August 15, 2006
by Anne Kosacheff, YKHC Physical therapist
This month's Physical Therapy article will share with you some information about the intricacies of the fingers. Because the mechanism is so complex, prevention and rehabilitation of hand and wrist problems will be covered in the next article.
As you read in last month's article, the muscular structures in the fingers are complicated and intricate. Each finger has several muscles to provide a flexion motion, others to provide an extension motion, as well as each finger motion getting assistance from the interossei and lumbrical muscles. The two flexion (bending) muscles are the flexor digitorum superficialis (FDS) and the flexor digitorum profundus (FDP). The FDS flexes the middle knuckle in your fingers, and the FDP flexes the last knuckle on your fingers. Both of these muscles start up on the inside of your elbow, attached to the bone that sticks out. They run down your arm into your fingers. You can see the FDL on figure 1. Looking at figure 2, you can see the white tendon of the FDS splitting to allow the FDP to run through to the end of your finger.
There are two other muscles that bend your thumb. They are the flexor pollicis longus (FPL) and flexor pollicis brevis (FPB). The FPL also starts up by your elbow, and the FPB starts at your wrist. Both the FPL and FPB run into your thumb on the palm side. Can you find the FPL and FPB in figure 1 and figure 2?
These lumbrical muscles are unusual in that they do not attach to bone, instead attaching to the tendons of flexor digitorum profundus (FDP) and the extensor expansions on the dorsal surface (back of) the hand. (more on this later). The function of the lumbricals is to allow flexion at the metacarpophalangeal joints while maintaining extension at the interphalangeal joints. Do you remember where these joints are? See if you can find them on the pictures.
There are four interossei muscles in each hand. They connect the metacarpal bones together (remember where these are?), and allow us to cup our hand to hold water in the palm, and assit in the grasping movement of the fingers.
The extensor tendons for the fingers begin as muscles that arise from the bones of the back side of the forearm. (With your palm facing forward, put your arm at your side. The side of your forearm facing backward is where the extensor tendon muscles start.) These muscles travel toward the hand, across the back of the wrist joint, and into the fingers. As they travel into the fingers, the extensor tendon becomes what is called the extensor hood. It flattens out to cover the top of the finger and sends out branches that connect to the last two bones in each finger. When the extensor muscle contracts it shortens and pulls on these attachments to straighten the finger.
Small ligaments also connect the extensor hood with other tendons that travel into the finger to bend the finger. These connections help balance the motion of the finger so that all the bones of the finger work together giving a smooth bending and straightening action. It is all very intricate, and works most often without conscious thought from us.
Finally, the index finger and little finger have their own extensor muscles, and the thumb has two extensors. Three of these four muscles start up in the forearm, near the elbow. Since many of the muscles we use to hold, twist, snatch, carry, pull, push, etc., start near the elbow, often elbow pain is related to overuse or heavy use of the hands. Sometimes a brace for the wrist or hands will help alleviate elbow pain. Sounds crazy, but if you look at how you are put together, it makes sense.
Watch for more information next time on easy rehabilitations exercises after an injury to the forearm, wrist and hand; and some activities to prevent injury to your wrist, elbow and forearm.