Ilium (bone)

The ilium () (plural ilia) is the uppermost and largest part of the hip bone, and appears in most vertebrates including mammals and birds, but not bony fish. All reptiles have an ilium except snakes, although some snake species have a tiny bone which is considered to be an ilium.

The ilium of the human is divisible into two parts, the body and the wing; the separation is indicated on the top surface by a curved line, the arcuate line, and on the external surface by the margin of the acetabulum.

The name comes from the Latin ('' ile'', ''ilis''), meaning "groin" or "flank".

Structure

The ilium consists of the body and wing. Together with the ischium and pubis, to which the ilium is connected, these form the pelvic bone, with only a faint line indicating the place of union.

The body ( la, corpus) forms less than two-fifths of the acetabulum; and also forms part of the acetabular fossa. The internal surface of the body is part of the wall of the lesser pelvis and gives origin to some fibers of the obturator internus.

The wing ( la, ala) is the large expanded portion which bounds the greater pelvis laterally. It has an external and an internal surface, a crest, and two borders—an anterior and a posterior.

Biiliac width

In humans, biiliac width is an anatomical term referring to the widest measure of the pelvis between the outer edges of the upper iliac bones.

Biiliac width has the following common synonyms: pelvic bone width, biiliac breadth, intercristal breadth/width, bi-iliac breadth/width and biiliocristal breadth/width.

It is best measured by anthropometric calipers (an anthropometer designed for such measurement is called a pelvimeter). Attempting to measure biiliac width with a tape measure along a curved surface is inaccurate.

The biiliac width measure is helpful in obstetrics because a pelvis that is significantly too small or too large can have complications. For example, a large baby or a small pelvis often lead to death unless a caesarean section is performed.

It is also used by anthropologists to estimate body mass.

Other animals

Dinosaurs

The clade Dinosauria is divided into the Saurischia and Ornithischia based on hip structure, including importantly that of the ilium. In both saurischians and ornithischians, the ilium extends laterally to both sides from the axis of the body. The other two hip bones, the ischium and the pubis, extend ventrally down from the ilium towards the belly of the animal. The acetabulum, which can be thought of as a "hip-socket", is an opening on each side of the pelvic girdle formed where the ischium, ilium, and pubis all meet, and into which the head of the femur inserts. The orientation and position of the acetabulum is one of the main morphological traits that caused dinosaurs to walk in an upright posture with their legs directly underneath their bodies. The brevis fossa is a deep groove in the underside of the postacetabular process, the rear part of the ilium. The brevis shelf is the bony ridge at the inner side of the ''fossa'', the bone wall forming the internal face of the rear part of the ilium, which functions as an attachment area for a tail muscle, the '' musculus caudofemoralis brevis''.Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. pg. 299-300. . Often, close to the hip-socket the lower edge of the outer face of the postacetabular process is positioned higher than the edge of the brevis shelf, exposing the latter in side view.

Ornithischia pelvis structure.svg, Ornithischian pelvic structure (left side)
Saurischia pelvis structure.svg, Saurischian pelvic structure (left side).

History

The 'English' name ''ilium'' as bone of the ''pelvis'' can be traced back to the writings of anatomists Andreas Vesalius, who coined the expression ''os ilium''.Hyrtl, J. (1880). ''Onomatologia Anatomica. Geschichte und Kritik der anatomischen Sprache der Gegenwart.'' Wien: Wilhelm Braumüller. K.K. Hof- und Universitätsbuchhändler. In this expression ''ilium'' can be considered as the genitive plural of the nominative singular of the noun ''ile''. Ile in classical Latin can refer to the ''flank of the body'',Lewis, C.T. & Short, C. (1879). ''A Latin dictionary founded on Andrews' edition of Freund's Latin dictionary.'' Oxford: Clarendon Press. or to the ''groin'', or the ''part of the abdomen from the lowest ribs to the pubes''. Ile is usually encountered as plural (''ilia'') in classical Latin. The ''os ilium'' can literally be translated as ''bone'' (Latin: ''os'' ) ''of the flanks''.

More than a millennium earlier the ''ossa ilium'' were described by the Greek physician Galen, and referred to as, with a quite similar expression, τά πλατέα λαγόνων ὀστᾶ, ''the flat bones of the flanks'', with λαγών for ''flank''.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie.'' Oxford: Clarendon Press. In anatomic Latin, the expression ''os lagonicum''Kossmann, R. (1895). Die gynäcologische Anatomie und ihre zu Basel festgestellte Nomenclatur. ''Monatsschrift für Geburtshülfe und Gynaekologie'', 2 (6), 447-472. can also be found, based on Ancient Greek λαγών. In modern Greek the nominalized adjective λαγόνιοSchleifer, S.K. (Ed.) (2011). ''Corpus humanum, The human body, Le corps humain, Der menschliche Körper, Il corpo umano, El cuerpo humano, Ciało człowieka, Människokroppen, Menneskekroppen, Τό ανθρώπινο σῶμα, ЧЕЛОВЕК.'' FKG. is used to refer to the ''os ilium''.

In Latin and Greek it is not uncommon to nominalize adjectives, e.g. ''stimulantia'' from ''remedia stimulantia''Arnaudov, G.D. (1964). ''Terminologia medica polyglotta. Latinum-Bulgarski-Russkij-English-Français-Deutsch.'' Sofia: Editio medicina et physcultura. or ὁ ἐγκέφαλος from ὁ ἐγκέφαλος μυελός.Kraus, L.A. (1844). ''Kritisch-etymologisches medicinisches Lexikon'' (Dritte Auflage). Göttingen: Verlag der Deuerlich- und Dieterichschen Buchhandlung. The name ''ilium'' as used in EnglishDorland, W.A.N. & Miller, E.C.L. (1948). ''The American illustrated medical dictionary.’’ (21st edition). Philadelphia/London: W.B. Saunders Company.Dirckx, J.H. (Ed.) (1997).''Stedman’s concise medical dictionary for the health professions.'' (3rd edition). Baltimore: Williams & Wilkins. can not be considered as nominalized adjective derived from the full Latin expression ''os ilium'', as ''ilium'' in this expression is a genitive plural of a noun and not a nominative singular of an adjective. The form ''ilium'' in English is however thought to be derived from the Latin word ''ilium'',Klein, E. (1971). A comprehensive etymological dictionary of the English language. Dealing with the origin of words and their sense development thus illustration the history of civilization and culture. Amsterdam: Elsevier Science B.V. an orthographic variant in Latin of ''ile'', ''flank'' or ''groin''. Whereas the expression of Andreas Vesalius ''os ilium'' appropriately expresses ''bone of the flanks'', the sole term ''ilium'' as used in English, lacks this precision and has to be literally translated as ''groin'' or ''flank''.

There exists however in classical Latin an adjective ''ilius/ilia/ilium''. This adjective however means not ''with respect to the flanks'', but ''Trojan''. ''Troy'' is referred to in classical Latin as ''Ilium'', ''Ilion'' or ''Ilios''Wageningen, J. van & Muller, F. (1921). ''Latijnsch woordenboek.'' (3de druk). Groningen/Den Haag: J.B. Wolters’ Uitgevers-Maatschappij and in ancient Greek as Ἴλιον or Ἴλιος.

The first editions of the official Latin nomenclature, '' Nomina Anatomica'' of the first 80 years (first in 1895) used the Vesalian expression ''os ilium''.His, W. (1895). ''Die anatomische Nomenclatur. Nomina Anatomica. Der von der Anatomischen Gesellschaft auf ihrer IX. Versammlung in Basel angenommenen Namen''. Leipzig: Verlag Veit & Comp.Kopsch, F. (1941). ''Die Nomina anatomica des Jahres 1895 (B.N.A.) nach der Buchstabenreihe geordnet und gegenübergestellt den Nomina anatomica des Jahres 1935 (I.N.A.)'' (3. Auflage). Leipzig: Georg Thieme Verlag.Stieve, H. (1949). ''Nomina Anatomica. Zusammengestellt von der im Jahre 1923 gewählten Nomenklatur-Kommission, unter Berücksichtigung der Vorschläge der Mitglieder der Anatomischen Gesellschaft, der Anatomical Society of Great Britain and Ireland, sowie der American Association of Anatomists, überprüft und durch Beschluß der Anatomischen Gesellschaft auf der Tagung in Jena 1935 endgúltig angenommen.'' (4th edition). Jena: Verlag Gustav Fischer.Donáth, T. & Crawford, G.C.N. (1969). ''Anatomical dictionary with nomenclature and explanatory notes.'' Oxford/London/Edinburgh/New York/Toronto/Syney/Paris/Braunschweig: Pergamon Press.International Anatomical Nomenclature Committee (1966). ''Nomina Anatomica''. Amsterdam: Excerpta Medica Foundation.International Anatomical Nomenclature Committee (1977). ''Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica''. Amsterdam-Oxford: Excerpta Medica. In the subsequent editions from 1983International Anatomical Nomenclature Committee (1983). ''Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica''. Baltimore/London: Williams & Wilkins and 1989International Anatomical Nomenclature Committee (1989). ''Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica''. Edinburgh: Churchill Livingstone. the expression ''os ilium'' was altered to ''os ilii''. This latter expression supposes a genitive singular of the alternate noun ''ilium'' instead of a genitive plural of the noun ''ile''. Quite inconsistently, in the 1983 edition of the ''Nomina Anatomica'' the genitive plural of ''ile'' (instead of ''ilium'') is still being used in such expressions as ''vena circumflexa ilium superficialis''. In the current 1998 edition of the ''Nomina Anatomica'', rebaptized as '' Terminologia Anatomica'', the expression ''os ilium'' is reintroduced and ''os ilii'' deleted.

Additional images

Pelvic girdle illustration.svg, Pelvic girdle
Gray236.png, Right hip bone. Internal surface.
Gray235.png, Right hip bone. External surface. (Body of ilium is the top of the blue circle in the center, and the wing of the ilium is the portion above that. Crest of ilium is labeled at top.)
Gray237.png, Plan of ossification of the hip bone.
Gray341.png, Left hip-joint, opened by removing the floor of the acetabulum from within the pelvis.
Skeletal pelvis-pubis.svg, Pelvis

See also

* Iliac crest
* Wing of ilium

References

External links

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Bones of the pelvis
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