; enters from posterior triangle of neck

 

Latissimus Dorsi (Pl 160)

Wide origin: spines of T7 ® T12 and lumbar fascia (hence all lumbar & sacral spines and iliac crest)

upper edge runs horizontally under lower trapezius, over inferior angle of scapula (may get slips from here)

reinforced by fibres from lower four ribs (interdigitate with EO); forms lumbar triangle.

Converges as lower border of axillary fold; spirals around lower border of teres major (397)

Narrow insertion: 3cm wide, inter intertubercular sulcus

because of spiral, lowest fibres insert highest and vice-versa (like pec major)

Nerve Supply

Thoracodorsal n C6-8 from post cord of BP, runs down medial-posterior wall of axilla ® med surface of LD; vulnerable in axillary clearance.

Action:

Extends shoulder joint, medially rotates humerus (fold arms behind back)

Powerful adductor with pec major (major climbing muscle)

Assists in deep inspiration

Compresses lower thorax eg in sneezing

Only upper limb to have pelvic attachment, \ useful in spinal patients

Test: abduct arm to right angle, then adduct against resistance; feel bulk below post axillary fold.

 

Rhomboids (395)

Minor: C7+T1 (spines) ® medial scapula at level of spine.

Major: T2-5 (spines) and intervening supraspinous ligaments ® medial scapula b/n spine and inf angle.

Nerve supply
Dorsal scapular n (off C5 root of brachial plexus); passes through scalenus medius (deep to levator scapulae which is supplies) on serratus posterior superior medial to transverse cervical artery.

Actions

Draw scapula medially and upwards (retract / square shoulders)

Test

Hands on hips, push elbows back against resistance; palpate, observe for symmetry.

 

Levator Scapulae (395)

Strap on floor of posterior triangle.

Arises: C1-2 (transverse processes) and C3-4 (posterior tubercles)

Inserts: medial border of scapula superior to spine

Supply: C3-4 (cervical plexus muscle), reinforced from dorsal scapula n.

Action: elevates scapula (with upper trapezius), and can laterally rotate neck.

 

Serratus Anterior (177)

= med wall of axilla; clothes sidewall of thorax; covered by pec major anteirorly.

Arises: digitations from upper 8 ribs, over its 1st digitation runs the neurovascular bundle to axilla.

Inserts: costal angle of scapula, ® 1st & 2nd digitations to upper angle, next 2 along vertebral border, lowest 4 at inferior angle

Nerve Supply

C5-7 roots of BP ® long thoracic n, runs in mid-axillary line on surface of SA (ant to thoracodorsal)

Action:

Protracts the scapula, elongating the upper limb

Rotates scapula laterally, (more than trapezius), raising the arm above the shoulder

Apposition of scapula surface to the chest wall.

Test

Outstretched hand pushed against wall ® ‘winging’.
Commonly divided in thoracotomy incisions but is the lower portion of it; so little denervation usually recognized.

 

Sternoclavicular Joint (171)

Manubrium meets medial clavicle (and adjoining first costal cartilage below is attached, though this is a simple firm primary cartilaginous attachment to manubrium).

Intervening disc of fibrocartilage separates the joint into two cavities

a capsule invests the joint like a sleeve; the disc attaches to this, to clavicle ends and to 1st CC.

Ant and post sternoclavicular ligs thicken the capsule.

synovial but not hyaline cartilage; atypical as is fibrocartilage.

Only the lower half of the clavicle meets the joint

interclavicular ligament joins two clavicle ends across the jugular notch

costoclavicular ligament binds clavicle to 1st rib and 1st CC in 2 laminae: anterior lamina run upwards and laterally posterior run upwards and medially (like EO / IO)

very strong: the major stabilising factor of the SC jt ; transfers strain instead to below.

Nerve supply: C3,C4 from cervical plexus via medial supraclavicular nerve.

Movements:

Reciprocal (opposite) movement to acromial end of clavicle and to forward and backward shoulder movement (typically occur between manubrium and the disc, ie disc moves with clavicle)

-           in rotary movement of arm, also moves reciprocally at this point, passively secondary to transferred force from coracoclavicular ligaments

 

Acromioclavicular Joint (394)

Synovial (but again atypical as covered in fibrocartilage)

Encapsulated by a fibrous sleeve, thickened on top as the acromioclavicular ligament.

an incomplete disc of fibrocartilage hangs down into the upper half of the cavity

Coracoclavicular ligament: strong, principal stabilising factor; 2 parts: (connected posteriorly)

conoid: inverted cone, coracoid to conoid tubercle under clavicle

trapezoid: coracoid to trapezoid ridge under clavicle

Nerve supply: suprascapular nerve C5-6 (and maybe C4)

Movements: passive. Three groups of movement combined in varying proportions, each transmitted through ligaments to clavicle at both ends:

protraction and retraction: acromion tip glides to-and-fro on tip of clavicle

rotation: scapular can rotate 60o. 20o from scapula, rest from clavicle rotation.

elevation and depression: medial end of clavicle moves but AC jt moves little.

Stability: coracoclavicular ligament.

the upper limb simply hangs off from conoid assisted by deltoid, triceps, biceps

forces ® glenoid ® clavicle via trapezoid ligament ® 1st rib via costoclavicular ligament

hence in FOOSH, no strain occurs at either end of the clavicle, rather in the middle.

 

Triangle of Auscultation
Upper horizontal border of Lat dorsi, lat trapezius, vertebral border of scapula (floored by fascia)
- deep to here is cardiac orifice of stomach, where succussion splash heard