The hand is a marvel of anatomy and its unique structure allows us to perform many complicated actions, according to eOrthopod. The hand is mobile, allowing us to manipulate objects; it is strong, allowing us to pick things up; and it is coordinated, allowing us to perform the precise movements that make up our fine motor skills. Many of the muscles that give the hand its flexibility originate up in the forearm. Their long tendons, which are tough bands of fibrous tissue, travel down into the hand to help it move.
The Extensor Tendons
The muscles that control the hand are divided into two groups; the extrinsic, which originate in the forearm, and the intrinsic, which are contained within the hand. The extensor tendons, which travel down the back of the hand, are the attachments of the extrinsic muscles found on the back of the forearm. The extensor tendons, which are flat and thin, allow us to straighten and extend our hand, according to ASSH. The extensor tendons split and break into smaller bands around the joints of the fingers, creating greater dexterity. The extensors pass through a band called the extensor retinaculum, which prevents bow-stringing of the tendons.
The Flexor Tendons
The flexor tendons, also extrinsic, originate on the elbow and the underside of the forearm and attach to the bones of the fingers. The flexors are responsible for flexing the hands and bending the fingers, according to ASSH, and are smooth and string-like. The integrity of the flexor tendons is maintained in the fingers, where they pass through fibrous rings that function as pulleys, ensuring they function efficiently and preventing bow-stringing.
The Intrinsics
In addition to the extensors and flexors, the hand also contains two groups of intrinsic muscles, according to CHI. The two groups are called the interosseous and the lumbrical. The interosseous muscles and their tiny tendons are responsible for fanning the fingers in and out. The lumbricals assist the fingers in making fine adjustments in position.
The Opposable Thumb
The movement of the thumb is extremely complicated. It is carried out by eight different muscles, according to CHI. There are two flexors, two extensors, two abductors--which fan the fingers out--one adductor--which pulls the fingers back toward center--and one that opposes the others, giving us the infinitely useful opposable thumb. It is called opposable because the thumb moves around to touch the other fingers, which gives people the ability to grasp.
Tendon Injuries
Tendon injuries should be taken seriously. They can affect the ability of the hand and fingers to function properly. According to the Merck Manuals, tendinitis is the inflammation of a tendon that causes pain and swelling. There are two types of tendinitis that affect the tendons of the hands. Tendinitis of the tendons that extend the thumb away from the hand is called de Quervain's syndrome and tendinitis of the flexor tendons of the fingers results in a trigger finger. When a tendon is cut, it can act like a rubber band, springing back up into the forearm, causing loss of function. It takes a surgical procedure to repair a cut tendon and restore function to the hand.
