MSK Session 2: arm, cubital fossa, limb development

Question 1

Biceps brachii origin?

Answer 1

Short head: coracoid process

Long head: supraglenoid tubercle

Question 2

Biceps brachii insertion?

Answer 2

Radial tuberosity and bicipital aponeurosis (forearm fascia)

Question 3

Biceps brachii innervation?

Answer 3

Musculocutaneous
C5,6
Mainly C6. Tap on biceps tendon tests spinal cord segment C6

Question 4

Biceps brachii action?

Answer 4

Supination
Flexion at elbow and shoulder
Short head resists shoulder dislocation

Question 5

Coracobrachialis origin?

Answer 5

Deep to biceps brachii. Coracoid process

Question 6

Corachobrachialis insertion?

Answer 6

Middle 1/3 of medial surface of humerus

Question 7

Corachobrachialis innervation?

Answer 7

Musculocutaneous

C5,6,7 (mainly C6)

Question 8

Corachobrachialis action?

Answer 8

Flexor at shoulder, helps ADduction, resists shoulder dislocation

Question 9

Biceps tendon rupture?

Answer 9

Tendon ruptures rare but this one of the commoner ones.
Long head tendon ruptures, produces characteristic sign on flexion of elbow with a bulge in the muscle belly: Popeye sign
Not much weaker as brachialis and supinator can still carry out the same actions

Question 10

Brachialis origin?

Answer 10

Deep to biceps, more distal

From distal half of anterior surface of humerus

Question 11

Brachialis insertion?

Answer 11

Coranoid process and ulnar tuberosity

Floor of cubital fossa

Question 12

Brachialis innervation?

Answer 12

Musculocutaneous
C5,6 (mainly C6)

AND
A small lateral portion innervated by radial nerve (C6-8)

Question 13

Brachialis action?

Answer 13

Flexes at elbow

Question 14

Location of heads of triceps brachii?

Answer 14

Medial head deep, covered by the long and lateral heads

Question 15

Insertion of triceps brachii?

Answer 15

Converge to a single tendon that attaches to the olecranon

Question 16

Origin of triceps brachii?

Answer 16

Long head: infraglenoid tubercle of scapula
Lateral head: posterior surface of humerus, superior to the radial groove
Medial head: posterior surface of humerus, inferior to the radial groove

Question 17

Innervation of triceps brachii?

Answer 17

Radial nerve
C6,7,8 (mainly C7 and C8)
Tap on triceps tendon tests spinal nerve segment C7

Question 18

Action of triceps brachii?

Answer 18

Extension at elbow

Long head resists dislocation of humerus during ADduction

Question 19

When in embryological development do the limbs develop?

Answer 19

Week 4 of gestation
Upper limb first, lower usually 2-3 days behind
Includes pectoral and pelvic girdles
Well-differentiated by week 8

Question 20

From where does the appendicular skeleton develop?

Answer 20

Limb buds that develop from the activation of mesenchymal cells in the somatic layer of the lateral mesoderm

Question 21

Describe the basic steps in limb formation

Answer 21

Limb buds appear on the ventrolateral body wall due to activation of mesenchymal cells in the somatic layer of the lateral plate mesoderm
Extent ventrally (from the front)
Elongation through proliferation of the mesenchyme core
Primordia of hands and feet develop and limbs adopt their adult structure

Question 22

What constitutes limb buds?

Answer 22

Undifferentiatted mesenchyme (core)
Apical ectodermal ridge (tips)

Question 23

How is the AER formed?

Answer 23

Thickening of distal border of limb

Question 24

How does the AER allow development of limbs from proximal to distal?

Answer 24

Cells furthest from the AER (proximal mesenchyme) differentiated into cartilage and muscle, as they are too far away to receive signals
Keeps mesenchyme underlying it undifferentiated so that elongation occurs
Final stage is appearance of paddles, then AER begins to regress

Marks boundary between dorsal and ventral limb ectoderm.

Question 25

Limb development order?

Answer 25

1. Stylopod (humerus and femur) 2. Zeugopod (radius, ulna, tibia, fibula) 3. Autopod (carpals, metacarpals, digits, tarsals, metatarsals)

Question 26

Zone of polarising activity?

Answer 26

Signalling centre at posterior base of limb bud Responsibilities: 1. Maintains the AER 2. Generates the anterior-posterior axis (asymmetry) of limbs

Question 27

Describe the axes in limb development

Answer 27

A-P axis: from 1st to 5th digits. Anterior=head, posterior=tail Dorsal: back of hand and top of foot Ventral: palm of hand and sole of foot Proximal-distal axis: base of limb to tips of digits

Question 28

What factors control axial specification?

Answer 28

A-P axis: ZPA P-D axis: AER D-V axis: ectodermal

Question 29

Describe the rotational changes in the upper and lower limb in week 7

Answer 29

Upper limb: rotates 90% LATERALLY so extensor muscles are on the lateral and posterior surfaces and lateral thumbs= position Lower limb: rotates 90% MEDIALLY placing extensor muscles on anterior side and the big toe medially

Question 30

Digital rays?

Answer 30

Mesenchyme condensations in plates that cause hyaline cartilage models to form AER influence decreases and it regresses Apoptosis of tissue between digits AER breaks up except at the tips of digital rays Remnants between fingers-webbing Joints formed in the cartilgainous condenssations and a joint interzone is induced

Question 31

How does bone form embryologically?

Answer 31

Signals from the AER to remain undifferentiated stop Lateral plate mesoderm condenses and differentiates Cartilage model forms Endochondral ossification

Question 32

Endochondral ossification?

Answer 32

Primary ossification centres appear in diaphyses (shafts) of long bones by W12 Progresses towards end of cartilage model Secondary ossification centres form as blood vessels invade the epiphyses Bone growth is maintained by epiphyseal plates (cartilage forming regions)

Question 33

Amelia?

Answer 33

Complete absence of one or more limbs

Question 34

Meromelia?

Answer 34

Partial absence of limb structures Phocomelia: absence of long bones. Rudimentary hands are attached to trunk by small, irregular bones Micromelia: all segments present but abnormally short

Question 35

Syndactyly?

Answer 35

Fusion of two or more digits Range from connective tissue fusion to bony fusion Failure of mesenchymal apoptosis

Question 36

Brachydactyly?

Answer 36

Shortened digits

Question 37

Polydactyly?

Answer 37

Recessive trait causing extra digits | Usually without proper muscle connections, usually bilateral

Question 38

Ectrodactyly?

Answer 38

Absence of a digit, usually bilateral

Question 39

How does limb musculature form?

Answer 39

Day 20 onwards: paraxial mesoderm creates somites 44 pairs formed, but regress until 31 pairs remain (31 spinal nerves in adult) Myogenic precursors (from dorsolateral cells of somites) migrate into limbs Initially segmented by somites from which derived Then combine into two common muscle masses around skeletal elements Further splittings and fusions Pattern determined by the connective tissue derived from lateral plate mesoderm

Question 40

Which directions contain which types of muscles?

Answer 40

Ventral-flexor Dorsal-extensor In upper limb: flexors anterior and extensors posterior (lateral rotation) In lower limb: flexors posterior and extensors anterior (medial rotation)

Question 41

Nerve involvement in embryology?

Answer 41

Spinal nerves enter limb buds early in development Upper limb buds-opposite caudal cervical spine segments Lower limb buds-opposite lumbar and sacral spine segments

Question 42

How does the brachial plexus arise?

Answer 42

Muscles compartmentalised and nerves grow in common muscle masses Anterior divisions for ventral compartment-form medial and lateral cords (supply flexors) Posterior divisions for dorsal compartment-form posterior cord (supply extensors)

Question 43

Contents of cubital fossa?

Answer 43

``` TAN-tendon artery nerve (medial to lateral) Really Need (Radial Nerve) Beer To (Biceps Tendon) Be At (Brachial Artery) My Nicest (Median Nerve) ``` Radial nerve not always considered a part of it

Question 44

Borders of cubital fossa?

Answer 44

Superior: imaginary line between the humeral epicondyles Medial: lateral border of pronator teres Lateral: medial border of brachioradialis

Question 45

Floor and roof of cubital fossa?

Answer 45

Floor: brachialis (proximal) and supinator (distal) muscles Roof: skin and fascia of bicipital aponeurosis

Question 46

Which vein is part of the superficial roof of the cubital fossa and what is its clinical relevance?

Answer 46

Median cubital vein Connects basilic and cephalic veins Venepuncture

Question 47

Describe the progress of the basilic vein

Answer 47

Originates from dorsal venous network of hand Ascends medial aspect of upper limb At border of teres major moves deep and combines with brachial veins forming axillary vein

Question 48

Describe the course of the cephalic vein

Answer 48

Arises from dorsal venous network of hand Ascends antero-laterally Passes anteriorly at elbow (joined with basilic in median cubital) Passes between deltoid and pec major and enters axilla through clavipectoral triangle Terminates by joining axillary vein

Question 49

Where can the brachial pulse be palpated?

Answer 49

Immediately medial to the biceps tendon in cubital fossa

Question 50

What type of fracture is a supraepicondylar fracture, and what are the complications?

Answer 50

Transverse: spans between the two epicondyles from falling on a flexed elbow Fragments may damage: median or radial nerves, or brachial artery (may cause ischaemia of forearm causing Volkmanns contracture: uncontrolled flexion)