Dominic Stone
The human wrist is a complex network of bones, muscles, nerves, tendons, and ligaments. There are 34 muscles in each hand, which work together to help you move your hand and fingers. To help you remember the muscles of the wrist, you can use several tricks and mnemonic devices. For example, all the extensor muscles that have a P in them are deep extensors, such as abductor Pollicis longus (APL) and extensor Pollicis brevis (EPB). Another example is the Rule of Three, which states there are three wrist flexors: FCR, PL, and FCU, and three finger flexors: FDS, FDP, and FPL.
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What You'll Learn
Wrist muscles and their functions
The wrist is a complex joint made of eight bones arranged into two rows. The wrist is a series of small joints that connect the radius and ulna (the two bones in the forearm) to the carpals in the hand. The wrist shares muscles with the forearm, and these muscles can be grouped into four types of movement:
Flexion
The muscles that let you move your wrist down, toward your palm. Muscles in this group include:
- Flexor Carpi Ulnaris (prime mover)
- Flexor Carpi Radialis (prime mover)
- Palmaris longus (tightens the skin and fascia in the palm)
- Flexor Digitorum Superficialis (finger flexor, assists only)
- Flexor digitorum Profundus
- Flexor Pollicis longus
- Pronator quadratus
Extension
The muscles that pull your wrist up, like you would to make a "stop" gesture. Muscles in this group include:
- Extensor Carpi Radialis Longus (prime mover)
- Extensor Carpis Radialis Brevis (prime mover)
- Extensor Carpi Ulnaris
- Extensor Digitorum (assists only)
- Extensor Carpi radialis longus (ECRL)
- Extensor Carpi radialis brevis (ECRB)
- Extensor Digitorum (ED)
- Extensor Digiti minimi (EDM)
- Extensor Carpi ulnaris (ECU)
- Abductor Pollicis longus (APL)
- Extensor Pollicis brevis (EPB)
- Extensor Pollicis longus (EPL)
- Extensor indicis Proprius (EIP)
Adduction
The muscles that let you bend your wrist in, toward the centre of your body. The muscles in this group include:
- Extensor Carpi Ulnaris (ECU)
- Flexor Carpi Ulnaris (FCU)
Abduction
The muscles that let you bend your wrist out, away from the centre of your body. The muscles in this group include:
- Flexor Carpi Radialis (FCR)
- Extensor Carpi Radialis Longus (ECRL)
- Extensor Carpi Radialis Brevis (ECRB)
The wrist is also capable of radial deviation, which is tilting the hand and wrist toward the thumb and radius. This motion is more important in weight-bearing activities like gymnastics. The muscles involved in radial deviation are:
- Flexor Carpi Radialis
- Extensor Carpi Radialis
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Forearm muscles and their relationship with the wrist
The forearm is the section of the upper limb that extends from the elbow to the wrist. The forearm muscles are divided into two compartments: the anterior flexor compartment and the posterior extensor compartment. The forearm contains twenty muscles that act on the elbow and wrist joints, as well as the carpometacarpal, metacarpophalangeal, and interphalangeal joints of the hand. The forearm muscles are essential for fine motor actions of the upper limb, allowing for complex movements of the arm, wrist, and fingers.
The anterior compartment of the forearm contains three layers of muscle: superficial, intermediate, and deep. The superficial muscles in the anterior compartment are the flexor carpi ulnaris, palmaris longus, flexor carpi radialis, and pronator teres. They all originate from a common tendon, which arises from the medial epicondyle of the humerus. The flexor carpi ulnaris allows you to move your wrist back and forth. The palmaris longus helps flex the wrist, and the flexor carpi radialis helps move your arm away from your body. The flexor digitorum superficialis is the only muscle in the intermediate layer. It splits into four tendons that attach to finger bones and help you bend your fingers and move your wrist. The deep layer of the anterior compartment contains three muscles: flexor digitorum profundus, flexor pollicis longus, and pronator quadratus. The flexor digitorum profundus allows you to bend your ring, middle, index, and pinkie fingers. The flexor pollicis longus flexes the interphalangeal joint and metacarpophalangeal joint of the thumb. The pronator quadratus is a square-shaped muscle that lets you turn your forearm downward.
The posterior compartment of the forearm contains six muscles: extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and anconeus. The extensor carpi radialis longus and extensor carpi radialis brevis extend the wrist and move the hand away from the direction of the thumb. The extensor digitorum splits into four tendons and connects to the finger joints, helping to straighten or extend the fingers. The extensor digiti minimi extends the little finger. The extensor carpi ulnaris helps to turn and extend the wrist. The anconeus helps extend the forearm at the elbow.
The intrinsic muscles of the forearm pronate and supinate the radius and ulna, while the extrinsic muscles flex and extend the digits of the hand. The brachioradialis muscle traverses the elbow joint, running from the arm to the wrist, and helps flex the elbow and turn the arm.
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The carpal tunnel and its role in the wrist
The carpal tunnel is a space in the wrist bones that acts as a passageway for tendons, ligaments, and nerves to reach the hand. It is formed by the carpal bones on the bottom of the wrist and the transverse carpal ligament across the top of the wrist. The tunnel is about an inch wide and contains the median nerve and flexor tendons that allow for the bending of the fingers and thumb.
The median nerve is one of the main nerves in the hand, providing sensory and motor functions to the thumb and three middle fingers. It originates as nerve roots in the neck, travelling down the upper arm, across the elbow, and into the forearm before passing through the carpal tunnel. The nerve helps control movement in the forearm and gives feeling to most of the fingers and hands.
Carpal tunnel syndrome is a common condition that occurs when the median nerve is irritated, damaged, or compressed as it travels through the carpal tunnel. This can be due to various factors, such as anatomical differences, repetitive hand use, hand and wrist position, or swelling and inflammation. The syndrome can cause pain, numbness, tingling, and weakness in the wrist, hand, and fingers, with symptoms often feeling like they are coming from inside the hand or wrist.
Treatment for carpal tunnel syndrome includes wearing a splint, anti-inflammatory medication, physical therapy, and, in some cases, surgery. It is important to seek treatment promptly to prevent permanent damage to the median nerve, which can lead to loss of sensation in the fingers and long-term dysfunction of the hand.
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Types of grip and wrist movement
The human hand and wrist are a complex network of bones, muscles, nerves, tendons, ligaments, and blood vessels. The muscles in the hand and wrist work together to help you move your hand and fingers, allowing you to touch and control objects.
There are two types of grip that the muscles and their possible movements can perform: power grip and precision grip. Power grip is where your grip strength comes from, such as when picking up a heavy box or opening a jar. Precision grip, on the other hand, involves using your hand and fingers to move or touch a smaller object. This type of grip uses your fingers' ability to meet your thumb (also known as an opposable grip) to pinch something between them. Examples of precision grip motions include picking up a pen off your desk and turning a key in a lock.
The wrist shares muscles with the forearm and can be categorised into four groups:
- Flexion: Muscles that let you move your wrist down, toward your palm.
- Extension: Muscles that pull your wrist up, such as when making a "stop" gesture.
- Adduction: Muscles that let you bend your wrist in, toward the centre of your body.
- Abduction: Muscles that let you bend your wrist out, away from the centre of your body.
Additionally, the wrist can be divided into six extensor compartments. The first compartment includes the abductor pollicis longus (APL) and extensor pollicis brevis (EPB) muscles, which originate from the radius and interosseous membrane. The second compartment includes the extensor carpi radialis longus (ECRL) and extensor carpi radialis brevis (ECRB) muscles. The third and fourth compartments include the extensor pollicis longus (EPL) and extensor indicis proprius (EIP) muscles, respectively, both of which originate from the ulna and interosseous membrane.
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Tendons, ligaments and connective tissue in the wrist
The wrist is a complex structure of joints, bones, muscles, ligaments, tendons, nerves, and blood vessels. The wrist is also known as the carpus, and is made up of about eight smaller wrist bones. The wrist serves as a transfer of force from the arm to the hand, allowing for a wide range of movement.
Tendons are cords of connective tissue that link muscles to bones. They are like strong, flexible ropes. The wrist contains two groups of tendons: extensor tendons and flexor tendons. Extensor tendons help to extend and straighten the fingers, hand, and wrist. Flexor tendons, on the other hand, help to flex and curl the fingers, hand, and wrist. The tendons that control the wrist originate from forearm muscles and insert into hand bones, but not into the carpal bones themselves.
Ligaments are another type of connective tissue in the wrist. They are fibrous bands of tissue that connect bones to one another and support them. Ligaments are like thick rubber bands that help joints move smoothly, protect them from bending too far, and keep them in proper alignment. The wrist contains a network of intrinsic and extrinsic ligaments. Extrinsic ligaments connect the wrist bones to the long bones of the forearm and the bones of the hand. Intrinsic ligaments attach the wrist bones to each other.
Injuries to the wrist can result in sprains, strains, dislocations, fractures, nerve injuries, or damage to blood vessels.
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Frequently asked questions
The wrist muscles are responsible for two types of grip: power and precision. Power grip is where your grip strength comes from, for example, when picking up a heavy box or opening a jar. Precision grip is using your hand and fingers to move or touch a smaller object, for example, picking up a pen off your desk or turning a key in a lock.
There are four types of wrist movements: flexion, extension, adduction, and abduction. Flexion is when you move your wrist down, toward your palm. Extension is when you pull your wrist up, like when making a "stop" gesture. Adduction is when you bend your wrist in, toward the center of your body. Abduction is when you bend your wrist out, away from the center of your body.
A pneumonic to remember the position of each bone in the wrist is to name the carpal bones in a circle, starting with the proximal row from the scaphoid towards the pinky, and then the distal row starting from the hamate towards the thumb.
