MSK Session 2: arm, cubital fossa, limb development Flashcards
Biceps brachii origin?
Short head: coracoid process
Long head: supraglenoid tubercle
Biceps brachii insertion?
Radial tuberosity and bicipital aponeurosis (forearm fascia)
Biceps brachii innervation?
Musculocutaneous
C5,6
Mainly C6. Tap on biceps tendon tests spinal cord segment C6
Biceps brachii action?
Supination
Flexion at elbow and shoulder
Short head resists shoulder dislocation
Coracobrachialis origin?
Deep to biceps brachii. Coracoid process
Corachobrachialis insertion?
Middle 1/3 of medial surface of humerus
Corachobrachialis innervation?
Musculocutaneous
C5,6,7 (mainly C6)
Corachobrachialis action?
Flexor at shoulder, helps ADduction, resists shoulder dislocation
Biceps tendon rupture?
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
Brachialis origin?
Deep to biceps, more distal
From distal half of anterior surface of humerus
Brachialis insertion?
Coranoid process and ulnar tuberosity
Floor of cubital fossa
Brachialis innervation?
Musculocutaneous
C5,6 (mainly C6)
AND
A small lateral portion innervated by radial nerve (C6-8)
Brachialis action?
Flexes at elbow
Location of heads of triceps brachii?
Medial head deep, covered by the long and lateral heads
Insertion of triceps brachii?
Converge to a single tendon that attaches to the olecranon
Origin of triceps brachii?
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
Innervation of triceps brachii?
Radial nerve
C6,7,8 (mainly C7 and C8)
Tap on triceps tendon tests spinal nerve segment C7
Action of triceps brachii?
Extension at elbow
Long head resists dislocation of humerus during ADduction
When in embryological development do the limbs develop?
Week 4 of gestation
Upper limb first, lower usually 2-3 days behind
Includes pectoral and pelvic girdles
Well-differentiated by week 8
From where does the appendicular skeleton develop?
Limb buds that develop from the activation of mesenchymal cells in the somatic layer of the lateral mesoderm
Describe the basic steps in limb formation
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
What constitutes limb buds?
Undifferentiatted mesenchyme (core) Apical ectodermal ridge (tips)
How is the AER formed?
Thickening of distal border of limb
How does the AER allow development of limbs from proximal to distal?
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.
Limb development order?
- Stylopod (humerus and femur)
- Zeugopod (radius, ulna, tibia, fibula)
- Autopod (carpals, metacarpals, digits, tarsals, metatarsals)
Zone of polarising activity?
Signalling centre at posterior base of limb bud
Responsibilities:
1. Maintains the AER
2. Generates the anterior-posterior axis (asymmetry) of limbs
Describe the axes in limb development
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
What factors control axial specification?
A-P axis: ZPA
P-D axis: AER
D-V axis: ectodermal
Describe the rotational changes in the upper and lower limb in week 7
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
Digital rays?
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
How does bone form embryologically?
Signals from the AER to remain undifferentiated stop
Lateral plate mesoderm condenses and differentiates
Cartilage model forms
Endochondral ossification
Endochondral ossification?
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)
Amelia?
Complete absence of one or more limbs
Meromelia?
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
Syndactyly?
Fusion of two or more digits
Range from connective tissue fusion to bony fusion
Failure of mesenchymal apoptosis
Brachydactyly?
Shortened digits
Polydactyly?
Recessive trait causing extra digits
Usually without proper muscle connections, usually bilateral
Ectrodactyly?
Absence of a digit, usually bilateral
How does limb musculature form?
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
Which directions contain which types of muscles?
Ventral-flexor
Dorsal-extensor
In upper limb: flexors anterior and extensors posterior (lateral rotation)
In lower limb: flexors posterior and extensors anterior (medial rotation)
Nerve involvement in embryology?
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
How does the brachial plexus arise?
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)
Contents of cubital fossa?
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
Borders of cubital fossa?
Superior: imaginary line between the humeral epicondyles
Medial: lateral border of pronator teres
Lateral: medial border of brachioradialis
Floor and roof of cubital fossa?
Floor: brachialis (proximal) and supinator (distal) muscles
Roof: skin and fascia of bicipital aponeurosis
Which vein is part of the superficial roof of the cubital fossa and what is its clinical relevance?
Median cubital vein
Connects basilic and cephalic veins
Venepuncture
Describe the progress of the basilic vein
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
Describe the course of the cephalic vein
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
Where can the brachial pulse be palpated?
Immediately medial to the biceps tendon in cubital fossa
What type of fracture is a supraepicondylar fracture, and what are the complications?
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)
