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Muscles acting on the joints of the hand and innervation
Muscles Acting on the Joints of the Hand and Their Innervation
The muscles acting on the joints of the hand allow for a wide range of movements, including flexion, extension, abduction, adduction, and opposition. These movements are essential for fine motor control, grip strength, and dexterity. The muscles responsible for these actions are divided into extrinsic and intrinsic muscles, each playing a critical role in the function of the hand. The innervation of these muscles is primarily provided by the median, ulnar, and radial nerves.
1. Extrinsic Muscles Acting on the Hand
Extrinsic muscles are those that originate outside the hand (in the forearm) but insert into the bones of the hand. These muscles are responsible for larger, more powerful movements of the hand and fingers, such as flexion, extension, abduction, and adduction.
Flexor Muscles of the Hand
These muscles are primarily located in the anterior compartment of the forearm and are responsible for flexion of the wrist and fingers.
Flexor Digitorum Superficialis (FDS)
Origin: Medial epicondyle of the humerus, coronoid process of the ulna, and the radius.
Insertion: Middle phalanges of the 2nd to 5th fingers.
Action: Flexes the proximal interphalangeal joints (PIP) and assists in flexing the metacarpophalangeal joints (MCP) and wrist.
Innervation: Median nerve (C7, C8, T1).
Flexor Digitorum Profundus (FDP)
Origin: Proximal 3/4 of the anterior and medial surfaces of the ulna and the interosseous membrane.
Insertion: Distal phalanges of the 2nd to 5th fingers.
Action: Flexes the distal interphalangeal joints (DIP) and assists in flexing the MCP and PIP joints and the wrist.
Innervation: Median nerve (C8, T1) for the 2nd and 3rd fingers, Ulnar nerve (C8, T1) for the 4th and 5th fingers.
Flexor Pollicis Longus (FPL)
Origin: Anterior surface of the radius and interosseous membrane.
Insertion: Distal phalanx of the thumb.
Action: Flexes the thumb at the interphalangeal joint (IP) and assists in flexing the wrist.
Innervation: Median nerve (C8, T1).
Extensor Muscles of the Hand
These muscles are located in the posterior compartment of the forearm and are responsible for extension of the wrist and fingers.
Extensor Digitorum (ED)
Origin: Lateral epicondyle of the humerus.
Insertion: Extensor expansions of the 2nd to 5th fingers.
Action: Extends the MCP, PIP, and DIP joints of the 2nd to 5th fingers.
Innervation: Radial nerve (C7, C8).
Extensor Indicis (EI)
Origin: Posterior surface of the ulna and interosseous membrane.
Insertion: Extensor expansion of the index finger.
Action: Extends the index finger and assists in wrist extension.
Innervation: Radial nerve (C7, C8).
Extensor Pollicis Longus (EPL)
Origin: Posterior surface of the ulna and interosseous membrane.
Insertion: Distal phalanx of the thumb.
Action: Extends the thumb at the IP joint and assists in wrist extension.
Innervation: Radial nerve (C7, C8).
Extensor Pollicis Brevis (EPB)
Origin: Posterior surface of the radius and interosseous membrane.
Insertion: Proximal phalanx of the thumb.
Action: Extends the thumb at the MCP joint.
Innervation: Radial nerve (C7, C8).
Abductor Pollicis Longus (APL)
Origin: Posterior surfaces of the radius and ulna and interosseous membrane.
Insertion: Base of the 1st metacarpal.
Action: Abducts and extends the thumb.
Innervation: Radial nerve (C7, C8).
2. Intrinsic Muscles of the Hand
Intrinsic muscles are located within the hand itself and are responsible for finer movements and dexterity. These muscles control the joints of the fingers and are involved in grip strength, opposition, and precision movements.
Thenar Muscles
These muscles control the thumb and are essential for thumb movements, such as opposition and flexion.
Abductor Pollicis Brevis (APB)
Origin: Flexor retinaculum and trapezium bone.
Insertion: Proximal phalanx of the thumb.
Action: Abducts the thumb.
Innervation: Median nerve (recurrent branch).
Flexor Pollicis Brevis (FPB)
Origin: Flexor retinaculum and trapezium bone.
Insertion: Proximal phalanx of the thumb.
Action: Flexes the thumb at the MCP joint.
Innervation: Median nerve (recurrent branch).
Opponens Pollicis (OP)
Origin: Flexor retinaculum and trapezium bone.
Insertion: Lateral side of the 1st metacarpal.
Action: Opposes the thumb to the other fingers.
Innervation: Median nerve (recurrent branch).
Hypothenar Muscles
These muscles control the little finger and allow movements such as flexion, abduction, and opposition of the 5th finger.
Abductor Digiti Minimi (ADM)
Origin: Pisiform bone.
Insertion: Proximal phalanx of the little finger.
Action: Abducts the little finger.
Innervation: Ulnar nerve (deep branch).
Flexor Digiti Minimi Brevis (FDM)
Origin: Hook of the hamate and flexor retinaculum.
Insertion: Proximal phalanx of the little finger.
Action: Flexes the little finger at the MCP joint.
Innervation: Ulnar nerve (deep branch).
Opponens Digiti Minimi (ODM)
Origin: Hook of the hamate and flexor retinaculum.
Insertion: Medial side of the 5th metacarpal.
Action: Opposes the little finger to the thumb.
Innervation: Ulnar nerve (deep branch).
Lumbricals
The lumbricals are muscles that originate from the tendons of the flexor digitorum profundus and insert into the extensor expansions. They are involved in the fine motor control of the fingers.
Lumbricals (1st and 2nd)
Origin: Tendons of the flexor digitorum profundus of the 2nd and 3rd fingers.
Insertion: Extensor expansions of the 2nd and 3rd fingers.
Action: Flex the MCP joints and extend the PIP and DIP joints.
Innervation: Median nerve (C8, T1).
Lumbricals (3rd and 4th)
Origin: Tendons of the flexor digitorum profundus of the 4th and 5th fingers.
Insertion: Extensor expansions of the 4th and 5th fingers.
Action: Flex the MCP joints and extend the PIP and DIP joints.
Innervation: Ulnar nerve (C8, T1).
Interossei Muscles
The interossei muscles are responsible for adduction and abduction of the fingers and assist in flexion and extension of the finger joints.
Dorsal Interossei (DAB)
Origin: Adjacent sides of the metacarpals.
Insertion: Proximal phalanges and extensor expansions of the 2nd, 3rd, and 4th fingers.
Action: Abduct the fingers (away from the midline).
Innervation: Ulnar nerve (deep branch).
Palmar Interossei (PAD)
Origin: Sides of the metacarpals.
Insertion: Proximal phalanges and extensor expansions of the 2nd, 4th, and 5th fingers.
Action: Adduct the fingers (towards the midline).
Innervation: Ulnar nerve (deep branch).
Innervation Overview
Median Nerve (C5-T1): Innervates most of the flexor muscles and **thenar
muscles**, and some lumbricals.
Ulnar Nerve (C8, T1): Innervates the hypothenar muscles, the interossei muscles, and the 3rd and 4th lumbricals.
Radial Nerve (C5-T1): Innervates the extensor muscles of the forearm, including the extensor digitorum, extensor pollicis longus, and extensor indicis.
Clinical Significance
Carpal Tunnel Syndrome: Compression of the median nerve at the wrist can lead to symptoms of numbness, tingling, and weakness in the thumb, index, and middle fingers.
Ulnar Nerve Injury: Damage to the ulnar nerve can result in claw hand, where the 4th and 5th fingers become hyperextended at the MCP joints and flexed at the PIP and DIP joints.
Tendon Injuries: Tendon injuries, such as those affecting the flexor digitorum profundus or the extensor digitorum, can lead to inability to flex or extend fingers properly, affecting hand function.
Dupuytren’s Contracture: A condition involving the thickening and shortening of the palmar fascia, which can limit the movement of the fingers, especially the ring and little fingers.
Summary
The muscles acting on the joints of the hand, both extrinsic and intrinsic, allow for fine and powerful movements, critical for grasping, manipulation, and dexterity. Proper innervation of these muscles, primarily through the median, ulnar, and radial nerves, is essential for their function. Clinical conditions such as carpal tunnel syndrome, ulnar nerve injury, and tendon injuries highlight the importance of these muscles and their associated nerve supply for optimal hand function.