Shoulder joint: Movements, bones and muscles - Human Anatomy | Kenhub

you're feeling all set for your anatomy exam you've absolutely nailed the shoulder joint you know everything what it looks like from the front from the back from the uh oh didn't look at it from the side it is a bit of an odd angle to study anatomy from but it gives us such a great perspective of the joint and really helps us with the interaction and relationships of muscles from the anterior and posterior sides in this tutorial we're going to explore the shoulder joint from a lateral view so when you get those questions on your

next exam you'll nail those too before we get started here's a quick overview of what we'll cover in this tutorial we'll start by reminding ourselves what the shoulder joint is including the bones involved and some of their features we'll then look at the joint cavity itself and identify a few specific features of it next we'll discover some ligaments associated with the joint and then move into muscles that strengthen and move the joint as well finally we'll look at a few bursi that help relieve pressure and friction within the joint before moving on to the clinical

notes ready for it here we go first up a quick review of the shoulder joint itself the shoulder joint also called the glenohumeral joint is in the proximal part of the upper limb it is a ball and socket type synovial joint which means it has a wide range of movements including flexion and extension abduction and adduction medial and lateral rotation and circumduction it is the most mobile joint in the body so which two bones actually make up this joint well the first bone we'll look at is the humerus the feature of the humerus that articulates

as part of the glenohumeral joint is this smooth articular surface here the head of the humerus other features of the humerus are related to structures that help to stabilize the joint these two raised areas on the anterior aspect of the proximal humerus the lesser and greater tubercles between them you'll find the inter-tubercular groove or sulcus while we're here i'd also like to point out the anatomical neck of the humerus all of these features are attachment sites for structures and we'll learn more about these a little bit later next up we have the scapula colloquially known

as the shoulder blade this triangular flat bone has a few key structures that are particularly relevant to the shoulder joint we'll look at them from the anterior aspect which you're probably used to and then from the more unusual lateral view which is our main focus of the tutorial the surface of the scapula that articulates in the shoulder joint is the glenoid cavity and is on the lateral aspect of the scapula we'll see this again later on at the superior end of the glenoid cavity is a bony process called the supraglenoid tubercle at the inferior end

is the infraglenoid tubercle both of these tubicals are attachment sites for muscles that support the shoulder joint this boning projection that is superior to the shoulder joint is the acromion process try palpating it yourself find the long hard ridge on the back of your shoulder and follow it laterally and superiorly when you come to the end just above your shoulder joint you've found your acromion and finally this bony feature that projects anteriorly is the coracoid process we'll see the importance of these processes in joint stabilization later on the image that we're going to be looking

at a lot today is with the humerus removed from the shoulder joint because of this we can see into the joint itself and get a better idea of how the ligaments and the muscles interact with the joint so in this image we see the scapula and the surrounding muscles isolated from the rest of the body and are looking at it from a lateral view to the right of the image is the anterior aspect and to the left of the image is the posterior aspect from this lateral view we can see those same five features of

the scapula that we just identified highlighted in green now is the glenoid cavity the articular surface of the scapula for the glenohumeral joint at the superior aspect is the supraglenoid tubercle and inferiorly is the infraglenoid tubercle the large bony process highlighted now is the one we palpated superior and posterior to the shoulder joint this is the acromion it's important to note that the acromion doesn't usually contribute to the glenohumeral joint but it does articulate with the clavicle to help form the shoulder girdle and the final feature we looked at is highlighted now the coracoid process

this more anterior projection of the scapula does not articulate with any other bones but is an important attachment site for ligaments that help to stabilize the shoulder joint all right so that's the basics covered let's get into the joint cavity itself and see what we can find there alright so i know this is the third time we're covering this already but i promise you it's the very last time okay so again we can see the glenoid cavity highlighted in green and there are just a few extra things i want to point out to understand the

shoulder joint it's best to look at it from an anterior aspect remember we said that the shoulder joint is a ball and socket joint while the glenoid cavity also called the glenoid fossa forms the socket part of the joint as you can see from its very shallow curve although it is the socket portion it isn't a very good one in addition the surface area of the humeral head is approximately four times larger than that of the glenoid cavity so as you can imagine that results in a relatively small contact area between the two at any

given time this is beneficial though for us in terms of mobility of the joint but it means stability is compromised there are however some extra structures that support the shoulder joint and help to give it some extra stability in fact the shoulder joint relies more on the surrounding muscles and ligaments for its stability than it does on its bony elements the first is this structure highlighted now called the glenoid labrum the glenoid labrum is a fibrocartilaginous ring attaching around the outer margin of the glenoid fossa this helps to deepen the glenoid fossa giving the socket

part of the joint a bit more of a functional socket shape surrounding the glenohumeral joint is the joint capsule which we can now see highlighted in green like all synovial joints the joint capsule made from an outer fibrous layer and an inner synovial membrane the inner synovial membrane secretes synovial fluid which fills the joint capsule lubricating it it's easy to forget looking at the lateral aspect that the structures in question extends beyond the plane of the glenoid cavity the fibrous part of the joint capsule actually engulfs the whole humeral head and extends far beyond the

margin of the articular surface to the anatomical neck of the humerus the glenoid cavity together with the capsule form a roughly spherical space around the humeral head called the osteofibrous acetabulum the joint capsule doesn't do all the work alone anteriorly and inferiorly the joint capsule is strengthened by some ligaments which we'll look at next as well as other supportive ligaments the first ligament we'll look at is highlighted in green now this is the coraco humeral ligament and you'll notice that its name is quite indicative of its attachments we can just about see it running from

the posterior aspect of this bony feature of the scapula that we identified earlier the coracoid process and the cut end here which will continue to insert on the humerus which is exactly what we can see if we switch to the anterior view of the joint from this anterior view we can't see the attachment of the ligament on the coracoid process very well that's because it's coming from the posterior aspect of it if we flip back to the lateral view image we can see that attachment point on the posterior side we can though see the humeral

attachment the ligament flares out into an anterior and posterior band attaching to the lesser tubercle and the greater tubercle respectively the coricohumeral ligament is important in preventing inferior displacement of the humerus next up we're looking at a set of three glenohumeral ligaments starting with the superior glenohumeral ligament in the image on the right we can also see it from an interior view it spans the joint from the supraglenoid tubicle of the scapula to the medial ridge of the inter-tubercular groove of the humerus this ligament works with the coricohumeral ligament to help prevent inferior displacement of

the humerus moving inferiorly we come across the middle glenohumeral ligament this ligament is across the anterior aspect of the joint originating inferior to the superior glenohumeral ligament and inserting on the lesser tubercle of the humerus the middle glenohumeral ligament adds to the anterior stability of the joint the last of the glenohumeral ligaments is the inferior glenohumeral ligament as i'm sure you've guessed it's the ligament that is running across the inferior aspect of the joint it originates mostly along the inferior edge of the glenoid margin we can see part of it from this anterior view as

well laterally the inferior glenohumeral ligament mostly attaches onto the neck of the humerus a little note here is that all the ligaments we've discussed so far blend with the capsule and are not clearly distinguishable this final joint supporting ligament we'll look at is quite different from the ligaments we've seen so far in that it is completely separate from the joint capsule this is the coracoacromial ligament from this lateral view we can see it running from the coracoid process anteriorly to the larger acromion process posteriorly this anterior view of the joint allows us to see this

ligament as well in both views we can see how this ligament provides a superior arch above the humerus you didn't think the ligaments do all the work to support the shoulder joints did you we also have lots of help from a group of muscles surrounding the joint so let's have a look at some of those let's start with a group of muscles that you might already be familiar with perhaps because of all the injuries we're quite used to hearing about and of course we're talking about the rotator cuff the rotator cuff is a group of

four muscles which creates a compressive force around the humeral head ensuring its stability against the glenoid cavity in every position and helping to center it the muscles that make up the rotator cuff are the supraspinatus the infraspinatus the teres minor and the subscapularis let's take a closer look at them one by one first up is the muscle found on the superior aspect of the joint this is the tendon of the supraspinatus the first of our rotator cuff muscles the supraspinatus muscle originates from the supraspinous fossa of the scapula and inserts on the greater tubercle of

the humerus it crosses the superior aspect of the shoulder joint where its tendon blends with the joint capsule we'll come across a structure in the next section called the bursa that helps to reduce friction between this muscle tendon and the surrounding structures posteriorly the joint capsule is strengthened by the infraspinatus muscle tendon which we can see highlighted now the infraspinatus originates from the infraspinous fossa of the scapula and also inserts on the greater tubercle of the humerus this tendon crosses the shoulder joint posteriorly strengthening it from that aspect moving inferiorly now we can see the

teres minor muscle and tendon also contributing to the strengthening of the shoulder joint capsule this muscle originates from the lateral border of the scapula and also inserts on the greater tubercle of the humerus the last of our rotator cuff muscles is also the only muscle on the anterior aspect of the glenohumeral joint we're looking of course at the subscapularis muscle from this anterior view of the scapula and humerus we can see that the subscapularis originating from the subscapular fossa and inserting onto the lesser typical of the humerus just like supraspinatus this muscle also has an

associated bursa which we'll discover soon now we're moving to muscles which are not part of the rotator cuff but still contribute to the stability of the shoulder joint highlighted now is the teres major muscle it crosses the joint much more inferiorly than the other muscles we've been looking at so it does not attach to or blend with the joint capsule as many of the others do it originates from the inferior angle of the scapula which we can see on this image of the posterior aspect of the joint and inserts on the anterior aspect of the

humerus specifically the medial lip of the intertubercular groove of the humerus if we swap back to our lateral view of the shoulder joint we can see the posterior to anterior trajectory of the muscle even at this cut level the most inferior aspect of the joint is where we find the long head of the triceps brachii muscle the long head of the triceps brachii originates from the infraglenoid tubercle which is the bony feature of the scapula highlighted on the image on the left it travels distally to blend with the other two heads of the triceps brachii

and insert on the olecranon process of the ulna the long head is the only head to cross the shoulder joint the final muscle that contributes closely to the stability of the glenohumeral joint is the long head of the biceps brachii the tendon of which we can now see highlighted in green the tendon of the long hand of the biceps brachii originates from the supraglenoid tubercle of the scapula in the image on the left we can see the tendon originating within the joint capsule it then continues to travel within the joint capsule over the humeral head

and into the inter-tubercular groove on the humerus it then merges with the short head of the biceps brachii and inserts into the radial tuberosity as well as the deep forum fascia via the bicipital aponeurosis okay so swapping from strengthening support we'll now look at some versi which act as cushions within the joint space bursi are small sac-like structures normally found between joints and ligaments or tendons the largest bursa associated with the glenohumeral joint that we can see from this angle is the subacromial bursa now highlighted in green these are the cut edges of the fluid-filled

sac you can see here that it lies deep to the coracochromial ligament and the acromion process which is how it gets its name inferior to it we find the joint capsule and the supraspinatus muscle tendon therefore the subacromial bursa creates padding between these structures if we look at the same structure from the anterior aspect we can again see the subacromial bursa highlighted just inferior to the acromion process and the coracoacromial ligament laterally the subacromial bursa extends to lie deep to the deltoid muscle so also has a portion called the sub deltoid bursa the subdeltoid portion

is the portion here these bursty together help to reduce friction protect the joint capsule and prevent wear of the supraspinatus tendon in particular during abduction it's important to note that this bursa does not normally communicate with the joint capsule so in case of an infection it likely won't spread to the glenohumeral joint the other bursa we can see from this lateral view of the shoulder is on the anterior aspect it is the subtendiness bursa of the subscapularis just as its name suggests it sits beneath the tendon of the subscapularis muscle to reduce friction and prevent

wear of the subscapularis tendon unlike the subacromial bursa we just looked at the subtendinous bursa of the subscapularis normally does have an opening which connects it to the glenohumeral joint this means that any infection arising in it will likely pass into the joint too and there you have it the structures of the glenohumeral joint as seen from a lateral view we mentioned a lot of structures today many of which can be damaged in this highly mobile joint we'll take a quick look at the clinical correlate of one of these structures now the subacromial bursa which

we can see highlighted with the subdeltoid bursa in this image can become inflamed causing subacromial bursitis this inflammation can result from overuse or trauma since the acromial bursa is between the tendon of the supraspinatus and the acromion process it is often aggravated when the shoulder is abducted but subacromial bursitis can also cause pain when lying on the affected shoulder those with damage to structures under the acromion process such as the subacromial bursa and the tendon of the supraspinatus often exhibit painful arc syndrome which is pain felt when the arm is abducted between 60 and 120

degrees at less than 60 degrees there usually isn't much pain and once the arm is abducted more than 120 degrees there's a great sense of relief this is because the injured structures are compressed and aggravated within the 60 to 120 degree range and there you have it you're now ready to ace your spotter exam looking at the shoulder from a lateral view but before i let you go let's quickly review what we looked at today we began with features of the joint cavity itself identifying the glenoid cavity of the scapula which is the articular surface

of the scapula involved in the glenohumeral joint the glenoid cavity is deepened by the glenoid labrum of the scapula a fibrocartilaginous ring we then saw the glenohumeral capsule which surrounds the entire joint next we looked at ligaments which helped to strengthen the capsule and stabilize the joint we started with the most superior one the coracohumeral ligament running from the coracoid process to the humerus anteriorly we identified the three glenohumeral ligaments the superior glenohumeral ligament the middle glenohumeral ligament and the inferior glenohumeral ligament the final ligament we identified was the coracoacromial ligament which forms a superior

arch over the shoulder joint the next group of structures we identified from this lateral view of the shoulder joint were muscles first we looked at the four muscles that make up the rotator cuff superiorly we found the tendon of the supraspinatus originating from the supraspinous fossa of the scapula inferior to that on the posterior aspect of the joint we saw the infraspinatus which inserts onto the greater typical of the humerus moving in fury again is where we found the teres minor also inserting onto the greatest tubercle of the humerus finally on the anterior aspect we

found the subscapularis muscle inserting onto the lesser typical of the humerus the most inferior of the muscles we looked at was the teres major traveling to the anterior aspect of the humerus to insert onto the medial lip of the intertubercular groove originating just inferior to the glenoid cavity on the infraglenoid tubule was the long head of the triceps brachii and finally superiorly we saw the long head of the biceps brachii within the joint capsule originating from the supraglenoid tubercle the final group of structures we identified were a couple of fluid-filled cushions called bursi first was

the subacromial bursa which is found between the acromion process and the tendon of the supraspinatus while the other bursa the subtendiness burst of the subscapularis is on the anterior aspect found deep to the tendon of the subscapularis lastly we looked at the subacromial bursitis and painful arc syndrome that is experienced by those with an inflamed subacromial bursa and that brings us to the end of our tutorial i hope you enjoyed it thanks for joining me but don't let your learning stop there visit kenhub.com where you can read interesting articles test your knowledge with challenging quizzes

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