Part 1. Anatomy of the shoulder region Flashcards
Skeletal components of the shoulder region
- clavicle and scapula (the pectoral girlde)
- humerus (has 2 tubercles; the greater and lesser tubercles). sitting between those 2 tubercles is a long grove called the intertubercular sulcus also known as the bicipital groove.
- the humerus has 2 necks; the surgical and anatomical neck, the surgical neck is more prone to fractures).
- At the distal end, we can see the epicondyles (the medial being more prominent than the lateral as well as condyles.
There are 2 joints
- Glenohumeral joint (highly mobile ball and socket joint) articulates between the head of the humerus and the glenoid fossa.
- Acromioclavicular joint; articulation between the acromion and the clavicle. its a synovial joint and can become dislocated. A synovial joint is the type of joint found between bones that move against each other.
Ligaments of the shoulder region
The ligaments Stabilize/support the shoulder region, so they are very strong.
- Coracoacromial Ligaments: coming from the coracoid and is passing into the clavicle
2. Acromioclavicular ligaments: coming from the acromion to the clavicle. this ligament surrounds and strengthens the acromioclavicular joints.
- Coracoclavicular
-
Glenohumeral ligaments; there are 3 of them. originating from the glnoid fossa and inserting into the anatomical neck of the humerus.
- Superior
- Middle
- Inferior
Coracoclavicular ligaments
its very strong. the whole of the upper limb is hanging from this ligament
- It is formed of 2 parts;
1. A trapezoid-shaped part laterally and a cone-shaped part medially.
Coracoacromial Ligament
- In between coracoid and the acromion
- Forms the Coracoacromial arch and the arch forms a space for the head of the humerus at the glenohumeral joint
- Provides support for the head of humerus
- Prevents superior dislocation of the humerus
- running below the Coracoacromial arch is a tendon, tendon of the supraspinatus muscle and the supraspinatus muscle is one of our rotator cuff muscle and this tendon can become trapped below the Coracoacromial arch.
Coracoacromial arch
Highly mobile ball and socket joint
- Abduction/Adduction
- Flexion/Extension
- Circumduction
- Lateral/Medial rotation
Glenohumeral joint
Highly mobile ball and socket joint that can form a whole range of movements
- Abduction/Adduction
- Flexion/Extension
- Circumduction (doing circles)
- Lateral/Medial rotation (aka external and internal rotation)
Abduction of the arm
Performed by deltoid
Origin: Spine of scapula + acromion + clavicle
Insert: Deltoid tuberosity
Supplied by the axillary nerve
-As well as being a very powerful abductor when all the fibres contract, the muscle can also;
Posterior fibres can perform : Extension + lateral rotation
Anterior fibres can perform: Flexion + medial rotation
Adduction of the arm
Performed by latissimus dorsi, pectoralis major
latissimus dorsi originates from the thoracolumbar fascia shown in the base of the spine. its a large flat muscle that spirals through the axilla to insert into the bicipital grove/ intertubercular sulcus.
As well as being a powerful adductor, it would medially rotate and it also extends the arm.
pectoralis major originates from the medial part of the clavicle, the sternum and the costal cartilages. its fibres come together to insert into the lateral lip of the inter tubercular sulcus/bicipital grove. as well as being a powerful adductor. it also flexes and medially rotates the arm at the glenohumeral joint.
Abduction/adduction of the arm
The Deltoid muscle is the major abductor muscle of the arm but as you abduct the arm, the glenohumeral joint can only accommodate part of that movement. when the deltoid contracts, it gets about as far as the arm is in the horizontal. about 90 degrees from the body). the shape of the skeleton limits any more movements.
However, you can lift your arm right above your head. you do this by rotating the scapula, the inferior angle of the scapula moves laterally which points the glenoid fossa in a superior direction.
This means that at the first part of abduction, the deltoid contracts bringing the arm to the horizontal then rotation of the scapula now means that you can lift the arm above the head.
which muscles rotate the scapula?
Its a combination of trapezius and serratus anterior.
-Trapezius is divided into upper fibres, middle fibres and lower fibres. All these fibres originate from the cervical thoracic vertebrae. The upper fibres mainly insert on the lateral part of the spine of the scapula. on the acromion.
- The lower fibres mainly inserts onto the most medIal part of the spine of the scapula
- when the upper and lower fibres contract together along with the lower digitation of serratus anterior, causes rotation of the scapula which points the glenoid fossa superiorly.
ADDUCTION (bringing your hand over your head and down towards your side). its all about gravity, however, levator scapulae inserts into the superior angle and the rhomboids that come from the lower cervical upper thoracic vertebrae sitting on the medial edge of the scapula contracts which brings the scapula back towards the midline.
SUMMARY
Abduction is about deltoid which brings the arm horizontally at 90 degrees and then raises your arm above your head, this rotates your scapula which is brought about by the upper and lower fibres of the trapezius and the serratus anterior.
Abduction is about gravity, bring your hand back down as well as contraction of the levator scapula and the rhomboids and then as we bring the arm back towards the midline, we contraction of the latissimus dorsi as well as the pectoralis major.
ANOTHER SUMMARY METHOD;
WHEN YOU ABDUCT THE ARM;
-Contraction of the upper and lower fibres of the trapezius, serratus anterior ,
WHEN YOU ADDUCT THE ARM:
-contraction levator scapulae and the rhomboid muscles
Flexion of the arm at the glenohumeral joint
The main muscles that flex the arm are our
1. Biceps muscle (has 2 head, the short head originates from the coracoid process and the long head inserts into the supraglenoid fossa just above the glenoid fossa). The tendon of the long head passes through the joint capsule and it passes down this intertubercular sulcus/bicipital grove). The muscle inserts into the intertubercular sulcus in the bicipital groove. the biceps muscle finally forms a tendon that inserts into the radial tiberosity.
We also have a bicipital aponeurosis which passes medially to insert eventually into the deep fascia and into the ulna.
so contraction of the biceps muscle as well as flexing the arm will also flex the forearm.
2. Corachobrachialis muscle; Another flexor of the arm. originates from the coracoid and inserts into the shaft of the humerus. The musculocutaneous nerve pierces through the coracobrachialis muscle to supply the anterior arm muscles. The brachialis muscle does not act at the glenohumeral joint, it is a flexor of the forearm.
3. Anterior Fibres of the deltoid
Extension of arm
1. TRICEPS MUSCLES; triceps brachii. has 3 heads. has a long head that comes from the infra Glenoid. tubercle, the bony process just below the glenoid fossa. It has a lateral and medial head that come from the shaft of the humerus and between that lateral and medial head we can see that radial grove and that spiral grove and in the grove is where we find the radial nerve and the profunda brachii artery. its only the long head of triceps that extends the arm. the 3 heads together extend the forearm but only the long head works to extends the arm. These 3 heads form a tendon and inserts into the olecranon at the back of the elbow joints.
2. POSTERIOR FIBRES OF THE DELTOID
3. LATISSIMUS DORSI
Glenohumeral joint stability
The main reason that the glenohumeral joint is so mobile is that you have a very large humeral head that is going to have an incredibly shallow small glenoid fossa. This makes it really unstable. In whatever position your arms is in, only part of the humeral head is against the glenoid fossa. It is one of the most commonly dislocated joints.
The most common type of dislocation is an anterior dislocation where the humeral head descends inferiorly and then pops up in front of the joint. It is frequently seen in throwers where we have a combination of abduction, lateral rotation and extension of the arm. However, there are lots of structures surrounding this joint that really helps to increase the stability.
Factors increasing the stability of the Glenohumeral joint
- Coracoacromial arch
- Glenohumeral ligaments
- Deepening of glenoid fossa by glenoid labrum
- Long heads of biceps (above) and triceps (below)
- The Tendons of a group of muscles called the rotator cuff muscles
Coracoacromial arch
This arch is formed by the coracoacromial ligament, it extends from the coracoid to the acromion. it is forming this void in which the head of the humerus can sit. This arch is preventing superior dislocation of the humerus by preventing the humerus from lifting upwards during movements of the joint.
Glenohumeral ligaments
Sits anterior to the glenoid fossa to the joints, so we are looking into our glenohumeral fossa . you can see the 3 glenohumeral ligaments (in yellow), we have the superior, the middle and the inferior ligaments. they attach to the edge of the glenoid fossa and on to that anatomical edge of the humerus.
These ligaments are preventing the humerus from moving anteriorly. They are supporting the joint in an anterior direction.
In the image, you can also see the CORACOHUMERal LiGAMENT that sits just superior to the glenoid humeral ligaments.
Glenoid labrum
It’s a ring of fibrous cartilage surrounding the glenoid fossa. It is deepening the glenoid fossa to improve the fit between the humerus and the scapula.
Long head of biceps and triceps
The tendon of the long head of the biceps which passes through the bicipital grove is held in place by the Transverse Humeral Ligament which spans between the greater and lesser tubercles.
Inferiorly, we have the long head of the triceps which is coming from the infraglenoid tubercle. this is passing down to form a large muscle belly of the long head of the triceps. both the long head of the biceps and triceps is splinting the joint, holding the head of the humerus in place.
The 4 rotator cuff muscles
- Supraspinatus
- Infraspinatus
- Teres Minor
- Subscapularis
*These 4 muscles sorround the glenohumeral joint, their tendons aorround the joint capsule.
*you have rotator cuff muscles anteriorly, posterioirly, and superioirly. The only place you dont have the muscle is inferioirly. This is why the anterioir dislocation is the most common type of dislocation because the head of the humerus drops inferioirly because of the contractions of the sorrounding rotator cuff muscles pulls the head of the humerus in front of the joint.
Also note the Subacromial bursa which is lubricating movement of the supraspinatus tendon. we alsio have the Subscapular bursa which is an an extension of the synovial membrane.
Rotator cuff muscles - origin
1. Supraspinatus; Comes from the Supraspinous fossa
- Infraspinatus; Comes from infraspinous fossa
3. Teres Minor; Teres meaning cylindrical. comes from the inferioir aspect of the scapula. you can see ther axillary nerve popping out from below the teres minor
Rotator cuff muscles - insertion
The rotator cuff muscles have been removed and now you can clearly see ht insertion of the muscles.
-
Supraspinatus, infraspinatus and teres minor insert into the greater tubercle of the humerus.
1. Supraspinatus inserts into the most superioir facet of the greater tubercle
2. infraspinatus inserts into the midle facet of the greater tubercle
3. Teres Minor inserts into hte most inferioir facet of the greater tubercle
Subscapularis – origin and insertion
This muscles is located in the anterioir region of the scapula, jjust behind the rib.
ORIGIN; subscapula fossa which is the anterioir surface of the scapula.
INSERTION: It inserts into the lesser tubercle. which is located more anterioirly to the humerus.
Rotator cuff function
When the muscles contract Together: They the humeral head on glenoid fossa
These muscles are able to rotate the joint and also cuff the joint.
The muscles pull on the humeral head in both the anterioir , posterioir and superioir region so that the humeral head is pushed and compressed against the glenoid fossa. This is called Concavity compression.
Although, the collaborative contraction of the muscles that helps us stabilise the glenhoumeral joint but individually , they are also able to rotate the joint.
1. Supraspinatus; - Initiates abduction and then deltoid takes over to do the real powerful abduction.
2. Infraspinatus; Lateral rotation of the glenohumeral joint
3. Teres minor; - Lateral rotation of the glenohumeral joint
Rotator cuff function; subscapularis
When this muscle contracts, its going to cause medial rotation or internal rotation of the arm at the glenohumeral joints.
Teres major
Not a rotator cuff muscle but it Should also be considered with the rotator cuff muscles.
-Performs medial rotation when it contracts, just liek the subscapularis.
-Teres major also has another riole in the abduction of the arm. when abduction the arm and the deltoid is onctracting, you also get teres major contracting and teres major help stabilise the head of the humerus on to the glenoid fossa. we call that an ECCENTRIC contraction.
-Stabilises the humerus during abduction
ORIGIN: inferioir angle of the scapula
INSERTION: the medial lip of the bicipital grove/intertubercular sulcus
Rotator cuff injuries
The rotator cuff that often gets injured is the supraspinatis.
Supraspinatus impingement
In the shoulder, the space where the supraspinatus passes through is very small. Its tendon can become inpinged in that space.
-This is particulaly common - Common in athletes that form repetitive overhead activities such as (throwers, swimmers, badmington players)
-supraspinatus impingment is very painful.
Blood supply to the shoulder region
- Rich blood supply and that is because it is a very mobile joint, you ahve to get blood to all those muscles in whatver position that tghe joint is in and this is known as the Scapula anastomosis.
- Allows continuous supply of blood to shoulder region during movement
- From subclavian and axillary arteries that contributes to the anstomosis.
Coming from the first part is the thyrocervical trunk which gives off the Suprascapular artery branch which wheezes across the top of the scapula to dive down just over the top of the Suprascapular notch.
The artery doesnt pass through the notch and it anastonose with branches from the axillary artery.
There is also a contribution from the dorsal scapula artery which comes from the 3rd part of the subclavian artery and also anastomnosis with branches from the axillary artery.
The axillary artery is then divided into 3 parts by the pectoralis minro muscle. first part is medial to it, 2nd part is behind to it and 3rd part is lateral to it.
The subscapular artery comes from. the third part (laterally) and forms the other limb of the anastomosis.
Scapular anastomosis
You can see the subclavianartery passing over the first rib
Nerve supply to the shoulder region
The trunks are sitting just over the first rib. The whole brachial plexus sits just over the first rib.
-Coming off the first trunk is the suprascapular nerve which passes throgh the suprascapula notch to reach the scapula and eventually innervates 2 of pur rotator cuff muscles ;
1. Supraspinatus muscle
2. Infraspinatus muscle
-Many of the structures in the shoulder region are supplied by branches from the posterioir cord.
Cords of the brachial plexus
Posterior cord
The posterioir cord gives off 3 little branches;
1. Upper/lower subscapular nerves - Subscapularis, teresmajor
2. Thoracodorsal nerve - Latissimus dorsi
- The posterioir cord terminates as the radial and axillary nerves.
- The radial nerve will innervate all the extensor muscles above the arm and the forearm. The radial nerve is innervating the triceps brachii.
- Axillary nerve is wheezing through the quadrangular space innervating the deltoid muscle which is a mjor abductor as well as the teres minor muscle.
Quadrangular space
The borders that make up the quadrangular space are the;
- Teres Minor muscle (superioir border of the space)
- Teres major (inferioir border)
- Long head of the Triceps (the medial border)
- Humerus (lateral border)
The structures passing therough this space include;
a) axillary nerve (innervating the deltoid posterioir and the teres minor muscle)
cutaneously, it innervates the millitary badge area.
b) posterioir circumflex humeral artery (this is gonna anastomose with the postrior circumflex humeral artery and provide blood supply to the structures around the surgical neck of the humerus.
What happens if you fracture the surgical neck of the humerus ?
damage to the nerve and blood vessel.
If you were to injure your axilalry nerve,, it will affect your ability to abdduct your arm.
Lateral cord
It terminates as pur
- Medial nerve
- Muculocutaneous nerve
The musculocutaneous nerve is innervating the arm flexors (biceps, coracobrachialis). It gives off a branch direct from the lateral cord and that branch of the lateral cord is anerve innervating the pectoralis muscle and this is called the lateral pectoral nerve.
Medial cord
- Median nerve
- Ulna nerve
The median nerve doesnt innervate anything in the arm. it innervates the forearm flexor muscles.
We have 3 branches from the median cord and they innervate the pectoralis muscles called the medial pectoral nerve .
There are also some branches which innervates the skin on the medial side of the arm as well as the medial side of the forearm.
