Anatomy of the Hand
Our hands are unique to us and allow for incredible dexterity. When you think about it, the everyday tasks we perform with our hands would be considered feats of engineering if constructed by us in a lab or warehouse. The strength, fine movements, dexterity, and spatial awareness involved in using our hands have become expected qualities on a daily basis, that is, until an injury to the hand occurs, which can have devastating consequences.
Most people are fortunate enough to avoid traumatic injuries or conditions that affect the long-term functioning of the hand. However, as we age, it becomes increasingly common to develop conditions like osteoarthritis, which can have its own debilitating effects.
So why is osteoarthritis common in the hands? How do are hands function to maintain a level of functionality? Knowing more about the anatomy of the hand can go a long way in understanding various injuries and conditions, as well as how you can prevent or treat them. While the detailed anatomy of the hand can be quite complex, this article is intended to provide you with a brief overview of the anatomy of the hand, hopefully providing you with a better sense of your everyday activities really are exceptional!
Bones and Joints of the Hand
When learning anatomy, I usually find it easiest to go from simple to more complex. In this case, the bones of the hand provide a good starting point, upon which we can build our knowledge into the muscles and nerves, which can sometimes be a little daunting without easing into it.
Technically, the carpal bones are part of the wrist, but they're hard to avoid when discussing the anatomy of the hand. If you look at the palm of your hand, the carpal bones can be found at the base of the hand between the two bigger muscles forming the ball of the hand. These bones help to form the distal radiocarpal joint of the wrist, as well as the midcarpal and intercarpal joints.
The carpal tunnel sits just below the carpal bones, which forms a passageway for many tendons, nerves, and arteries. For a recap of this information, feel free to check out our article on the wrist joint, as well as our info about good wrist braces for injuries.
The metacarpal bones are the next bones up from the carpals, and they start to take on the appearance of fingers. When looking at your own hand, these bones are still found in the main hand region (as opposed to in the fingers), but by feeling around in the palm and dorsal aspect of your hand, you can actually feel these individual bones quite easily. There is one metacarpal per finger, and they serve as the connection between the wrist and then fingers. The metacarpals are often listed according to number, whereby the 1st metacarpal is below the thumb, and the 5th metacarpal is below the pinky finger.
Each metacarpal bone contributes to two different joints. At the proximal aspect, the metacarpals and carpal bones form to join the carpametacarpal joints, more commonly referred to as the CMC joints. At the distal end of the carpal bones, you can find the metacarpophalengeal joints, also known as the MCP joints, or by the much more common knuckle joints. When you make a fist, the MCP joints form the primary knuckles.
The phalanges, or phalangeal bones, are your fingers. However, you have likely noticed that your fingers are capable of bending in different spots. Each finger actually has three different phalangeal bones, with the exception of the thumb, which only has two. Fortunately, the naming system is pretty easy. Each phalanx is preceded with its location. For example, the proximal phalanx (closest to the metacarpals), the middle phalanx, and the distal phalanx (fingertip).
Together, the proximal phalanx and the metacarpals form the previously mentioned MCP joints. The joints between the proximal and distal phalanges form the proximal interphalangeal joints (PIP joints) are formed between the proximal and middle phalanges, while the distal interphalangeal joints (DIP joints) are formed between the middle and distal phalanges. The thumb only has two phalanges, so there is no middle phalanx. Therefore, there is only one IP joint in the thumb.
Movements of the Joints in the Hand
All the joints of the hand are responsible for different movements. For example, the midcarpal joint is useful in helping the wrist achieve full flexion and extension. The intercarpal joints, which are formed between individual carpal bones, actually don't provide much motion, but they are capable of small gliding movements, making the hand much more compliant.
The MCP joints are capable of flexion, extension, abduction, adduction, and circumduction, basically all the movements, but some are more limited than others. The thumb is capable of opposition, which is basically the movement that occurs when you touch your thumb to your pinky finger.
The IP joints are bound strongly by ligaments and tendons, and as such, they are only capable of flexion and extension, but together with all the other joints in the hand, this provides us with a wealth of possible movements.
Muscles of the Hand
We won't go into every muscle in the hand, as there are many, and it can get really confusing after a while. The main thing to know here is that there are essentially two different groups of muscles, one group being responsible for strong large-scale movements, the other is more responsible for finer movements requiring dexterity.
The first group, which is responsible for the larger movements, are the forearm muscles. As their tendons pass through the carpal tunnel in the wrist, they continue on to attach to the fingers, where they can perform flexion and extension at ease. The muscles on the front of your forearm are responsible for flexion (and some other movements, albeit minor ones), and the muscles on the back of your forearm are responsible for extension, among other more minor movements. These muscles and their tendons allow us to position our hnd where it needs to be and powerfully grip objects.
The second group, often called the intrinsic hand muscles, are much smaller muscles located within the hand itself, that is, the muscle bellies and tendons both reside within the hand. Given these muscles are much smaller, they are also a lot more weak than the forearm muscles, but they advantage here is that they allow us to coordinate fine movements of the hand. Any activity, from holding a pen while we write, to playing the guitar or piano, are all dependent on the finer capabilities of the small intrinsic hand muscles.
If you're interested in this and are looking at your hands, you may wonder why the balls of your hands (below the pinky and thumb) are considered "small" muscles, as they look fairly beefy. This is because these balls of the hand are actually compartments of muscles, each of which contains three separate muscles. We won't get into the exact breakdown here, but if you're interested in doing more research, the thumb compartment is often termed the thenar compartment, and the pinky compartment is often termed the hypothenar compartment.
Nerves and Arteries of the Hand
If the hands have muscles and bones, then there must also be networks of nerves and arteries. When looking at an anatomical image of the hand, it can look really confusing, with small branches of nerves and arteries going every direction. These branches all rise from common sources a little more proximal up the hand and wrist, and fortunate for our memory, there aren't too many of them!
In terms of nerves, the main nerves of the hand are the recurrent branch of the median nerve, which supplies most of the muscles in the thenar and central compartments of the hand, and the deep branch of the ulnar nerve, which supplies most of the hypothenar muscles and a couple others. For reference, the median nerve is the structural victim of carpal tunnel syndrome, and if you hit your funny bone, you're actually hitting your ulnar nerve as it passes under a bony prominence of the elbow.
The arteries are a little more variable from person to person, but the main networks in the hand and fingers include the common palmar digital arteries and the proper palmar digital arteries. One artery of high clinical significance is the palmar carpal branch of the radial artery. This artery crosses the scaphoid bone (one of the carpal bones) on the side of the palm. When someone falls onto an outstretched arm and lands on the palm of their hand, a fracture to this bone can actually damage the artery as well, sometimes leading to decreased blood flow to the bone. This can result in avascular necrosis of the scaphoid, which is when the bone cells die due to lack of adequate blood supply. When this happens, the bone itself becomes weakened, and eventually collapses.
This very brief introduction to the anatomy of the hand should give you an idea of the basic functioning of the hand, as well as the complexity of the anatomy in detail. It is incredibly important that we take care of our hands, as they are responsible for an immense amount of work on a daily basis. Understanding the anatomy is a good first step. For more detailed information, we suggest checking out an online anatomy resource, or even borrowing a textbook from a friend or library. Textbooks seem intimidating, but anatomy books are quite visual and explained in a down-to-earth manner. All the best!