Fun Facts About Our Hands
Since we love to treat hand injuries, here are some fun and interesting facts about our hands that you probably did not know!
One third of all acute injuries seen in emergency rooms involve the upper extremities.
Two thirds of upper extremity injuries occur to individuals in their working years.
The most common disabling work injuries in the United States involve the upper extremities, accounting for over one fourth of all disabling work injuries. One out of six disabling work injuries involve the fingers, most often due to the finger striking or being struck against a hard surface.
One fourth of athletic injuries involve the hand and wrist.
Children under the age of six are at the greatest risk for crushing or burning injuries of the hand.
We work our fingers by remote control. Of course, in one sense, we work all of our moving body parts by remote control - the control center is our brain. However, the fingers are special, because there are no muscles inside the fingers. The muscles which bend the finger joints are located in the palm and up in the mid forearm, and are connected to the finger bones by tendons, which pull on and move the fingers like the strings of a marionette.
Wrinkles
When the hand is kept wet, the skin of the palm wrinkles. Why? The exact mechanism is not known, but it is clearly controlled by nerves. When the nerve that supplies feeling to an area of skin on the palm is cut, that area of skin not only becomes numb, but loses its ability to wrinkle when wet. It also loses the the ability to sweat.
Numbers
Each hand contains (plus or minus... everyone is different, and everyone counts these things differently...)
29 major and minor bones (many people have a few more).
29 major joints.
At least 123 named ligaments.
34 muscles which move the fingers and thumb:
17 in the palm of the hand, and 18 in the forearm.
48 named nerves:
3 major nerves.
24 named sensory branches.
21 named muscular branches.
30 named arteries and nearly as many smaller named branches.
Finger strength
The muscles which power the fingers are strong - strong enough for some people to climb vertical surfaces supporting their entire weight at times by a few fingertips. The muscles which accomplish this feat are stronger than you might imagine, for the biomechanics of the hand require that the force generated by the muscles which bend the fingertips must be at least four times the pressure which is produced at the fingertips.
Opposition
Contrary to popular opinion, humans - homo sapiens - are not the only primates possessing opposable thumbs. Chimpanzees and monkeys can oppose the thumb to the index digit. What makes the human hand unique in the animal kingdom is the ability of the small and ring fingers to rotate across the palm to meet the thumb, owing to the unique flexibility of the carpometacarpal joints of these fingers, down in the middle of the palm. This is referred to as "ulnar opposition" and adds unparalleled grip, grasp, and torque capability to the human hand. This feature developed after the time of Lucy, a direct human ancestor, who lived about 3.2 million years ago.
Hand and Brain
About a quarter of the motor cortex in the human brain (the part of the brain which controls all movement in the body) is devoted to the muscles of the hands. This is usually illustrated with a drawing of a human figure draped over the side of the brain, body parts sized proportional to the amount of brain devoted to their movement, referred to as a homunculus
The skin of the palm
The skin on the palm side of the hand and fingers is unique for these reasons and more:
No hair (the medical term is glabrous).
Fingerprints.
Usually neither color nor the ability to tan.
Tough and durable, yet sensitive.
Anchored down to the bones beneath through an intermediate layer of fascia. This arrangement keeps the skin of the palm from sliding around like a rubber glove when we use our hands to grip and twist. In some people, this layer of fascia shrinks and thickens, leading to Dupuytren's disease.
Overlapping fingers
When one curls the fingers into a fist, the fingertips naturally group together side by side. If the fingertips all bend together, they continue into the palm side by side. However, the natural tendency is for each fingertip to aim for the same point at the base of the thumb, which is obvious when touching each finger down to the base of the palm. For this reason, if a hand problem (stiffness, swelling, etc.) prevents a finger from meeting the side of the adjacent fingertip midway into making a fist, that finger will tend to cross over and overlap the adjacent finger when making a fist.
Urban legends
"If you can move your finger, it isn't broken" False.
"Cold hands, warm heart" Well, it really depends on why ones hands are cold...
"Computer use causes carpal tunnel syndrome" Probably false.
"Eating gelatin makes your fingernails stronger" False - no evidence to support this.
"Cracking your knuckles gives you arthritis" False - no evidence to support this.