UE Anatomy Lectures

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Components of the brachial plexus and variations

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Components: VPR of C5-C8 and greater part of T1, small contributions from C4 and T2

  • roots: C4-T2
  • Trunks: Upper (C4-C6), Middle (C7), Lower (C8,T1,T2)
  • Divisions: each trunk has anterior and posterior
  • Cords: Lateral, medial, and posterior

prefixed plexus: contribution from C4 is large, then T2 is lacking and T1 contribution is reduced

Postfixed plexus: contribution from C4 is reduced or absent, C5 contribution is reduced, T1 is larger than normal, and T2 is always present


neurovascular compression syndrome

when the scalenus anterior and scalenus medius muscles are tight or in spasm and they compress the brachial plexus nerves and subclavian artery


quadrangular space

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above: teres minor, medial: long head of triceps, lateral: Humerus, below: teres major

axillary nerve passes through with the posterior circumflex humeral artery


triangular space

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above: teres minor, below: teres major, lateral: long head of triceps

circumflex scapular artery passes through


suprascapular (scapular) foramen

superior transverse ligament of scapula covers suprascapular (scapular) notch on superior border of scapula to create the suprascapular foramen

suprascapular artery goes over the foramen

suprascapular nerve goes under the ligament and through the forament


carpal tunnel syndrome

entrapment of the median nerve in the fascia (carpal) tunnel in the wrist after passing under the flexor retinaculum (transverse carpal ligament)

can have major effects on hand function

  • loss of thumb opposition and sensation in lateral hand

ulnar nerve unjury

ulnar nerve passes through the following potential sites for entrapment:

  • arcade of struthers-fascia bridge between the medial intermuscular septum and the medial head of triceps
  • cubital tunnel- behind the medial epicondyle
    • where the ulnar nerve is most vulnerable to injury
  • tunnel of guyon-osseofibrous tunnel between the pisiform and hook of the hamate and covered by the carpal ligament
  • "claw hand"- posturing of the hand with an ulnar nerve injury
    • extension of MCP joints and flexion of IP joints
  • damaged in crutch paralysis and sleep palsies

radial nerve injury

Arcade of Frosche: nerve passes between the 2 heads of the supinator muscle

  • wrist drop due to weakness in the extensor muscles of the forearm
  • no loss of sensation

damaged in crutch paralysis and sleep palsies


Erb's palsy

  • injury to upper trunk of brachial plexus (from fall to side of head and shoulder or birth injury)
  • weakness in muscles from C5 and C6
    • especially: deltoid, biceps, brachialis, brachioradialis, supraspinatus, infraspinatus and supinator
  • arm hangs at side and medially rotates, and the forearm is extended and pronated

klumpke's paralysis

injury to lower trunk of brachial plexus involving nerve fibers from the C8 and T1 levels

weakness in intrinsic muscles of the hand and wrist and finger flexors


crutch paralysis

occurs from excessive pressure from crutch pads on nerves running through axilla

radial nerve is usually first to be injured, then ulnar nerve


sleep palsies

from prolonged pressure on the nerves in the axilla

typically occurs with deep sleeps when under the influence of alcohol or drugs, where the person will fall asleep with the arm hanging over the back of a chair

"Saturday Night Palsy"


Structures damaged in humerus surgical neck fractures and shoulder dislocations

both have damage to posterior circumflex humeral artery and axillary nerve

  • fractures are common in the elderly

triangle of auscultation

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medial: medial border of scapula

lateral: trapezius

inferior: latissimus dorsi

can see rhomboid major inside of triangle


lumbar triangle

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medial: external oblique

lateral: latissimus dorsi

inferior: iliac crest

can see internal oblique muscle inside triangle


differences in arterial anatomy on the right and left sides of the chest

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Right: the brachiocephalic trunk ends by dividing into the subclavian and the common carotid arteries

left: brachiocephalic rises directly from the aortic arch


posterior triangle

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  • borders:
    • anterior: sternocleidomastoid
    • posterior: trapezius
    • inferior: clavicle
    • inferior belly of omohyoid muscle subdivides the posterior triangle into an upper occipital triangle and a lower supraclavicular triangle

cervical rib syndrome and scalenus anterior syndrome

cervical rib: subclavian artery can get kinked where it passes between the cervical rib and scalenus anterior

scalenus anterior: subclavian artery is compressed between scalenus anterior and scalenus medius in the absence of a cervical rib

presents with tingling, numbness, and decreased circulation to UE


walls of the axilla

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pulse of the axillary artery may be felt against the lateral wall of lower part of the axilla (pyramidal region)

Medial wall: ribs and serratus anterior

lateral wall: Humerus and coracobrachialis

posterior axillary fold: subscapularis, teres major, and latissimus dorsi

anterior axillary fold: pectoralis major and minor


cervicoaxillary canal

where the axillary vessels and nerves enter the axilla through its apex

formed by 1st rib (medially), clavicle (anteriorly), and scapula(posteriorly)


scapular anastamosis

anastomosis around the dorsal and costal surfaces of scapula

collateral circulation to upper extremity if there is a blockage to the arterial trunk between the thyrocervical trunk of the subclavian artery and the subscapular branch of the axillary artery

costal surface arteries: thoracodorsal branch of subscapular artery and lateral thoracic artery (both from axillary)

dorsal surface arteries: suprascapular branch of thyrocervical trunk (subclavian), dorsal scapular artery (subclavian), and circumflex scapular branch of the subscapular artery (axillary)


cubital fossa

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  • Superior: imaginary line connecting the medial and lateral epicondyles
  • Medial: pronator teres
  • Lateral: brachioradialis

Floor: brachialis and supinator

Roof: deep fascia and bicipital aponeurosis

Contents (from lateral to medial - BAM)

  • Biceps Tendon
  • Brachial Artery
  • Median Nerve

bicipital aponeurosis

protective function for brachial artery and median nerve in the cubital fossa

forms a fascial bridge, separating the artery and nerve from the median cubital vein (used for protection during blood sampling and IV injections into the median cubital or median basilica veins)


cubital tunnel

fascial tunnel formed by space between the medial epicondyle and olecranon process

floor: medial collateral ligament of elbow

roof: ligament of osborne

symptoms of entrapment of the superior ulnar collateral branch of brachial artery and ulnar nerve: increase with elbow flexion (taut ligaments decrease the diameter of tunnel)


elbow anastamosis

important for collateral circulation to radial and ulnar arteries if the brachial artery is blocked distal to the inferior ulnar collateral artery

arteries in anastomosis:

  • Middle collateral (of arteria profunda)
  • Radial collateral (of arteria profunda)
  • Superior ulnar collateral (of brachial)
  • Inferior ulnar collateral (of brachial)
  • Radial recurrent (of radial)
  • Anterior ulnar recurrent (of ulnar)
  • Posterior ulnar recurrent (of ulnar)
  • Interosseous recurrent (of posterior interosseous)

allen test

clinical test to evaluate the patency of blood supply from ulnar and radial arteries to the hand


potential areas for entrapment of the ulnar and radial arteries and their branches

  • radial artery: between heads of 1st and 2nd metacarpals and 1st dorsal interosseus muscle to enter the palmar surface
  • superficial palmar branch of radial artery: as it passes through the thenar muscles
  • ulnar artery: going deep to flexor digitorum superficialis with medial nerve through fascial tunnel
  • deep palmar branch of ulnar artery: between the pisiform and the hook of the hamate through the tunnel of guyon (under volar carpal and pisohamate ligaments)

fascia of arm

pectoral fascia (over proximal anterior arm/chest) & infraspinous fascia (over proximal posterior arm/chest) -> deltoid fascia (over deltoid, clavical, acromion, and spine of scapula) -> brachial fascia (humeral epicondyles and olecranon processes) -> antebrachial fascia (forearm) -> extensor and flexor retinaculae at wrist

bracial fascia is continuous with lateral and medial intermuscular septum


locations of intermuscular septums of arm and attached structures

lateral: from lower lateral lip of intertubercular groove, along lateral supracondylar ridge to lateral epicondyle

  • partial attachment to: triceps, brachialis, brachioradialis and extensor carpi radialis longus
    • blends with deltoid tendon
  • Perforated by radial nerve and radial collateral branch of arteria profunda brachii

medial: medial lip of intertubercular groove, along supracondylar ridge to medial epicondyle

  • Gives partial attachment to triceps & brachialis
    • blends with tendon of coracobrachialis
  • Perforated by ulnar nerve, superior ulnar collateral artery and posterior branch of inferior ulnar collateral artery

transverse septa separate deep and superficial muscles in anterior and posterior forearm


Autonomic nervous system

  • includes parts of CNS and PNS
  • innervates viscera, glands, blood vessels, and non-striated muscle
  • systems: sympathetic (SNS) and parasympathetic (PNS)
    • act in opposities (one system is activated, the other in inhibited)
  • target organs have both SNS and PNS innervation
    • except: peripheral blood vessels, sweat glands, and pilomotor muscles that have SNS only
  • always active: PNS= basal tone of gut, SNS= basal tone of arterioles

systems that are controlled by the SNS only

peripheral blood vessels

sweat glands

pilomotor muscles



a junction between two neurons in the Autonomic Nervous System in which storage, release, synthesis, and degradation of the neurotransmitters are done


somatic pathway

no peripheral synapses

primary neuron leaves CNS -> directly innervates effector organ

ex. muscle


Autonomic pathway

>1 peripheral synapse (2 or more neuron chain)

preganglionic neuron leaves CNS -> synapses with postganglionic neuron -> effector organ


parasympathetic nervous system (PNS)

  • Vegetative system (rest and digest) - involved in conservation of body energies
  • Reactions are generally localized- Occur right at or close to organ
  • Craniosacral Outflow- flow of energy is primarily between the head and sacrum

PNS actions

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  1. Decrease in heart rate
  2. vasoconstriction of coronary vessels
  • Respiratory
    1. Decrease in respiratory rate
    2. bronchoconstriction (vessels to bronchii vasodilate)
  • Gastrointestinal
    1. Increase in glandular activity
    2. increase in peristaltic activity of gut (increase in movement through digestive system)
    3. vasodilation in gut
    4. secretomotor for release of digestive enzymes
    5. relaxation (inhibition) of sphinctors of GI tract

Preganglionic and postganglionic nerve descriptions of SNS and PNS

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peripheral ganglia from cranial part of PNS

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  1. Ciliary- Associated with III (oculomotor)
  2. Pterygopalatine- Associated with VII (facial)
  3. Submandibular- Associated with VII
  4. Otic- Associated with IX

no ganglia associated with cranial nerve 10, even though it travels with the PNS


Ciliary ganglion

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from cranial nerve 3 (occulomotor)

2 effector organs (muscles) work together:

  • constrictor pupillae: constricts pupils
  • ciliary muscle: accommodation to thicken lens when pupil constricts

pterogopalatine and submandibular ganglia

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from cranial nerve 7 (fascial)

lacrimal gland: cry

submandibular and sublingual glands: salivary glands


otic ganglion

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from cranial nerve 9 (glossopharyngeal)

parotid gland: salivary gland next to ear


autonomic pathway for cranial nerve 10 (Vagus)

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postganglionic cell bodies are within walls of the viscera that they innervate

intestinal- increases activity up until the bend between the transverse and descending colon (does not include the descending colon or rectum, they are innervated by sacral plexus)

  • inhibit iliocecal sphincter: opens the valve between the small and large intestines

Sacral part of PNS

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  • carry preganglionic visceral fibers which branch off to form pelvic splanchnic nerves
    • are distributed to ganglia within the walls of the viscera
  • Functions:
    • visceromotor to rectum and bladder
    • inhibitory to (relaxes) sphincters of rectum and bladder
    • vasodilator to erectile tissue of genitalia
    • visceromotor to sigmoid colon and descending colon up to left colic flexure (in between descending and transverse colon)

sympathetic nervous system

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  • fight or flight- mobilization of body energies for increased activity
  • involved in mass responses- wider distribution than PNS
  • includes: paired sympathetic trunks on either side of spinal cord, their branches, plexuses, and collateral ganglia
  • thoracolumbar outflow- preganglionic cells from T1-L2/L3 (red in picture, since intermediate zone is only in T levels)

SNS Actions

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  • Vasomotor - general constriction of peripheral vessels with consequent increase (vasodilation) in blood to heart, muscles and brain
    • Increase in blood pressure, Increase in heart rate
  • Sudomotor- sweat
  • Pilomotor- erector muscles of hair
  • Pupillary dilation
  • Contraction of sphincters in GI track
    • Decrease in peristaltic activity of gut (movement through digestive system)
    • Relaxation of bladder muscle (inhibition of bladder sphincters)

processes of preganglionic neurons of SNS

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  • processes emerge from spinal cord and travel in spinal nerves and branch from VPR as white (due to myelination) rami communicans then go to 1 of 4 places
  • 1) synapse in corresponding ganglion of sympathetic trunk (shown in black at T1 level in picture)
  • 2) pass through corresponding ganglion and ascend or descend to synapse at a ganglion at a different level (in black at C8 level in pic)
  • 3) pass through corresponding ganglion and ascend or descend to at a different level or leave trunk at same level and emerge as splanchnic nerve
    • enters autonomic plexus and synapse in a collateral ganglion (black at T1 level in pic)
  • 4) pass through corresponding ganglion and travel directly to the adrenal gland to terminate on cells in adrenal medulla
    • results in secretion of epinephrine into circulating blood

processes of postganglionic neurons of SNS

processes may go to 1 of 4 places, but we only need to know:

  1. pass back into corresponding spinal nerve as gray (unmyelinated) rami communicans
    • distributed through ventral and dorsal primary rami then branch to blood vessels of skeletal muscle and skin, sweat glands, and piloerector muscles
      • these do not have PNS innervation
  2. emerge from the ganglion as a medial branch to be distributed to viscera

sympathetic nerves in trunk

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  • chains of interconnected ganglia are located on either side of the vertebral column from skull to coccyx
    • swellings are cell bodies connected via cords
    • preganglionic cells are only in thoracolumbar cord
      • white rami communicans only in levels T1-L2 (but fibers can continue beyond those levels and give input to gray rami)
    • gray rami communicans (postganglionic cells) are found at all spinal levels

cervical ganglia of sympathetic trunk

  • supply to head and neck: from T1-T3 pregang cells to one of the 3 cervical ganglia
  • Superior- largest, at C2-C3 level
    • send gray rami to upper 4 cervical spinal nerves for innervation to head and neck via internal carotid nerve
    • branches to cranial nerves IX, X, and XI to distribute to heart, larynx, and pharynx
  • Middle- smallest, C6 level
    • sends gray rami communicans to C5 and C6 spinal nerves to periphery (some fibers to upper extremity)
    • branches to thyroid gland, heart, trachea, and esophogus
  • Inferior (ce rvicothoracic or stellate ganglion)- usually fused with 1st thoracic ganglion
    • sends gray rami communicans to C7, C8, and T1 spinal nerves
    • receives white rami communicans from T1
    • branches to heart and blood vessels
    • primarily supplies SNS to the lower trunk of the brachial plexus

internal carotid nerve

  • derived from pregang cells at T1 cord level which synapse with postgang cells in superior cervical ganglion
  • carries postgang fibers into cranial cavity with the internal carotid artery (that supplies it)
  • distributes to blood vessels and sweat glands of head and neck, dilator pupillae, non-striated muscles in eyelids, and inhibits salivary glands
  • lesion at T1 cord level or anywhere along its path= Horner's syndrome
    • Pupillary constriction, ptosis (drooping of eyelid), enopthalmos (eyeball sinks into socket), and absence of sweating in face and neck
    • lose sympathetic innervation to head on same side as the damage to the cord

thoracic ganglia of sympathetic trunk

  • inferiorly passes under medial arcuate ligament to continue as lumbar sympathetic trunk
  • connected by spinal nerve by both white and gray rami communicans
  • branches to thoracic aorta, pulmonary plexus, and cardiac plexus
  • 3 pairs of splanchnic nerves which pass into adominal cavity:
    1. greater splanchnic nerve
    2. lesser splanchnic nerve
    3. least splanchnic nerve

lumbar ganglia of sympathetic trunk

continues as sacral sympathetic trunk behind common iliac artery

sends gray rami communicans to all lumbar spinal nerves

travels with femoral and obturator nerves to supply blood vessels, sweat glands, and piloerector muscles of thigh

4 lumbar splanchnic nerves: distribute to celiac, renal, intermesenteric, and superior hypogastric plexuses (body cavity of viscera)

pregang cells from T10-L2 cord levels supply the postgang cells to the lumbar and sacral plexuses to the Lower extremity


sacral ganglia of sympathetic trunk

sends gray rami communicans to sacral and coccygeal spinal nerves

travel with tibial and common peroneal nerves

supplies blood vessels, sweat glands, and piloerector muscles of leg and foot

pregang cells from T10-L2 cord levels supply the postgang cells to the lumbar and sacral plexuses to the Lower extremity


examples of plexuses of ANS

  1. cardiac plexus
    • branches of vagus nerve (PNS) and SNS nerves
    • SNS: increase HR and contractility, dilate coronary arteries
    • PNS: opposite of SNS
  2. pulmonary plexus
    • branches of vagus nerve (PNS) and SNS nerves (T2-T5)
    • SNS: bronchodiate, vasoconstrict in lungs
    • PNS: bronchoconstrict, vasodilate and increase secretions in lungs
      • PNS is overactive in asthma
  3. celiac plexus
    • greater and lesser splanchnic nerves (SNS) and branches from vagus nerve (PNS)
    • autonomic supply to abdominal viscera
  4. inferior hypogastric plexus
    • autonomic supply to pelvic viscera

higher centers involved in autonomic control

  • Hypothalamus- main control
    • regulation of body temperature, water balance, carbohydrate and fat metabolism, reproduction and sexual response, blood pressure, emotions and sleep
  • Brainstem Centers
    • reflex control of vital functions (respiration, bladder control, etc.)
    • Medullary and Pontine Reticular Formation- “Pacemaker neurons” - spontaneous discharge maintains tonic activity of efferents to viscera
  • Limbic System
    • integration of emotional state with motor and visceral activities (visceral response to emotions)
  • Cerebral Cortex
    • highest level of integration of somatic and visceral functions

visceral afferent fibers

  • primarily unmyelinated
  • involved in mediation of visceral sensations (pain, pressure, etc.)
  • carried into CNS by vagus nerve, splanchnic nerves, pelvic nerves, and other autonomic nerves
  • important in autonomic reflexes and in informing CNS about status of viscera
    • receptor in viscera (picking up sensation) -> visceral afferent -> integrating center in CNS -> visceral efferent (directions for organ) -> effector organ (smooth muscles and glands)

types of shoulder movements and normal end ranges of motion

  • Flexion - 150 - 1800
  • Extension - 50 – 600
  • Abduction - 150 - 1800
  • External rotation – 80-900
  • Internal rotation - 70 - 900
  • Horizontal abduction
  • Horizontal adduction

controls of glenohumeral motion

  • passive restraints:
    • capsule and ligaments
    • some bony stability
    • labrum
    • negative intra-articular pressure
  • active restraints
    • muscles and tendons
      • "stearing " muscles- rotator cuff, "power" muscles- other muscles that invoke the movement
      • muscle activity compresses the humeral head into the glenoid (a lot from deltoid)
  • interaction of passive and active restraints

bony geometry of glenohumeral joint


  • head is convex, completely covered in articular cartilage, and pointed 1350 from the longitudinal axis of the Humerus and is angled 300 posteriorly
  • glenohumeral joint capsule attaches to the anatomical neck
  • axillary nerve and posterior circumflex artery lie close to the medial aspect of the surgical neck (through quadrangular space)

glenoid fossa

  • concave surface that faces laterally, superiorly, and anteriorly
    • superior orientation provides a "shelf" for the Humerus to sit on
  • much smaller than the humeral head

glenoid labrum

fibrocartilage ring attached to the margin of the glenoid cavity

deepen and widens the cavity to improve congruency with the humerus

attached to the joint capsule- injury to the capsule often causes injury to the labrum


Name the capsuloligamentous structures of the glenohumeral joint

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  • capsule is in yellow
    • attachments- glenoid and labrum to anatomical neck of humerus
    • inferior capsule limits: elevation, is loose with arm at side
  • Glenohumeral ligaments:
    • Superior glenohumeral ligament (SGHL)- pink
    • Middle glenohumeral ligament (MGHL) - blue
    • inferior glenohumeral ligament (IGHL) complex- between black and white
      • anterior band- black
      • posterior band- white
  • Coracohumeral ligament
    • anterior and posterior bands

Superior glenohumeral ligament (SGHL)

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Superior glenohumeral ligament (SGHL)- pink

  • attachments- glenoid rim (1 o'clock) to anatomical neck near medial lip of intertubercular groove
  • limits: external rotation and inferior translation of the Humerus with arm at side (0o abduction)

Middle glenohumeral ligament (MGHL)

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  • Middle glenohumeral ligament (MGHL) - blue
    • attachments- glenoid rim (1-3 o'clock) to anatomical neck medial to the lesser tuberosity
    • limits: external rotation and inferior translation of Humerus with the arm at 45o abduction
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inferior glenohumeral ligament complex (IGHLC)

  • inferior glenohumeral ligament (IGHL) complex- between black and white (axillary pouch)
    • attachments: inferior 2/3 of glenoid to inferior 1/3 of humeral head
    • anterior band- black
      • attachments- glenoid rim (2-4 o'clock) to below the lesser tuberosity
      • limits: external rotation and inferior translation of Humerus with the arm at 90o abduction
    • posterior band- white
      • attachments- glenoid rim (7-9 o'clock)
      • limits: internal rotation with arm in any position of abduction

Coracohumeral ligament (C-H)

  • attachments: lateral end of coracoid process then splits into 2 bands:
    • posterior band: blends with supraspinatus tendon then inserts near greater tuberosity
    • anterior band: blends with subscapularis tendon to insert near the lesser tuberosity
  • limits: both limit inferior translation of humeral head
    • posterior: flexion
    • anterior: extension of glenohumeral joint

restraints to external rotation of glenohumeral joint

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  • 00 abduction (arm at side)- SGHL, C-H & subscapularis
  • 450 abduction- SGHL & MGHL
  • 900 abduction- anterior band IGHLC

restraints to internal rotation of the glenohumeral joint

  • 00 abduction- posterior band IGHLC
  • 450-900 abduction- anterior & posterior band IGHLC (whole complex)
    • posterior band rotates up, and anterior band rotates down

restraints to inferior translation of the glenohumeral joint

0o abduction- SGHL and C-L

90o abduction- IGHLC


movements of the glenohumeral joint in the scapular plane

  • scapular planes produce less tension for movements than cardinal planes, but movements are more reproduceable in cardinal planes
  • abduction/adduction- 120 degrees
    • runs anteriomedially to posterolaterally
    • abduction requires external rotation to allow the greater tuberosity to pass under the coraco-acromial arch >120o
  • flexion/extension- 120 degrees
    • flexion: anteriomedial, extension: posterolateral direction
    • end range of flexion requires internal rotation due to tension in posterior band of C-H ligament
  • internal/external rotation
  • horizontal abduction/adduction

arthrokinematics of glenohumeral motion

  • convex Humerus moving on concave glenoid- roll opposite glide
  • Abduction - Superior roll, inf glide
  • Flexion - Ant/sup roll, post/inf glide
  • Extension- post roll, Ant/sup glide
  • External rotation - Post roll, ant glide
  • Internal rotation - Ant roll, post glide
  • if the posterior/inferior capsule is too tight, or at end range of flexion- kinematics are altered and there is limited joint motion

prime movers of glenohumeral joint

  • Deltoid
  • Pectoralis major
  • Latissimus dorsi
  • Teres major
  • Biceps
  • Coracobrachialis
  • Triceps

rotator cuff muscles

  • Subscapularis
  • Supraspinatus
    • compression from having arm at side can reduce blood flow to the tendon and lead to degeneration
  • Infraspinatus
  • Teres Minor

force couples acting on glenohumeral joint

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transverse plane: subscapularis vs infraspinatus/teres minor (anterior vs posterior rotator cuff)

  • medial (subscap) vs lateral (infra) rotation
  • provides anterior and posterior balance to keep humeral head centered on glenoid

coronal plane: deltoid vs inferior rotator cuff (subscap, infra, teres minor)

  • upward rotation (deltoid) vs depression (inferior rotator cuff) of humerus

supraspinatus is not part of force couples


rotator cuff tears

  • supraspinatus: force couples maintained, normal strength and function possible
    • most common location for tear (in avascular zone)
  • supraspinatus/posterior cuff: essential force couples disrupted
    • weakness with external rotation, little active elevation possible
  • supraspinatus/subscapularis: essential force couples disrupted
    • weakness with internal rotation, little active elevation possible
    • may elevate scapula (hike shoulder) to compensate for lack of elevation
  • Massive Tear: essential force couples disrupted
    • weakness with external and internal rotation, little active elevation possible
    • shoulder may translate a lot superiorly with very little abduction without the rotator cuff muscles

suprahumeral (subacromial) space borders

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  • Confined space bounded by:
    1. head of humerus inferiorly
    2. coraco-acromial arch superiorly. Coraco-acromial arch formed by:
      • coracoid process, coraco-acromial ligament, acromium, inferior surface of A-C joint

contents of suprahumeral (subacromial) space (from inferior to superior)

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  1. head of humerus
  2. long head of biceps tendon
  3. superior capsule
  4. supraspinatus
  5. upper margins of subscapularis and infraspinatus
  6. sub-acromial/sub-deltoid bursa
  7. inferior surface of coraco-acromial arch

clinical relevance of subacromial (suprahumeral) space

  • impingement is of the structures in the subacromial space in between the greater tuberosity and coraco-acromial arch
    • impingement results in inflammation and paine ("painful arch" between 90-120o of abduction until the greater tuberosity clears)
    • primary impingement: structural stenosis (narrowing) of subacromial space (bony abnormality on acromion, clavicle, or Humerus)
    • secondary impingement: abnormal kinematics causing functional stenosis
  • Avoidance of impingement during elevation/abduction of arm requires:
    • external rotation of humerus to clear greater tuberosity
    • upward rotation of scapula to elevate lateral end of acromion
    • "thumbs up" during elevation minimizes impingement

scapulothoracic (S-T) joint

  • physiological joint (not a synovial joint) between scapula and posterolateral corner of thorax
  • scapula is suspended on thorax by scapulothoracic muscles on an anteriomedial to posterolateral plane that forms a 30o angle with frontal plane
    • movement is in scapular plan
    • provides 60o of total elevation (+120o from g-h joint =180 total elevation)
  • consists of 2 spaces:
    1. between serratus anterior and scapula/subscapularis
    2. between serratus anterior and thoracic wall

scapulothoracic motion and coordinates

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  • Protraction/retraction- anterior/posterior tipping
    • X (medial-lateral) axis
  • Upward/downward rotation of genoid cavity
    • Y (anterior-posterior) axis
  • Elevation/depression
    • Z (vertical) axis

scapulothoracic muscles

  • Posterior:
    • Trapezius
    • Serratus anterior
    • Rhomboids
    • Levator scapulae
  • Anterior:
    • Pectoralis minor
    • Subclavius

force couples at scapulothoracic joint

  • Serratus anterior produces anterio-lateral movement of inferior angle
  • Upper trapezius pulls scapula medially
  • greater protraction with flexion
  • greater lateral rotation with abduction

Acromioclavicular (A-C) joint

  • articulation between the antero-medial border of acromion and distal end (lateral) of clavicle
  • planar joint- allows sliding between joint surfaces (not very congruent joint)
    • intra-articular disc helps with congruency (only present in 1/3 of people)
  • other components of A-C joint:
    • capsule, A-C ligaments, coracoclavicular ligaments (conoid (medial), trapezoid (lateral))

A-C joint ligaments

  • acromio-clavicular ligament- from clavicle to acromion
    • reinforces the A-C joint capsule superiorly
  • coracoclavicular ligaments- coracoid process to inferior surface of clavicle
    • most important structure to maintain congruity of the A-C joint
    • when ruptures: distal end of clavicle elevates and scapula drops down
    • 2 parts:
      • conoid ligament: fan shaped with apex pointing inferiorly; in the frontal plane
      • trapezoid ligament: medial border of upper surface of coracoid process to the inferior surface of the clavicle; plane is a right angle to the conoid lig.

movements in the A-C joint

  • Axial rotation of clavicle (spin)~ 30o necessary for upward rotation of scapula on thorax
    • Rotation of clavicle on scapula
  • Angulation between scapula & clavicle
    • During protration/retraction
  • more likely to have too much motion than decreased motion

sternoclavicular (S-C) joint

articulation between proximal (medial) end of clavicle and clavicular notch of manubrium of sternum and cartilage of 1st rib

sellar (saddle) joint

consists of:

  • Joint capsule
  • Anterior & posterior S-C ligaments
  • Intra-articular disc- between clavicle and 1st rib
    • greater movement between clavicle and disc than disc and manubrium
  • Interclavicular ligament
  • Costoclavicular ligament

capsuloligamentous structures of S-C joint

  • capsule: thick anteriorly/posteriorly, thin superiorly/inferiorly
  • anterior sterno-clavicular ligament: from proximal end of clavicle to sternum on the anterior side
  • posterior sterno-clavicular ligament: from proximal end of clavicle to sternum on posterior side
  • inter-clavicular ligament: connects the sternal ends of the clavicles
  • costoclavicular ligament: upper border of 1st rib to inferior surface of clavicle

movement of S-C joint

  • elevation and depression of distal end of clavicle (convex clavicle surface on manubrium -> roll and glide in opposite directions)
    • elevation: clavicle rolls superior, inferior/lateral glide
  • protraction and retraction of distal end of clavicle(concave clavicle surface on manubrium -> roll and glide in same direction)
    • protraction: anterior rotation, anterior glide
  • axial rotation of clavicle (spin) about its long axis

scapular rotation

must include movement at S-C, S-T, and A-C joints (closed kinetic chain)

180 deg elevation = 120 deg g-h motion and 60 deg s-t motion

  • Phase I (first 30o of upward rotation)
    • Upper & lower portions of trapezius & serratus anterior produce upward rotatory force on scapula
    • Motion at A-C joint prevented by coracoclavicular ligament
    • internal Rotation of scapula occurs as elevation of clavicle at S-C joint
    • motion of scapula occurs about an axis that passes through base of spine of scapula
  • Phase II (final 30o of upward rotation)
    • Further motion at S-C joint prevented by costoclavicular ligament
    • Continued upward rotation of scapula pulls on coracoclavicular ligament causing posterior rotation of clavicle (A-C joint) which allows further upward rotation of scapula
    • motion of scapula occurs about an axis that passes through the acromion

why scapular rotation is necessary

  • Enhance glenohumeral stability
    • by keeping scapula under humeral head
  • Elevate acromion to avoid impingement
  • Maintain effective length tension relationship of scapulohumeral muscles

Features of Distal humerus

  • trochlea (medial) and capitulum (lateral)are covered by articular cartilage over 300o
  • medial lip of Humerus is more prominent and projects more distally
    • Trochlear-capitellar articular axis is slightly superior on the lateral side and more distal on the medial side
    • reason hand comes to chest in flexion
    • valgus orientation with radius and humerus
  • condyles have a 30o anterior rotation in relation to humeral axis
    • trochlear notch has the same 30o angle to complement (full congruency)

humeroulnar and humeroradial articulation

  • Humeroulnar articulation - between the trochlea and the trochlear notch
    • flexion/extension
  • Humeroradial articulation - between the capitulum and the head of the radius
    • pronation/supination, flex/ ext

elbow joint classification

  • on of the most congruent joints
    • 50% stability from bony architecture, 50% from soft tissue (ligaments, anterior capsule, muscles)
  • hinge (ginglymus) synovial joint
  • cubital complex= 1 joint + 1 capsule
  • flexion/extension and pronation/supination

carrying angle of elbow

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angle between Humerus and ulna is usually valgus by 14o+

due to orientation of trochlear groove and distal projection of medial edge of trochlea of humus

causes a lateral, valgus orientation of the ulnar shaft

allows the elbow to come to center of body when you flex


capsule of elbow

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completely encloses joint and blends with annular ligament

loose to allow free movement

sides are reinforced by collateral ligaments

anterior capsule and collateral ligaments are major soft tissue stabilizers

lined with a synovial capsule (including annular ligaments and continues as sacciform recess on the neck of radius- allows the radius to rotate within the annular ligament without tearing the synovial capsule)


fat pads of cubital complex

3 fat pads situated between fibrous capsule and synovial membrane:

over olecranon fossa

over coronoid fossa

over radial fosse


bursae of cubital complex

  • Subcutaneous olecranon bursa- between skin and olecranon process
  • Subtendinous olecranon bursa- between tendon of triceps and olecranon process
    • Student's elbow- inflammation from too much friction/pressure on elbow
  • Bicipitoradial bursa - between biceps tendon and radial tuberosity
  • Radioulnar bursa- between extensor digitorum, radiohumeral joint, and supinator
  • main function: reduce friction (mostly near tendons)

medial complex of elbow

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formed by medial (ulnar) collateral ligament-originates on anterioinferior medial epicondyle

maintains medial joint stability to valgus stress

3 bundles

  • anterior- strongest and stiffest, primarily stabilizes from 30-120o
    • anterior band- taut close to extension (30-60o)
    • deep middle portion- isometric during movement
    • posterior band- taut in flexion (60-120o)
  • posterior- co-restraint of elbow at terminal elbow flexion
  • transverse- little role in elbow stability

radial head is a secondary ulnohumeral joint stabilizer to valgus loads (hits against capitulum)

flexor and pronator muscles provide additional support


MCL injuries


  • Chronic attenuation (throwing athletes )- combination of valgus and external rotation force, many repitions
  • Posttraumatic , usually after a fall onto an outstretched arm (FOOSH)- associated injuries include fractures of radial head, olecranon, or medial epicondyle
  • MCL injury can be iatrogenic (human caused-excessive medial epicondylectomy for cubital tunnel syndrome may cut the MCL)

lateral complex of elbow

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Lateral collateral Ligament (LCL)- Y shaped, composed of:

  1. radial collateral ligament-from lateral Humerus to annular ligament
  2. lateral ulnar collateral ligament- from lateral epicondyle to broad insertion on proximal ulna
  3. annular ligament- anterior radial notch of ulna and wraps around the radial head to the posterior radial notch
    • also in proximal radioulnar joint
  4. accessory lateral collateral ligament
  • Key stabilizer for varus stress and posterolateral stability (rotation)
  • primary restraint to maintain ulnohumeral and radiocapitellar joints in reduced (flexed and supinated) loaded position
    • instability results in subluxation of ulna and rotation of radius on capitellium from Humerus (FOOSH traumatic injury, RU joint is undisturbed)
  • secondary restraints are extensor muscles, their fascial bands and intermuscular septa

ligaments of proximal radioulnar joint (RUJ)

annular ligament- wraps around proximal radius and inserts on radial notch of ulna

  • also in lateral complex of elbow

quadrate- neck of radius to inferior radial notch of ulna, just under annular ligament

  • anterior fibers are taut during forearm supination
  • posterior fibers are taut in pronation

connective tissue of middle radioulnar joint

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not actual joint: shafts of radius and ulna are connected by interosseus membrane (IM) syndesmosis and oblique cord

  • IM (red)- provides stability for superior and inferior RUJ
    • resists proximal displacement of radius on ulna during pushing movements
  • Oblique cord (green)- resists distal displacement of radius during pulling

distal radioulnar joint capsule

fibrous capsule encloses joint- weak anterior and posterior bands

capsule lined with synovial membrane/capsule

sacciform recess- proximal extension of synovial capsule to accommodate twisting during pronation


ligaments of distal radioulnar joint

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anterior and posterior radioulnar ligaments (both weak)

significant DRUJ stability is provided by:

  1. triangular fibrocartilage complex
  2. extensor carpi ulnaris
  3. interosseous ligament
  4. pronator quadratus
  5. associated forearm muscles

elbow flexion and extension

in ulnohumeral and radio-capitellar joints

  • extension: to 0 degrees or with hyperextension with ligamentous laxity
    • limited by bony contact (olecranon) and tension of anterior muscles and ligaments
  • flexion
    • passive- limited by bony contact and posterior soft tissue tension
    • active- limited by position of contracting anterior muscles

arthrokinematics of elbow

  • Distal humerus has 2 convex surfaces: trochlea & capitulum
  • Proximal ulna has concave trochlear notch and Proximal radius has concave proximal portion of radial head
  • non-WB: concave on convex= same direction
  • During flexion there is an anterior ( volar ) roll and glide of ulna and radius on humerus
  • During extension there is a posterior (dorsal) roll and glide of ulna and radius on humerus

movements of radioulnar joint (not arthrokinematics)

  • physiological movements: pronation and supination
    • rotation of head of radius on capitulum about its axis
    • supination: radius and ulna are parallel, ulna is shorter than radius (ulnar-negative)
      • limited by tension in interosseous membrane and volar capsule of DRUJ
    • pronation- radius and ulnar are crossing
      • ulna is "relatively" longer than radius (ulnar-positive)
  • accessory movements:
    • gliding of radial head relative to capitullum
    • during pronation: lateral displacement of radial head due to larger anteroposterior head diameter

artrokinematics of radioulnar joint

Proximal RU:

  • Ulna has concave radial notch; radius has convex radial head
  • Pronation : anterior roll and posterior glide of radial head on proximal ulna
  • Supination : posterior roll and anterior glide of radial head on proximal ulna

Distal RU

  • Medial aspect of radius is concave AP (ulnar notch); radial aspect of distal ulna is convex AP
  • Pronation : anterior roll and glide of distal radius on ulnar head
  • Supination : posterior roll and glide of distal radius on ulnar head

elbow dislocations

  • Dislocations may be simple or complex (w fractures)
    • associated fractures are more common in children and elderly
  • Posterior dislocation (most common): due to fracture of coronoid process or humeral condyles (compressive force with extended elbow)
  • Anterior dislocation: involve olecranon fracture or triceps disruption (require surgical correction)
  • Brachialis is very close to anterior capsule and calcium deposits can form there during rehabilitation

tennis elbow

inflammation (small microtears) of the lateral epicondyle and common wrist extensor tendon due to repeated strenuous contraction

principally in extensor carpi radialis brevis

may involve radioulnar bursa (between extensor digitorum, radiohumeral joint, and supinator)


golfer's elbow

inflammation of medial epicondyle and common wrist flexor tendon

due to overuse- similar to tennis elbow for the lat condyle


medial nerve entrapment

  • Median and anterior interosseous nerves pass through the 2 heads of pronator teres
    • The 2 heads are joined by the tendinous arch of the FDS
  • Median nerve can be entrapped proximally (pronator syndrome) or distally (anterior interosseous nerve syndrome)

compartment syndrome in forearm

Due to decreased compartmental size (casts) or increased content (bleeding, swelling, muscle hypertrophy)

  • Dorsal Compartment Syndrome
    • Weakness of thumb and finger extensors
    • Painful passive thumb and finger flexion (stretching muscles)
    • Tenseness of the dorsal forearm
    • No sensory loss because superficial branch of radial n. does not enter dorsal compartment
  • Volar Compartment Syndrome
    • Sensory loss - ulnar and median nerves
    • Weakness of thumb and finger flexors
    • Painful passive thumb and finger extension
    • Tenseness of the volar forearm

components (joints) of the wrist joint

  • Distal RU Joint
  • Radiocarpal Joint – Wrist Joint
  • Intercarpal Joints (Midcarpal)
  • Carpometacarpal Joints
  • Intermetacarpal Joints

radiocarpal joint- wrist proper

card image
  • proximal= radius and articular disk over ulna, distal= scaphoid, lunate, triquetrum
  • Condyloid (ellipsoid) synovial joint
    • articular disc is concave, proximal carpals are convex
  • flexion/extension, adduction/abduction, and circumduction
  • ulnar variance (ulnar negative)= radial styloid is 1cm distal to ulnar styloid
    • limits radial deviation

colles fracture

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  • most common distal radius fracture
  • FOOSH fracture of distal radial metaphysis
    • fractured distal fragment points in the palmar direction and the hand and writ are dorsally displaced
  • common in adults, rare in children
  • usually occurs within 2cm from the articular surface

triangular fibrocartilage complex (TFCC)

  • between the distal ulna and carpus (prox row carpal bones)
  • force-transmitting and stability
  • Consists of:
    • articular disk
      • biconcave (volar and dorsal aspects are thick and center is thin- more ulnar negative wrists have thicker disks)
      • inserts into ulnar styloid
      • blood supply is greater in the periphery- healing capacity
    • distal radio-ulnar ligaments, meniscal homolog, ulnolunate and ulnotriguetral ligaments, extensor carpi ulnaris sheath, and ulnar capsule
  • carries 20% of axial load in wrist (radial side carries 80%)

force transmission across wrist

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  • Compressive forces:
    1. Capitate
    2. Scapholunate junction
    3. Distal radius
    4. TFCC
  • Removal of TFCC reduces load on ulna by 12%
  • Increase in ulnar negative variance may cause decreased vascular supply to the Lunate (Kienbock's disease)

Kienbock's disease

  • Avascular necrosis (decreased vascular supply) of the lunate
  • Affects young adults
  • Related to repetitive trauma (martial arts, handball, volleyball)
  • Ulnar negative variance is a risk factor

radiocarpal articular capsule and ligaments

card image
  • from distal radius and ulna to prox row of carpal bones
  • lined by synovial membrane
  • strengthened by:
    • radial carpal ligament- radius to scaphoid and trapezium
    • ulnar carpal ligament- ulna to pisiform and triquetrum
    • dorsal/volar radial/ulnar collateral ligaments

radiocarpal, intercarpal, CMC, and IMC joints blood and nerve supplies

all joints have:

  • Blood – articular arteries from dorsal and palmar carpal arterial arches
    • CMC only: add metacarpal arteries
  • Nerve – from:
    • anterior interosseous branch of median n.
    • posterior interosseous branch of radial n.
    • dorsal and deep branches of ulnar nerve.

intercarpal joints

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  • between each of the neighboring carpals
    • midcarpal joint- between prox and distal row
    • pisotriquetral joint- between pisiform and triquetral
  • plane synovial joint
  • sliding movements- increases mainly flexion and radial deviation
    • much more sliding between carpals from dist and prox rows than between carpals of the same rows
    • can look like rotation in the medial portion of the midcarpal joint (sometimes referred to as a Condyloid joint)
  • vascular supply is mostly through ligaments and branches of the radial artery

intercarpal capsule and ligaments

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  • one capsule lined by a synovial membrane for the entire intercarpal joint
    • Pisotriquetral joint has its own fibrous and synovial cavity
  • Interosseous (intercarpal) ligaments
    • connecting proximal row carpals and distal row carpals
    • very strong connecting carpals in the same row, not very string between prox and distal rows
  • Palmar intercarpal ligaments
  • Dorsal intercarpal ligaments

scapholunate and lunotriquetral tears

card image
  • Scapholunate tears
    • FOOSH with ulnar deviation, SL lig is disrupted (volar)
    • Small tears may not result in instability (cause of ganglion cyst that should go away on its own)
    • Large tears cause scapholunate dissociation
  • Lunotriquetral tears
    • Less common, LT lig is disrupted (dorsal)

wrist closed and open packed positions

Close Packed: full extension (all ligaments are taut) or radial deviation.

Open Packed: slight flexion


wrist movements and axes

card image
  • 2 Axes (2 df):
  • Flex/ ext: coronal axis between lunate and capitate; sagittal plane of motion
    • flexion: anterior (volar) roll, posterior glide: + midcarpal movement
      • Limited by dorsal radiocarpal lig.
    • ext: posterior (dorsal) roll, anterior glide: + radiocarpal
      • Limited by volar radiocarpal and ulnocarpal lig.
    • distal carpals glide in the same direction the hand rolls (prox row= convex, dist row= concave)
  • Rad/ulnar dev: sagittal or A-P axis between lunate & capitate; frontal plane of motion
    • radial dev: distal carpals move radially, prox move towards ulna
      • limited by: bony contact of radius and carpal bones, and stress on the UCL
    • ulnar dev is opposite of rad dev and limited by stress on the RCL
  • Circumduction: polyaxial (axis keeps changing)

carpometacarpal (CMC) and intermetacarpal (IMC) joints- fingers 2-5

card image
  • Digits II-V = Plane synovial; sliding
    • cavity continuous with intercarpal
  • amount of motion increase as you move from 2nd -> 5th digit
    • 2nd and 3rd: immobile (highly congruent),4th: glide in flex/ext, 5th: 10-20 deg flex/add
  • closed packed: full fist
  • open packed: neutral
  • interosseous ligaments in between bones, dorsal and palmar ligaments above and below

carpometacarpal (CMC) and intermetacarpal (IMC) joints of thumb

  • CMC
    • saddle synovial joint- angular movements in any plane
    • flex/ext, abd/add, opposition
    • prone to osteoarthritis due to repetitive use
    • articular capsule is loose to allow for movement and is separate from the rest of the carpus
    • closed packed: opposition
    • open packed: neutral

extensor tendon synovial sheaths

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located in osseofibrous canals

only extend slightly before and after the retinaculum

reduce friction between tendons and walls of canals


extensor tunnels at the wrist (lat -> med)

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  1. T1- Abductor pollicis longus & extensor pollicis brevis
    • most common tendonopathy in the wrist from repetitive motions causing shear stress on the tendons
  2. T2 - Extensor carpi radialis longus & brevis
    • inflammation at crossing of muscles in T1 and T2 from sports with forceful repetitive flex/ext (tender, "squeky" during wrist flex/ext)
  3. T3- Extensor pollicis longus
  4. T4- Extensor digitorum & Extensor indicis
  5. T5- Extensor digiti minimi
  6. T6- Extensor carpi ulnaris

anatomical snuff box borders and floor

Anterior border: abductor pollicis longus and extensor pollicis brevis (T1)

Posterior border: extensor pollicis longus(T3)

Floor: scaphoid & trapezium


flexor tendon synovial sheaths

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2 walls of synovial membrane inside the tunnels to cover the flexor tendons all the way to their final attachment

4 pulleys and 3 intervening cruciate attachments hold the sheaths and tendons so they are close to the bones

protects and nourishes the tendons


carpal tunnel

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  • Roof - Transverse Carpal Lig (same as flexor retinaculum): from trapezium/scaphoid to hamate/pisiform
  • Floor: Palmar Carpal Arch
  • Contents: Median nerve, FDS III & IV, FDS II & V, FPL, FDP
  • carpal tunnel syndrome: decreased tunnel size compresses the median nerve (radial side of hand)

guyton's tunnel/canal

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  • Roof: Volar carpal lig. (part of flexor retinaculum)
  • Floor: Transv. Carpal and pisohamate ligs.
  • Walls: Pisiform and hook of hamate
  • Contents: Ulnar n. & artery

basic hand functions

  • both sensory and motor (fine motor control)
  • essential function: prehension (gasping/holding)
    • key: thumb orientation and rich supply of sensory receptors

arches of the hand

  • Longitudinal
    • Carpometacarpo-phalangeal arches (along fingers)
  • Transverse
    • Proximal transverse – carpal arch
    • Distal transverse – level of metacarpal heads
  • Oblique
    • Thumb during opposition with other fingers

MCP joints

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Condyloid joints (2 degrees of freedom)- oval convex MC had, oval concave base of phalanx

  • Flex/Ext - Sagittal plane about transverse axis
  • Abd/Add - Frontal plane about A-P axis
  • Circumduction
  • thumb has 2 extracapsular sesamoid bones on volar plate where the FPL glides
  • capsule: continuous volarly with volar plate
    • lax in extension, taut in flextion
  • ligaments: 2 collateral, 2 accessory, and volar plate, transverse metacarpal
  • closed pack: full flexion, open pack: slight flexion

MCP ligaments

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  • Collateral:
    • Strong, oriented obliquely
    • Tension increases with flexion
    • Resist Abd/Add
  • Accessory:
    • In flexion firmly holds volar plate against volar surface of MC head
  • Volar Plate
    • Attachments: palmar side from MC head to base of prox phalanx
    • loosely attached at MC, firmly attached at prox phalanx
    • function:
      • Ext: increases contact surface with MC head, resists hyperextension
      • Flex: glides proximally, prevents flexor tendon pinching
  • Transverse Metacarpal Ligament
    • blends with volar plate
    • connects adjacent lateral borders of 2-5 digits
    • forms tunnel that surrounds flexor tendons
    • facilitates adaptability to size and shape of objects

IP joints 2-5

  • Bicondylar joints (1 degree of freedom)- biconvex head of phalanx, biconcave base
  • transverse axis= flex/ext
  • similar capsule and ligaments to MCP, but no transverse ligament
  • PIP: volar plate has thick distal insertion and 2 check ligaments proximally
    • strong ligaments prevent hyperextension
    • reinforced by pulleys of flexor sheath
    • ruptures occur in the thicker distal insertion (allowing hypertext.)
  • digits flex towards thumb (5 moves more than 2)= tighter grip on ulnar side of hand
  • closed pack: full ext, open: slight flexion

extensor expansion

  • broad, flat aponeurotic band composed of extrinsic extensor tendons (ED, EI, EDM) that continues as central band
  • 2 lateral bands formed by the tendons of the interosseus and lumbrical muscles
    • lateral bands come from the palmar side then cross on to the dorsal side over the PIP
    • lat bands flex MCP, extend DIP and PIP
  • hood is on the dorsal side over the PIP and DIP joints

mallet finger

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Rupture at the terminal extensor tendon (extensor mechanism) or bony avulsion at its attachment into distal phalanx

line of pull is disrupted- cannot extend DIP joint


extensor expansion dysfunction (swan-neck and boutonniere deformities)

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  • swan-neck
    • subluxation of lateral bands
    • damage to volar plate of PIP
    • causes hyperextension of PIP which causes the lateral bands to slide into the dorsal side
    • can no longer pull DIP joint (flexed, cannot ext)
  • Boutonniere
    • injury to the central slip with inferior subluxation of lateral bands
    • puts middle phalanx into flexion and distal phalanx into hyperextension

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