Victor Forge
The thumb is one of the most important parts of the hand, with its versatility in movement compared to the other digits. The movement of the thumb is modulated by a diverse set of specific muscles within the hand. The abductor pollicis longus (APL) is one of the deep extensors of the forearm and is responsible for facilitating movement and stabilization of the thumb. The abductor pollicis brevis is a muscle in the hand that functions as an abductor of the thumb.
| Characteristics | Values |
|---|---|
| Name | Abductor pollicis longus (APL) |
| Type | Deep extensor of the forearm |
| Functions | Abduction of the thumb, extension of the first carpometacarpal joint, assists in radial deviation and flexion of the wrist |
| Tendon Location | Lateral border of the anatomical snuffbox, a triangular space found at the base of the thumb |
| Nerve Supply | Recurrent branch of the median nerve (Roots C8-T1) |
| Arterial Supply | Proximal part supplied by the lateral branch of the posterior interosseous artery, distal part vascularised by a branch of the anterior interosseous artery |
| Muscle Belly Location | Posterior forearm |
| Interactions | Works with abductor pollicis brevis for thumb abduction, assists abductor pollicis brevis in thumb movement towards fingertips, works with long and short extensors of the thumb for full thumb extension |
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What You'll Learn
- The abductor pollicis longus (APL) muscle pulls the thumb away from the palm
- The abductor pollicis brevis muscle is a flat, thin muscle under the skin
- The APL is one of the deep extensors in the forearm
- The APL is important in the diagnosis of DeQuervain's Syndrome
- The adductor pollicis is a unique, triangular-shaped muscle
The abductor pollicis longus (APL) muscle pulls the thumb away from the palm
The abductor pollicis longus (APL) muscle is a deep extensor of the forearm responsible for pulling the thumb away from the palm. It is one of nine muscles that contribute to the diverse movements of the thumb. The APL muscle is located deep to the extensor digitorum and lateral to the extensor pollicis longus muscle. Its tendon is found in the anatomical snuffbox, a triangular space at the base of the thumb, and is joined by the tendon of the extensor pollicis brevis muscle.
The APL muscle has several important functions. Firstly, it abducts the thumb, pulling it away from the palm and facilitating movement and stabilization of the thumb. This abduction occurs at the first metacarpophalangeal joint, and the APL works in synergy with the abductor pollicis brevis muscle to achieve this movement. Secondly, the APL assists in the extension of the first carpometacarpal joint, which is important for activities such as bowling and shoveling. By working together with the long and short extensors of the thumb, the APL also helps to fully extend the thumb at the metacarpophalangeal joint, allowing for the loosening of the hand grip.
The APL muscle is supplied by the lateral branch of the posterior interosseous artery proximally and vascularised by a perforating branch of the anterior interosseous artery distally. The posterior interosseous nerve and artery pass over the APL's superficial surface. The muscle belly of the APL lies in the distal half of the posterior forearm and consists of three parts, resulting in two divisions of tendons. The deep part of the muscle originates from the ulna, interosseous membrane, and radius and is covered by the extensor digitorum longus.
The strength of the APL muscle can be assessed by asking an individual to abduct their thumb with the forearm in a neutral position. Resistance is applied against the lateral aspect of the distal end of the first metacarpal, and the strength of the APL can be determined by the amount of resistance the individual can withstand. This simple test can provide valuable information for clinical evaluation and diagnosis.
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The abductor pollicis brevis muscle is a flat, thin muscle under the skin
The abductor pollicis brevis muscle is a flat, thin muscle located just under the skin. It is a thenar muscle, contributing to the bulk of the palm's thenar eminence. The muscle originates from the flexor retinaculum of the hand, the tubercle of the scaphoid bone, and sometimes the tubercle of the trapezium. Running lateralward and downward, it is inserted by a thin, flat tendon into the lateral side of the base of the first phalanx of the thumb and the capsule of the metacarpophalangeal joint.
The abductor pollicis brevis muscle is supplied by the recurrent branch of the median nerve (Roots C8-T1). Abduction of the thumb is the movement of the thumb anteriorly, perpendicular to the palm. The abductor pollicis brevis muscle is responsible for this movement, acting across both the carpometacarpal and metacarpophalangeal joints. It also assists in opposition and extension of the thumb.
The abductor pollicis brevis is the most lateral and superficial of the thenar muscles. It is involved in the abduction of the thumb at the carpometacarpal joint, working in synergy with the abductor pollicis longus muscle. This action is important for the proper functioning of the hand, such as grasping round objects or performing precise tasks like writing and sewing.
The median nerve supplies the abductor pollicis brevis muscle at the lateral border of the thenar eminence. Wasting of the interossei and softening and flattening of the hypothenar eminence, with sparing of the abductor pollicis brevis, can indicate an ulnar nerve lesion. The muscle is commonly used in neuroscience studies to examine muscle responses during surgical procedures.
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The APL is one of the deep extensors in the forearm
The Abductor Pollicis Longus (APL) is a muscle that is responsible for abducting the thumb. It is one of the deep extensors in the forearm, which means it is located in the posterior compartment of the forearm, also known as the extensor compartment. This compartment is further divided into superficial and deep layers, with the APL being part of the deep layer.
The forearm muscles are divided into two main compartments: the anterior flexor compartment and the posterior extensor compartment. The deep fascia of the forearm encircles the musculature related to the ulna and radius, and the compartments are separated by the intermuscular septum and the interosseous membrane. The APL is situated in the distal half of the posterior forearm, just distal to the supinator muscle.
The APL has a tendon that is located in the first extensor compartment of the wrist, which is the lateral border of the anatomical snuffbox. This is a triangular space found at the base of the thumb, distal and posterior to the styloid process of the radius. The tendon of the APL passes through a groove on the lateral surface of the distal end of the radius, joining with the tendon of the extensor pollicis brevis muscle before passing beneath the extensor retinaculum.
The APL is supplied by the lateral branch of the posterior interosseous artery proximally and by a perforating branch of the anterior interosseous artery distally. The posterior interosseous nerve and artery course between the APL and the extensor digitorum, passing over the APL's superficial surface. The main function of the APL is to abduct the thumb, pulling it away from the palm, and it also assists in radial deviation and flexion of the wrist.
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The APL is important in the diagnosis of DeQuervain's Syndrome
The abductor pollicis longus (APL) is a deep extensor of the forearm that facilitates movement and stabilisation of the thumb. The APL pulls the thumb away from the palm, producing mid-extension and abduction of the thumb at the first metacarpophalangeal joint. This action is seen in activities such as bowling and shovelling.
De Quervain's syndrome, or De Quervain's tenosynovitis (DQT), is a repetitive stress condition that affects the APL and the extensor pollicis brevis (EPB) tendons in the first extensor compartment of the wrist. It is characterised by pain or tenderness at the radial side of the wrist, and thickening and inflammation of the APL and EPB tendons, resulting in swelling in the first extensor compartment of the wrist.
The APL is important in the diagnosis of De Quervain's syndrome as it is one of the primary sites of pain and inflammation. The thickening of the APL tendon and the overlying extensor retinaculum creates a fibro-osseous tunnel, restraining normal gliding within the sheath and exacerbating inflammation. This inflammation can be managed with ice, non-steroidal anti-inflammatory drugs (NSAIDs), and daily KT taping.
Furthermore, the strength of the APL can be assessed as part of the diagnostic process for De Quervain's syndrome. The test for clinical diagnosis, known as Finklestein's test, involves asking the subject to abduct the thumb with the forearm in a neutral position. Resistance is applied against the lateral aspect of the distal end of the first metacarpal in the direction of adduction of the thumb. This test helps to evaluate the strength and function of the APL and EPB tendons, which are crucial for thumb movement and stability.
The management of De Quervain's syndrome depends on the severity of the condition and can include conservative treatments such as activity modification, physical therapy, orthotics, and manual therapy. Early splinting during the acute phase can prevent tissue aggravation and allow patients to perform essential activities. In some cases, surgical management may be required, especially if there is an intertendinous septum present between the APL and EPB.
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The adductor pollicis is a unique, triangular-shaped muscle
The adductor pollicis muscle is a unique, triangular-shaped muscle with a two-headed structure. It is a fleshy, flat, triangular, and fan-shaped muscle deep in the thenar compartment beneath the long flexor tendons and the lumbrical muscles at the centre of the palm. It is one of the most important muscles in the hand, contributing to the diverse movements of the thumb.
The adductor pollicis muscle has two heads: the transverse head and the oblique head. The transverse head, or adductor transversus pollicis, is deeply seated and triangular in shape. It arises from the lower two-thirds of the palmar surface of the third metacarpal bone, with fibres converging to insert into the ulnar side of the base of the proximal phalanx of the thumb. The oblique head, or adductor obliquus pollicis, arises from the capitate bone, the bases of the second and third metacarpals, and other structures. The two heads merge laterally, forming a tendon that inserts into the ulnar side of the base of the proximal phalanx of the thumb.
The adductor pollicis muscle is an intrinsic muscle of the hand, lying in the deepest muscular plane of the palm within the adductor compartment. It is anterior to the plane of the interossei, crossing the palm of the hand. The muscle is innervated by the deep branch of the ulnar nerve (C8-T1), and the radial artery passes between its two heads as it travels from the back of the hand into the palm.
The main function of the adductor pollicis muscle is to adduct the thumb, bringing it into a position of opposition at the centre of the palm. It can also bring the thumb alongside the palm and index finger. This ability is critical for hand dexterity, allowing for pinching and gripping movements. The strength of the adductor pollicis muscle can be assessed using Froment's sign, which measures the strength of adductor pollicis contraction when the ulnar nerve is stimulated.
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Frequently asked questions
The abductor pollicis longus (APL) is the muscle that abducts the thumb. It pulls the thumb away from the palm.
The abductor pollicis longus is a deep extensor of the forearm. Its tendon is present in the first extensor compartment of the wrist.
The main function of the abductor pollicis longus is to abduct the thumb and extend the first carpometacarpal joint. It also assists in radial deviation and flexion of the wrist.
