Embryology

• Paraxial mesoderm

• Lateral Plate mesoderm—Shoulder Girdle

• Neural Crest

• Limb buds visible at the end of 4th week

• In 7th week upper limb rotates laterally 90 deg

• Pre axial border in embryo becomes lateral border in adults

• Cartilaginous condensations

• Chondrogenesis is arrested

• Joint inter-zone induced

• Cells increase in no. and density

• Joint cavity formed by cell death

• Surrounding cells differentiate to form joint capsule

• Inductive Signal for Joint Positioning: WNT 14

• Limb positioning : HOX genes

• AP axis patterning: ZPA (zone of polarizing activity)

ZPA produces retinoic acid which expresses sonic hedgehog.

SHOULDER JOINT

• Multiaxial, ball & socket, synovial joint• 4:1 disproportion• Deepened by labrum

Capsular attachments:1. scapula-beyond supraglenoid tubercle2. Anatomical neck of humerus EXCEPT

inferiorly where it is on surgical neck

• Bridges gap between GT and LT as Transverse Humeral Ligament

• Gap in ant. Capsule for communication with subscapularis bursa

• Thick, tough BUT lax

• Long tendon of biceps - Intracapsular

SYNOVIAL MEMBRANE:

Attached to glenoid labrum and lines

capsule at:

1. Articular margin humeral head

2. Invests long head of biceps

3. Covers bare area – surgical neck

4. Reflected along flr of IT sulcus; lines THL

HILTON’S LAW: “Nerves crossing a joint give off branches and innervate it.”

1. Axillary nerve

2. Suprascapular nerve

3. Musculocutaneous nerve

4. Subscapular nerve

Muscles around shoulder

• Subscapularis

• Supraspinatous

• Infraspinatous

• Teres Minor

• Teres Major

• Deltoid

Ligaments around shoulder• Glenohumeral ligament3 thick bands btw glenoid labrum and humerusReinforce anterior capsuleVisible only from within the joint cavityFunction depends on:1. Collagenous integrity2. Attachment site3. Position of the arm

Inf. GHL is main stabiliser of abducted armAnt. And posterior bands. (Hammock like)

• Coracohumeral ligamentCoracoid process to front of GTBlends with the capsule

• Coracoacromial ligamentFlat triangular bandMedial border of acromion ant. to AC jt. to

lateral border of coracoidLies above humeral headSeparated from rotator cuff by subacromial

bursa

Movements• Flexion: Cl. Head pect. Major

Ant. Deltoid

Coracobrachialis

Short head biceps

• Extension: Lat. Dorsi

Teres major

Post. Deltoid

Sternocostal part of pectoralis major can extend a fully flexed arm and flex a fully extended arm

• Abduction: supraspinatous Deltoid >120 deg Trapezius/Serratus anterior

• Medial Rotation: Subscapularis Teres Major

• Lateral Rotation: Teres Minor Infraspinatous

• Circumduction

AXILLARY ARTERY• Continuation of 3rd part of subclavian

• Starts @ outer border 1st rib

• Ends @ lower border teres major

• Lies on 1st digitation of serratus anterior

• Enclosed in sheath with Br. plexus cords

• Divided by pectoralis minor into parts

Above, behind and below

Dorsal

Scapular artery

Suprascapular A.

Subscapular A.

Circumflex

Scapular A

Scapula vascularity

• Vessels in muscle taking origin from it

• Vessels communicate with bony vessels

• Circulation in scapula is metaphyseal

• Periosteal vessels larger than usual

• Communicate freely with medullary vessels

• Nutrient artery enters through lateral supra/infrascapular fossa

Sternoclavicular Joint

• Clavicle protrudes superiorly and posteriorly

• Ant. And post sternoclavicular ligs.• Disk divides jt• Disk attached to 1st rib below and to sup.

Surface of clavicle through interclavicular lig

• Elevn - depression in jt bet clavicle & disk• AP and rotn between disk & sternum

• 30-35 deg elevation

• 35deg AP movt.

• 44-50 deg rotation

• Elevation occurs at 30- 90 deg arm elevation

• Rotation occurs after 70-80 deg elevation

• Blood supplyClavicular branch thoracoacromial AInternal mammery ASuprascapular A.

• Nerve supply:N. To subclaviusMedial supraclavicular N.

• Relation: Ant: SCMPost: Sternohyoid, SternothyroidGreat vessels and trachea

AC Joint• Capsule has diarthrodial joint incompletely divided by

perforated disk• Inferiorly capsule is thin• 20 deg rotation btw acromion and clavicle in 1st 20 deg and last 40 deg of elevation

• Blood supplyAcromial A. br. Of deltoid A of thoracoacromial ASuprascapular A

• Nerve SupplyLateral pectoralAxillarySuprascapular

• AP stability: Acromioclavicular lig

• Sup & Inf translation: Conoid and trapezoid parts of Coracoclavicular lig

• Types of acromion (Bigliani)

1. Flat undersurface

2. Curved

3. Hooked (Max. chance of impingement)

Humerus• Radius of curvature of head 2.25 cm

• Humeral retroversion 25 deg

• Intertubercular groove lies 1cm lateral to midline of humerus

• Axis of humeral head passes 9mm post to bicipital groove

• Head shaft angle 135 deg

• Head size correlates best with height

• Because of its distance from centre of rotation, GT lengthens lever arm of supraspinatus as elevation increases beyond 30 deg

• It also acts as a pulley by increasing lever arm of deltoid below 60 deg.