MSK sessions 1-4 Flashcards
When do the limb buds appear?
Towards the end of the fourth week of development
Do both limb buds appear at the same time?
The development of the upper limb precedes that of the lower limb by a few days.
Embryo development from cranial to caudal end.
What makes up the limb bud?
A mass of proliferating mesenchyme covered by a layer of ectoderm
Apical ectodermal ridge- formed by division of ectodermal cells at apex of the bud
How do limb buds elongate?
The AER is thought to exert an inductive influence on the limb mesenchyme that promotes proliferation
What controls axial specification when the limb is developing?
Proximal-distal axis = apical ectodermal ridge (AER)
Dorsal-ventral axis = ectoderm
Anterior- posterior axis = zone of polarising activity (ZPA)
How does the AER cause proximal to distal growth?
AER signals to stimulate affect only localised mesenchyme
AER signals inhibit differentiation of mesenchyme
Proximal mesenchyme is now far away and not under the influence of AER
Proximal mesenchyme begins to differentiate into constituent tissues
Panels appear in distal most part of limb bud.
AER induces the development of digits within the hand/foot places
What maintains the AER?
ZPA
What are the functions of ZPA?
Generation of asymmetry in the limbs (between pinky and thumb)
Maintains the AER
Where is the ZPA found?
Posterior base of the limb bud
How do the digits form?
AER is maintained only over the tips of the digital rays
Apoptosis occurs between them
Digital rays develop into cartilaginous models
What is syndactyly?
Fusion of digits- may involve CT or bones may fuse
What is polydactyly?
Extra digits
What is amelia?
Complete absence of a limb
What is meromelia?
Partial absence of one or more limb structures
What is phocomelia?
Hand or feet are connected directly to the trunk
What is usually the cause of malformation resulting in abnormalities of the limb?
Genetics
Inherited mutation or spontaneous mutation of a gene coding for a protein involved in coordination of an event
What is constriction banding and how does it cause abnormalities in the limbs?
Normal limbs are formed.
Strands of amniotic membrane fall off and encircle the limb, constricting it and causing truncation.
Can truncation of the limbs due to constriction banding be genetically inherited?
NO
Normal limbs form- obstruction has affected a normal pathway
How did thalidomide cause abnormalities in the limbs?
Teratogenic agent which disrupts AER so stops elongation of limb buds
What initiates compartmentalisation of the limb buds?
Mesenchyme loses the signal from AER to stay undifferentiated.
Describe compartmentalisation of limb buds?
- Cartilaginous models of skeletal stem appears creating a dorsal and ventral compartment.
- Myogenic precursors migrate into limbs from somites and sit either dorsally or ventrally. Ventral = flexor. Dorsal = extensor
- Individual muscles split from muscle masses
- Somites develop either side of the neural tube and each somite develops its own spinal nerve. The spinal nerve will innervate derivatives of this somite
Describe rotation of the limbs
Upper limbs laterally
Lower limbs medially
What are the six motions of the hand?
Grip Hook Spherical grip Tip to tip Palmar Lateral
Describe the composition of the brachial plexus.
Roots Trunks Divisions Cords Branches
What are the trunks of the brachial plexus?
Upper trunk = c5 and c6
Middle trunk = c7
Lower trunk = c8 and t1
Describe the divisions of the brachial plexus
Each trunk splits into anterior and posterior divisions.
Anterior divisions- go on to supply the anterior compartments of the upper limb
Posterior divisions- go on to supply the posterior compartments of the upper limb
Describe the cords of the brachial plexus.
This is relative to the axillary artery
Lateral cord
Anterior division of the superior trunk
Anterior division of the middle trunk
Posterior cord
Posterior division of the superior trunk
Posterior division of the middle trunk
Posterior division of the inferior trunk
Medial cord
Anterior division of the inferior trunk
Describe the anatomical boundaries of the axilla.
Lateral wall
Intertubercular groove of the humerus
Medial wall
Serratus anterior and thoracic wall
Anterior wall
Pectoralis major and underlying pectoralis minor and subclavius
Posterior wall
Subscapularis, teres major, latissimus dorsi
Apex
Lateral border of first rib
Superior border of scapula
Posterior border of clavicle
Describe the contents of the axilla
Axillary artery and its branches
Axillary vein and its tributaries
Infraclavicular part of the brachial plexus
Five groups of axillary lymph nodes and associated lymphatics
Long thoracic and intercostobrachial branches
Axillary fat and areolar tissue
What is thoracic outlet syndrome?
The apex of the axilla is an opening between the clavicle, the first rib and the scapula
In the apex, vessels and nerves may become compressed
Presentation:
Pain in limb, tingling, muscle weakness and discolouration
- where depends on what nerve is affected
What is a lymph node biopsy used for?
Diagnosis of breast cancer
65% of lymph from breast drains into axillary lymph nodes
Axillary lymph nodes may need to be removed to prevent cancer spreading in axillary clearance. What structure is at risk of damage in this process and what are the consequences?
Long thoracic nerve
Winged scapula
What is the quadrangular space?
Gap in posterior wall of the axilla which allows access to the posterior arm and shoulder area.
Bounded by: Subscapularis and capsule of shoulder joint superiorly Teres major inferiorly Long head of triceps medially Surgical neck of humerus laterally
Structures passing through:
Axillary nerve
Posterior circumflex humeral artery
What is the clavipectoral triangle?
Opening in anterior wall of axilla
Bounded by:
Pectoralis major
Deltoid
Clavicle
Structures passing through:
Cephalic vein
Medial pectoral nerve
Lateral pectoral nerve
What are the two passageways exiting the axilla?
Quadrangular space
Clavipectoral triangle
What are the contents of the fibrous axillary sheath?
Axillary artery
Axillary vein
Cords and branches of the brachial plexus
For the purpose of anatomical description, the axillary artery is divided into three sections. What are the anatomical landmarks that define these three sections?
First part- begins at lateral border of first rib as a continuation of the subclavian artery
Second part- posterior to pectoralis minor
Third part- lateral to pectoralis minor and continues as the brachial artery at the inferior border of teres major
Explain what happens if the AER is disrupted and give one mechanism causing its disruption.
Shortened limbs/no limb growth
Mechanism: Interference affecting blood vessels of AER
What is the structural defect underlying congenital dislocation of the hip (CHD)?
Underdevelopment of acetabulum and head of femur.
CHD is associated with breech presentation (i.e. the buttocks of the fetus are inferior and would be delivered first, rather than the head). Speculate on why this might be so.
Breech presentation may place undue pressure on the developing hip joint: fails to complete normal development.
For the purpose of anatomical description, the axillary artery is divided into three sections. What are the anatomical landmarks that define these three sections?
The first part of the axillary artery begins at the lateral border of the first rib as a continuation of the subclavian artery.
The second part of the axillary artery lies posterior to pectoralis minor.
The third part lies lateral to pectoralis minor and continues as the brachial artery at the inferior border of teres major.
What is the difference between palmar abduction and radial abduction of the hand?
Palmar abduction- occurs in sagittal plane
Radial abduction- continuation of extension in coronal plane
What is the most common arrangement of fascicles?
Parallel - fibres run parallel to force generating axis
How are the fibres organised in the biceps brachial muscle?
Parallel-fusiform
Wide and cylindrically shaped in the centre
Taper off at the ends
How are the fascicles arranged in the deltoid muscle?
Multipennate
What is the difference between an origin and insertion in terms of stability?
Origin = proximal, greater mass, more stable during contraction
Insertion = distal, moved by contraction
What is compartment syndrome?
Trauma in one compartment can cause internal bleeding which exerts pressure on blood vessels and nerves.
When there is a fracture, there is bleeding into a compartment of the forearm which is enclosed by fascia.
Pressure increases and veins have distensible walls so these collapse
As pressure increased further, blood supply to this compartment is cut off.
This results in ischaemia and necrosis of the muscles in this compartment
How does compartment syndrome present?
Deep constant poorly localised pain
Aggravated by passive stretch of a muscle group
Parasthesia
Compartment may feel tense
Swollen shiny skin, sometimes with obvious bruising
Prolonged capillary refill time
EARLY
Pain our of proportion to the injury
Pain with passive movement
LATER Paralysis Pulselessness Parasthesia Pallor Poikilothermia (perishing cold)
How is compartment syndrome treated?
Fasciotomy - incision of overlying fascia or a septum to relieve pressure in the compartment concerned
What is the difference between neutralisers and fixations?
Neutralisers prevent unwanted actions of a muscle
Fixators stablise a joint
What are the two types of isotonic contraction?
- Concentric contraction
Muscle shortens - Eccentric contraction
Refers to active contraction of muscles whilst they are lengthening
Which type of isotonic contraction is damaging to muscles and results in delayed onset of pain?
Eccentric contraction = pain is not felt for about 8 hours and is maximal 1 or 2 days later
What is titin?
Protein that connects the Z line to the M line in the sarcomere.
Limits the range of motion of the sarcomere in tension, contributing to the passive stiffness of muscle.
What is the most common lever found in the body?
Third class lever Effort is between load and fulcrum
What is malignant hyperthermia and what is it triggered by?
Triggered by volatile anaesthetic agents and succinylcholine in susceptible individuals
Leads to uncontrolled increase in oxidative metabolism and an increase in body temperature
What is the most common genetic cause of malignant hyperthermia?
Polymorphism in the ryanodine receptor
Receptor activated by volatile anaesthetic agents
Massive increase in intracellular calcium from intracellular stores
High activity of SERCA pump which consumes ATP
Excessive heat production
What is myotonia congenita?
Cause:
mutations in chloride channel
Recessive or dominant
Symptoms:
muscle stiffness, particularly in leg muscles, enhanced by cold and inactivity, relieved by exercise
Treatment:
None, symptoms received with anticonvulsant drugs
What is rigor mortis?
ATP depleted
Myosin heads cannot detach
What is tetany?
Consecutive action potentials result in summation giving a slightly larger force with each contraction.
Eventually a limit is reached where no further force can be produced and this is tetany.
What is tetanus?
Muscles contract continuously due to bacterial infection and release of tetanus toxin which prevents the neuromuscular synapse from relaxing
What is hypotonia?
Lack of skeletal muscle tone
(All muscle has some degree of baseline tone due to the elasticity of the muscle tissue and low levels of motor neurone activity)
What are the causes of hypotonia?
Damage to the motor cortex or cerebellum or spinal cord
Degeneration of muscle itself (myopathy)
Which physiological process, occurring within the muscle fibre, causes skeletal muscle relaxation?
Active transport of Ca2+ ions from cytosol back into SR
What is the shoulder girdle?
Clavicle and scapula
Name the joints present at the shoulder girdle.
Sternoclavicular joint
Acromioclavicular joint
Scapulothoracic joint
Glenohumeral joint
What is the glenoid labrum?
Fibrocartilage rim that deepens the glenoid fossa to reduce the disproportion in surfaces and increase stability
Describe what the joint capsule of the shoulder is and where it is.
Fibrous sheath which encloses structures of the joint.
Extends from the anatomical neck of the humerus to the border of the glenoid fossa
What are the main clinically relevant bursae of the shoulder joint?
Subacromial bursa
Inferior to deltoid and acromion
Superior to supraspinatus and joint capsule
Inflammation of this bursa is the cause of many shoulder problems
Subscapularis bursa
Between subscapularis tendon and scapula
Reduces wear and tear on tendon during movement of the shoulder joint
What are the intracapsular ligaments of the shoulder joint?
Superior, middle and inferior glenohumeral ligaments Thickenings of the joint capsule
Between glenoid fossa and anatomical neck of the humerus
Stabilise anterior aspect of the joint
What are the extracapsular ligaments of the shoulder joint? (4)
Coracohumeral ligament
Between coracoid process and humerus
Coracoacromial ligament
Between acromion and coracoid process
Coracoclavicular joint
Between clavicle and coracoid process
Transverse humeral ligament
Between greater and lesser tubercle of humerus
Which arteries are at greatest risk of damage in a shoulder dislocation?
Anterior and posterior humeral circumflex arteries
What is Erb’s palsy?
Upper brachial plexus injury- will affect shoulder joint function
Which is the only rotator cuff muscle that does not have a role in external rotation of the shoulder?
Subscapularis- internal rotation
What are the static stabilisers of the shoulder joint?
Glenoid labrum= fibrocartilage ring that deepens the glenoid fossa by about 50%
Capsule
Glenohumeral ligaments = reinforce joint capsule
Extra-capsular ligaments = form coraco-acromial arch
Negative intra-articular pressure = negative pressure sucks in glenoid
What are the dynamic stabilisers of the shoulder joint?
Rotator cuff muscles = SITS, (no. 7,8,9,10) surround the shoulder joint, attaching to the tubercles of the humerus, whilst fusing with the joint capsule. The resting tone of these muscles act to pull the humeral head into the glenoid cavity
Biceps brachii
Muscles crossing the shoulder - pectoralis major, latissimus dorsi etc.
What position are clavicular fragments likely to be displaced in a mid-clavicular fracture?
Lateral fragment
Inferiorly- weight of arm
Medially- pec major attaches here and adducts upper limb
Medial fragment
Superiorly- action of sternocleidomastoid
Which parts of the brachial plexus are at most risk of injury when the clavicle is fractures?
Trunks and divisions- lie posterior to the fracture point of the clavicle
Explain how you would assess a patient for damage to the brachial plexus caused by clavicular fracture.
Minimal movement of shoulder and arm to avoid damage to the neurovascular structures by the fragments during examination.
Sensation - test dermatomes C5-T1
Motor- test movements whilst stabilising the shoulder and arm
Which artery and vein are at most risk of damage from a clavicular fracture?
Anterior to posterior: Clavicle Subclavian vein Subclavian artery Trunks of brachial plexus
In a proximal clavicular fracture, auscultation of the chest must be performed and a chest X-ray may also be needed. What rare but important complication needs to be excluded?
Pneumothorax
What is the coracoacromial arch and what is its role at the shoulder when falling on an outstretched hand?
Coraco-acromion ligament between the inferior surface of the acromion and the coracoid process forms an osseo-ligamentous structure.
Functions:
-protective arch so prevents superior displacement of the head of the humerus from the glenoid cavity of the scapula
What structures can be affected by a fracture of the surgical neck of the humerus?
Surgical neck is a constriction beneath the tubercles of the greater tubercle and lesser tubercle
May cause damage to:
- axillary nerve
- posterior circumflex humeral artery
These go through the quadrangular space. The surgical neck of the humerus is the lateral border of this space.
Which nerve is most likely to be injured in mid-shaft humeral fracture and why?
Radial nerve
The nerve runs in the radial groove on the posterior surface of the shaft of the humerus
In a patient there is... Flattening/squaring of their shoulder. A prominent coracoid process. Arm is externally rotated and slightly abducted Diagnosis?
Antero-inferior dislocation of the shoulder
What is a bankart lesion and when does it occur?
Can occur due to an anterior shoulder dislocation
Avulsion (pulling/tearing away) of the antero-inferior glenoid labrum at its attachment to the antero-inferior glenohumeral ligament complex. There is a rupture of the joint capsule and inferior glenohumeral ligament injury.
What is a Hill-sachs lesion and when does it occur?
Can occur due to an anterior dislocation of the shoulder
A posterolateral humeral head indentation fracture can occur as the soft base of the humeral head impacts against the relatively hard anterior glenoid.
Acromioclavicular dislocations can be categorised with the rockwood classification. What injury are the lower and higher classes associated with?
Lower- Damage to acromioclavicular ligament
Higher-Damage to coracoclavicular ligament and acromioclavicular ligament
A patient has an undisplaced humeral fracture. Would surgery usually be considered?
No- bone with heal by normal fracture repair
A patient has a displaced humeral fracture. Will surgery be considered?
Yes= may require fixing or joint replacement
There is bone sitting in the axilla with no blood supply so ischaemic necrosis will occur
What complications should be considered in a humeral neck fracture?
Damage to axillary nerve
Damage to posterior circumflex artery
What complications should be considered in a mid-shaft humeral fracture?
Damage to radial nerve which runs in radial groove on posterior surface of humerus
How would movement in the arm at the elbow, wrist and fingers be affected in a mid-shaft humeral fracture if the radial nerve had been damaged?
Flexion of elbow normal
No effect or mildly compromised extension of elbow
Poor wrist extension (wrist drop)
Poor finger extension
Where do clavicle fractures usually occur?
Middle of third of clavicle/ junction of middle 2/3 and lateral 1/3
In which direction to clavicle fragments move in a clavicle fracture? Why?
The lateral fragment is most likely to be displaced medially (overlying the medial fragment) due to the action of pectoralis major adducting the upper limb; and inferiorly due to the weight of the upper limb pulling downwards on the fracture fragment. The medial fragment is likely to be displaced superiorly by the action of sternocleidomastoid, exacerbating the degree of non-alignment of the fracture fragments.
What complications should be considered in a clavicle fracture?
Brachial plexus damage - roots and trunks
Subclavian artery damage
Subclavian vein damage
Pneumothorax
What is calcific tendinitis and where does it usually occur in the shoulder?
Tendon deposits calcium hydroxyapatite in subacromial space
This gets in the way when you abduct your arm- if you keep abducting it will burst
Patient has: 2 day history of pain in shoulder Rapidly progressive pain 10/10 severity Resolves in 1 to 2 weeks. Diagnosis?
Calcific tendinitis
Resolves in 1-2 weeks- phagocytes resorb material
Patient presents with a ‘Popeye muscle’. What has caused this? How is it treated?
Rupture of long head of biceps.
No treatment- patient would not notice much weakness in upper limb due to action of brachialis and supinator muscles
What is the subacromial space and which structures are found here?
Space between the acromion and head of humerus
Within this space: Subacromial bursa Rotator cuff tendons Capsule Long head of biceps
Which movement can cause exacerbated impingement of soft tissue in the subacromial space?
Abduction
Patient has low painful arc
Tenderness over tuberosity
Hawkins test positive
Diagnosis?
Impingement
What are the common causes of impingement in the subacromial space?
Tendinitis- swollen long head of biceps and rotator cuff tendons (usually due to overuse)
Bursitis- infection subacromial bursa
This increases friction at the joint especially in the middle of abduction
What is painful arc?
Pain in the middle of abduction
20-120 degrees
- Very small gap between acromion and head of humerus, means that things can get trapped at certain points during abduction
- Subscapularis tendon sometimes impinged under CAA, which leads to inflammation and infections (subacromial bursitis)
- Causes specific pain between 50 and 130 degrees abduction
- More likely with repetitive movements, age etc
At which joints in the shoulder girdle does osteoarthritis usually occur? (2)
Glenohumeral
Acromioclavicular
Patient has:
Severe, progressive jerk pain in shoulderwhen exerting themselves eg. When catching something that’s falling quickly
Progressive stiffness follows
Diagnosis?
Frozen shoulder
Adhesive capsulitis
How are rotator cuff tears treated?
Can sometimes be repaired
Sometimes requires an allograft
What are the effects of ageing on joints? (4)
Variable among individuals, affected by genetic factors, wear and tear
- decreased production of synovial fluid
- thinning of articular cartilage
- shortening of ligaments and a decrease in ligamentous flexibility
- degenerative changes in load-bearing joints
Describe the structure and organisation of skeletal muscle.
- Striated
- Multinucleate
- Distinct myofibrils
- T-tubules at z line
- Can be red, white or intermediate
- No cell to cell junctions
- Each cell surrounded by endomysium
- Groups of fibres surrounded by perimysium
- The entire muscle is surrounded by epimysium
What is fasciculation?
Involuntary unsynchronised contraction of fascicles.
Sign of multineurone disease.
What is a dermatome?
Area of skin supplied by a single spinal nerve root.
Explain the embryonic development of dermatomes.
Paraxial mesoderm is arranged into somites at the 4th week of gestation. Somites are blocks of mesoderm cells around a small cavity. From each somite, dermatomyotome ( from which dermatome and myotome develops) and sclerotome develops.
Dermatomyotome develops in association with a specific neural level of a spinal cord. They take a nerve supply with them from the neural tube as a spinal nerve. Therefore, skin and muscle derived from a single dematomyotome have a common spinal nerve supply.
Nerves grow into the developing limb buds. As the limb bud increases in size, the nerves are dragged along with the structures they innervate eventually producing the adult pattern.
Does laceration of a single dorsal spinal nerve root lead to anaesthesia of the entire corresponding dermatomal area?
Each dermatome is named according to the spinal nerve which supplies most of its sensory innervation. In general, contiguous areas of skin are supplied by contiguous spinal nerves. There is considerable overlap between adjacent dermatomes so laceration of a single dorsal spinal nerve root does not usually lead to anaesthesia of the entire dermatomal area.
Is there overlap of innervation in areas that are on either side of the axial line?
No
Which nerve roots innervate the upper limb?
The upper limb is innervated by the anterior primary rami of spinal nerves
What are spinal nerve roots?
They connect each spinal nerve to a ‘segment’ of the spinal cord.
What kind of nerve fibres do dorsal roots contain?
Sensory/afferent nerve fibres only
What does the dorsal root ganglion contain?
Cell bodies of the sensory neurones from the periphery
What nerves do ventral roots of a spinal nerve contain?
Motor/efferent and autonomic nerve fibres only