Posterior compartment of the forearm

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Posterior compartment of the forearm
Forearm muscles back superficial.png
Extensor compartment of the forearm and hand
Details
System Musculoskeletal system
Artery Radial artery, radial recurrent artery, profunda brachii, posterior interosseous artery
Nerve Radial nerve, [1] posterior interosseous nerve
Identifiers
Latin compartimentum antebrachii posterius
TA98 A04.6.01.007
TA2 2494
FMA 38411
Anatomical terminology

The posterior compartment of the forearm (or extensor compartment) contains twelve muscles which primarily extend the wrist and digits. [2] It is separated from the anterior compartment by the interosseous membrane between the radius and ulna.

Contents

Structure

Muscles

There are generally twelve muscles in the posterior compartment of the forearm, which can be further divided into superficial, intermediate, and deep. Most of the muscles in the superficial and the intermediate layers share a common origin which is the outer part of the elbow, the lateral epicondyle of humerus. The deep muscles arise from the distal part of the ulna and the surrounding interosseous membrane.

The brachioradialis, flexor of the elbow, is unusual in that it is located in the posterior compartment, but it is actually a muscle of flexor / anterior compartment of the forearm. The anconeus, assisting in extension of the elbow joint, is by some considered part of the posterior compartment of the arm.

The majority of muscles found in the posterior compartment are extrinsic, meaning that their origin has some distance from the part moved. The brachioradialis and the anconeus are considered intrinsic muscles because they both arise within the forearm and they both move the forearm.

LevelMuscleExtrinsic/IntrinsicInnervation [3]
superficial brachioradialis intrinsic radial nerve
superficial extensor carpi radialis longus extrinsic radial nerve
superficial extensor carpi radialis brevis extrinsic radial nerve (deep branch)
superficial extensor carpi ulnaris extrinsic radial nerve (as posterior interosseous nerve)
superficial anconeus intrinsic radial nerve
intermediate extensor digitorum extrinsic radial nerve (as posterior interosseous nerve)
intermediate extensor digiti minimi extrinsic radial nerve (as posterior interosseous nerve)
deep abductor pollicis longus extrinsic radial nerve (as posterior interosseous nerve)
deep extensor pollicis longus extrinsic radial nerve (as posterior interosseous nerve)
deep extensor pollicis brevis extrinsic radial nerve (as posterior interosseous nerve)
deep extensor indicis extrinsic radial nerve (as posterior interosseous nerve)
deep supinator intrinsic radial nerve (deep branch)

Extensor tendon compartments

Extensor tendons pass through the extensor retinaculum at wrist joint in 6 synovial sheaths, also referred to compartments. [3]

The supinator and the anconeus are the two extensor muscles in the posterior compartment of the forearm that do not pass through wrist extensor compartments. [3]

Wrist extensor compartments (numbered).PNG
  1. The first compartment locating the most radial is occupied by the extensor pollicis brevis and the abductor pollicis longus to insert to the thumb.
  2. The second compartment is occupied by the two radial wrist extensors, the extensor carpi radialis longus and the extensor carpi radialis brevis.
  3. The third compartment exclusively accommodates the extensor pollicis longus, which hooks around Lister's tubercle of radius and inserts to the thumb.
  4. The fourth compartment is the largest of all. It is occupied by the extensors of the digits, the extensor digitorum communis and the extensor indicis proprius. The extensor indicis proprius usually runs and inserts onto the ulnar side of the extensor digitorum communis of the index finger. [4]
  5. The fifth compartment is occupied by the extensor digiti minimi, the extensor of the little finger.
  6. The extensor carpi ulnaris passes through the sixth compartment to insert to the base of the fifth metacarpal bone.

Innervation

The muscles of the posterior compartment of the forearm are innervated by the radial nerve and its branches. [3] The radial nerve arises from the posterior cord of the plexus. The somatomotor fibers of the radial nerve branch from the main radial nerve at the level of the radial groove of the humerus.

Development

In the early stage of development, the extensor precursor divides into 3 layers namely, superficial layer, radial layer and deep layer. [5] [6] The superficial group develops to become the extensor digitorum communis, the extensor carpi ulnaris and the extensor digiti minimi. The radial layer forms the extensor carpi radialis longus, the extensor carpi radialis brevis and the brachioradialis. The deep layer differentiates to become the abductor pollicis longus, the extensor pollicis longus and the extensor pollicis brevis.

Phylogenetic origin [6] Embryologic origin [6] Representatives in humans [6]
Brachioantebrachial groupRadial layerBrachioradialis
Extensor carpi radialis longus
Extensor carpi radialis brevis
Supinator
Superficial layerExtensor digitorum communis
Extensor carpi ulnaris
Extensor digiti minimi
Antebrachiomanual groupDeep layer (radial)Extensor pollicis brevis
Abductor pollicis longus
Deep layer (ulnar)Extensor pollicis longus
Extensor indicis proprius
Extensor digitorum brevis manus [7]
Manual group--

Variations

The deep layer of the precursor extensor mass is known to be phylogenetically unstable and is undergoing evolution as high variability is seen in non-human primates. [5] [8] [9] [10] In humans, anomalous or additional muscles can be seen in small portion of population.

Anomalous muscles in human extensor compartment are listed as follow:

Clinical significance

Outer part of the elbow (lateral epicondyle) where tennis elbow occurs Tennis elbow.JPG
Outer part of the elbow (lateral epicondyle) where tennis elbow occurs

Tennis elbow

Tennis elbow or lateral epicondylitis is a chronic or an acute inflammation of the tendons that arise from the outer part of the elbow. The affected tendons are the tendons of extensor muscles which originate from the lateral epicondyle of humerus. It is caused by the repetitive movements and overuse. It damages the tendons which results in pain and tenderness on the outer part of the elbow. [11]

De Quervain's syndrome

De Quervain's syndrome is a medical condition when the synovial sheath surrounding tendons in the first extensor tendon compartment becomes inflamed, so called tenosynovitis. [12] The tendons of the abductor pollicis longus and the extensor pollicis brevis run narrower due to the thickening of the synovial sheath, which causes pain when extending and moving the thumb outward. [13]

Fourth compartment syndrome

The presence of an additional tendon may result in a condition called fourth compartment syndrome. [14] Supernumerary tendons are common in the fourth extensor tendon compartment. Supernumerary tendons can refer to the additional tendons of normal structures or tendons of rare anatomical variants such as the extensor medii proprius or the extensor digitorum brevis manus. The increased pressure in the synovial sheath is known to directly or indirectly compress the posterior interosseous nerve of radial nerve. [14] Also, the extra pressure causes synovitis which results in pain in the dorsal part of the wrist. [15]

Misdiagnosis of rare anatomical variants

Anatomical variants are often encountered in the extensor compartment of the forearm. Clinical expressions of the extensor digitorum brevis manus are often mistaken for a ganglion, cyst or tumour. [16] [17] [18]

In other animals

In the superfamily hominoidea or apes, configurations of the muscles of the posterior compartment of the forearm share similar characteristics. However, the anconeus is usually not present in the hylobates (gibbons). [19] Also, the extensor pollicis brevis is only present in the genus homo (humans) and the genus hylobates because the extensor pollicis brevis and the abductor pollicis longus exist as a single muscle in other genera. [20]

See also

Additional images

Related Research Articles

<span class="mw-page-title-main">Radial nerve</span> Nerve in the human body that supplies the posterior portion of the upper limb

The radial nerve is a nerve in the human body that supplies the posterior portion of the upper limb. It innervates the medial and lateral heads of the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial compartment of the forearm and the associated joints and overlying skin.

<span class="mw-page-title-main">Extensor carpi radialis longus muscle</span> One of five forearm muscles controlling the wrist

The extensor carpi radialis longus is one of the five main muscles that control movements at the wrist. This muscle is quite long, starting on the lateral side of the humerus, and attaching to the base of the second metacarpal bone.

In human anatomy, extensor carpi radialis brevis is a muscle in the forearm that acts to extend and abduct the wrist. It is shorter and thicker than its namesake extensor carpi radialis longus which can be found above the proximal end of the extensor carpi radialis brevis.

<span class="mw-page-title-main">Wrist drop</span> Medical condition

Wrist drop is a medical condition in which the wrist and the fingers cannot extend at the metacarpophalangeal joints. The wrist remains partially flexed due to an opposing action of flexor muscles of the forearm. As a result, the extensor muscles in the posterior compartment remain paralyzed.

<span class="mw-page-title-main">Radius (bone)</span> One of the two long bones of the forearm

The radius or radial bone is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna. The ulna is longer than the radius, but the radius is thicker. The radius is a long bone, prism-shaped and slightly curved longitudinally.

<span class="mw-page-title-main">Upper limb</span> Consists of the arm, forearm, and hand

The upper limbs or upper extremities are the forelimbs of an upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to and including the digits, including all the musculatures and ligaments involved with the shoulder, elbow, wrist and knuckle joints. In humans, each upper limb is divided into the shoulder, arm, elbow, forearm, wrist and hand, and is primarily used for climbing, lifting and manipulating objects. In anatomy, just as arm refers to the upper arm, leg refers to the lower leg.

<span class="mw-page-title-main">Extensor digitorum muscle</span> Forearm muscle which extends the four fingers

The extensor digitorum muscle is a muscle of the posterior forearm present in humans and other animals. It extends the medial four digits of the hand. Extensor digitorum is innervated by the posterior interosseous nerve, which is a branch of the radial nerve.

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.

<span class="mw-page-title-main">Extensor pollicis brevis muscle</span> Forearm muscle which moves the thumb

In human anatomy, the extensor pollicis brevis (EPB) is a skeletal muscle on the dorsal side of the forearm. It lies on the medial side of, and is closely connected with, the abductor pollicis longus. The extensor pollicis brevis belongs to the deep group of the posterior fascial compartment of the forearm. It is a part of the lateral border of the anatomical snuffbox.

<span class="mw-page-title-main">Posterior interosseous nerve</span> Nerve of the forearm

The posterior interosseous nerve is a nerve in the forearm. It is the continuation of the deep branch of the radial nerve, after this has crossed the supinator muscle. It is considerably diminished in size compared to the deep branch of the radial nerve. The nerve fibers originate from cervical segments C7 and C8 in the spinal column.

<span class="mw-page-title-main">Extensor indicis muscle</span> Forearm muscle which extends the index finger

In human anatomy, the extensor indicis (proprius) is a narrow, elongated skeletal muscle in the deep layer of the dorsal forearm, placed medial to, and parallel with, the extensor pollicis longus. Its tendon goes to the index finger, which it extends.

<span class="mw-page-title-main">Extensor retinaculum of the hand</span> A thickened fascia holding the tendons of the hand extensor muscles in place

The extensor retinaculum is a thickened portion of the antebrachial fascia that holds the tendons of the extensor muscles in place. It is located on the back of the forearm, just proximal to the hand. It is continuous with the palmar carpal ligament.

<span class="mw-page-title-main">Cervical spinal nerve 8</span> Spinal nerve of the cervical segment

The cervical spinal nerve 8 (C8) is a spinal nerve of the cervical segment.

Extensor digitorum brevis manus is an extra or accessory muscle on the backside (dorsum) of the hand. It was first described by Albinus in 1758. The muscles lies in the fourth extensor compartment of the wrist, and is relatively rare. It has a prevalence of 4% in the general population according to a meta-analysis. This muscle is commonly misdiagnosed as a ganglion cyst, synovial nodule or cyst.

<span class="mw-page-title-main">Mucous sheaths on back of wrist</span>

The mucous sheaths of the tendons on the back of the wrist are protective coverings for tendons in the wrist. Between the dorsal carpal ligament and the bones six compartments are formed for the passage of tendons, each compartment having a separate mucous sheath. One is found in each of the following positions:

  1. on the lateral side of the radial styloid process, for the tendons of the Abductor pollicis longus and Extensor pollicis brevis;
  2. behind the styloid process, for the tendons of the Extensores carpi radialis longus and brevis;
  3. about the middle of the dorsal surface of the radius, for the tendon of the Extensor pollicis longus;
  4. to the medial side of the latter, for the tendons of the Extensor digitorum communis and Extensor indicis proprius;
  5. opposite the interval between the radius and ulna, for the Extensor digiti quinti proprius;
  6. between the head and styloid process of the ulna, for the tendon of the Extensor carpi ulnaris.
<span class="mw-page-title-main">Extrinsic extensor muscles of the hand</span>

The extrinsic extensor muscles of the hand are located in the back of the forearm and have long tendons connecting them to bones in the hand, where they exert their action. Extrinsic denotes their location outside the hand. Extensor denotes their action which is to extend, or open flat, joints in the hand. They include the 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), and extensor indicis (EI).

<span class="mw-page-title-main">Extensor medii proprius muscle</span> Variant muscle of the forearm

The extensor medii proprius is a rare anatomical variant in the extensor compartment of the forearm. The aberrant muscle is analogous to the extensor indicis with the insertion being the middle finger instead of the index finger.

<span class="mw-page-title-main">Extensor indicis et medii communis muscle</span> Variant muscle of the forearm

The extensor indicis et medii communis is a rare anatomical variant in the extensor compartment of forearm. This additional muscle lies in the deep extensor layer next to the extensor indicis proprius and the extensor pollicis longus. The characteristics of this anomalous muscle resemble those of the extensor indicis proprius, with split tendons to the index and the middle finger. This muscle can also be considered as a variation of the aberrant extensor medii proprius.

<span class="mw-page-title-main">Extensor pollicis et indicis communis muscle</span> Accessory muscle in the forearm

In human anatomy, the extensor pollicis et indicis communis is an accessory muscle in the posterior compartment of forearm. It was first described in 1863. The muscle has a prevalence from 0.5% to 4%.

References

  1. ↑ lesson5musofpostforearm at The Anatomy Lesson by Wesley Norman (Georgetown University)
  2. ↑ Chaudhry, Mohammad; Aminullah, Humna; Sinkler, Margaret A.; Arain, Abdul (2022), "Anatomy, Shoulder and Upper Limb, Forearm Compartments", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID   30969606 , retrieved 2022-11-27
  3. 1 2 3 4 Netter, Frank. H. (2014-11-14). Atlas of Human Anatomy, 6th Edition | Frank Netter |. store.elsevier.com. ISBN   9781455704187 . Retrieved 2015-06-16.
  4. ↑ "Anatomy of the human body". archive.org. Retrieved 2015-06-16.
  5. 1 2 Straus WL (1941) The phylogeny of the human forearm extensors. Hum Biol 13, 23–50.
  6. 1 2 3 4 Cavdar, S.; Dogan, T.; Bayramiçli, M.; Sehirli, U.; Yüksel, M. (Jan 1998). "An unusual variation of extensor digitorum brevis manus: a case report and literature review". The Journal of Hand Surgery. 23 (1): 173–177. doi:10.1016/S0363-5023(98)80108-1. ISSN   0363-5023. PMID   9523974.
  7. ↑ Souter, W. A. (September 1, 1966). "The extensor digitorum brevis manus". British Journal of Surgery. 53 (9): 821–823. doi:10.1002/bjs.1800530923. ISSN   1365-2168. PMID   5911774. S2CID   42145116.
  8. ↑ Wood, John (1866). "Variations in Human Myology Observed during the Winter Session of 1865-66 at King's College, London". Proceedings of the Royal Society of London. 15: 229–244. Bibcode:1866RSPS...15..229W. doi: 10.1098/rspl.1866.0054 . ISSN   0370-1662.
  9. ↑ Yoshida, Y.; Yasutaka, S.; Seki, Y. (August 1984). "[A study on the extensor digitorum brevis manus muscle in man]". Kaibogaku Zasshi. 59 (4): 313–321. ISSN   0022-7722. PMID   6524291.
  10. ↑ Čihák, Radomír (1972). Ontogenesis of the Skeleton and Intrinsic Muscles of the Human Hand and Foot. Springer Science & Business Media. ISBN   9783662090817.
  11. ↑ "Tennis Elbow (Lateral Epicondylitis) -OrthoInfo - AAOS". orthoinfo.aaos.org. Retrieved 2015-06-16.
  12. ↑ Ilyas, Asif M.; Ilyas, Asif; Ast, Michael; Schaffer, Alyssa A.; Thoder, Joseph (Dec 2007). "De quervain tenosynovitis of the wrist". The Journal of the American Academy of Orthopaedic Surgeons. 15 (12): 757–764. doi:10.5435/00124635-200712000-00009. ISSN   1067-151X. PMID   18063716.
  13. ↑ "de Quervain Syndrome". Handcare.org. Retrieved 2015-06-16.
  14. 1 2 Hoffman, J.; Ellison, M. R. (Mar 1987). "Extensor digitorum brevis manus in the nondominant hand of two brothers". The Journal of Hand Surgery. 12 (2): 293–294. doi:10.1016/s0363-5023(87)80293-9. ISSN   0363-5023. PMID   3559091.
  15. ↑ Tan, S. T.; Smith, P. J. (May 1999). "Anomalous extensor muscles of the hand: a review". The Journal of Hand Surgery. 24 (3): 449–455. doi:10.1053/jhsu.1999.0449. ISSN   0363-5023. PMID   10357521.
  16. ↑ Ogura, T.; Inoue, H.; Tanabe, G. (Jan 1987). "Anatomic and clinical studies of the extensor digitorum brevis manus". The Journal of Hand Surgery. 12 (1): 100–107. doi:10.1016/s0363-5023(87)80171-5. ISSN   0363-5023. PMID   3805622.
  17. ↑ Patel, M. R.; Desai, S. S.; Bassini-Lipson, L.; Namba, T.; Sahoo, J. (Jul 1989). "Painful extensor digitorum brevis manus muscle". The Journal of Hand Surgery. 14 (4): 674–678. doi:10.1016/0363-5023(89)90190-1. ISSN   0363-5023. PMID   2754202.
  18. ↑ Anderson, M. W.; Benedetti, P.; Walter, J.; Steinberg, D. R. (Jun 1995). "MR appearance of the extensor digitorum manus brevis muscle: a pseudotumor of the hand". AJR. American Journal of Roentgenology. 164 (6): 1477–1479. doi:10.2214/ajr.164.6.7754896. ISSN   0361-803X. PMID   7754896.
  19. ↑ Diogo, R.; Abdala, V.; Lonergan, N.; Wood, B. A. (Oct 2008). "From fish to modern humans--comparative anatomy, homologies and evolution of the head and neck musculature". Journal of Anatomy. 213 (4): 391–424. doi:10.1111/j.1469-7580.2008.00953.x. ISSN   1469-7580. PMC   2644766 . PMID   18657257.
  20. ↑ Aversi-Ferreira, T. A.; Diogo, R.; Potau, J. M.; Bello, G.; Pastor, J. F.; Aziz, M. Ashraf (Dec 2010). "Comparative anatomical study of the forearm extensor muscles of Cebus libidinosus (Rylands et al., 2000; Primates, Cebidae), modern humans, and other primates, with comments on primate evolution, phylogeny, and manipulatory behavior". Anatomical Record. 293 (12): 2056–2070. doi:10.1002/ar.21275. ISSN   1932-8494. PMID   21082733. S2CID   12648729.
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