Superficial Back and Shoulder

Overview

motion at a joint: determined by shape of the articular processes; ligaments and joint capsule limit the range of motion; orientation of the muscles (muscles can only contract on the long axis of their fibers); fibers may be arranged simply, or in a complicated fashion such as in the deltoid

pectoral girdle: formed by scapulae and clavicles; sternum is not part of the girdle

the upper limb has little constraint on movement

scapuloclavicular joint is the only direct articulation between the upper limb and the thorax; rest of the scapula is embedded in muscle

human thorax is lateromedially wide Þ scapula is more posterior-lateral than in monkeys allowing for a lateral position of the arm Þ greater freedom (especially rotation)

clavicle acts as a strut to keep the scapula in a lateral position

scapular-humeral rhythm: combined movement of the scapula and humerus to raise the arm

movement about the glenoid can only achieve 90°; further raising of the arm requires scapular rotation

freedom of motion at the shoulder is at the expense of stability

dislocation: humerus is displaced from the glenoid

separation: clavicle is displaced from the acromion

scapular winging: rhomboids and serratus anterior hold the scapula against the thoracic wall

damage to the long thoracic nerve Þ malfunction of serratus anterior Þ scapula protrudes posteriorly

co-lateral circulation or the shoulder: in case of axillary disruption

dorsal scapular artery Þ subscapular artery

suprascapular artery Þ circumflex scapular artery

anatomic neck of the humerus: at the ball on the head of the humerus; more proximal than the surgical neck

surgical neck of the humerus: more distal than the anatomic neck; at greater risk for fracture

Surface Anatomy

external occipital protuberance: bump on occipital bone (back of head, superior to C1)

scapula:

vertebral border; axillary border; superior border

inferior angle; superior angle

acromion process: ‘point of the shoulder’; point of articulation with the clavicle

coracoid process

spine: ridge which projects from the posterior aspect of the scapula

supraspinous fossa: superior to the spine of the scapula

infraspinous fossa: inferior to the spine of the scapula

glenoid process (fossa): superolatteral point of articulation with the humerus; lined with a fibrous cartilage

suprascapular notch: in the superior border of the scapula; bridged by the suprascapular ligament

clavicle: the only bony connection of the upper limb to the thorax; articulates with sternum and acromion of scapula

margins of trapezius

vertebra prominens: C7; the first prominent spinous process; visible on the surface anatomy (with neck flexed)

contours of deltoid

spinous processes; posterior extension of vertebrae (visible surface anatomy)

greater tuberosity of the humerus: lateral tubercle on head of the humerus; insertion of rotator cuff muscles

Structures in Back

trapezius

origin: external occipital protuberance; superior nuchal line; ligamentum nuchae (C7 - T12)

insertion: lateral third of clavicle; spine of scapula; acromion

innervation: spinal accessory nerve (cranial nerve XI)

action: adducts and rotates scapula; draws back acromion

latissimus dorsi

origin: spines of T7-T12; lumbosacral fascia; iliac crest

insertion: floor of bicipital groove of humerus

innervation: thoracodorsal

action: adducts, extends, medially rotates humerus

rhomboid major

origin: spine of T2-T5

insertion: vertebral border of scapula

innervation: dorsal scapular

action: adducts, rotates scapula

rhomboid minor

origin: ligamentum nuchae; spine of C7, T1

insertion: medial portion of scapular spine

innervation: dorsal scapular

action: adducts, rotates scapula

levator scapulae

origin: transverse process of C3, C4

insertion: vertebral border of scapula superior to the spine

innervation: dorsal scapular; 3^rd and 4^th cervical

action: raises scapula or inclines neck

serratus anterior

origin: outer surface of upper 8 or 9 ribs

insertion: costal surface of vertebral border of scapula

innervation: long thoracic

action: abducts scapula; raises ribs when scapula is fixed

cranial nerve XI: innervates the trapezius

cutaneous nerves

dorsal scapular nerve from brachial plexus; runs with the artery; innvervates rhomboids, levator scapulae

dorsal scapular artery arises from subclavian (70%) or transverse cervical a (30%); runs deep to rhomboids and supplies rhomboids, levator scapulae, serratus anterior

triangle of auscultation: ‘window’ to inferior lobes of lung; formed by: latissimus dorsi, trapezius, rhomboid major

thoracolumbar fascia

ligamentum nuchae: between the left and right superior aspects of the trapezius; attaches to spinous processes of vert.

Structures in the Dorsal and Lateral Shoulder

deltoid

origin: lateral third of clavicle

insertion: deltoid tuberosity of humerus

innervation: anterior and posterior branches of axillary n

action: abducts arm

rotator cuff

supraspinatus

origin: supraspinous fossa of scapula

insertion: superior facet of greater tubercle of humerus; capsule of shoulder

innervation: suproscapular

action: abducts arm; fixes head of humerus in glenoid; rotates head laterally

infraspinatus

origin: infraspinous fossa of scapula

insertion: middle facet of greater tubercle of humerus; capsule of shoulder

innervation: suproscapular

action: rotates head of humerus laterally

teres minor

origin: dorsal surface of axillary border of scapula

insertion: lowest facet of greater tubercle

innervation: posterior branch of axillary

action: adducts, rotates humerus laterally; draws humerus to glenoid

subscapularus

origin: subscapular fossa

insertion: lesser tubercle of humerus; capsule of shoulder joint

innervation: upper and lower subscapular

action: rotates humerus medially; draws it forward and down when arm is raised

teres major

origin: dorsal surface of inferior angle of scapula

insertion: medial lip of bicepital groove of humerus

innervation: lower subscapular

action: adducts and medially rotates humerus and draws it back

posterior humeral circumflex artery: branch of axillary artery; passes through the quadrangular space, into the deltoid, then spilts to ascending and descending branches

profunda brachii artery axillary artery changes name to brachial artery after the branch of the posterior humoral circumflex artery

suprascapular artery passes superior to the suprascapular ligament and runs with the suprascapular n

transverse cervical artery

radial nerve C5-8, from brachial plexus

axillary nerve C5, 6 from brachial plexus

suprascapular nerve runs between suprascapular ligament and notch

suprascapular notch and ligament: notch at superior boarder of scapula; ligament bridges the notch

triceps brachii (long and lateral heads): long and lateral heads form the trangular interval

quadrangular space: formed by teres major and minor, long and lateral heads of the triceps; posterior humeral circumflex artery and axillary nerve run through here

triangular space: formed by teres major and minor; circumflex scapular artery runs deep to space

triangular interval: formed by lateral and long heads of triceps; radial nerve and profunda brachii can be seen though here