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You are watching: The ray of the hand consists of

StatPearls . Endowment Island (FL): StatPearls Publishing; 2021 Jan-.


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Introduction

The carpal bones are bones that the wrist that connect the distal elements of the radial and also ulnar skeletal of the forearm to the bases of the five metacarpal skeletal of the hand. There space eight carpal bones, which divide into two rows: a proximal row and a distal row. The proximal heat of carpal bones (moving indigenous radial come ulnar) room the scaphoid, lunate, triquetrum, and pisiform, if the distal heat of carpal skeletal (also indigenous radial come ulnar) comprises the trapezium, trapezoid, capitate, and hamate. These bones comprise most the the skeletal framework of the wrist and enable different neurovascular structures and also tendons that get in the wrist come reach details muscle groups and bony structures, respectively and administer the innervation and also blood supply vital for them to function.


Structure and also Function

Each carpal bone has actually its own distinctive features that add to a specific duty in the wrist. Beginning from the proximal row, the scaphoid, named for that boat-like appearance, forms the radial border the the proximal carpal row. Many of the surface of the scaphoid is spanned by articular cartilage, which enables it to leg the joint in between the 2 rows that carpal bones. The lunate, described for its crescent shape, is located between the scaphoid and also the triquetrum and also lies near the median nerve. The triquetrum is a pyramid-shaped bone that articulates with the pisiform, lunate, and also hamate bones. Last, the pisiform is a pea-shaped bone that articulates with the triquetrum ~ above its dorsal surface and serves as an attachment website for assorted tendons and also ligaments.<1>

Moving beside the distal row, the trapezium sits between the scaphoid and also the base of the first metacarpal bone. It has a saddle-shaped facet because that articulation through the first metacarpal and also provides a site for a few tendons and also ligaments to either pass v or attach. The trapezoid is the smallest carpal bone and also is located between the trapezium and also the capitate. Whereas the capitate is the largest and also most central carpal bone through articulations to number of bones and also attachments to several intercarpal ligaments. Last, the hamate, called for that hook-like hamulus, develops the ulnar border the the distal carpal heat that serves to safeguard the ulnar artery and also nerve within Guyon"s canal and carry out attachments to several ligaments as well.<1>

In general, the skeletal of the hand discover their plan in 3 arches: one longitudinal arch, spanning the hand lengthwise, and also two transverse arches, one in ~ the level of the metacarpal head and the second transverse arch in ~ the level the the carpus. This anatomy mechanically contributes to the hand"s ability to grasp objects. In particular, the setup of the carpal skeletal in a transverse arch makes up the floor that the carpal tunnel and also provides support and protection come the finger flexor tendons and also the mean nerve. Moreover, the scaphoid and trapezium both have prominent tubercles projecting anteriorly that not only contribute considerably to the bony anatomy that the carpal tunnel however also administer a sustaining base for the ignorance to allow it to protest the rest of the hand and, thus, additional enhance the hand’s capacity to master objects.<1>


Embryology

Upper limb development initiates with the activation the a team of mesenchymal cells in the lateral mesoderm towards the finish of the fourth week, with the body buds becoming visible approximately day 26 or job 27. Every limb bud comprises a massive of mesenchyme extended by ectoderm. This mesenchyme remains undifferentiated until it is ready to build into bone, cartilage, and also blood vessels later on in development. Meanwhile, at the apex of every limb bud, the ectoderm thickens to form the apical ectodermal ridge, i m sorry stimulates the growth and breakthrough of the upper limb bud in the proximal-distal axis. Other signaling centers and primary morphogens such as the zone that polarizing activity, acquired from an accumulation of mesenchymal cell in the body bud, and the Wnt pathway, expressed native the dorsal epidermis the the limb bud, likewise contribute to the breakthrough of the upper limb buds by regulating development along the anteroposterior axis and also the dorsoventral axis, respectively.<2>

At the finish of the sixth week the development, digital rays type in the hand plate. By the saturday week, the carpal chondrification procedure begins. The capitate and also the hamate carpal bones room the very first chondrogenic centers to show up as immature cartilage beforehand in the eighth week while the pisiform is the last to appear later in the eighth week. The hamulus, otherwise well-known as the “hook the the hamate,” additionally appears together an immature cartilaginous tissue towards the end of the eighth week and also does not finish its advance until the thirteenth week. Last, in the fourteenth week, a vascular bud penetrates the lunate cartilage mold, an early sign the the osteogenic process that will complete during the first year of life.<3>


Blood Supply and Lymphatics

The radial artery, ulnar artery, and their anastomoses administer the blood it is provided of the wrist. The radial artery primarily supplies the thumb and the lateral next of the table of contents finger when the ulnar artery provides the remainder of the digits and the medial next of the table of contents finger. In particular, vascular supply takes ar via the anastomotic network consisting of three dorsal and three palmar arches, i m sorry arise native both the radial and ulnar arteries, the overlie the carpal bones.<4> The scaphoid, capitate, and also a decimal of lunates (20%) all have one intraosseous courage supply. The note, the scaphoid has a solitary blood supply from the radial artery that enters from the distal part of the bone to it is provided the proximal portion, for this reason making that is proximal pole most breakable to avascular necrosis. The trapezoid and also hamate both have actually two locations of blood supply without intraosseous anastomoses. The trapezium, triquetrum, pisiform, and most lunates (80%) have two locations of blood supply and also consistent intraosseous anastomoses. Therefore, the remainder of the carpal bones, excluding the scaphoid, capitate, and the minority of lunates, have actually a reduced risk of arising avascular necrosis adhering to a fracture.<5>


The lateral antebrachial cutaneous nerve, the posterior interosseous nerve, the dorsal branch and the perforating branches that the ulnar nerve, and the superficial branch that the radial nerve innervate the wrist joint from the dorsum. The palmar cutaneous branch that the mean nerve, the anterior interosseous nerve, and the key trunk and deep branch of the ulnar nerve innervate the wrist joint from the palmar side.<6>


Muscles

Two types of muscles consist of the muscle of the hand: extrinsic and also intrinsic. Extrinsic muscles have muscle bellies the originate in ~ the forearm and tendons that go into the wrist and duty to boost wrist security by keeping the hand put into the concave radial surface throughout co-contraction. Intrinsic muscles originate in ~ the hand chin and likewise contribute to wrist security by balancing flexor and extensor forces through your attachment come metacarpal bases.<1>

Some carpal bones offer as web page of origin or together sites that insertion for the extrinsic and also intrinsic muscles of the hand. The flexor carpi ulnaris is the just extrinsic muscle the inserts onto carpal bones, especially the pisiform and hook the the hamate, and the base of the 5th metacarpal bone, which enables it to flex and also adduct the wrist joint. All the intrinsic muscles have their beginning sites top top the carpal bones. The thenar muscles, which include the opponens pollicis, abductor pollicis brevis, and flexor pollicis brevis, have origin sites the involve the prominent tubercles that the scaphoid and also trapezium. The adductor pollicis bring away its origin from the capitate and the 2nd and 3rd metacarpal bones. Last, the hypothenar muscles such together the abductor digiti minimi, flexor digiti minimi brevis, and also opponens digiti minimi, originate from the pisiform and hook the the hamate.<7>


Physiologic Variants

Although uncommon, the number of carpal bones may vary in the existence of accessory bones, separation bones, anatomical variants, or congenital anomalies. Reports exist the over twenty accessory carpal bones, with the most usual variants being the os centrale carpi, the os radiale externum, the triangle bone, and also the styloideum bone. Other instances of extr carpal bones may involve break-up bones the the scaphoid, lunate, and also even the hamate. Anatomical variants causing extra carpal skeleton arise because of a fail of fusion from carpal bone ossification centers. Last, congenital anomalies causing fewer carpal skeletal can happen either because of congenital absence of typical bone (which mostly occurs with the scaphoid, lunate, or triquetrum) or from a coalition in between two carpal bones, which most generally involves the lunate and also triquetrum.<8>


Surgical Considerations

Surgical philosophies to the carpus have the right to be split into basic and specific carpal exposures. Basic exposures, excellent either native a dorsal approach or a volar approach, provide broad exposure to big areas the the wrist and permit surgeons accessibility to pathology that involves multiple joints or carpal bones. Details exposures provide limited exposure and permit accessibility to a solitary bone, most typically the scaphoid, or joint for instances where the diagnosis is clear and management is precise.<9>

Because the the proximity in between the deep frameworks of the hand and the carpus, surgical ideologies to the hand and also wrist call for meticulous care. Close attention to the anatomical relationship between important ligaments, tendons, nerves, and blood vessels begins with the early stage skin incision. The architecture of the incision must think about the intimacy in between these frameworks to avoid damages to integral contents of the hand and also wrist. These include the sensory nerves come the hand that consist of much the the sensory homunculus, the creases the the skin to avoid contracture, the blood it is provided to the skin or skin flaps for primary wound healing, and even the cosmetics the the hand for the services of the patient.<9>


Clinical Significance

Athletes commonly incur injuries come the hand or wrist; reports indicate that sporting activities account for about 22% of all hand fractures in adults. Of all hand fractures in adults, carpal fractures space the least common (12%) contrasted to metacarpal fractures (34%) and also phalangeal fractures (54%).<10> among carpal fractures, the most commonly injured carpal bone is the scaphoid. Over there is a high incidence of scaphoid fractures in university football players and raising incidence of woman athletes.<11> top top falling on an outstretched hand (FOOSH injury), the scaphoid receives most of the force transmitted indigenous the radius because of its size and anatomic location. The importance, the proximal pole that the scaphoid bone is very susceptible come avascular necrosis following fractures across the waist of the scaphoid as result of its minimal blood supply and also poor collateral circulation.<1><5>

Scaphoid fractures generally present v radial-sided wrist pain and tenderness in the anatomical snuffbox, ~ above axial loading of the thumb, and also during pincer grasp. Lock are regularly diagnosed with radiographic imaging but can be diagnosed through a CT scan as well. However, in specific cases, non-displaced fractures deserve to be to let go either as result of subtle fracture present or even the irregular edge of the bone. In these cases, MRI or bone scintigraphy might be used to confirm the diagnosis.<11>

Treatment of scaphoid fractures depends on their location and whether bone displacement has occurred. Distal pole scaphoid fractures have the right to be cure conservatively vice versa, proximal pole fractures must undergo surgical repair. Displaced fractures have actually an raised risk of nonunion, hence require surgical procedure with headless compression screw fixation, which offers the more quickly recovery and a return to sports. Management of non-displaced fractures is with actors immobilization.

See more: Which Of The Answers Best Describes Chronology ? What Answer Best Describes Chronology

<11>

Other carpal injuries include hook of the hamate fractures and also lunate dislocation:


Hook the the hamate fracture: 
Lunate dislocation:

Review Questions


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Figure

English: Left hand, anterior view. Carpus presented in red.Distal row:E: TrapeziumF: Trapezoid boneG: Capitate boneH: Hamate boneProximal row:A: Scaphoid boneB: Lunate boneC: Triquetral boneD: Pisiform bone. Contributed by Wikimedia User: Dr. Jochen (more...)


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Figure

3D medical illustration the the wrist skeletal of human being body. Added from the Wikimedia Gallery: https://www.scientificanimations.com/wiki-images/ (CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0/deed.en)


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Figure

Carpal Bones, Phalanges, Ulna, Lunate, Triquetrum, Pisiform, Hamate, Capitate, Scaphoid, Trapezoid, Trapezium, Metacarpals, Proximal phalanx, Distal phalanx, Proximal phalanx, middle phalanx, Distal phalanx. Illustration by Emma Gregory


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