Shoulder Complex Notes

Shoulder Complex

• One of the most mobile segments of the human body.

  • Shoulder flexion/extension: $0-180$ and $0-60$ degrees.

  • Shoulder abduction/adduction: $0-180$ degrees.

  • External/Internal Rotation.

• Mobility is provided by 6 moving areas (joints).

Osseous Parts

Clavicle

• Long slender bone lying horizontally at the root of the neck.

• Orientation:

  • Middle 2/3: Convex anteriorly (concave posteriorly).

  • Lateral 1/3: Concave anteriorly (convex posteriorly).

• Most commonly fractured bone in the human body.

• Mechanism of Injury (MOI):

  • FOOSH (fall on outstretched hand).

  • FOS (fall on shoulder) – more common in elderly patients due to delayed response.

  • Medially-directed Blow to Shoulder.

• Fractured segments – occurs with muscle guarding.

  • Medial Fragment – tilts superiorly by Sternocleidomastoid (SCM).

  • Lateral Fragment – pulled downward by gravity; pulled medially by pectoralis major.

    • Lateral segment is attached to the shoulder (heavy) = gravity.

• Costoclavicular space

  • Formed between the clavicle and 1st rib.

  • Structures:

    • Subclavian artery – passes forward and downward.

    • Brachial plexus.

• Complete fracture → surgery.

  • Damaged subclavian artery means brachial, radial, ulnar, palmar arteries are damaged too (check pulse to know if subclavian artery is completely fractured).

• Incomplete fracture → figure of 8 bandage.

  • The “8” is at the back to retract the shoulder (pull backwards).

Scapula

• Flat triangular bone that lies on the posterior thoracic wall between the 2nd and 7th ribs.

• Important landmarks for palpation of the spinous processes of the vertebral column.

  • Superior angle – T2.

  • Spine of scapula – T3 (between T3 and T4).

  • Inferior angle – T7 (between T7 and T9).

• Acromion Process

  • Summit of the shoulder (highest point).

  • Orientation: posterior, lateral, superior.

  • Types:

    • Type 1: Flat

    • Type 2: Curved

    • Type 3: Hooked

    • Type 4: Upturned (rare)

  • Type of acromion process associated with Impingement Syndrome: TYPE 3 (Hooked).

  • Painful arc for Impingement Syndrome: $60$ to $120$ degrees.

    • $60$ degrees: Marked approximations of bony structures occur → impingement.

    • $> 120$ degrees: Humeral head begins to glide inferiorly (humerus moves superiorly).

• Coracoid Process

  • Orientation: anterior and superior.

  • Coracoacromial Ligament – prevents superior translation of humerus.

• Spinous Process of the Scapula

  • Extension of the acromion process medially.

  • Used to locate (but not to palpate) structures:

    • Supraspinous Fossa – above; supraspinatus muscle origin.

    • Infraspinous Fossa – below; infraspinatus muscle origin.

  • Subscapular Fossa – anterior; subscapularis muscle origin.

    • Spine of scapula (posterior) is not used to locate subscapular fossa (anterior).

• Glenoid Fossa

  • Shallow cavity.

  • Glenoid Labrum – enhances the depth of the fossa by $50$%.

Humerus

• Humeral Head

  • Forms 1/3 of a sphere.

  • Intracapsular (because of anatomical neck as the end attachment).

• Anatomical Neck

  • Immediately below the head.

  • End attachment of the shoulder joint capsule.

• Surgical Neck

  • More prone to fracture (fractures are more common near the shaft than the head).

  • Nerve usually damaged: Axillary Nerve.

    • Muscles to test for possible weakness to confirm axillary nerve damage: Deltoids (not teres minor because there are a lot of external rotators).

• Tuberosities

  • Greater: Lateral, Internal Rotation, Supraspinatus (Abduction), Infraspinatus (External Rotation), Teres minor

  • Lesser: Medial, External Rotators, Subscapularis (Internal Rotation)

  • SIT at the greater, Sub at the lesser.

  • Greater tuberosity is best viewed (imaging) in: External Rotation.

• Bicipital Groove

  • aka “Intertubercular Groove”.

  • Long head of biceps passes here.

    • Held in place by the Transverse Humeral Ligament (THL).

  • Common test for THL rupture: Yerguson’s test.

• Spiral Groove

  • Oblique groove at the posterior portion of the humerus.

  • Radial nerve (“Musculospiral nerve”) passes here.

  • Commonly fractured → damages the radial nerve.

  • Spared muscle in the radial nerve damage at the level of the spinal groove: Long head of Triceps (innervated at the proximal level before spiral groove).

Joints

• True Joint: (+) bone-to-bone contact

• False Joint: (–) bone-to-bone contact

• True Joints:

  1. Sternoclavicular joint

  2. Acromioclavicular joint

  3. Glenohumeral joint

• False Joints:

  1. Bicipital groove

  2. Subacromial joint

  3. Scapulothoracic joint

• Most important true joint: Glenohumeral joint

  • It’s a synovial ball and socket (provides the greatest mobility).

• Most important false joint: Scapulothoracic joint

  • Due to the scapulohumeral rhythm.

True Joints

Sternoclavicular Joint

• Type: Saddle/Stellar (has convex and concave parts on each bone).

  • Elevation-depression: opposite (clavicle moves superiorly, joint glides inferiorly).

  • Protraction-retraction: same (clavicle moves anteriorly, joint glides anteriorly).

• Articulation: Medial end of clavicle + manubrium of sternum.

• Ligaments:

  • Interclavicular ligament (IC)

    • Found between 2 clavicles (found above).

    • Limits excessive depression.

  • Costoclavicular ligament (CC)

    • Found between 1st rib and clavicle.

    • Limits excessive elevation.

  • Sternoclavicular ligament (SC)

    • Anterior SC ligament – limits retraction.

    • Posterior SC ligament – limits protraction.

• Accessory Structure: Sternoclavicular Disc

  • Function: for shock absorption.

  • Elevation-depression: disc becomes part of the sternum.

  • Protraction-retraction: disc is part of the clavicle.

• Kinematics: 3 DOF, 3 axes

  • Elevation and depression.

  • Protraction and retraction.

  • Long axial rotation (primarily posteriorly during shoulder abduction).

  • Contribution of the SC joint during arm elevation:

    • Elevation <$90$ deg.

    • Posterior rotation >$90$ deg.

  • Without posterior rotation of the clavicle, arm elevation is up to how many degrees? $110$ deg only.

Acromioclavicular Joint

• Type: Synovial plane joint.

• Articulation: lateral end of clavicle + acromion process.

• Ligaments:

  • Acromioclavicular Ligament

    • Superior: prevents inferior translation; primary (thicker).

    • Inferior: prevents superior translation; not primary (thin).

  • Coracoclavicular Ligament

    • Conoid ligament

      • Triangular; posterior; medial (inferior to clavicle).

      • Vertical fibers.

      • Prevents superior translation of the clavicle.

      • Primary ligament.

    • Trapezoid ligament

      • Quadrangular; anterior; lateral.

      • Horizontal fibers.

      • Prevents medial displacement of the scapula.

    • Conoid & trapezoid ligaments connect what structures: Coracoid & Clavicle.

• Accessory Structure: Acromioclavicular Disc

  • <$2$ y/o – fibrocartilaginous union

  • >$2$ y/o – fibrocartilaginous remnant that is meniscoid (i.e., AC disc).

• Kinematics: 3 DOF, 3 axes

  • ER and IR – for horizontal curvature.

  • Anterior and posterior tilting – for vertical curvature.

  • Upward and downward rotation – for shoulder elevation.

• Contribution of AC joint during arm elevation: upward rotation and posterior tilting (because abduction occurs slightly anteriorly).

Glenohumeral Joint

• Type: Synovial ball and socket

• Articulation: humeral head + glenoid fosa

  • Orientation:

    • Humeral head – Medial, Posterior, Superior.

    • Glenoid fossa – Superior, Anterior, Lateral.

  • Angles of humeral head

    • Angle of Inclination – Normal Value: $130-150$ deg

      • Formed by the axis of the humeral head and neck + axis of the humeral shaft

      • Tilts head superiorly

    • Angle of Torsion – Normal Value: approx. $30$ deg of retrotorsion

      • Formed by the axis of the humeral head + axis of the humeral condyles

      • Tilts head posteriorly

• Ligaments

  • Coracohumeral Ligament

    • Coracoid process to the greater and lesser tuberosities

    • Located anteriorly and superiorly

    • Limits excessive ER

    • Prevents downward translation of humerus

    • Ligament in company with supraspinatus muscle that prevents inferior translation of humerus: Coracohumeral ligament

    • Greatly involved in adcap (adhesive capsulitis/frozen shoulder)

    • Those with DM will likely have adcap due to lack of blood supply

      • Coracohumeral ligament thickens

      • Shoulder capsular pattern: ER > AB > IR (max mod mid)

        • Min loss of IR: ligament thickens pulling humerus into IR

        • Mod loss of AB: to abduct beyond 90, ER is needed to complete 180 abduction

        • Max loss of ER: because thickened ligament, more limited ER

  • Glenohumeral Ligament

    • Limits excessive ER (GH is located anteriorly)

      • Superior: $0-45$ deg

      • Middle: $45-90$ deg

      • Inferior: $>90$ deg

    • Common direction of shoulder dislocation: anteroinferior

    • Foramen:

      • Between superior and middle: Foramen of Weitbrecht

      • Between middle and inferior: Foramen of Rouvier

• Accessory Structure: Glenoid labrum

• Kinematics: multiaxial joint

  • Flexion and extension

  • Abduction and adduction

  • ER and IR

False Joints / Functional Joints

Bicipital Groove (“Intertubercular Groove”)

• Boundaries:

  • Medial: Teres major

  • Lateral: Pectoralis major

  • Floor: Latissimus dorsi

  • Roof: Transverse humeral ligament THL

Subacromial Joint (“Suprahumeral Joint” / “Supraspinatus Outlet”)

• Most vulnerable: Supraspinatus muscle

  • Most easily damaged in the Subacromial joint

• Acromiohumeral interval (distance between acromion process and humerus)

  • Arms at side: $10$ mm

  • Arms elevated: $5$ mm

• Subacromial bursa – prevents friction of supraspinatus with acromion process

Scapulothoracic Joint

• Note that there is an important relationship between the ST and GH joint

Scapulohumeral Rhythm

• After $30$ degrees of abduction, a 2:1 ratio occurs

  • $0-30$ degrees = GH joint

  • 2 = GH joint; 1 = ST joint

• Phases of Scapulohumeral Rhythm

  • Phase 1

    • Humerus: 30 deg

    • Scapula: Setting phase

    • Clavicle: Elevation 30

  • Phase 2

    • Humerus: 40 deg

    • Scapula: 20 deg from UR

    • Clavicle: Elevation 90

  • Phase 3

    • Humerus: 60 deg

    • Scapula: 30 deg

    • Clavicle: Posterior rotation 120

  • Phase 2: scapula only moves when abduction is beyond $30$ deg

  • Phase 2: clavicle elevates still because total abduction is $90$ deg ($40 + 20 + 30$)

  • Phase 3: posterior rotation of clavicle only occurs beyond $90$ deg abd ($120$)

Stability

Static Stability / Structural Stability

• Less stability

  • Only connection of shoulder complex to axial skeleton is SC joint

• Contributors to structural stability:

  • Negative intraarticular pressure (no air inside—suction—won't fall)

  • Upward tilt of the fossa provides bony block against inferior translation

  • Passive tension from the ligaments

Dynamic Stability

• Provided by muscles

• Terminologies

  • Force couple – two opposing forces create rotation

  • Positive translatory force – upward force, muscles that pull humerus superiorly

  • Negative translatory force – downward force; muscles that pull humerus inferiorly

  • Action line: direction of force created by the muscle

• Deltoids and GH stabilization

  • Action line of deltoids: large positive translatory force + small rotary force

    • Deltoids alone cannot abduct the shoulder because the positive translatory force is too large → jams in the acromion

    • Another muscle needs to counter it

• Rotator Cuff and GH Stabilization

  • Action line of ITS (infraspinatus, teres minor, subscapularis): negative translatory force

  • Deltoids + ITS = force couple (creates rotation)

• Supraspinatus and GH Stabilization

  • Action line of supraspinatus: small positive translatory force

  • Force is opposed by the negative translatory force of gravity

  • Supraspinatus + gravity = force couple (creates rotation)

• The contractions of these muscles keep the humeral head apposed to the glenoid fossa

Important landmarks

• Anterior wall: Pecs major, Pecs minor, Subclavius

• Posterior wall: Subscapularis, Latissimus dorsi, Teres major

• Lateral wall: Biceps in the bicipital groove, Coracobrachialis

• Medial wall: Ribs 2-6, Serratus anterior

• Quadrangular and Triangular Space

  • Quadrangular space – near the surgical neck Superior (Teres minor), Inferior (Teres major), Medial (Long head of triceps), Lateral (Humerus)

  • Triangular (Teres minor), Inferior (Teres major), Medial (Long head of triceps)

  • Structures that pass through the spaces:

    • Quadrangular: Posterior circumflex humeral artery, Axillary nerve

    • Triangular: Circumflex scapular artery

Brachial Plexus

• Originates from anterior rami of C5 – T1

• RoTonDaCubao (roots, trunks, division, cord, branches)

• Dorsal scapular nerve – innervates rhomboids and levator scapulae

• Long thoracic nerve – innervates serratus anterior

  • Injury the Long thoracic nerve results in medial winging of scapula / open-book

• Largest branch of the brachial plexus: Radial Nerve

• Cause of weak deltoid and weak wrist extensors: Posterior cord

  • Weak deltoid is due to axillary nerve

  • Weak extensors are due to radial nerve

• Branches and Roots (C5 C6 C7 C8 T1—5 fingers)

  • Musculocutaneous nerve: C5, C6, C7

  • Axillary nerve: C5, C6

  • Median nerve: C5-T1

  • Radial nerve: C5-T1

  • Ulnar nerve: C8, T1