The human hand is unique in its dexterity and range of abilities. Our hands hold, move, grasp, feel and manipulate the world and the objects around us.
The hand is made up of 27 bones in total. It comprises the joint with the wrist, which allows us to bend, tilt & stretch our hands; the thumb, that helps us to grasp; the fingers, essential to grip; and the palm, which attaches all of these elements together, whilst giving us a large and flat surface area for the hands to hold things within.
The wrist is a condyloid synovial joint, which means it consists of an oval-shaped protrusion that fits within a space that is the negative shape of that protrusion. This allows movement such as up (flexion), down (extension) and both sideways movements: abduction (furthest side from the body moving further away from the body) and adduction (closest side to the body moving towards the body). All of these movements can be combined to make a circular motion (circumduction).
There are 10 bones that all come together to make up the wrist. Two of them are the ends of the bones that make up the forearm (therefore attaching the hand to the arm), called the radius and the ulna. These are attached to 8 bones in the palm that are arranged in two rows of four, known collectively as carpal bones, who’s shapes vary from square to oval and triangular. The row closest to the radius and ulna are the proximal row and comprises the scaphoid, lunate, pisiform and triquetral bones. The following row, called the distal row, is made up of the bones hamate, capitate, trapezoid and trapezium bones. This row connects to the fingers as well as the proximal row.
The wrist is therefore made up of an impressively large number of joints, as every one of these 8 bones has a small joint connecting them to their neighbouring bones.
The movement of the thumb is controlled by the carpometacarpal joint, which allows for the previously mentioned flexion/extension and abduction/adduction movements. An additional movement of the thumb is moving it forward to, and back from, the fingers, a movement called opposition/reposition which allowes for grasping.
This movement in particular allows the hands to be incredibly versatile. The thumb and fingers work together in this way to give us a precision grip, in a similar fashion to that of tweezers, allowing us to pick up small objects or hold a pen in an extremely controlled and delicate way. The power grip is less about the finer details and more about the weight of the object and strength required to lift it. Again, the thumb plays an important part in this, as it is able to be positioned opposite (or on top of) the fingers as they curl around the object being manoeuvred.
The bones of the fingers are made up of metacarpals (one per digit, which connect to the carpal bones) and phalanges. Each finger has three phalange bones, which connect to the metacarpal bone. The thumb has just two phalanges.
Aside from helping us to literally feel the world around us (see a future blog post on this subject!), fingers are crucial to interacting with the world. Our fingers can move in most of the same ways as the thumb, however their range of extension, abduction and adduction are quite limited when compared to their ability to flex.
Hand & wrist related AnatomyStuff resources:
Further reading / sources
How do hands work?