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Overview of the humerus and scapula.
If there is one thing that creates drama in an action movie or a hit t.v. medical series is someone with a dislocated shoulder. I mean these movies or on t.v., dislocated shoulders are usually treated in two ways. One, there is a fearless action hero who is obviously far too badass to feel pain. He simply just snaps his shoulder back into place with an uncomfortably loud crunch and jumps right back into action. Or, two, a brave doctor who grabs his patient’s arm and jerks it dramatically back into place with a painful scream and, once again, that shattered-making crunch noise just for dramatic effect.
Fortunately, in reality, shoulder dislocations, although painful are not always so widely torturous and dramatic. With the right conditions and technique, a dislocation can be fixed or reduced in medical term lingo with minimal effort – just like this.
Interested to know more? I hope so, because in this tutorial, we will be learning all about this as we explore the beautiful humerus and scapula.
So, in this tutorial, we are going to study and explore the two primary bones of the shoulder joint which are, of course, the humerus – the long bone of the arm – and the scapula, which you and I might commonly refer to as the shoulder blade. In our illustration, you can also see this bone here, which is the clavicle, but we’ll be leaving the discussion of that bone for another tutorial. We will, of course, be looking closely at how the humerus and scapula articulate together to form then the shoulder joint, which you might also hear refer to as sometimes on your anatomy class as the glenohumeral joint.
The shoulder joint is one of the most flexible and mobile joints of the entire body and is capable of performing a wide range of specialized movements. The high mobility of the shoulder joint comes with a price, however, and it is also one of the most unstable joints of the body and can become dislocated relatively easily. But more on that later. Let’s first get to know the two member bones of this articulation, beginning with the humerus.
So here we are at the anterior view of the humerus and the first structure that you can clearly see here is the head of the humerus which is dome-shaped in appearance. You could see it lies at an angle to the shaft or body of the humerus, which then allows to articulate with this structure here which is known as the glenoid cavity of the scapula.
Now moving laterally from the head, you can see this prominence here which is known as the greater tubercle, and medially, you’ll find another prominence, a smaller one, known as the lesser tubercle. Now as you can see here, each tubercle forms a well-defined ridge along its length which is known as a crest. So, the crest formed by the greater tubercle is known as the crest of the greater tubercle, and similarly the lesser tubercle forms another crest known as – you guessed it – the crest of the lesser tubercle.
Now between these two crests formed by the greater and lesser tubercles, you’ll find the sulcus or groove known as the intertubercular sulcus, also commonly referred to as the bicipital groove. The reason it’s known as the bicipital groove is because this is where you will find the proximal tendon of the long head of the biceps brachii muscle as it courses distally towards its muscular belly in the arm, and one final point in relation to the proximal end of the humerus are the necks of the humerus.
Yes, you did hear me correctly I said necks, just to make things a little bit more complicated. The humerus has not one but two defined necks for us to then examine. The first is this one here which is known as the anatomical neck of the humerus. The anatomical neck is located around the circumference of the humeral head proximal to both tubercles. The second neck of the humerus is the surgical neck which you can now see highlighted in green. This is located distal to the tubercles and is called the surgical neck due to the fact that this region is quite prone to fracture which often requires then – you guessed it – surgery for treatment.
And we’re going to continue distally now along the length of the humerus which is known as the shaft or body of the bone. From an anterior perspective, we can divide the surface of the bone into an anteromedial and anterolateral surfaces by following the anterior border which runs from the crest of the greater tubercle to the distal end of the humerus.
I’m going to draw now your attention to the lateral midshaft of the humerus where we’re going to find another prominence with the somewhat roughened appearance. This is known as the deltoid tuberosity. And as the name suggests, this is a point of insertion or distal attachment for one of your muscles – yes, that muscle in your shoulder which is known as the deltoid muscle.
Now if we move distally, you’re going to be finding a pair of fossae or depressions on the anterior aspect of the distal end. The first is the fossa here known as the radial fossa which is located laterally, and on the medial side, you will see the second fossa which is known as the coronoid fossa. And true to their names, these fossae accommodate the head of the radius and coronoid process of the ulna respectively.
And just distal to these fossae are two important landmarks. The first one is this one right here, this is known as the capitulum which articulates with the head of the radius. Just medial to the capitulum, you’re going to find another structure known as the trochlea and this is what’s going to articulate with the ulna. A little bit of knowledge that might help you connect the dots here is that the term “trochlea” comes from the Latin word for “pulley”, and if you look at the shape of this landmark, you can easily see how it got its name.
Along the medial border of the distal end, you will see a prominent expansion which is known as the medial epicondyle which provides attachment for several of the anterior or flexor muscles of the forearm. Just proximal to the medial epicondyle and continuous with the medial border which we identified earlier is the medial supracondylar ridge.
On the opposite side, we have a similar but smaller expansion which is known as the lateral epicondyle and in a similar fashion to its medial counterpart provides attachment to some of the muscles – to the posterior muscles or extensor muscles of the forearm, to be more specific. And once again if we examine the distal end proximal to the lateral epicondyle, we have the lateral supracondylar ridge which is continuous with the lateral border of the shaft.
We’re now going to flip over to the posterior aspect of the humerus where you can still see the clavicle here, and the scapula also on their posterior views. Focusing specifically again on the humerus, the first structure that we explored on the anterior view was the head of the humerus which you can still see it here. And, remember, along the perimeter of the humeral head, we identified the anatomical neck of the humerus.
Moving a little more lateral, we will again see the greater tubercle that we identified on the anterior view. If we look across the length of the posterior shaft of the humerus, remember that we defined this region here as the surgical neck of the humerus. On your right is the lateral border of humerus, and on the left, we have the medial border. Now, the surface area between these two borders is then unsurprisingly referred to as the posterior surface of the humerus.
Along the posterior shaft, we have one major landmark of interest to quickly mention, which is this groove here curving outwards towards around the lateral border – and this is known as the radial groove. You may also sometimes hear it referred to as the spiral groove or the groove for the radial nerve. The last name, of course, gives away what structure runs through this groove and that is the radial nerve.
Continuing down to the distal end of the bone, let me quickly introduce you to once again the medial epicondyle and supracondylar ridge as well as the lateral epicondyle and supracondylar ridge. One important thing to notice here is this depression just lateral to the medial epicondyle, we call it ulnar groove or groove for the ulnar nerve – and I’m sure you can guess what nerve passes here.
And continuing laterally, we can again see the trochlea of the humerus which we said articulates with the ulna. Right above the trochlea, you can see a very clear and noticeable fossa here. This is known as the olecranon fossa in which, true to its name, accommodates the olecranon of the ulna.
And with that, we have covered the major parts, surfaces, and landmarks of the humerus, it’s time to move on to the second bone of this tutorial which is, of course, the scapula.
The scapula is this flat triangular-shaped bone seen here in green, and as I mentioned earlier, it is commonly also known as the shoulder blade due to the fact that its sharp borders and spine are easily palpable behind the shoulder. So before we go on and define and talk about the different bony landmarks of the scapula, we should first talk about the borders and the angles that you find in this bone.
We’re going to first start defining the angles and being a triangle, there are three that you need to know. The first two are both located along the medial aspect of the bone. Here we have the inferior angle and here is the superior angle which you might also hear refer to as the medial angle of the scapula. Moving across to the lateral aspect of the bone, we see that the third angle is less well defined compared to the other two but is still referred to as the lateral angle of the scapula or perhaps more commonly known as the glenoid process.
Now that we have defined the three angles, we’re going to talk about the borders and, once again, there are three that you need to know. The first one is known as the medial border, this is the longest border and as you can see here, it extends from the superior angle all the way down to the inferior angle. The second border that you need to know is the lateral border which extends from the lower margin of the glenoid process all the way down to the inferior angle. And the last border for us to name is this one which is the superior border. This is the shortest and thinnest of the three borders and extends from the superior angle across to this narrowing of the glenoid process which is known as the neck of the scapula.
Now, it is time for us to talk about the bony features of the scapula and we’re going to start first by looking at the scapula from an anterior perspective. As you can see in this beautiful illustration, the anterior surface is dominated by a large single depression or concavity which is known as the subscapular fossa. Most of the surface of the subscapular fossa gives origin to the subscapularis muscles which extends laterally to the humerus. The concave anterior surface of the scapula is also known as the costal surface, due to the fact that it largely lies upon the convex superolateral surface of your rib cage forming what is known as the scapulothoracic joint. This is what’s known as a physiological joint as opposed to a true anatomical joint due to the fact that there is no bony articulation here.
Our last point of interest on the anterior aspect of the scapula is this rather unusual looking process extending anterolaterally from the superior border of the scapula. This is known as the coracoid process of the scapula. The term coracoid is of Greek origin and said to refer to something like the hook or beak-shaped, so I’m sure you can see why the coracoid process got its name. This landmark is an important attachment site for several muscles such as the short head of the biceps brachii, pectoralis minor, and coracobrachialis muscles.
We’re now going to turn our attention to the posterior aspect of the scapula and once again, you can also see a few structures that are specific to the posterior side, and the first and most obvious one is this structure here which is the spine of the scapula. The structure first and foremost acts as a divider for the posterior surface of the scapula into two major convex fossae. These are the supraspinous fossa – supra meaning above the spine – and also the infraspinous fossa – infra meaning then below the spine. We can also clearly see that the infraspinous fossa is much larger than the supraspinous fossa. Both of these surfaces each provide attachment for muscle of the rotator cuff which are the supraspinatus and infraspinatus muscles respectively, but you should have no problem remembering that.
One interesting point about the scapula that many students don’t realize is exactly how thin the body of the scapula is so much so it’s translucent – meaning it’s thin enough to allow light to pass through. To really appreciate this, check out this cross-section of the thorax and upper limbs. If you look closely, you can see the thickened medial and lateral borders of the scapula here with the fine and delicate body of the scapula here, sandwiched between the subscapularis and infraspinatus muscles.
Now looking along the length of the spine of the scapula, you’re going to find a triangular base medially which arises laterally across the scapula to terminate in a large flattened process. This is the famous acromion, highlighted now for you in green. The acromion terminates as its apex where it articulates with the acromial end of the clavicle bone and what’s known as the acromioclavicular joint. This somewhat small articulation is extremely important for the positioning of the scapula and shoulder joint as a whole.
With that in mind, we’re going to move on to the next structure that we’re going to see now just inferior to the acromion which is, of course, the glenoid cavity, also known as the glenoid fossa. This is a very important surface located laterally on the scapula at the distal end of the glenoid process. The glenoid cavity articulates directly with the head of the humerus, as you can see here on this image, to form the glenohumeral joint which we all commonly known as, yeah, the popular shoulder joint.
The glenohumeral joint forms what is known as a ball-and-socket joint, which the head of the humerus is a ball and the glenoid cavity is then the socket. As you may have already noticed, the glenoid cavity is relatively shallow and barely concave in form, therefore, some support structures are needed to hold the head of the humerus in place. And this support is largely supplied by a group of muscles which are known as the rotator cuff muscles.
If you’re curious to find out more about these muscles, be sure to check out our video tutorial on this very topic, which you can find on our website.
Now before we finish up with the glenoid process, there are two small bony landmarks worth mentioning. The first is this one here located just superior to the glenoid cavity which is known as the supraglenoid tubercle. This provides the proximal attachment point or origin of the long head of the biceps brachii muscle, and then below the glenoid cavity, you’re also going to find another tubercle known as the infraglenoid tubercle, which provides attachment for the long head of the triceps brachii muscle.
And to complete our study of the scapula, I want to give you some helpful notes in regards to the position of the scapula on the thoracic wall. First point is that the base of the scapular spine is usually at the same level of the third or fourth thoracic vertebrae. The next point is that the inferior angle of the scapula lies between the ribs seven and eight. The third and final point to make on this tutorial is that when your arm is in the abducted position, the medial margin should be roughly parallel to the row of the spinous processes on your vertebrae.
And with that, we have discussed all you need to know about the scapula. Now before we move on to the nitty-gritty on the shoulder dislocations – I’m sure you’re looking forward to that part – but let’s briefly take a look at some of the soft tissue structures related to the scapula and humerus namely ligaments found in this region. These are easy to learn, thankfully, as their names all tell us where they are found.
Now let’s take a look and first up is this ligament here which is known as the coracoclavicular ligament which as its name suggests extends between the coracoid processes of the scapula to the clavicle. It’s actually composed of two ligaments. The more medial is known as the conoid ligament which originates from the knuckle of the coracoid process and the trapezoid ligament which runs from the trapezoid edge of the coracoid process. One primary function of this ligament is to hold the acromial end of the clavicle in place preventing it dislocating from the acromioclavicular joint.
Next up is the coracoacromial ligament which as I’m sure you’ve guessed extends from the coracoid process to the acromion of the scapula. This ligament forms what is known as the coracoacromial arch, and which you will find this structure here which is the subacromial-subdeltoid bursa. The final group of ligaments which I would like to mention today are these ones surrounding the shoulder joint which are the glenohumeral ligaments, also known as Flood’s ligament.
There are three ligaments in this group which are the superior, middle and inferior glenohumeral ligaments. All three generally function to reinforce the articular capsule of the glenohumeral joint but each have specific roles in the stabilization of the head of the humerus depending on the position and rotation of the arm.
And that’s it. If you can remember the anatomy we’ve learned today, you will surely be a whiz when it comes to the anatomy of the humerus and scapula. To finish off today, let’s take more of a clinical focus on the shoulder joint for a moment and return to the expected topic of shoulder dislocation.
So, first things first, if you find yourself in a situation where you have dislocated your shoulder, please don’t try to pop it in, no matter how tough you think you are. Now shoulder dislocation, the method of treatment for dislocation of the shoulder is known as shoulder reduction. And since this is a relatively common injury, a long list of reduction techniques have been developed over the years using various methods to manipulate the head of the humerus back into the glenoid cavity.
One thing which many of them have in common, they hurt. And because of this, most patients undergoing shoulder reduction needs some form of sedation to help them manage their pain during the procedure. Fortunately, though, pain is not always prescribed for shoulder reduction, and one method which is considered relatively painless is the Cunningham method – one of the more recently developed techniques for shoulder reduction.
The Cunningham method is particularly suited for reduction of anterior dislocation of the shoulder joint, which means the humeral head has moved anteriorly out of the glenoid cavity. The method involves no pulling, jerking or twisting but rather massaging of the trapezius, deltoid and biceps brachii muscles with particular emphasis on the biceps with the arm in an adducted position. When the biceps brachii is fully relaxed, the patient is directed to shrug their shoulders which encourages the humeral head to slip back into place. Of course, this method is not always successful as it relies on the patient to relax enough to cooperate, which is understandable, or sometimes it’s not possible to bring the arm into an abducted position.
And that’s it, our tutorial is now complete, but before I let you go, I would like to do a quick summary of the structures, the anatomy that we talked about on this tutorial. We started our tutorial with the proximal end of the humerus where we explored the head of the humerus as well as the greater and lesser tubercles, which were separated by the intertubercular sulcus. At the proximal end of the humerus, we discovered not one but two necks of this bone which were the anatomical neck located around the circumference of the humeral head and the surgical neck which is found distal to the tubercles at the proximal end of the shaft of the humeral.
On the lateral aspect of the shaft, we identified this prominence here which is the deltoid tuberosity and moving on to the distal end of the humerus, we defined several bony landmarks which included the medial and lateral epicondyles as well as the medial and lateral supracondylar ridges. Between the epicondyles, we located two fossae which were the radial and coronoid fossae. The distal end of the humerus articulates with both radius and ulna of the forearm via these two bony structures which are the capitulum and trochlea of the humerus. We then turned our attention to the posterior aspect of the humerus where we identified some additional points of interest such as the radial groove and the olecranon fossa, which brought to an end our study of the humerus.
In regards to the scapula, we first identified three angles and borders of this triangular-shaped bone. They were the inferior angle located here, the medial angle, and the lateral angle which we can also refer to as the glenoid process. On the anterior aspect of the scapula, we looked at the subscapular fossa which covers almost the entire anterior surface of the bone. After that, we examined this bony protrusion here known as the coracoid process which is located just lateral to this landmark that is the suprascapular notch.
Turning now to the posterior aspect of the scapula, our major point of reference is this structure here which is the spine of the scapula that separates the posterior surface of the scapula into the supraspinous and infraspinous fossae. At the lateral end of the spine, we examined the flattened process here known as the acromion which extends anterolaterally to articulate with the clavicle at the acromioclavicular joint. Now our final region of interest of the scapula was this surface here which is the glenoid cavity of the scapula which accommodates the humeral head.
And before we finished our anatomical study of these two bones, we briefly identified some of the major ligaments found here which included the coracoclavicular ligament, the coracoacromial ligament, and the glenohumeral ligaments.
Now that you have completed this tutorial, please be sure to continue your learning experience by applying your knowledge using our quiz section as well as exploring our articles and atlas pages – everything you need to continue and really solidify this topic on the humerus and scapula.
So good luck everyone and I will see you next time.