Know Your Digits: Finger and Hand Anatomy

A couple of weeks ago, I was toproping a route and felt quick and sharp pain running down my hand as I grabbed a sidepull. I stopped and shook it out but didn’t feel any pain for the rest of it. Came down to rest then started to get ready for another route. As I put my hand into my chalkbag and curled, it hurt to do so.

It was a sure sign to stop climbing. I taped my wrist to give it some support. Wasn’t sure if it was my wrist or finger that was stressed or hurt. But I needed to do something for it. I did put an ice pack on my hand, and that seemed to help.

This incident led me to do a little research on finger and hand anatomy because they’re significant for climbing and I want to make sure I prevent another injury from happening.

Hand and Finger Anatomy 101

When I began exploring, I didn’t realize most finger tendons are in the forearm. There are different ones to bend fingers and straighten them. I also didn’t think the hand was that complex of a body part, but it is. So, I will try to explain the components as best as I can. The images are from the American Society for Surgery of the Hand.

Flexors FDP and FDS

Flexor digitorum profundus (FDP) tendons help bend the index, middle, ring, and small fingers at the fingertip joint. Flexor digitorum superficialis (FDS) tendons help bend the index, middle, ring, and small fingers as well but at the middle finger joint. The muscles that move these tendons are a part of a muscle belly shared by all the fingers. It divides into four tendons. They run down the forearm and within the carpal tunnel.

The four FDP tendons glide in sheaths along the hand and fingers and insert into the fingertip bone. These tendons run closer to the bone compared to the rest of the flexors. At the level of the fingers, each FDS tendon splits into two separate cords and then insert into the middle bone of the finger on either side of the FDP tendon that runs farther down the finger.

Extensors

Extensor digitorum communis (EDC) tendons straighten the index, middle, ring, and small fingers. These share a muscle belly by all the fingers. The tendons travel down the forearm through a sturdy band of tissue on top of the wrist. The band or retinaculum, holds the tendons in place but allows them to slide up and down the arm.

The four tendons then continue along the back of the hand and onto each finger. In the finger, the ends of other tendons that start in the hand join to make the fingers move. Together, these combined tendons extend the fingers at the three finger joints.

The extensor digiti minimi (EDM) straightens the small finger. It works with the EDC to the little finger. The muscle belly is in the forearm. The tendon travels through a retinaculum at the wrist and then into the hand. It holds them in place but allows them to slide up and down the arm as well. It works with other tendons that attach to the dorsum or back of the finger to straighten the three small finger joints.

The extensor indicis proprius (EIP) tendon straightens the index finger. It works with the EDC in the index finger. It has its muscle belly in the forearm and then, as it becomes a tendon, it travels through a retinaculum in the wrist. It holds them in place but allows them to slide up and down the arm. It goes down the hand and attaches to the back of the index finger to straighten the three index finger joints.

Thumb Tendons

The abductor pollicis longus (APL) tendon runs on the radial side of the wrist (the side the thumb is on). Its muscle belly is in the forearm and then travels inside a retinaculum across the wrist. It holds the tendons in place but allows them to slide up and down the arm. It attaches to the metacarpal bone of the thumb and helps pull the thumb away from the rest of the hand.

The flexor pollicis longus (FPL) tendon bends the thumb. It starts as a muscle in the forearm and then travels as a tendon in the wrist through the carpal tunnel. It’s covered by a tunnel, or sheath, and inserts into the most distal (farthest from your body) bone in the thumb.

The extensor pollicis longus (EPL) straightens the most distal (farthest from your body) joint of the thumb. Its muscle belly is in the forearm, and the tendon travels along the wrist and enters the third compartment of the band that holds the tendons in position at the wrist. It then goes around a prominent part of the radius bone that acts like a pulley. It is called Lister’s tubercle. The tendon then attaches to the most distal bone in the thumb.

The extensor pollicis brevis (EPB) tendon, along with the APL, also moves the thumb away from the hand. The EPB tendon is in the forearm and then runs along the radial side of the wrist. This tendon also travels in the first compartment of the band that holds them in position at the wrist.

Wrist Tendons

The flexor carpi radialis (FCR) tendon is one of two tendons that bend the wrist. The flexor carpi ulnaris (FCU) tendon is the other. Their muscle belly is in the forearm. The FCR travels along the inside of the forearm and crosses the wrist. It attaches to the base of the second and third-hand bones. It also connects to the wrist bone called the trapezium.

The FCU travels along the inside of the forearm on the side of the small finger and crosses the wrist too. It attaches to the wrist bone, the pisiform, and as well as the 5th hand bone.

The palmaris longus (PL) tendon is a tendon with little function. Its muscle belly is in the forearm. It travels into the wrist and joins the fascia in the palm. This tendon is often used to repair other tendons.

The extensor carpi radialis brevis tendon (ECRB) is one of 3 tendons, including ECRL and ECU, which act together to bend back the wrist. Their muscle belly is in the forearm and then travels to the thumb side of the wrist on the back part of the forearm. Along with the ECRL, it attaches to the base of the hand bones. It is shorter and thicker than the ECRL.

The extensor carpi radialis longus tendon (ECRL) acts along with the ECRB and ECU to bend back the wrist. ECRL and ECRB also help bend the wrist in the direction of the thumb. It is thinner and longer than ECRB. It travels along the back aspect of the forearm and attaches to the base of the hand bones.

The extensor carpi ulnaris (ECU) tendon works along with the ECRL and ECRB to straighten the wrist. It differs from these other two tendons in that it moves the wrist in the direction of the pinky. It travels along the back forearm, through a groove in the ulna, and attaches to the base of the hand bones.

Whew! So many tendons! Now we know what keeps our hands flexible, in the next article, I’ll talk about how and what we can do to prevent injuries so we can keep climbing. Until next time, happy bouldering!