Anatomy of the shoulder region Flashcards
Skeletal components of the pectoral girdle
- Clavicle
- Scapula
Two key joints in the shoulder
- Glenohumeral joint
- Acromioclavicular joint
Ligaments of the shoulder region
Stabilise/support the shoulder region - very strong
- Coracoclavicular
- Acromioclavicular
- Coracoacromial
- Glenohumeral (superior, middle, inferior)
Attachments are all in the name
Features of coracoclavicular and coracoacromial ligaments
Coracoclavicular - two parts, major stabilising ligament
Coracoacromial - forms arch, provides support for head of humerus, prevents superior dislocation
Features of the glenohumeral joint
Highly mobile ball and socket joint
- Abduction/adduction
- Flexion/extension
- Lateral/medial rotation
- Circumduction
Function of the deltoid
- Abduction of the arm
Deltoid - origin
- Spine of scapula + acromion + clavicle
Deltoid - insertion
- Deltoid tuberosity
Innervation of the deltoid
Supplied by axillary nerve
Posterior fibres - extension + lateral rotation
Anterior fibres - flexion + medial rotation
Which muscles perform adduction of the arm
- Performed by latissimus dorsi and pectoralis major
Joints involved in abduction/adduction of the arm
- Glenohumeral joint accommodates parts of movement
- Rotation of scapula increases range of movement
Other muscle fibres involved in abduction
- Upper fibres of trapezius
- Lower fibres of trapezius
- Serratus anterior (for lateral rotation of scapula)
Other muscle fibres involved in adduction
- Levator scapulae
- Rhomboids
Muscles involved in the flexion of the arm
- Short head of biceps
- Long head of biceps
- Coracobrachialis
- Brachialis - flexes forearm
- Anterior fibres of deltoid
Muscles involved in extension of arm
- Long head of triceps
- Lateral head of triceps(extend forearm)
- Medial head of triceps(extend forearm)
- Posterior fibres of deltoid
- Latissimus dorsi
Why is the glenohumeral joint unstable
- Large humeral head
- Shallow glenoid fossa
- Most frequently dislocated joint - anterior dislocation common (humeral head descends inferiorly and ends up anterior)
Factors which increase glenohumeral joint stability
- Coracoacromial arch
- Glenohumeral ligaments
- Deepening of glenoid fossa by glenoid labrum
- Long heads of biceps (above) and triceps (below)
- Tendons of rotator cuff muscles
What does the coracocromial arch prevent
- Prevents superior dislocation
What do the glenohumeral ligaments support
- Supports anterior of joint
How does the glenoid labrum increase glenohumeral stability
- Deepens glenoid fossa
Long head of biceps - origin
- Supraglenoid tubercle
- Long head biceps passes through joint capsule of the transverse humeral ligament
Long head of triceps - origin
- Infraglenoid tubercle
Features of the rotator cuff muscles
- Four muscles
- Insert on humerus close to joint
- Fuse with the joint capsule
- Forms cuff around joint
Which sides do the rotator cuff muscles surround
- Rotator cuff muscles surround on all sides except inferiorly
What is the subacromial bursa
- The subacromial bursa is the synovial cavity located just below the acromion, which communicates with the subdeltoid bursa
Rotator cuff muscles - insertion
- Supraspinatus, infraspinatus and teres minor insert into the greater tubercle
Rotator cuff function
Together: stabilise humeral head on glenoid fossa
Supraspinatus - initiate abduction
Infraspinatus - lateral rotation
Teres minor - lateral rotation
Subscapularis - medial rotation
Function of teres major
- Should also be considered with the rotator cuff muscles
- Performs medial rotation
- Stabilised the humerus during abduction (eccentric contraction)
Rotator cuff injuries
Supraspinatus impingement:
- Supraspinatus most commonly injured
- Limited space for tendon under coracoacromial arch
- Impingement due to repetitive overhead activities (common in athletes such as throwers)
Blood supply to the rotator cuff
- Rich blood supply
- Scapula anastomosis
- Allows continuous supply of blood to shoulder region during movement
- From subclavian and axillary arteries
What is the scapular anastomosis(memorise diagram)
- The scapular anastomosis is a system connecting certain subclavian artery and their corresponding axillary artery, forming a circulatory anastomosis around the scapula
- It allows blood to flow past the joint in case of occlusion, damage, or pinching of specific scapular arteries
Nerve supply to the shoulder
From the brachial plexus - suprascapular nerve(supraspinatus and infraspinatus)
Location of the cords of the brachial plexus
- Within axilla
- Below pectoralis minor
Specific innervation of deltoid and teres minor + triceps brachii
Posterior cord:
Axillary - deltoid and teres minor
Radial - triceps brachii
Specific innervation of subscapularis, teres major and thoracodorsal nerve
Upper and lower subscapular nerves - subscapularis, teres major
Thoracodorsal nerve - latissimus dorsi
Boundaries of the quadrangular space
above/superior: the teres minor (inferior margin).
below/inferior: the teres major (superior margin)
medially: the long head of the triceps brachii (lateral margin)
laterally: the surgical neck of the humerus
anteriorly: the subscapularis
What can a fracture of the surgical neck of the humerus result in
- Possible damage to the axillary nerve and posterior circumflex humeral artery
Which branch of the lateral cord of the brachial plexus supplies pectoralis major
- Lateral pectoral nerve
Branches of the medial cord that innervate pec major and minor
- Medial pectoral nerve (pectoralis major and minor)
- Medial cutaneous nerves to arm and forearm
