shoulder

SHOULDER

Kaan Yücel M.D., Ph.D 27.December.2011 Tuesday

Region of upper limb attachment to the trunk. Proximal segment of limb that overlaps parts of the trunk (thorax and back) and lower lateral neck.

Shoulder includes Pectoral ScapularDeltoid regions of the upper limblateral part (greater supraclavicular fossa) of lateral cervical region. Overlies half of the pectoral girdle.

The pectoral (shoulder) girdle is a bony ring, incomplete posteriorly, formed by:Scapulae and clavicles completed anteriorly by the manubrium of the sternum (part of the axial skeleton).

Bone framework of the shoulder Clavicle & scapula [form pectoral girdle-shoulder girdle-]

&Proximal end of humerus

The superficial muscles of the shoulder trapezius & deltoid muscles

together form the smooth muscular contour over the lateral part of the shoulder.

Connect scapula to trunk & clavicle to arm.

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The 3 joints in the shoulder complex :

Sternoclavicular jointAcromioclavicular jointGlenohumeral joint

JOINTS

Muscles

The two most superficial muscles of the shoulder are the trapezius and deltoid muscles. Together, they provide the characteristic contour of the shoulder:

Trapezius attaches scapula & clavicle to the trunkDeltoid attaches scapula & clavicle to the humerus

Both the trapezius and deltoid are attached to opposing surfaces and margins of the spine of the scapula, acromion, and clavicle.

The scapula, acromion, and clavicle can be palpated between the attachments of trapezius and deltoid.

SUPERFICIAL POSTERIOR AXIOAPPENDICULAR MUSCLES

EXTRINSIC SHOULDER MUSCLES

Trapezius & latissimus dorsi

• Descending (superior) fibers elevate the scapula (e.g., when squaring the shoulders).• Middle fibers retract the scapula (i.e., pull it posteriorly).• Ascending (inferior) fibers depress the scapula and lower the shoulder.

Movement to 180 degrees (elevation) is brought about by rotation of the scapula upwards by the trapezius and serratus anterior.

Trapezius

Passes from the trunk to the humerus and acts directly on the glenohumeral joint and indirectly on the pectoral girdle (scapulothoracic joint).

In combination with the pectoralis major, the latissimus dorsi is a powerful adductor of the humerus and plays a major role in downward rotation of the scapula in association with this movement.

Latissimus dorsi

Levator scapulae & rhomboids

Provide direct attachment of appendicular skeleton to the axial skeleton

DEEP POSTERIOR AXIOAPPENDICULAR MUSCLES EXTRINSIC SHOULDER MUSCLES

SCAPULOHUMERAL (INSTRINSIC SHOULDER) MUSCLES

6 scapulohumeral muscles Deltoid, teres major, supraspinatus, infraspinatus, subscapularis, and teres minorpass from scapula to humerus Act on the glenohumeral joint.

All the intrinsic muscles but the deltoid and the subscapularis are muscles of the posterior scapular

region.

Deltoid

Large and triangular in shapeBase attached to the scapula and clavicle Apex attached to the humerus

Deltoid Originates along a continuous

U-shaped line of attachment to clavicle & scapula mirroring the adjacent insertion sites of the trapezius muscle.

Inserts into deltoid tuberosity on the lateral surface of the shaft of the humerus.

DeltoidMajor function: Abduction of the arm beyond the initial 15° accomplished by supraspinatus

Clavicular: flexes and medially rotates armAcromial: abduction of armSpinal: extends and laterally rotates arm

DeltoidInnervation: Axillary nerve branch of the posterior cord of the brachial plexus

Thick, triangular muscle Lies on the costal surface of the scapula

Subscapularis

Originates from the subscapular fossa on the anterior surface of the scapula

Attaches to the lesser tubercle of the humerus

Primary medial rotator of the arm Adducts the arm.

Joins the other rotator cuff muscles in holding the head of the humerus in the glenoid cavity during all movements of the glenohumeral joint (i.e., it helps stabilize this joint during movements of the elbow, wrist, and hand).

Innervation: Superior and inferior subscapular nerves

Subscapularis

POSTERIORSCAPULAR

REGION

The posterior scapular region occupies the posterior aspect of the scapula and is located deep to the trapezius and deltoid muscles.

Contains 4 musclespass between the scapula and proximal end of humerus: supraspinatus, infraspinatus, teres minor, teres major

The posterior scapular region also contains part of one additional muscle, the long head of the triceps brachii, which passes between the scapula and the proximal end of the forearm.

This muscle, along with other muscles of the region and the humerus, participates in forming a number of spaces through which nerves and vessels enter and leave the region.

Originate from 2 large fossae, 1 above and 1 below the spine, on the posterior surface of the scapula.

Insert on greater tubercle of the humerus.

Supraspinatus initiates abduction of the arm. Infraspinatus laterally rotates the humerus.

Supraspinatus & Infraspinatus

Supraspinatus & Infraspinatus

A cord-like muscle

Originates from a flattened area of the scapula immediately adjacent to its lateral border below the infraglenoid tubercle.

Inserts on inferior facet of greater tubercle of humerus.

Laterally rotates the humerus and is a component of the rotator cuff.

Teres minor

Originates from a large oval region on the posterior surface of the inferior angle of the scapula.

Attaches to the medial lip of the intertubercular sulcus on the anterior surface of the humerus.

Medially rotates and extends the humerus.

Teres major

4 intrinsic shoulder muscles1) Supraspinatus2) Infraspinatus3) Teres minor4) Subscapularis

ROTATOR CUFF MUSCLES

(SITS muscles)

Form a musculotendinous rotator cuff around the glenohumeral joint.

Insertion exception:

ROTATOR CUFF MUSCLES

Supraspinatus Infraspinatus Teres minor

greater tubercle

Subscapularis

lesser tubercle

ROTATOR CUFF MUSCLESFunctional exception:

All except supraspinatus are rotators of the humerus

Supraspinatus, besides being part of the rotator cuff, initiates and assists the deltoid in the first 15° of abduction of the arm.

Suprascapular foramen The route through which structures pass between the base of the neck and the posterior scapular region.

Gateways to the posterior scapular region

Formed by suprascapular notch of scapula & superior transverse scapular (suprascapular) ligament, which converts the notch into a foramen.

The suprascapular nerve passes through the suprascapular foramen;

Suprascapular artery & suprascapular vein follow the same course as the nerve, but normally pass immediately superior to the superior transverse scapular ligament and not through the foramen.

Gateways to the posterior scapular region

Quadrangular spaceTriangular space Triangular interval

Gateways to the posterior scapular region

The two major nerves of the posterior scapular region: Suprascapular & Axillary nerves

originate from the brachial plexus in the axilla.

Nerves

Originates where?Base of the neck from superior trunk of brachial plexusReach where through which space? Posterior scapular region through suprascapular foramenWhich muscles innervates ?Supraspinatus muscle & infraspinatus

Suprascapular nerve

Axillary nerveOriginates where?Posterior cord of brachial plexusReach where through which space? From the posterior wall of axilla to posterior scapular region through quadrangular spaceWhich muscles innervates ?Deltoid & teres minor

Axillary nerveCutaneous branch?Superior lateral cutaneous nerve of the armcarries general sensation from the skin over the inferior part of the deltoid muscle.

3 major arteries in the posterior scapular region

Suprascapular artery Posterior circumflex humeral artery Circumflex scapular artery

Arteries

These arteries contribute to an interconnected vascular network around the scapula.

Formation of anastomosis around the surgical neck of humerus

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Posterior circumflex humeral artery anastomoses with anterior circumflex humeral artery and also with branches from:

profunda brachii (brachial artery) suprascapular (subclavian artery) thoracoacromial (axillary artery) arteries

Scapular anastomosis system

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A system connecting each subclavian artery and the corresponding axillary artery, forming an anastomosis around the scapula. It allows blood to flow past the joint regardless of the position of the arm. It includes:transverse cervical artery (subclavian artery)transverse scapular artery (subclavian artery)subscapular artery (axillary artery)branches of thoracic aorta This collateral circulation allows for blood to continue circulating if the subclavian is obstructed.

Testing the deltoid muscle To test the deltoid (or the function of the axillary nerve that

supplies it), the arm is abducted, starting from approximately 15°, against resistance.

If acting normally, the deltoid can easily be seen and palpated.

Quadrilateral Space Syndrome

A clinical syndrome resulting from compression of the axillary nerve and posterior circumflex humeral artery in the quadrilateral space

The passage of the axillary nerve backward from the axilla through the quadrangular space makes it particularly vulnerable here to downward displacement of the humeral head in shoulder dislocations or fractures of the surgical neck of the humerus.  

Quadrilateral Space Syndrome

Paralysis of the deltoid and teres minor

Cutaneous branches of the axillary nerve, including the upper lateral cutaneous nerve of the arma loss of skin sensation over the lower half of the deltoid muscle.

Movements of the shoulder girdleAbduction of the shoulder is initiated by the supraspinatus; the deltoid can then abduct to 90 degrees. Further movement to 180 degrees (elevation) is brought about by rotation of the scapula upwards by the trapezius and serratus anterior. As soon as abduction commences at the shoulder joint, so the rotation of the scapula begins.

Principal muscles acting on the shoulder jointAbductorsSupraspinatusDeltoidAdductorsPectoralis majorLattisimus dorsiExtensorsTeres majorLattisimus dorsiDeltoid (posterior fibres)FlexorsPectorali majorCoracobrachialisDeltoid (anterior fibres)

Medial rotatorsPecroralis majorLattisimus dorsiTeres majorDeltoid (anterior fibres)SubscapularisLateral rotatorsInfraspinatusTeres minorDeltoid (posterior fibres)