The Wrist's 8 Carpal Bones

 What is the Wrist?

The wrist is located between, and connects, the hand and the forearm. The wrist is of multiple ligaments, joints, muscles, and most importantly 8 bones. The 8 bones of the wrist are also known as the carpal bones, and include the hamate, capitate, trapezoid, trapezium, pisiform, triangular or triquetrum, lunate, and scaphoid (Kelley & Petersen, 2013, p. 626). These carpal bones are small and comes in different sizes and shapes to allow the wrist to flex, extend, rotate, and cause ulnar and radial deviations (Pulse Radiology Institute, n.d., slide 5). Each carpal bone is lined with cartilage to allow these smooth movements (Pulse Radiology Institute, n.d., slide 5). Along with providing movement for the hand, the wrist is also the pathway for many tendons, nerves, and blood vessels to pass through hand to the fingers (Pulse Radiology Institute, n.d., slide 5). 


How to Identify the 8 Carpal Bones on an Image

Now that we know the 8 carpal bones of the wrist, can you identify them on an image? I think trying to memorize these small 8 carpal bones can be quite difficult. That is why I created a way to memorize and identify these carpals. 

Take your left hand and put it facing down on a table; your hand should be in the prone position, also known as the coronal plane on an MRI of the wrist. Now, we are going to divide the 8 carpals bones into 2 groups, distal row and proximal row, with 4 bones in each row. Starting on the distal row, which is the distal end from body, from the pinky to the thumb, we have the mnemonic:

 Hammy's - Hamate

 Cirus - Capitate

[has]

 Trampolinists - Trapezoid (think of the like "O" in each word)

[and]

 Trapezist - Trapezium

 

On the proximal end, from the pinky to the thumb, we have the mnemonics:

 Princess - Pisiform

 Tiana - Triangular/Triquetrum

 Likes - Lunate

 Sam - Scaphoid

See picture below to match the colors to the respected carpal bone.

Left, dorsal view of the carpal bones in the CT coronal plane (Kelley & Petersen, 2013, p. 627)


Now how about trying to remember the look of each carpal bone? Well, to be honest, that is a struggle by itself. The carpal bones are irregular. This mean that no carpal bone on a wrist is the same. For this, I think it is much more difficult to remember the shape and sizes of each carpal bone to help identify them in an image. Also, shapes of each carpal bone changes in looks according to a specific plane. For example, the capitate bone looks different in a coronal plane than in a sagittal plane. Basically, it is more helpful to locate the carpal bones in their respected order than to remember the shapes of each. 

When scanning a wrist in MRI, not every patient is going to be position the same way. Some may have their wrist by their side, some may have their wrist over their head, and some may not be able to position their wrist in the supine position. So, how can be identify the carpals bones in different positions and planes in MRI?  Simple, let's start with the wrist in the supine position, or anterior view. We will be reading the carpal bones the opposite way from the order above, which is in the posterior view or prone. For example, reading from left to right, making the carpal bones on the thumb side be first and going in the order: trapezium, trapezoid, capitate, hamate on the distal row, and scaphoid, lunate, triquetrum, pisiform on the proximal row.

On an axial plane, we will be reading the slices from distal to proximal, meaning we will see the carpal bones on the distal end first and the slices will proceed through the proximal bones to follow (Burghart & Finn, 2012, p. 184). 


CT, Axial view of the distal carpal bones (Kelley & Petersen, 2013, p. 629)

On a sagittal plane, we will be scanning from the lateral to the medial side of the wrist (Burghart & Finn, 2012, p. 185). This means, we will be seeing the carpal bones on the thumb end first and slices all the way through the carpal bones on the medial side, where the pinky is. For example, we will see the trapezium (distal) and scaphoid (proximal) bone first, along with the radius. This applies when the wrist and hand is in the anatomical position, palm up. 

Don't forget, the distal end of the forearm is included in a scan of an MRI wrist. This means the ulna and radius is also included. In the anatomical position, the radius is on the lateral side of the forearm, or more easily, it is on the side of the thumb. The ulna is the thinner bone on the medial side of the forearm, where the pinky is.

I hope the tips that I provided in this blog helps you get a better understanding of the locations of each carpal bones and how to properly identify them in an MRI exam in different planes and positions. By learning the location of these carpal bones, you will also be able to identify other structures of the wrist, like the ligaments and joints surrounding the bones.

 

References

Burghart, G., & Finn, C. A. (2012). Handbook of MRI Scanning - E-Book. Elsevier Health Sciences.

Kelley, L. L., & Petersen, C. (2013). Sectional Anatomy for Imaging Professionals - E-Book. Elsevier Health Sciences.

Pulse Radiology Institute. (n.d.). Week 12: Wrist, Hand, and Finger. [PowerPoint Slides]. Canvas@PulseRadiologyInstitute.



Comments

Post a Comment

Popular posts from this blog

The 14 Facial Bones

Image
What are the Facial Bones? Did you know that the face is made up of multiple bones and not just one large bone? Matter of fact, the face consists of 14 facial bones (6 paired and 2 unpaired). The 14 bones are: two zygoma/zygomatic bones, two lacrimal bones, two inferior nasal conchae bones, two palatine bones, two maxilla bones, two nasal bones, one vomer bone, and one mandible bone ( Kelley & Petersen, 2013, p. 49 ). The irregular sizes and shapes of these facial bones are fused together and articulates with joints that form different cavities, sinuses, and structures of the face. The facial bones serve as structural framework for the face, protect and provide support for vital organs and vessels of the face and skull, and aid in the movements and motion of the face and mouth ( Facial Bones – List of Names, Anatomy, & Labeled Diagram , 2022) .  Now let's learn more about these facial bones: Maxilla (or maxillary) (2/paired) : the largest, immovable facial bones that forms...
Read more

What are the Adrenal Glands?

Image
  What are the Adrenal Glands? Have you ever looked at a diagram of the kidneys and wonder what the yellowish, triangles on top are? Well, that is what we call the adrenal glands, and they have a special and important purpose in the human body. The adrenal glands are retroperitoneal structures and are located superior to the kidneys. They are part of the endocrine system, and its main purpose is to produce hormones that aid in metabolism, regulating stress, and other functions of the body (Pulse Radiology Institute, n.d., slide 14).  The adrenal glands also consist of the adrenal cortex (outer layer that produces dozens of adrenocortical steroids/corticosteroids) and the adrenal medulla (the inner layer that is responsible for the hormones epinephrine and norepinephrine, or flight-or-fight response) (Kelley & Petersen, 2013, pgs. 444-445).  Diagram of the adrenal glands (G, 2023) How to Identify the Adrenal Glands in an Image Unlike the easy recognizable structure of ...
Read more