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Surface anatomy of the thorax and upper limb

Overview of the surface anatomy landmarks found on the thorax and upper limbs.

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Hey everyone! This is Nicole from Kenhub, and in this tutorial, we’ll be looking at the surface anatomy landmarks of the thorax, the upper limb, and the back.

With a bit of luck, you’ll unlikely to have a patient walk into your surgery looking like this. Fortunately, or perhaps, unfortunately, from a diagnostic perspective, most of our anatomy is hidden away, out of sight. It’s therefore important that we are able to recognize the landmarks that we can see, referred to as the surface anatomy, so that we’re able to find our way around the body. In fact, knowledge of surface anatomy is required to perform a range of classic methods of examination such as palpation, percussion, auscultation, inspection, and function testing.

In this particular tutorial, we’ll be focusing on the surface anatomy of the thorax, the upper limb, and the back. If you’d like to learn about the surface anatomy of other parts of the body, be sure to check out our other tutorials focusing on the head and neck as well as the abdomen and lower limb in more detail. For now though, let’s begin as promised by looking at the surface anatomy landmarks of the thorax.

Let’s start by looking at the jugular notch of the sternum. This notch is also known as the suprasternal notch and as we can see here is the small depression found at the upper border of the manubrium of the sternum. The lateral borders of this notch tend to be obscured by the tendons of the sternocleidomastoid muscle which we can see here extending upwards into the neck. Helping to form the lateral borders of this notch are the clavicles. The clavicles can be easily seen and palpated in most people and are commonly referred to as the collar bones. These elongated S-shaped bones also make up part of the shoulder girdle and allow for the attachment of quite a few important muscles and ligaments – for example, those that support the bones of the shoulder girdle.

The next landmark I want to draw your attention to is this slight bump on the top of the shoulder just here. This bony protuberance can be seen in most individuals and is formed by the acromioclavicular joint. This is the shoulder joint formed between the acromion of the scapula and the clavicle just here.

Moving down to the lower edge of the thorax, the next major landmark we can see is the costal margin. The term “costal” means rib which lets us know that this landmark is formed by the bottom edge of the rib cage resulting in the inverted V-shape we can see here. The costal margin marks the lower portion of the chest as well as the location of the diaphragm. This makes it an important clinical landmark and is used for some surgical procedures.

In this area, we can also identify the subcostal angle. Also known as the infrasternal angle, the subcostal angle is situated at the lower end of the sternum between the sternal attachments of the seventh costal cartilages. This is the point at which we can find the xiphisternal joint.

Depending on the build of the individual, the ribs themselves or the rib cage can also be visualized and easily palpated. The flattened external surfaces of the ribs are especially easier to define on either side of the thorax from the axilla or armpit downward. All of the individual ribs can be palpated relatively easily with the exception of the first ribs as they are covered by the clavicles.

Some of the muscles that cover the thorax may also be distinguished relatively easily in some individuals, one of these being the pectoralis major muscle, highlighted here, as well as the serratus anterior muscle, which can be quite prominent in individuals that are relatively physically fit or in individuals that do weight training.

Let’s flip around and look at some female surface anatomy for a little bit. So, also quite prominent and visible on the thorax mostly so on females but not exclusively are the mamma or the breasts. The size of the mamma in both males and nulliparous females – that is, women who have previously not given birth – varies, but in spite of this, they’re easily distinguishable. Also visible in this area is the nipple-areola complex comprised of areola and the nipple. The inframammary region is the region just beneath the breasts.

The midsternal line is really an imaginary landmark. Don’t mistake it for being unimportant, though, as this vertical line runs through the middle of the sternum between the mamma and is very important because it can help us determine the approximate location of the apex of the heart specifically at the level of the fifth intercostal space and nine centimeters to the left of the midsternal line.

Also somewhat easy to visualize and palpate in most individuals is the sternal angle, also known as the manubriosternal junction or the angle of Louis. The sternal angle is formed by the articulation of the manubrium and the body of the sternum as we can see better here if we look at the underlying skeletal anatomy. This joint is synarthrotic which means that it doesn’t facilitate any movement. This is a really useful landmark for a couple of reasons. Firstly, it indicates the level of the second pair of the costal cartilages and therefore the second ribs making it a useful reference point for our counting the ribs and, secondly, it indicates the level of the intervertebral disc between the fourth and fifth thoracic vertebrae.

Let’s move on to look at the surface anatomy of the upper limb. The first landmark of the upper limb we can see highlighted here is the rounded shape at the top of the arm caused by the deltoid muscle. This powerful and prominent muscle actually gets its name from its shape which short of resembles the Greek letter delta as you can see here. As we can see, this muscle forms the rounded contour of the shoulder which is why it is commonly known as the shoulder muscle.

The shape of the deltoid muscle can also be seen clearly from a posterior view and if we take a look at the muscle itself, we can see how this muscle wraps around and attaches to the scapula to help form the shapes we see on the tops of the shoulders.

If we remain here looking at the posterior aspect of the arm, the outline of the triceps brachii can also be easily distinguished. If an individual is relatively lean or very muscular, you may be able to see this upside down U-shape when the muscle becomes flexed. This impression is created by the shape of the tendinous fibers underneath as we can see in this image just here.

Looking now at the posterior aspect of the cubital fossa, a bony eminence can be seen which is the olecranon of the ulna. This eminence is more commonly known as the elbow. The olecranon serves as the attachment point for the triceps brachii muscles that straighten the arm, a sort of lever if you like. It also prevents the elbow from overextending. The prominence of this landmark while having its uses unfortunately carries the tradeoff of also making it pretty susceptible to trauma.

Turning around to look at the other side of the elbow close to the inferior insertion of the biceps brachii muscle, we can see a triangular area known as the cubital fossa. Also known as the elbow pit or the antebrachial fossa, this area is clinically important as it is where a stethoscope is placed over the brachial artery during blood pressure measurements. In addition, the superficial area just above the cubital fossa is often used for venous access or venipuncture and the brachial pulse can also be palpated at this fossa.

Just superior to the cubital fossa, the form of the underlying biceps brachii muscle is easily visualized. This two-headed muscle, like the triceps brachii, is also quite prominent when in action – for example, when you flex your arm or make a really tight fist.

Nearby, we can also see the region known as the axilla, more commonly known as the armpit or the underarm. This region is located directly under the glenohumeral joint at the junction of the upper limb and the thorax. This area of the body is typically characterized by hair growth and the formation of body odor due to the presence of a significant number of apocrine sweat glands.

The muscles that form the shape of the forearm that we see here are known as the antebrachial muscles. There are quite a few muscles in the forearm but we don’t need to list them all individually to understand their effect on the surface anatomy.

The lateral group forms this thickening we see here on the radial aspect of the forearm while the medial group also form a smaller but still palpable shape just here.

So now that we’ve gone through all the surface anatomy landmarks on the front of the body, now let’s look at the landmarks found on the back. Let’s start with this small bump at the top of the back known as the vertebral prominence. This landmark is the result of the spinous process of the seventh cervical vertebra which is especially long and therefore creates a bony surface bump that can be easily palpated. In this same region, we can spot the surface landmarks created by the underlying trapezius muscle. As we can see here, the trapezius is a very large, diamond-shaped quadrilateral muscle of the shoulder girdle that covers a particularly large portion of the back and also forms part of the shape of the neck.

Remaining on the upper portion of the back still, the outline of the scapula is also quite easily distinguishable and can be palpated here. The spine of the scapula as well as the medial margin and the inferior angle of the scapula are all quite easily identifiable. The scapula isn’t a stationary bone so keep in mind that its associated surface marks will also change position depending on the movement of the arm.

An interesting clinical note is that there’s a relative thinning of the musculature of the back situated along the medial borders of the scapulae. This area is known as the triangle of auscultation of the lungs, and during clinical examination, a stethoscope is placed on this region of the back allowing the clinician to hear the respiratory sounds more clearly.

Along the midline of the back, we can also see a longitudinal depression known as the spinal furrow. This landmark is continuous from the cervical region down to the gluteal cleft and overlies the vertebral column. It is formed by the combination of this and the adjacent sacrospinalis muscles. This line is easy to see in most people as it tends to be present regardless of the body fat percentage.

Another landmark on the back is one that is not always visible in all individuals. This rhumba-shaped contour is known as the rhombus of Michaelis and is believed to be of some clinical significance with respect to normal childbirth. Two landmarks that may also be visible in this region are the dimples of Venus. These dimples represent the point of which the sacrum attaches to the ilium of the pelvis. They are believed to genetic and so may not be present on all individuals. Also similarly distinguishable on the surface of the lower back is the form of the sacral triangle. This refers to the surface area over the sacrum which is a large triangular bone at the base of the spine highlighted in green just here.

Finally, moving further down, we can plainly see the gluteal region, which is characterized by the buttocks. The buttocks are formed by a group of three gluteal muscles – the gluteus maximus, the gluteus medius, and the gluteus minimus. At the inferior aspect of the buttocks, a sulcus or fold is formed known as the gluteal sulcus. Finally, in between the two buttocks, is a vertical groove known as the anal cleft. This groove which separates the two buttocks is also known as the intergluteal cleft.

Before we conclude the tutorial, let’s quickly summarize what we’ve covered.

We first saw how the surface anatomy landmarks play an important role in classic methods of examination such as palpation, percussion, auscultation, inspection, and function testing. Starting with the landmarks of the thorax, the first of these we looked at was the jugular notch of the sternum which is formed by the superior part of the manubrium and the clavicles. We then looked at the clavicles, otherwise known as the collarbones, and they form this ridge highlighted just here. At the distal ends of the clavicles, we can see the bump created by the acromioclavicular joint.

Moving down the thorax, we can palpate the costal margin which is essentially the border of the rib cage at the level of the diaphragm. The subcostal margin can be used to find the subcostal angle, and of course, as we saw, the ribs themselves form an easily palpable landmark on the thorax. All but the first rib can usually be felt on most individuals. On top of the ribs, we can often palpate the pectoralis major muscles which help form the shape of the chest. And also visible on muscular and lean individuals is the serratus anterior muscle.

Next, we hopped over to our female model, although the next set of landmarks are not exclusive to females. First, we have the breasts which are where we also find the areola which is the area of skin surrounding the nipple. Below the breasts, we also have the inframammary region and running down the center of the chest is the sternal line, which is really an imaginary landmark but is important in that it can help us locate the apex of the heart. Just superior to the sternal line is the sternal angle. This is a bony landmark created by the joint between the manubrium and the body of the sternum.

Moving on from the thorax to the upper limb, the next landmark we looked at was the shape of the shoulder formed by the deltoid muscle. Looking posteriorly further down the arm, we have the triceps brachii muscle which help to form the shape of the back of the arms.

A prominent bony landmark we can see here is the olecranon, otherwise, referred to as the elbow which serves as the attachment point for the triceps brachii and prevents the overextension of the joint. The prominence of this joint can make it susceptible to trauma.

Looking at the elbow joint again, this time anteriorly, we can see the cubital fossa or the pit of the elbow. This clinically relevant landmark is a common site for venipuncture and it is where a stethoscope is placed over the brachial artery during blood pressure measurements. Just superior to the cubital fossa, we then saw the distinguishable form made by the biceps brachii muscle and this also contribute to the form of the axilla or the armpit.

Moving down to the forearm region, we saw that the forms here are created by a lateral group of muscles and a less prominent medial group.

Turning over to look at the landmarks of the back, we then saw that the spine of the seventh cervical vertebra forms an easily palpable bony prominence just here. In the same area, we can also distinguish the forms created by the large trapezius muscle which extends down the spine almost to their lumbar region of the back. The landmarks created by the scapula can also be particularly prominent depending on the position of the arm. The medial margin of the scapula creates a landmark here. Whilst the inferior angle of the scapula can also be easily palpated, these landmarks are especially easy to distinguish when the arm is extended forwards.

We also saw that the spinal furrow created by the spinal column and the sacrospinalis muscle is easily distinguishable, even on overweight individuals.

Next looking at the base of the back, we can see the next couple of landmarks more clearly on our female model. We saw this shape referred to as the rhombus of Michaelis which is also where we might find the dimples of Venus on some individuals. Similarly here, we can palpate the sacral triangle which is caused by the underlying sacrum at the base of the spine.

Finally, we looked at the forms of the gluteal region which are the result of the buttocks or more specifically, the gluteus maximus, the gluteus medius, and the gluteus minimus. Also visible on the surface are the gluteal sulcus here and the anal cleft just here.

So that concludes this tutorial on the surface anatomy landmarks of the thorax, the upper limb, and the back. Be sure to check at our other tutorials on the surface anatomy landmarks elsewhere on the body.

See you next time!

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