The hand tendons include two groups of tendons divided into flexors and extensors. The flexors emerge from the common flexor tendon in the arm and are responsible for bending and curving motions. The extensors, arising from the common extensor tendon, straighten the fingers and wrist. These tendons are controlled by muscles in the forearm, making the hand essentially like a marionette on strings.
The flexor tendons include the flexor digitorum, which splits into five tendons that split off again into the flexor digitorum sublimis and flexor digitorum profundus when they reach the fingers, although thumb has only one flexor tendon. The profundus is a longer tendon designed to mobilize the upper joint in the fingers, while the sublimis is shorter and moves the middle joint.
In addition, bending movements of the hand are controlled by the flexor carpi ulnaris and the flexor carpi radialis, and many people, but not all, also have a palmaris longus, a tendon in the wrist that will create an obviously visible ridge when the hand is flexed. The other flexor tendon of the hand is the pronator teres, used to turn the arm to invert the hand towards the body.
Extensor tendons of the wrist include the extensor carpi radialis and the extensor carpi ulnaris. In addition, a large tendon called the extensor digitorum feeds the individual fingers with flexor tendons. A special smaller tendon, the extensor minimi digiti, straightens the little finger.
Together, the network of hand tendons works to control the hands, providing a very high degree of motor control. Humans can perform a wide variety of complex tasks with their hands with the assistance of the hand tendons. Because of the heavy usage seen by the hands, these tendons are particularly prone to inflammation and associated health problems.
Injuries to the hand tendons are very common. The tendons lie close to the surface of the hand, making them vulnerable to bruising, and relatively shallow cuts to the fingers can result in a severed or strained tendon. If a tendon is severed, it will tend to snap back into the hand, because the tendons are placed under considerable pressure. Surgery is required to fish the tendon out of the hand and repair it, and the patient may need to use a traction device to hold the tendon in place while it heals. Damage to the hand tendons can result in contractures of the fingers or immobility of an injured finger.