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Extensor pollicis longus muscle
Extensor pollicis longus muscle
Extensor pollicis longus muscle
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Extensor pollicis longus muscle
Posterior surface of the forearm. Deep muscles. Extensor pollicis longus muscle is labeled in purple.
Details
OriginMiddle third of posterior surface of ulna, interosseous membrane
InsertionThumb, distal phalanx
ArteryPosterior interosseous artery
NervePosterior interosseous nerve (branching from the radial nerve)
ActionsExtension of the thumb (metacarpophalangeal and interphalangeal)
AntagonistFlexor pollicis longus muscle, flexor pollicis brevis muscle
Identifiers
Latinmusculus extensor pollicis longus
TA98A04.6.02.051
TA22516
FMA38521
Anatomical terms of muscle

In human anatomy, the extensor pollicis longus muscle (EPL) is a skeletal muscle located dorsally on the forearm. It is much larger than the extensor pollicis brevis, the origin of which it partly covers and acts to stretch the thumb together with this muscle.

Structure

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The extensor pollicis longus arises from the dorsal surface of the ulna and from the interosseous membrane,[1] next to the origins of abductor pollicis longus and extensor pollicis brevis.[2]

Passing through the third tendon compartment,[1] lying in a narrow, oblique groove on the back of the lower end of the radius,[3] it crosses the wrist close to the dorsal midline before turning towards the thumb using Lister's tubercle on the distal end of the radius as a pulley.[2]

It obliquely crosses the tendons of the extensores carpi radialis longus and brevis, and is separated from the extensor pollicis brevis by a triangular interval, the anatomical snuff box in which the radial artery is found.[3]

At the proximal phalanx, the tendon is joined by expansions from abductor pollicis brevis and adductor pollicis.[2]

The tendon is finally inserted on the base of the distal phalanx of the thumb.[1]

6.7 to 9.7 centimetres (2.6 to 3.8 in) in length, the tendon passes through a long and superficial synovial sheath which, passing obliquely from the radial border of the forearm into the thumb, extends from the proximal border of the extensor retinaculum to the first carpometacarpal joint. In the synovial sheath a proximal and a distal mesotendon connect the tendon to the floor of the sheath.[4]

Relations

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Together with the tendons of the extensor pollicis brevis and the abductor pollicis longus, its tendon crosses the radial artery.[3]

Blood supply

[edit]

The tendon of extensor pollicis longus is supplied by branches from various arteries. Before the tendon enters its synovial sheath, arteries from the anterior interosseous artery or its muscular branches enter the tendon. The sheath itself is supplied by the posterior ramus of the same artery. In the metacarpal region, beyond the synovial sheath, the tendon is supplied directly from the radial artery. At the phalanges, the tendon forms a dorsal aponeurosis which is supplied by a digital branch of the first dorsal metacarpal artery.[4]

Innervation

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The extensor pollicis longus muscle receives innervation from the posterior interosseous nerve (C7 and C8) which is the continuation of the deep branch of the radial nerve.

Function

[edit]

Extensor pollicis longus extends the terminal phalanx of the thumb. While abductor pollicis brevis and adductor pollicis, both attached to the extensor pollicis longus tendon, can extend the thumb's interphalangeal joint to the neutral position, only extensor pollicis longus can achieve full hyperextension at the interphalangeal joint. This complete extension at the interphalangeal joint is not possible, or considerably more difficult, with the carpal, carpometacarpal, and metacarpophalangeal joints simultaneously extended. Likewise, flexion at the interphalangeal joint by flexor pollicis longus is considerably reduced in wrist flexion.[2]

It also applies an extensor force at the metacarpophalangeal joint together with the extensor pollicis brevis and extends and adducts at the carpometacarpal joint of the thumb.[2]

Clinical significance

[edit]

Injury

[edit]

Tenosynovitis, inflammatory irritation of the synovial sheath, is relatively common in the third compartment after repetitive activities such as drum playing.[5]

Additional images

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  • Anatomical snuff box
    Anatomical snuff box
  • Bones of left forearm. Posterior aspect.
    Bones of left forearm. Posterior aspect.
  • Bones of the left hand. Dorsal surface.
    Bones of the left hand. Dorsal surface.
  • Tendons of forefinger and vincula tendina.
    Tendons of forefinger and vincula tendina.
  • Cross-section through the middle of the forearm.
    Cross-section through the middle of the forearm.
  • Posterior surface of the forearm. Superficial muscles.
    Posterior surface of the forearm. Superficial muscles.
  • Posterior surface of the forearm. Deep muscles.
    Posterior surface of the forearm. Deep muscles.
  • Transverse section across the wrist and digits.
    Transverse section across the wrist and digits.
  • Arteries of the back of the forearm and hand.
    Arteries of the back of the forearm and hand.
  • The mucous sheaths of the tendons on the back of the wrist. (Extensor pollicis longus visible at center right.)
    The mucous sheaths of the tendons on the back of the wrist. (Extensor pollicis longus visible at center right.)
  • Muscle of the hand . Posterior view.
    Muscle of the hand . Posterior view.

Notes

[edit]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Extensor pollicis longus muscle

View on Grokipedia
from Grokipedia
The extensor pollicis longus (EPL) is a slender muscle located in the deep , serving as one of the extrinsic responsible for extending the interphalangeal (IP) joint and adducting the thumb at the metacarpophalangeal (MCP) joint. It originates from the middle third of the posterior surface of the ulnar and the adjacent , forming part of the third dorsal extensor compartment. Its long tendon passes through the extensor retinaculum, looping around on the dorsal , before inserting at the base of the distal of the thumb. Innervated by the (a branch of the ) from spinal roots C7 and C8, the EPL enables precise movements essential for fine motor tasks such as pinching and grasping. supply to the muscle and its is provided primarily by branches of the posterior interosseous artery, with additional contributions from the anterior interosseous artery, , , dorsal carpal arch, and the first dorsal metacarpal artery's digital branch. The muscle's forms the medial boundary of the , a clinically important on the radial aspect of the . Clinically, the EPL is prone to in its third extensor compartment, often due to repetitive motions, and is at risk of spontaneous rupture following distal fractures, occurring in up to 5% of adult cases treated with dorsal plating. Such ruptures can lead to inability to extend the IP joint, resulting in a "thumb drop" , and may require surgical interventions like tendon transfer from the extensor indicis proprius. Anatomical variants, though rare (prevalence of about 1%), include accessory slips or dual tendons, which can influence surgical planning.

Anatomy

Origin and insertion

The extensor pollicis longus muscle originates from the posterior surface of the middle third of the , specifically along the ulnar shaft below the proximal third, and from the adjacent of the . This attachment on the provides a stable proximal leverage point, enabling the muscle to transmit force distally for thumb extension. The tendinous portion of the extensor pollicis longus inserts on the dorsal aspect of the base of the distal phalanx of the . The muscle belly itself has an average length of approximately 12.5 cm, while the tendon measures 6.7 to 9.7 cm in length, facilitating its extension from the origin to the distant insertion.

Course and relations

The extensor pollicis longus muscle occupies the deep , where its belly runs obliquely in a radial direction toward the , lying deep to the extensor digitorum and superficial to the extensor indicis. As it approaches the , the muscle transitions into a long, slender tendon that passes through the third dorsal extensor compartment, an osteofibrous tunnel formed by the extensor retinaculum over the lunate bone and distal radius. Emerging from the third compartment, the tendon curves sharply around on the posterior aspect of the distal radius, directing it toward the thumb. Distally, the tendon traverses the , a triangular depression on the radial aspect of the , before proceeding to the base of the distal phalanx of the thumb. In the forearm, the muscle relates medially to the extensor digitorum and laterally to the extensor indicis within the deep layer. At the wrist, the tendon forms the ulnar (medial) boundary of the , with the abductor pollicis longus tendon constituting the radial (lateral) border and the extensor pollicis brevis tendon contributing to the roof. Within this space, the tendon crosses dorsal to the .

Blood supply

The extensor pollicis longus muscle receives its primary blood supply from branches of the posterior interosseous , a major terminal branch of the common interosseous that arises from the in the proximal . These branches, including recurrent and muscular perforators, provide perfusion to the muscle belly in the deep , particularly along its superficial and deep surfaces. Additional vascular contributions to the muscle originate from perforating branches of the anterior interosseous , which supplies the deep aspect of the muscle and aids in nourishing the musculotendinous junction. As the tendon progresses distally through the extensor retinaculum and into the hand, its vascularization shifts to include branches from the dorsal carpal arch—formed by anastomoses between the dorsal branches of the radial and ulnar arteries—and direct supply from the radial artery itself over the first metacarpal. Near the insertion at the base of the distal phalanx of the thumb, the first dorsal metacarpal artery (a branch of the radial artery) provides terminal branches to the tendon's distal portion, ensuring perfusion to the area lacking synovial sheath coverage. This distal network forms a characteristic "T"-shaped anastomosis with smaller ascending and descending vessels, enhancing longitudinal flow along the tendon. The overall vascular pattern of the extensor pollicis longus features periosteal branches at the origin from the middle third of the and , transitioning to intrinsic longitudinal vessels within the substance. These create potential watershed zones, particularly in the mid- segment within the synovial sheath, where relative avascularity may predispose to ischemic vulnerability under stress. Complementing this, the benefits from a dual blood supply mechanism: intrinsic vessels extending from the muscle belly proximally and extrinsic contributions from the synovial sheath and surrounding mesotendinous folds distally, promoting overall viability.

Innervation

The extensor pollicis longus muscle is innervated by the , which is the continuation of the deep branch of the . This innervation is exclusively motor, providing neural input solely for the muscle's contractile function without any sensory components. The spinal root origins of this innervation are primarily from C7 and C8, though occasional contributions from C6 have been noted in anatomical variations. The reaches the extensor pollicis longus by first piercing the at the proximal , where it emerges into the posterior compartment after passing through the . From there, it travels distally along the posterior , lying in the plane between the superficial and deep extensor muscles of the , before branching to supply the muscle belly of the extensor pollicis longus in the deep posterior compartment.

Anatomical variations

The extensor pollicis longus (EPL) muscle displays several anatomical variations, though these are generally rare and typically discovered incidentally during dissections or surgery. Absence or of the EPL is rare, as reported in isolated case studies, where thumb extension may be compensated by the extensor indicis proprius muscle. Fusion of the EPL tendon with adjacent muscles, such as the extensor pollicis brevis or abductor pollicis longus, has been observed in cadaveric studies, potentially altering the tendon's course through the third extensor compartment and affecting differential extension of the thumb joints. Accessory slips or additional heads of the EPL, arising from the or , have been documented in dissections and case reports, often representing duplicated tendons or supernumerary fibers that may share the same sheath or insert variably on the distal . These variations have been observed in case reports, some showing bilateral occurrence, though large-scale comparative data remain limited. Such anatomical deviations heighten the risk of misidentification during tendon repair procedures, underscoring the value of preoperative to avoid iatrogenic .

Function

Thumb joint actions

The extensor pollicis longus (EPL) muscle primarily functions to extend the interphalangeal (IP) joint of by pulling on its terminal , which inserts at the base of the distal . This action allows for isolated extension of the distal phalanx, enabling precise movements such as pinching or releasing objects. Unlike the intrinsic thumb muscles, such as the adductor pollicis, which extend the IP joint only to a neutral position via the extensor hood, the EPL can produce full hyperextension at this joint. In addition to its primary role at the IP joint, the EPL contributes secondarily to extension at the metacarpophalangeal (MCP) joint and adduction at the carpometacarpal (CMC) joint, particularly when acting in with other muscles. For instance, when combined with the extensor pollicis brevis, the EPL facilitates extension of the entire across both the MCP and IP joints, enhancing overall thumb retraction. At the CMC joint, its adduction effect helps position the toward the palm, supporting grip stability. The biomechanical efficiency of the EPL in thumb extension is enhanced by the tendon's circuitous path around on the dorsal , which acts as a to create an effective moment arm. This configuration provides a strong extensor leverage for the IP joint, with an approximate moment arm of 9-10 mm at the CMC level that supports distal extension forces.

Wrist and overall hand contributions

The extensor pollicis longus (EPL) tendon passes through the third dorsal extensor compartment, where it is stabilized by the extensor retinaculum to maintain alignment and prevent bowstringing during movements. This positioning allows the EPL to function effectively in coordination with the primary wrist extensors, enhancing overall stability at the radiocarpal joint during integrated hand actions. In broader hand function, the EPL stabilizes the thumb during pinch grips and opposition by extending and adducting the metacarpophalangeal and interphalangeal joints, thereby countering flexor forces from muscles like the flexor pollicis longus to preserve precise thumb positioning. It further aids in key pinch maneuvers via adduction at the , where its insertion supports lateral thumb compression against the fingers for tasks requiring firm lateral grip. The EPL operates in synergy with the extensor carpi radialis longus and brevis during thumb retraction, where coordinated activation ensures smooth integration of thumb and wrist movements without excessive deviation. In composite hand actions like opening the hand, the EPL facilitates a significant portion of thumb excursion by extending the interphalangeal joint alongside contributions from the extensor pollicis brevis and abductor pollicis longus.

Clinical significance

Tendon rupture and trauma

The extensor pollicis longus (EPL) tendon is particularly vulnerable to rupture following distal radius fractures, such as Colles' fractures, where the incidence ranges from 0.2% to 5%. This spontaneous rupture typically occurs due to mechanical abrasion of the tendon against the rough bony callus at Lister's tubercle or vascular compromise within the anatomical snuffbox, leading to ischemic attrition of the tendon. These ruptures often present delayed, 4 to 8 weeks after the initial fracture, allowing time for progressive tendon weakening. Acute traumatic ruptures of the EPL tendon can also arise from direct lacerations caused by sharp objects or high-impact injuries in sports, disrupting the tendon's integrity immediately upon trauma. Risk factors that predispose individuals to EPL tendon rupture include underlying , which promotes chronic and tendon attrition; local or systemic injections, which may impair tendon vascularity and tensile strength; and repetitive microtrauma from occupational or recreational activities, accelerating degenerative changes. Diagnosis of EPL tendon rupture begins with clinical evaluation, characterized by isolated loss of interphalangeal joint extension of the while other motions, such as metacarpophalangeal extension, remain intact, often revealing a characteristic "thumb drop" posture. Confirmation is achieved through , with demonstrating tendon discontinuity, retraction of the proximal stump, and possible fluid-filled gaps, while MRI provides detailed visualization of the rupture site and surrounding involvement. The condition was first described in 1876 by Duplay as a spontaneous rupture associated with underlying pathology. Recent studies since 2020 underscore the importance of early surgical intervention, such as tendon transfer using the extensor indicis proprius, to restore thumb extension and avert chronic deformities like mallet thumb.

Inflammatory and overuse conditions

The extensor pollicis longus (EPL) muscle is susceptible to inflammatory conditions, primarily , which involves inflammation of the within the third dorsal extensor compartment of the . This condition arises from repetitive microtrauma or friction against the surrounding bony structures, such as , leading to synovial irritation and potential adhesions. Symptoms typically include localized pain in the , exacerbated by thumb extension or ulnar deviation, along with swelling and palpable during tendon gliding. Overuse-related tenosynovitis of the EPL is commonly observed in occupations or activities involving prolonged repetitive thumb and wrist motions, such as drumming or work. For instance, drummers who perform extended sessions may develop "drummer's tendinitis," characterized by stenosing due to the high-frequency extension of the and . Similarly, workers engaging in precise, repetitive grasping tasks experience elevated risk from cumulative strain on dorsal wrist tendons. Recent studies from the 2020s have linked excessive use to increased incidence of and tendinopathies, including pain and rigidity in heavy users, though primarily associated with conditions like De Quervain's . There is notable overlap with De Quervain's tenosynovitis, which primarily affects the abductor pollicis longus and extensor pollicis brevis in the first dorsal compartment, but isolated EPL involvement can occur and mimic the presentation due to adjacent compartment irritation. Diagnosis frequently relies on the Finkelstein test, where ulnar deviation of the clenched fist provokes sharp pain along the radial , though confirmation is recommended to differentiate isolated third-compartment involvement. Systemic inflammatory diseases, such as , can induce EPL tenosynovitis through synovial proliferation and formation, leading to thickening and potential bony erosion at stress points like the dorsal . In rheumatoid patients, extensor occurs in approximately 30% of cases on evaluation, with the EPL frequently implicated among extensor tendons due to its anatomical positioning. These conditions show patterns similar to related stenosing , with higher prevalence often noted in females, attributed to hormonal influences and occupational exposures. Initial treatment is conservative, emphasizing thumb spica splinting to immobilize the and , alongside nonsteroidal drugs (NSAIDs) to reduce , achieving symptom relief in most mild cases. For persistent symptoms, injections into the third compartment provide targeted relief, while refractory cases may require surgical tenosynovectomy to release adhesions and restore gliding.

References

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  4. https://nervesurgery.wustl.edu/deep-branch/extensor-pollicis-longus/
  5. https://www.orthobullets.com/anatomy/10039/extensor-pollicis-longus
  6. https://radiopaedia.org/articles/extensor-pollicis-longus-muscle?lang=us
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  8. https://eurjanat.com/v1/journal/paper.php?id=120061br
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