In addition to its complex bone structure, the wrist also contains a network of ligaments, tendons, and other soft tissues that give the wrist flexibility and strength to move.

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Wrist Ligaments and Their Function

All the bones in the wrist are attached to each other by a network of ligaments.

The purpose of the small ligaments that attach the carpal bones to each other is to keep the bones in place with respect to each other as the wrist moves. There are also a few larger ligaments on the front, back, and sides of the wrist—known as the collateral ligaments—to keep the wrist from bending too far in any direction.

Wrist sprains are most commonly caused by injury of the scapholunate ligament, which connects scaphoid and lunate carpal bones.

See Scaphoid Fracture and Other Types of Wrist Fractures

Another common injury site is the triangular fibrocartilage complex (TFCC), a collection of ligament and cartilage structures that sit between the ulna bone in the forearm and a few carpal bones. Its purpose is to provide a larger, more even surface for the ulnocarpal joint and improve its function.

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Wrist Tendons

The motion of the hand and wrist is powered by tendons, which connect bones to muscles. Tendons of the wrist include the flexor tendons that run through carpal tunnel and allow fingers and thumb to curl and the extensor tendons on the back of the hand that allow the fingers to straighten.

In addition, there are several tendons that specifically enable wrist motion:

  • Flexor carpi radialis and flexor carpi ulnaris—these bend the wrist inward
  • Extensor carpi radialis brevis and extensor carpi radialis longus—these straighten the wrist and/or bend it toward the thumb
  • Extensor carpi ulnaris—this straightens the wrist and/or bends it toward the pinky finger

The thumb has special tendons of its own:

  • Abductor pollicis longus
  • Extensor pollicis brevis
  • Extensor pollicis longus

These tendons allow the thumb to move independently of the other fingers and be opposable. When they become inflamed, this can cause De Quervain’s tenosynovitis.

See De Quervain’s Tenosynovitis

The tendon that “pops out” of wrist when one curls the hand and flexes the wrist is the palmaris longus tendon. It’s a vestigial tendon with no real function, and an estimated 25% of people don’t have this tendon.1

Nerves of the Hand and Wrist

The three nerves of the hand—the median, ulnar, and radial nerves—all start near the shoulder in a cluster of nerve roots and branches known as the brachial plexus.

Each provides sensation for different parts of the hand:

  • The median nerve passes into the lower part of the upper arm, then inside the elbow and forearm, through the carpal tunnel in the wrist, and then into the thumb, index finger, middle finger, and part of the ring finger. When this nerve becomes impinged in the carpal tunnel, it causes carpal tunnel syndrome.
  • See What Is Carpal Tunnel Syndrome?

  • The ulnar nerve passes through the bottom of the upper arm, over the outside of the elbow very close to skin’s surface (causing “funny bone” shocks when it’s jarred), through the inner forearm, between two carpal bones, a structure known as Guyon’s canal, and finally into the ring and pinky fingers.
  • The radial nerve path is peculiar. From the brachial plexus, it wraps around the humerus bone to the underside of the arm, passes over the elbow, then across the back of the forearm, and finally into the back of the thumb and first two fingers.

The vast majority of wrist injuries are the result of one simple cause: falling onto an outstretched hand. This can cause strains and sprains, dislocations, and even fractures—especially for those with weaker bones because of osteoporosis.

See Is My Wrist Broken or Sprained?

References:

  1. Tendons. American Society for the Surgery of the Hand. Accessed May 2017.
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