Scaphoid bone
| Scaphoid bone | |
|---|---|
 Left hand anterior view (palmar view). Scaphoid bone shown in red. | |
 The left scaphoid bone | |
| Details | |
| Pronunciation | /ˈskæfɔɪd/ |
| Articulations | Articulates with five bones radiusproximally trapezoid boneandtrapezium bonedistally capitateandlunatemedially |
| Identifiers | |
| Latin | os scaphoideum, os naviculare manus |
| MeSH | D021361 |
| TA98 | A02.4.08.003 |
| TA2 | 1250 |
| FMA | 23709 |
| Anatomical terms of bone | |
Thescaphoid boneis one of thecarpalbonesof thewrist.It is situated between thehandandforearmon thethumbside of the wrist (also called the lateral or radial side). It forms theradialborder of thecarpal tunnel.The scaphoid bone is the largest bone of the proximal row of wrist bones, its long axis being from above downward, lateralward, and forward. It is approximately the size and shape of a mediumcashew nut.
Structure
[edit]The scaphoid is situated between theproximal and distalrows ofcarpal bones.It is located on the radial side of the wrist,[1]: 176 adjacent to thestyloid process of the radius.[2]It articulates with theradius,lunate,trapezoid,trapezium,andcapitate.[1]: 176 Over 80% of the bone is covered in articularcartilage.[3]
Bone
[edit]The palmar surface of the scaphoid is concave, and forming a distaltubercle,giving attachment to thetransverse carpal ligament.The proximal surface is triangular, smooth and convex.[3]The lateral surface is narrow and gives attachment to theradial collateral ligament.The medial surface has two facets, a flattened semi-lunar facet articulating with the lunate bone, and an inferior concave facet, articulating alongside the lunate with the head of the capitate bone.[4]
The dorsal surface of the bone is narrow, with a groove running the length of the bone and allowingligamentsto attach, and the surface facing the fingers (anatomically inferior) is smooth and convex, also triangular, and divided into two parts by a slight ridge.[4]
Blood supply
[edit]It receives its blood supply primarily from lateral and distal branches of theradial artery,via palmar and dorsal branches. These provide an "abundant" supply to middle and distal portions of the bone, but neglect the proximal portion, which relies onretrogradeflow.[1]: 189 The dorsal branch supplies the majority of the middle and distal portions, with the palmar branch supplying only the distal third of the bone.[3]
Variation
[edit]The dorsal blood supply, particularly of the proximal portion, is highly variable.[1]: 189 Sometimes the fibers of theabductor pollicis brevisemerge from the tubercle.[4]
In animals
[edit]In reptiles, birds, and amphibians, the scaphoid is instead commonly referred to as theradialebecause of its articulation with theradius.
Function
[edit]The carpal bones function as a unit to provide a bony superstructure for the hand.[5]: 708 The scaphoid is also involved in movement of the wrist.[1]: 6 It, along with thelunate,articulates with theradiusandulnato form the major bones involved in movement of the wrist.[5]The scaphoid serves as a link between the two rows of carpal bones. With wrist movement, the scaphoid may flex from its position in the same plane as the forearm to perpendicular.[1]: 176–177
Clinical significance
[edit]Fracture
[edit]
Fractures of the scaphoidare the most common of the carpal bone injuries, because of its connections with the two rows of carpal bones.[1]: 177
The scaphoid can be slow to heal because of the limited circulation to thebone.Fractures of the scaphoid must be recognized and treated quickly, as prompt treatment by immobilization or surgical fixation increases the likelihood of the bone healing in anatomic alignment, thus avoiding mal-union or non-union.[6]Delays may compromise healing. Failure of the fracture to heal ( "non-union" ) will lead to post-traumaticosteoarthritisof the carpus.[1]: 189 One reason for this is because of the "tenuous" blood supply to the proximal segment.[3]Even rapidly immobilized fractures may require surgical treatment, including use of a headless compression screw such as theHerbert screwto bind the two halves together.
Healing of the fracture with a non-anatomic deformity (frequently, a volar flexed "humpback" ) can also lead topost-traumatic arthritis.Non-unions can result in loss of blood supply to the proximal pole, which can result inavascular necrosisof the proximal segment.
Scaphoid fractures may be difficult to diagnose via plain x-ray. A repeat x-ray may be required at a later date, as might cross-sectional imaging via MRI or CT scan.[6]
Other diseases
[edit]A condition calledscapholunate instabilitycan occur when thescapholunate ligament(connecting the scaphoid to thelunate bone) and other surrounding ligaments are disrupted. In this state, the distance between the scaphoid andlunatebones is increased.[1]: 180
One rare disease of the scaphoid is calledPreiser's Disease.
Palpation
[edit]The scaphoid can bepalpatedat the base of theanatomical snuff box.It can also be palpated in the volar (palmar) hand/wrist. Its position is the intersections of the long axes of the four fingers while in a fist, or the base of thethenar eminence.When palpated in this position, the bone will be felt to slide forward during radial deviation (wrist abduction) and flexion.
Clicking of the scaphoid or no anterior translation can indicate scapholunate instability.
Etymology
[edit]The wordscaphoid(Greek:σκαφοειδές) is derived from the Greekskaphos,which means "a boat", and the Greekeidos,which means "kind".[7]The name refers to the shape of the bone, supposedly reminiscent of a boat. In older literature abouthuman anatomy,[4]the scaphoid is referred to as the navicular bone of the hand (this time from the Latinnavisfor boat); there is alsoa bone in a similar position in the foot,which is called the navicular. The modern term for the bone in the hand isscaphoid;in human anatomy the termnavicularis reserved for the bone in the foot.
Additional images
[edit]-
Scaphoid bone of the left hand (shown in red). Animation. -
Scaphoid bone of the left hand. Close up. Animation. -
Scaphoid bone. -
Scaphoid shown in yellow. Left hand. Palmar surface. -
Scaphoid shown in yellow. Left hand. Dorsal surface. -
Cross section of wrist (thumb on left). Scaphoid (labelled as "Navicular" ) shown in red. -
Wrist joint. Deep dissection. Posterior view. -
Scaphoid forms the radial (thumb-side) border of thecarpal tunnel.Wrist joint. Deep dissection. Anterior (palmar) view.
References
[edit]
- ^abcdefghiBeasley RW (2003).Beasley's Surgery of the Hand.New York: Thieme.ISBN978-1-282-95002-3.OCLC657589090.
- ^Martini, Frederic; Tallitsch, Robert B.; Nath, Judi L. (2017).Human Anatomy(9th ed.). Pearson. p. 182.ISBN9780134320762.
- ^abcdEathorne SW (March 2005). "The wrist: clinical anatomy and physical examination--an update".Primary Care.32(1): 17–33.doi:10.1016/j.pop.2004.11.009.PMID15831311.
- ^abcdGray H (1918)."6b. The Hand. 1. The Carpus".Anatomy of the Human Body.4– via Bartleby.
- ^abDrake RL, Vogl W, Mitchell AW (2005).Gray's anatomy for students.Illustrated by Richard Tibbitts and Paul Richardson. Philadelphia: Elsevier/Churchill Livingstone.ISBN978-0-8089-2306-0.OCLC646533128.
- ^abWijetunga AR, Tsang VH, Giuffre B (March 2019)."The utility of cross-sectional imaging in the management of suspected scaphoid fractures".Journal of Medical Radiation Sciences.66(1): 30–37.doi:10.1002/jmrs.302.PMC6399186.PMID30160062.
- ^Anderson K, Anderson LE, Glanze WD (1994).Mosby's Medical, Nursing & Allied Health Dictionary(4th ed.). St. Louis: Mosby. p. 1396.ISBN978-0-8016-7225-5.OCLC461378724.
