The wrist, also known as the carpus, is located on the proximal region of the hand. Connected by several ligaments, there are eight small bones (carpals) arranged in two rows of four that articulate with each other, along with the radius and ulna. They are named according to their shape, and are as follows:
* Scaphoid: Boat-like.
* Lunate: Moon-shaped.
* Triquetrum: Three-cornered.
* Pisiform: Pea-shaped.
* Trapezium: A four sided figure that has no two parallel sides.
* Trapezoid: A four sided figure that has two parallel sides.
* Capitate: Head-shaped.
* Hamate: Hooked.
Many people utilize various mnemonics to remember the anatomical locations of all the carpals. A quick search will provide you with many options. One popular one is: Some Lovers Try Positions That They Can’t Handle (Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, and Hamate). This covers the carpals from lateral to medial, proximal to distal.
The radiocarpal joint consists of the distal end of the radius, the scaphoid, the lunate, and the triquetrum. It is classified as a diarthrosis synovial joint. This means that it has a synovial cavity, which permits free movement among its two axes. It can further be called a condyloid synovial joint, meaning one component has an oval-like projection, and the others together form an oval-like depression.
The intercarpal joints are a bit more complicated. They consist of the connection between the proximal and distal rows of carpal bones and between the carpals themselves. All of these individual connections are diarthrosis synovial joints. For a more indepth classification, the hamate, scaphoid, and lunate all form a saddle joint, while the rest are considered to be planar.
With all of the joints between each individual surface, it is no wonder that the function of the wrist is so complex and prepared for fine movements. The wrist can flex, extend, abduct, adduct, circumduct, glide, and rotate slightly.
Amidst all of these bones and joints a concave space is formed by the pisiform, the hamate, the scaphoid, and the trapezium. This makes up the infamous carpal tunnel. The median nerve and flexor tendons for the thumb and digits all pass through here. When there is inflammation surrounding the carpals this tunnel can become narrowed, causing a condition commonly known as carpal tunnel syndrome.
Of course, with all of the intricacies that make up the carpus, there are many injuries that can also occur. According to Principles of Anatomy and Physiology, 11th Edition (Tortora, Derrickson), nearly 70% of wrist fractures only the scaphoid is affected.
It is no secret that the wrist is a complex, amazing joint. The next time you are writing, typing, or playing a sport, take a minute to marvel at the wonder of your body and all it allows you to do.