POSTERIOR COMPARTMENT FOREARM MUSCLES

GENERAL INFORMATION

The posterior compartment of the forearm contains muscles responsible for extending the wrist and fingers and aiding in the supination of the forearm. These muscles play a critical role in movements such as gripping, lifting and stabilising the hand and wrist during functional tasks.

ORIGIN

The muscles of the posterior forearm compartment primarily originate from the lateral epicondyle of the humerus and the posterior surfaces of the radius and ulna:

• Extensor Carpi Radialis Longus: Originates from the lateral supracondylar ridge of the humerus.
• Extensor Digitorum: Originates from the lateral epicondyle of the humerus.
• Extensor Carpi Ulnaris: Originates from the lateral epicondyle of the humerus and the posterior border of the ulna.
• Supinator: Originates from the lateral epicondyle of the humerus and the supinator crest of the ulna.
• Abductor Pollicis Longus: Originates from the posterior surfaces of the radius, ulna and interosseous membrane.

INSERTION POINT

The posterior compartment muscles insert into various parts of the hand and fingers to facilitate extension and supination:

• Extensor Carpi Radialis Longus: Inserts into the base of the second metacarpal bone, allowing wrist extension and radial deviation.
• Extensor Digitorum: Inserts into the extensor expansions of the fingers, enabling finger extension.
• Extensor Carpi Ulnaris: Inserts into the base of the fifth metacarpal, controlling wrist extension and ulnar deviation.
• Supinator: Inserts into the lateral surface of the radius, aiding in forearm supination.
• Abductor Pollicis Longus: Inserts into the base of the first metacarpal, helping abduct and extend the thumb.

MAJOR ARTERIES

The posterior forearm muscles receive their blood supply from the following arteries:

• Posterior interosseous artery: Supplies blood to the deep muscles of the posterior forearm.
• Radial artery: Supplies blood to the extensor muscles along the radial side of the forearm.

NEURAL INNERVATION

The muscles in the posterior compartment of the forearm are innervated by:

• Radial nerve: Provides motor and sensory innervation to the extensor muscles of the forearm, enabling wrist and finger extension.
• Posterior interosseous nerve: A branch of the radial nerve that innervates the deeper muscles, including the extensor indicis and abductor pollicis longus.

TRIGGER POINT

Trigger points can develop in the posterior forearm muscles, particularly in the extensor carpi radialis longus and extensor digitorum, leading to pain and restricted motion. These trigger points often arise from overuse, repetitive strain, or poor ergonomics.

CONCENTRIC FUNCTION

The concentric function of the posterior forearm muscles allows for movements such as:

• Extensor Carpi Radialis Longus: Extends and radially deviates the wrist, aiding in lifting and grasping.
• Extensor Digitorum: Extends the fingers, enabling movements like opening the hand or releasing objects.
• Extensor Carpi Ulnaris: Extends and ulnarly deviates the wrist, stabilising the hand during functional tasks.
• Supinator: Contracts to supinate the forearm, allowing the palm to face upwards.
• Abductor Pollicis Longus: Abducts and extends the thumb, aiding in grip and pinch movements.

ECCENTRIC FUNCTION

The posterior compartment muscles play a crucial role in controlling movements during the release of tension:

• Extensor Carpi Radialis Longus: Eccentrically controls wrist flexion during the lowering phase of lifting or gripping tasks.
• Extensor Digitorum: Slowly lengthens to control finger flexion, ensuring smooth release of the fingers from an object.
• Extensor Carpi Ulnaris: Eccentrically controls ulnar deviation and wrist flexion, stabilising the wrist during dynamic movements.
• Supinator: Controls the pronation of the forearm by eccentrically lengthening during forearm rotation.

ISOMETRIC FUNCTION

Isometric contraction in the posterior forearm muscles stabilises the wrist and fingers during static tasks:

• Extensor Carpi Radialis Longus: Engages isometrically to stabilise the wrist during activities like holding a weight in place.
• Extensor Digitorum: Maintains finger extension during isometric tasks such as holding an open hand or stabilising grip on an object.
• Extensor Carpi Ulnaris: Provides wrist stability during static tasks that require wrist extension and ulnar deviation.
• Supinator: Stabilises the forearm in a supinated position during tasks that require controlled rotation.

RELATED MUSCLES SCIENTIFIC NAMES

• Extensor Carpi Radialis Longus: Extends and stabilises the wrist, aiding in radial deviation.
• Extensor Digitorum: Extends the fingers, allowing for movements such as opening the hand or releasing objects.
• Extensor Carpi Ulnaris: Controls wrist extension and ulnar deviation, providing stability during grip-related tasks.
• Supinator: Aids in supination, turning the forearm so the palm faces upwards.
• Abductor Pollicis Longus: Abducts and extends the thumb, helping in grip and thumb movements.

ANTAGONIST

• Flexor Carpi Radialis: Opposes the action of the extensor carpi radialis longus by flexing the wrist and assisting in radial deviation.
• Flexor Digitorum Profundus: Acts as an antagonist to the extensor digitorum by flexing the fingers and balancing extension.
• Flexor Carpi Ulnaris: Opposes the extensor carpi ulnaris by flexing and ulnarly deviating the wrist.
• Pronator Teres: Opposes the supinator by pronating the forearm, turning the palm downwards.
• Adductor Pollicis: Opposes the abductor pollicis longus by adducting the thumb and pulling it toward the hand.

COMMON INJURIES

• Lateral Epicondylitis (Tennis Elbow): Inflammation of the tendons attaching to the lateral epicondyle, often caused by overuse of the extensor muscles, leading to pain and reduced grip strength.
• Extensor Tendonitis: Inflammation of the tendons in the posterior forearm, commonly resulting from repetitive wrist extension, causing pain and swelling in the forearm and wrist.
• Radial Tunnel Syndrome: Compression of the radial nerve as it passes through the forearm, leading to pain, weakness and reduced mobility in the wrist and fingers.
• De Quervain’s Tenosynovitis: Affects the tendons of the extensor pollicis brevis and abductor pollicis longus, causing pain and swelling near the base of the thumb.
• Supinator Muscle Strain: Overuse or strain of the supinator muscle can lead to pain and limited mobility in forearm rotation, especially during repetitive supination.

EXERCISES

• Wrist Extensions: Strengthens the extensor muscles by lifting the wrist upward against resistance, improving wrist stability and function.
• Finger Extensions: Targets the extensor digitorum by extending the fingers against resistance, enhancing finger strength and mobility.
• Reverse Wrist Curls: Focuses on the extensor carpi radialis and ulnaris by curling the wrist upward with a lightweight, improving grip endurance.
• Supination with Resistance Band: Strengthens the supinator by rotating the forearm from a pronated to a supinated position using a resistance band, improving rotation control.
• Thumb Abductions: Strengthens the abductor pollicis longus by lifting the thumb away from the hand against resistance, improving thumb mobility and grip.

STRETCHES

• Wrist Extensor Stretch: Extending the arm and gently pulling the fingers downward, stretching the extensor muscles and relieving tension.
• Finger Stretch: Gently stretch the fingers backwards to lengthen the extensor digitorum, improving flexibility and reducing stiffness.
• Supinator Stretch: Involves rotating the forearm to a pronated position and holding it to stretch the supinator muscle, relieving tightness in the forearm.
• Forearm Stretch: Extending the arm and pulling the hand back, stretching the extensor muscles to improve flexibility and reduce tension.
• Thumb Stretch: It involves gently pulling the thumb away from the hand, stretching the abductor pollicis longus and improving mobility in the thumb.