Video: Regions of the upper limb

Whether you enjoy watching monkeys swing along tree branches at the zoo or have fond memories of playing on the monkey bars as a child, I bet you were too captivated to consider the specific regions of the upper limb that help accomplish the motion in these activities. You might be thinking, “Well, everyone knows the parts of their arms; after all, we use them every day.” However, the regions of the upper limb might not look as obvious as you think and understanding them, their descriptive terminology, and the contents of each region is crucial to recognize and communicate the location of structures, injuries, or pathologies. So hold on tight as we take a closer look at the main regions of the upper limb.

During this tutorial, we're going to review the main anatomical regions of the upper limb or extremity. We will take a look at the important terms related to the shoulder, the arm, the elbow, the forearm, and the hand. As we go through, we will take a deeper look at the subdivisions, main contents, and boundaries of these regions. Before we dive in, let's take a step back to establish a clear understanding of the regional anatomy within the upper limb. So, what exactly is meant by the term regions in this context?

Well, the upper limb is divided into different areas, or regions, that are assigned based on the positioning or the function of the underlying structures. Smaller regions often correspond to and are named after a specific structure such as the deltoid region being named after the deltoid muscle, whereas larger regions like the entire shoulder and more complex regions like the hand are further organized into subdivisions. With this knowledge, we are ready to explore precisely how regions are assigned in the upper limb.

Throughout its entirety, the upper limb is divided into anterior and posterior aspects based on the anatomical position. Furthermore, the arm, forearm, and hand are separated into anterior and posterior compartments by intervening fascia and a connective tissue intermuscular septum. So, are you ready to strengthen your knowledge of the upper limb? Great! Without further ado, let's get started with the shoulder region.

The shoulder is the most proximal region of the upper limb. Situated between the chest and the upper arm, the shoulder is bordered medially by the pectoral muscles of the chest, superiorly by the clavicle, posteriorly by the scapula, and inferiorly by the upper arm. The bony articulation of the humerus and the scapula forms one of the main contents of the shoulder – the glenohumeral or shoulder joint. The shoulder also contains two important subdivisions – the deltoid region and the axillary region.

The deltoid region spans around the shoulder and corresponds to the underlying triangular deltoid muscle. While this muscle creates a recognizable contour of the shoulder, it's important to understand that the deltoid region is distinct from the shoulder region and these terms are not interchangeable. As a subregion of the shoulder, the deltoid region is located superficially and laterally overlying the rotator cuff muscles that anchor and supports the shoulder joint itself.

The deltoid region can be further subdivided into the anterior and posterior deltoid regions. Situated along the medial border of the deltoid muscle and adjacent to the pectoralis major muscle is the deltopectoral groove. Although its name is hardly creative, this is an important landmark to keep in mind as it houses the cephalic vein and is the location where the coracoid process of the scapula is most easily palpable.

Residing underneath the shoulder joint at the junction between the superior portion of the upper limb and the thorax is the axillary region. Perhaps better known as the armpit, the axilla is a busy passageway of crucial neurovasculature to the upper limb. Within the axilla, the pyramidal-shaped space or gap created between the lateral thoracic wall and upper limb is known as the axillary fossa. The axillary fossa contains neurovasculature of the upper limb and muscles of the arm.

The axilla is boarded anteriorly by the pectoral muscles and posteriorly by muscles of the shoulder and back. Medially, it's bordered by the anterior thoracic wall, while laterally its border is the humerus. The apex of the axilla is the cervicoaxillary canal while its floor is the fascia of the armpit.

That wraps up the shoulder. Now let's move one region down and see what we can find in the arm.

The arm, or brachial region, is often thought of as the entire upper limb; however, this is not anatomically accurate. In anatomy, the arm only extends from the deltoid region of the shoulder superiorly down to the elbow region inferiorly. The arm region comprises an anterior and a posterior aspect. The anterior arm region contains the flexor muscles of the arm, the humerus bone, and the neurovasculature that supplies this region or continues its path down the limb.

The shape of the arm muscles creates two surface landmarks. The more medial of the two is known as the medial bicipital groove. It is a shallow indentation formed between the biceps brachii of the anterior arm and the triceps brachii of the posterior arm. If you have something medial, there'll be something lateral, right? Correct! The lateral counterpart of the medial bicipital groove is known as the lateral bicipital groove. It is formed by the contours of the same two muscles of the arm.

Let's now take a quick peek at the posterior region of the arm, also known as the posterior brachial region. Just like the anterior region, it covers the area between the deltoid and the elbow regions. This region contains the extensor muscles of the arm and corresponds to the posterior compartment of the arm muscles. The triceps brachii muscle is the primary extensor of the arm and defines the surface anatomy of this area.

That wraps up the regions of the arm. It's time to move on to the elbow.

The elbow region is pretty straightforward. It is a small area bordered superiorly by the arm and inferiorly by the forearm. Alternatively, this region is known as the cubital region and is divided into an anterior and posterior aspect. Situated between the anterior arm region and the anterior forearm region is the anterior region of the elbow. Within this region is a triangular depression called the cubital fossa, or simply, the elbow pit, which you may be familiar with if you've ever had your blood drawn. The main contents of this region are the tendon of the biceps brachii muscle and the neurovasculature traveling to the forearm.

Can you guess what's next? Buckle up, because it's the posterior region of the elbow. Also known as the posterior elbow region or the olecranon region, this pointed area contains the olecranon – a bony feature of the ulna that many traditionally envision as the elbow itself.

The time has come to move on to the elbow's immediate neighbor and take a look at the forearm.

Located just distal to the elbow is the forearm region, also referred to as the antebrachial region. There are two landmarks that you should know about in this region. When an individual is in the anatomical position, the most medial region is known as the medial border of the forearm, while the most lateral region is called the lateral border of the forearm. Easy!

The anterior region of the forearm, also known as the anterior antebrachial region, corresponds to the anterior compartment of the forearm. It contains the flexor muscles of the forearm, the ulna, and the radius and the neurovasculature of the forearm.

I'm pretty sure you can deduce what we're going to cover next – elementary, my dear Watson! It's the posterior forearm, also known as the posterior antebrachial region. This region corresponds to the posterior compartment of the forearm. Its contents include the extensor muscles of the forearm as well as the radial nerve and its deep branch, which innervate these muscles.

That wraps up the forearm. Let's now take a look at the small, yet busy region called the wrist.

The wrist, or the carpal region, corresponds to the area occupied by the underlying bones of the wrist called carpal bones. It allows for the passage of neurovasculature and muscle tendons into the hand. Considering we use our hands at pretty much everything, the wrist has a pretty important job.

The anterior region of the wrist houses the flexor retinaculum. As you can probably guess by its name, it keeps in place the tendons of the flexors of the digits as well as the median nerve, while also forming the roof of the carpal tunnel. Considering how many structures need to pass through this small area, it's not surprising that things can go haywire. You may be already familiar with the carpal tunnel syndrome, given how common it is. But if you want to learn more about it, stay tuned until the end, since we'll be sinking our teeth into all things carpal tunnel syndrome.

Can you figure out our next topic? That's right! It's the posterior region of the wrist. What you'll find in this region is actually really similar to the anterior region, but instead of flexor, we're now talking about all things extensor, specifically, the extensor retinaculum, overlaying the tendons of the extensor muscles that traverse this area.

That's the wrist done and dusted and we have finally reached our last, and arguably, the most complex region of the upper limb. That's right! It's the hand.

So, what's so special about the hand? Well, it has a very complex structure with a number of small bones and muscles. Collectively, they enable you to do tasks such as writing, using tools. and playing Candy Crush on your phone. This complexity is also reflected in the way that the hand is further subdivided into smaller regions.

Onto our first two regions!

While we always had an anterior and posterior division in the other regions of the upper limb, in the hand, we have the palm of the hand and the dorsum of the hand. As you can see, the palm does not comprise the whole anterior aspect of the hand, but rather, only the region between the wrist and the digits. Generally speaking, this region contains the flexor muscles of the hand as well as the associated neurovasculature.

The outline of these muscles is visible on the palm of the hand as two raised areas. Each of them is given a specific name based on their underlying muscle groups. The thenar eminence is the rounded area at the base of the thumb. It corresponds to the underlying thenar muscles responsible for fine movements of the thumb. The hypothenar eminence is a smaller and less pronounced area close to the medial margin of the hand, which repeats the shape of the hypothenar muscles found in this area. The hypothenar muscles are responsible for the movements of the little finger.

Where to next? We're off to the dorsum or back of the hand, of course.

This region contains the extensor muscles and tendons, dorsal interossei, and some neurovasculature. There's also a small important region on the dorsum of the hand. The radial foveola, perhaps more famously known as the anatomical snuffbox, is a triangular depression on the lateral part of the dorsum of the hand. It is found just distal to the wrist and is best visualized when the thumb is abducted. It contains neurovasculature supplying the hand.

Based on the underlying bones, the hand can also be divided into the metacarpal region and the digits. The metacarpal region is really straightforward. It simply corresponds to the area occupied by the metacarpal bones in the palm of the hand. Corresponding to the underlying phalangeal bones, we have the digits of the hand. The digits are numbered 1 through 5, starting with the most lateral digit known as the thumb moving sequentially to the index finger, the middle finger, the ring finger, and the little finger, sometimes also known as the pinky. Digits are often used synonymously with fingers. In anatomy, only digits 2 to 5 are fingers. The thumb or the first digit is not.

Two aspects are defined on the surface of the digits. The palmar surfaces of the digits of the hand are – you guessed it – on the same side as the palm of the hand or the anterior aspect of the hand. Contained within the palmar surfaces of the digits are the distal flexor tendons that bend the fingers, along with other muscles for intricate finger movements.

The dorsal aspect of the digits corresponds to the dorsum, or the posterior surface of the hand. It contains the phalanges and the distal extensor tendons, which help to extend the fingers.

The final structure we'll look at in this tutorial is not actually a structure. We're talking about the interdigital spaces. These are simply the spaces between the digits. There are four spaces for each hand.

Now that we've learned all about the upper limb, let's put on a white coat and get clinical.

As promised earlier, we're going to talk now about carpal tunnel syndrome. The carpal tunnel itself is a narrow corridor in the anterior region of the wrist that allows for passage of muscle tendons and pivotal neurovasculature including the median nerve. Compression of the median nerve by the overlying flexor retinaculum is the cause of carpal tunnel syndrome. Common symptoms include pain, burning, and tingling sensations in digits 1 to 4, but never the pinky.

Carpal tunnel syndrome commonly results in thenar muscle wasting. The syndrome worsens over time and often surgery is needed to fully alleviate the symptoms. This can be done through a procedure called carpal tunnel release, where the flexor retinaculum is cut to relieve the pressure on the median nerve.

All right, you can give yourself a pat on the back because you've mastered the regions of the upper limb. Before you run off though, let's summarize everything we learned today.

To start, we looked at the most proximal part of the upper limb – the shoulder. Next, we reviewed the subregions of the shoulder including the deltoid region and the deltopectoral groove. Next, we covered the axillary region, commonly known as the armpit. Then we move down into the arm, or brachium, to review the anterior arm region containing the flexor muscles. We also took a look at the medial bicipital groove and lateral bicipital groove within this region.

On the opposite side, we covered the posterior arm region containing the extensor muscles of the arm, namely, the triceps brachii. Just distal to the arm, we looked at the elbow. Here we went over the anterior region of the elbow containing the cubital fossa and the posterior region of the elbow which contains the bony olecranon of the ulna.

Continuing distally, we reviewed the forearm. Within its anterior and posterior subdivisions, we saw the flexor and extensor muscles of the forearm, respectively. Linking the forearm to the hand, the wrist was our next stop in the upper limb. We learned that the anterior carpal region contains the flexor retinaculum, tendons of the flexor muscles, and the median nerve. Within the posterior carpal region, we saw the extensor retinaculum and tendons of the extensor muscles.

Continuing on, we explored the complexity of the hand. In this region of the upper limb, we ditched the anterior and posterior terminology for the palm of the hand and the dorsum of the hand. We saw that the palm of the hand resides between the wrist and the digits and contains both the thenar and hypothenar eminences. The main contents of the dorsum of the hand included the extensor muscles and tendons and dorsal interossei muscles. We then took a closer look at the radial foveola, or the anatomical snuffbox.

Next, we briefly identified the metacarpal region and the five digits. We then mentioned the palmar surfaces of the digits and the dorsal surfaces of the digits. Finally, we concluded our tutorial by reviewing the four interdigital spaces of the hand that are simply the spaces between the digits.

For the clinical notes section, we looked at carpal tunnel syndrome. Specifically, we reviewed how it's caused by the flexor retinaculum compressing on the median nerve. We also discussed the associated symptoms and how it can be treated surgically through a carpal tunnel release.

We did it! Great work, guys! We hope you enjoyed this tutorial. See you next time and happy studying!