The Rotator Cuff Muscles
So a break from our previous focus on the abdomen - a brief detour into the world of the rotator cuff muscles, but first - what are they?
Rotator cuff muscles are basically the muscles which surround and support the shoulder joint. The shoulder joint is also known as the glenohumeral joint, and is a synovial ball and socket joint between the glenoid fossa of the scapula (a shallow hollow in the scapula) and the head of the humerus. The joint is deppened by a lip around the glenoid fossa - the glenoid labrum.
It is surrounded by a capsule which attaches to the anatomical neck of the humerus, and is lax underneath where it descends to the surgical neck of the humerus.
I found the rotator cuff muscles a bit difficult to conceptualise when I first learnt about them, but actually they are quite simple when you apply five simple rules.
Rule 1: There are four rotator cuff muscles. These can be remembered with the acronym SITS.
S = supraspinatus
I - infraspinatus
T = teres minor
S = subscapularis
Rule 2: Posterior muscles laterally rotate the arm (external rotation). Anterior muscles medially rotate the arm.
This is important as it helps you to remember what the rotator cuff muscles do.
- There are three posterior muscles: supraspinatus, infraspinatus and trees minor (SIT: you can remember these are posterior by the fact that you sit on your posterior) - these laterally rotate. This makes sense if you imagine their attachment - they go behind the shoulder and attach to the greater tubercle, so they will pull the arm towards the origin in that direction, laterally rotating the arm.
- There is one anterior muscle: subscapularis - this medially rotates
--> Rotator cuff muscles provide 80% of the force for laterally rotating the arm <--
Rule 3: If all else fails, think of a virtual hug to remember the actions.... :)
Supraspinatus - comes from the supraspinous fossa (a hollow under the acromium)
Infraspinatus - comes from the infraspinous fossa
Subscapularis - comes from the sub scapular fossa.
(The only exception is the trees minor from the lateral border of the scapula).
Hint: Surface anatomy....
If you want to feel for the origins of the muscles
Rule 5: The posterior muscles attach to the greater tubercle, the anterior muscles attach to the lesser tubercle of the humerus
Supraspinatus - superior facet of the greater tubercle
infranspinatus - middle facet of the greater tubercle
teres minor - inferior facet of the greater tubercle
subscapularis - lesser tubercle
So now we have a selection outline for the skeletal muscles - we just have to fill in the gaps, but first let's review what we know so far.... (the words in red we haven't covered yet, but we will come to in the next section)
Innervation of the rotator cuff muscles: The rotator cuff nerves are all C5, C6 "C5 and 6, rotator tricks"
- The supraspinatus is supplied by the suprascapular nerve
- The infraspinatus is supplied by the suprascapular nerve
- The trees minor is supplied by the axillary nerve
- The subscapularis is supplied by the upper and lower sub scapular nerve
Tears to the rotator cuff muscles
- Normally the supraspinatus is torn because...
a. It is an avascular tendon
b. It runs through the subacromial space - the bursa can impinge on it.
Dislocated shoulder joint: the shoulder normally dislocates anteriorly, most frequently when the arm is abducted and laterally rotated with force, placing pressure on the weakest part of the joint capsule. This is because when the arm is in this position, it has the lowest amount of anterior support from the subscapularis.
- Axillary and radial nerves can be injured if the shoulder becomes dislocated - why?
well if the shoulder joint is dislocated anteriorly...
a. The radial nerve becomes stretched because there is now a longer distance between shoulder and elbow.
b. The axillary nerve may be injured because it travels below the shoulder joint capsule through the quadrangular space (see my later blog post on "spaces in the body").
How do we test for the rotator cuff muscles?
1. Supraspinatus - as the subject to move their arm away from their body on both the affected and unaffected side. This allows you to compare the affected arm with the normal range of movement. Ask how long it has gone on for, and quantify.
Differentials? Suprascapular nerve problem, something wrong with the neck. You can also ask the subject to push your hands away to see if they have equal strength on both sides
2. Infraspinatus and trees minor - get the subject to clench their fists out and then push fists in lateral rotation.
3. Subscapularis - get the subject to push outwards
Extra information....
.... about the Supraspinatus:
Teach me anatomy
Problem Based Anatomy, Canby
rotator cuff picture from https://shoulderelbow.org/2016/12/12/arthroscopic-rotator-cuff-repair/
Medicalook.com
http://anatomyvideo.blogspot.co.uk/2013/04/the-anastomoses-around-scapula.html
 |
| http://human-anatomy101.com/anatomy-of-the-hand-muscles/ |
It is surrounded by a capsule which attaches to the anatomical neck of the humerus, and is lax underneath where it descends to the surgical neck of the humerus.
I found the rotator cuff muscles a bit difficult to conceptualise when I first learnt about them, but actually they are quite simple when you apply five simple rules.
Rule 1: There are four rotator cuff muscles. These can be remembered with the acronym SITS.
S = supraspinatus
I - infraspinatus
T = teres minor
S = subscapularis
Rule 2: Posterior muscles laterally rotate the arm (external rotation). Anterior muscles medially rotate the arm.
This is important as it helps you to remember what the rotator cuff muscles do.
- There are three posterior muscles: supraspinatus, infraspinatus and trees minor (SIT: you can remember these are posterior by the fact that you sit on your posterior) - these laterally rotate. This makes sense if you imagine their attachment - they go behind the shoulder and attach to the greater tubercle, so they will pull the arm towards the origin in that direction, laterally rotating the arm.
- There is one anterior muscle: subscapularis - this medially rotates
--> Rotator cuff muscles provide 80% of the force for laterally rotating the arm <--
Rule 3: If all else fails, think of a virtual hug to remember the actions.... :)
Arm around a friend - like supraspinatus
Arm around front - like subscapularis
Can you think of what the equivalent actions would be for infraspinatus and trees minor?
Rule 4: The clue for the origins the muscles is in the name:Supraspinatus - comes from the supraspinous fossa (a hollow under the acromium)
Infraspinatus - comes from the infraspinous fossa
(The only exception is the trees minor from the lateral border of the scapula).
Hint: Surface anatomy....
If you want to feel for the origins of the muscles
Rule 5: The posterior muscles attach to the greater tubercle, the anterior muscles attach to the lesser tubercle of the humerus
Supraspinatus - superior facet of the greater tubercle
infranspinatus - middle facet of the greater tubercle
teres minor - inferior facet of the greater tuberclesubscapularis - lesser tubercle
So now we have a selection outline for the skeletal muscles - we just have to fill in the gaps, but first let's review what we know so far.... (the words in red we haven't covered yet, but we will come to in the next section)
Innervation of the rotator cuff muscles: The rotator cuff nerves are all C5, C6 "C5 and 6, rotator tricks"
- The supraspinatus is supplied by the suprascapular nerve
- The infraspinatus is supplied by the suprascapular nerve
- The trees minor is supplied by the axillary nerve
- The subscapularis is supplied by the upper and lower sub scapular nerve
Tears to the rotator cuff muscles
- Normally the supraspinatus is torn because...
a. It is an avascular tendon
b. It runs through the subacromial space - the bursa can impinge on it.
 |
| From: https://www.ebmconsult.com/articles/anterior-shoulder-dislocation-review |
Dislocated shoulder joint: the shoulder normally dislocates anteriorly, most frequently when the arm is abducted and laterally rotated with force, placing pressure on the weakest part of the joint capsule. This is because when the arm is in this position, it has the lowest amount of anterior support from the subscapularis.
- Axillary and radial nerves can be injured if the shoulder becomes dislocated - why?
well if the shoulder joint is dislocated anteriorly...
a. The radial nerve becomes stretched because there is now a longer distance between shoulder and elbow.
b. The axillary nerve may be injured because it travels below the shoulder joint capsule through the quadrangular space (see my later blog post on "spaces in the body").
How do we test for the rotator cuff muscles?
1. Supraspinatus - as the subject to move their arm away from their body on both the affected and unaffected side. This allows you to compare the affected arm with the normal range of movement. Ask how long it has gone on for, and quantify.Differentials? Suprascapular nerve problem, something wrong with the neck. You can also ask the subject to push your hands away to see if they have equal strength on both sides
2. Infraspinatus and trees minor - get the subject to clench their fists out and then push fists in lateral rotation.
3. Subscapularis - get the subject to push outwards
Extra information....
.... about the Supraspinatus:
- - Literally found
on top of the spine, underneath the deltoidjh
- What does it do? It is responsible for the
first 15 degrees of abduction. After that the deltoid takes over – so sometimes
in the clinic if the supraspinatus is injured and they can't abduct their arm, you can start to help the patient to abduct their arm so they can do the rest/ they
lean over to use the force of gravity in order to abduct the shoulder a bit so
the deltoid can do the rest.
,,...about blood supply to the rotator cuff
Now, this topic used to really confuse me, so I will give a quick summary below with a diagram - but then talk through the blood vessels step by step with pictures: probably more for my benefit than yours, but hopefully it is helpful..
- a. The anterior and posterior circumflex humeral artery gives branches to the rotator cuff muscles. These originally come from the axillary artery.
-b. The supra scapular and sub scapular arteries also supply the rotator cuff muscles. The subscapular artery is a branch of the thyrocervical trunk, which in turn comes from the subclavian artery.
c. Circumflex scapular artery - this is a branch of the sub scapular artery These arteries anastomose with the superficial branch of the anterior circumflex at a place non as the critical zone because this is where pathology can frequently occur.
1Okay so now for my step-by-step explanation (illustrated by Gray's Anatomy picture, from Elesvier).
The arterial supply to the arm arises from the subclavian artery - remember, one of the branches from the heart?
- Once the subclavian artery passes over the first rib it is called thaxillary artery. Specifically the axillary artery begins at the "lateral border of the first rib" (later it will end at the inferior border of teres major, but don't worry about that for now).
e
The axillary artery can then be considered in three parts. The first, before pec minor. The second part, as the artery passes behind pec minor, and the third after the muscle passes pec minor. We will look at these below.
a. The first part of the axillary artery - before it reaches pec minor: The axillary artery is enclosed in the axillary sheath. It gives of an arterial branch - The first branch of the axillary artery - this supplies the muscle serratus anterior.
b. The 2nd part of the axillary artery (posterior to pec minor): this gives off two branches:
1. The thoraco-acromial artery: supplies the anterior axillary wall and passes
medial to pec minor: from the second part of the axillary artery. This artery has four branches:
These supply the pectoral muscles and the breast.
The third part of the axillary artery: this is the part of the axillary artery distal to pectorals minor and gives off three branches
a. Subscapular artery: largest branch, divides into circumflex scapular and thoracodorsal arteries, supplies serratus anterior, teres major, subscapularis, and latissimus dorsi muscles. Did you notice one of the rotator cuff muscles? Yep, the sub scapular artery from the third part of the axillary artery supplies the subscapualris. The circumflex scapular also makes a connection with the deep branch of the transverse artery which comes off from the thyrocervical trunk (which itself is a branch from the subclavian artery).
b. Anterior and posterior circumflex humeral arteries
,,...about blood supply to the rotator cuff
Now, this topic used to really confuse me, so I will give a quick summary below with a diagram - but then talk through the blood vessels step by step with pictures: probably more for my benefit than yours, but hopefully it is helpful.. - a. The anterior and posterior circumflex humeral artery gives branches to the rotator cuff muscles. These originally come from the axillary artery.
-b. The supra scapular and sub scapular arteries also supply the rotator cuff muscles. The subscapular artery is a branch of the thyrocervical trunk, which in turn comes from the subclavian artery.
c. Circumflex scapular artery - this is a branch of the sub scapular artery These arteries anastomose with the superficial branch of the anterior circumflex at a place non as the critical zone because this is where pathology can frequently occur.
1Okay so now for my step-by-step explanation (illustrated by Gray's Anatomy picture, from Elesvier).
The arterial supply to the arm arises from the subclavian artery - remember, one of the branches from the heart?
- Once the subclavian artery passes over the first rib it is called thaxillary artery. Specifically the axillary artery begins at the "lateral border of the first rib" (later it will end at the inferior border of teres major, but don't worry about that for now).
e
The axillary artery can then be considered in three parts. The first, before pec minor. The second part, as the artery passes behind pec minor, and the third after the muscle passes pec minor. We will look at these below.
 |
| From Duke's Anatomy Website - an extremely good resource |
a. The first part of the axillary artery - before it reaches pec minor: The axillary artery is enclosed in the axillary sheath. It gives of an arterial branch - The first branch of the axillary artery - this supplies the muscle serratus anterior.
b. The 2nd part of the axillary artery (posterior to pec minor): this gives off two branches:
1. The thoraco-acromial artery: supplies the anterior axillary wall and passes
medial to pec minor: from the second part of the axillary artery. This artery has four branches:
-a. Pectoral: supplies the breast, it gives off branches to the internal thoracic artery and lateral thoracic artery.
b. Deltoid: passes into the clavipectoral triangle with the cephalic vein
c Clavicular
è
Acromial - anastomoses with the supra scapular and posterior circumflex humeral arteries (see below).
2. Lateral thoracicThese supply the pectoral muscles and the breast.
The third part of the axillary artery: this is the part of the axillary artery distal to pectorals minor and gives off three branches
a. Subscapular artery: largest branch, divides into circumflex scapular and thoracodorsal arteries, supplies serratus anterior, teres major, subscapularis, and latissimus dorsi muscles. Did you notice one of the rotator cuff muscles? Yep, the sub scapular artery from the third part of the axillary artery supplies the subscapualris. The circumflex scapular also makes a connection with the deep branch of the transverse artery which comes off from the thyrocervical trunk (which itself is a branch from the subclavian artery). 
b. Anterior and posterior circumflex humeral arteries- Termination: The axillary artery passes behind pectorals minor, becomes the brachial artery distal to the inferior border of teres major.
T
The shoulder joint itself will be discussed in more detail in a later post.
-
Reference:
Subscapularis - https://media.baselineresearch.com/images/551517/551517_full.jpg
Supraspinatus - http://inboundchurch.org/2015/02/09/7-nonsexual-physical-love-touches-5-love-languages/
Teach me anatomy
Problem Based Anatomy, Canby
rotator cuff picture from https://shoulderelbow.org/2016/12/12/arthroscopic-rotator-cuff-repair/
Medicalook.com
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