Anatomy Atlases(tm) : A digital library of anatomy information

Home | About | FAQ | Reviews | Search

Anatomy Atlases: Illustrated Encyclopedia of Human Anatomic Variation: Opus V: Skeletal System: Sacrum and Coccyx

Illustrated Encyclopedia of Human Anatomic Variation: Opus V: Skeletal Systems: Vertebral column

Sacrum and Coccyx

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD

Peer Review Status: Internally Peer Reviewed

The number of vertebrae in the sacrum may be increased by fusion of the first coccygeal, by (less often) addition of the last (fifth) lumbar, or by addition of both the last lumbar and first coccygeal vertebrae.

The number may be reduced to four by the "lumbarization" of the first sacral vertebra. In one study of 631 bodies, the sacrum was composed of five vertebrae in 77%, six in 21.7%, four in 1%, and seven in 0.2%.

The lumbosacral junction is occasionally composed of a vertebra with characteristics of a lumbar vertebra on one side and a sacral on the other (so-called hemilumbarization or hemisacralization).

The articular surface of the sacrum may extend variably, over no more than the first two vertebrae or to the fourth sacral vertebra. Accessory articular facets may occur on the lateral sacral crest at the level of the first or second dorsal sacral foramen; these have been found to be unpaired or bilateral and to articulate with appropriate facets on the ilium.

The sacral canal may open dorsally because of failure of laminar fusion. Coalescence of the coccyx and sacrum occurs more often and earlier in males.

The subdural and subarachnoid spaces extend into the sacral canal as far as the middle third of the body of the second sacral vertebra; however, in 46% of 56 cadavers, these spaces extend caudal to this level.

The female sacrum is usually broader (in proportion to length), less curved, and directed more obliquely dorsally than the male sacrum. The curvature of the female sacrum occurs in the caudal part of the bone; in the male, the curvature is distributed over the entire length of the bone. But the sex characterics cited above , however, are subject to considerable variation in different skeletons (Trotter, 1926).

The sacrum and coccyx may be absent.

The presence of a tail in humans has been reported on several occasions. In one case, the tail was 23 cm in length.

Racial differences: the human sacrum is characterized by its great breadth in comparison to its length. The proportion is expressed by the following equation: sacral index = breadth x 100/ length. The average sacral index in British males is 112; in the female, 116. Sacra in which the index is above 100 are platyhieric, as in Europeans, Negroes, Polynesians; those under 100 are dolichohieric, as in Australians, Bushmen, Andamanese (Turner, 1886).

Pubic Tubercles and Pubic Spines

Sacrum, Left Lateral View

Sacral Facet


Absence of Sacral Dorsal Arches

Accessory Iliosacral Articulations

Three Sacra

Sacrum Composted of Five and Six Vertebrae. Coccys Composed of Four Vertebrae.


Persistence of the Tail


Lumbar Sacralization


Anderson, R.J. (1883) Observations on the diameters of human vertebrae in different regions. J. Anat. Physiol. 17:341-344.

Armstrong, J.R., Crisp, E.J., Freedman, B., Gillespie, H.W., Golding, F.C., Jackson, H. and K. Lloyd. (1950) Discussion on the significance of congenital abnormalities of the lumbosacral region. Proc. R. Soc. Med. 43:635-640.

Badgley, C.E. (1941) The articular facets in relation to low-back pain and sciatic radiation. J. Bone Joint Surg. 23:481-496.

Bársony, T. and K. Winkler. (1937) Beiträge zur Röntgenologie der Wirbelsäule. Röntgenpraxis 9:601-608.

Bartels, M. (1880-81) Ueber Menschenschwänze. Archiv für Anthropolgie (Braunschweig) 13: 141.

Barton, P.N. (1948) The significance of anatomical defects of the lower spine. Industr. Med. 17:37-40.

Blumel, J., Evans, E.B. and G.W.N. Eggers. (1959) Partial and complete agenesis or malformation of the sacrum with associated anomalies. J. Bone Joint Surg. (Am) 41:497-518.

Boos, O. (1953) Zur Genese der Wirbelsäulendefeckte. Ein weiterer klinischer Beiträg zur Kenntnis der Defektbildungen an der kaudalen Wirbelsäulenabschnitten. Dtsch. Med. Wochenschr. 78:485-487.

Boucher, B. (1957) Sex differences in the foetal pelvis. Am. J. Phys. Anthropol. N.S. 15:581-600.

Brailsford, J.F. (1928-29) Deformities of the lumbosacral region of the spine. Brit. J. Surg. 16:562-627.

Brandt, K. (1933-34) Über die konstante Form der Lendenwirbelquefortsätze 3 und 4. Arch. Orthop. Unfall-Chir. 34:445-450.

Braun, H. (1955) Seltene Anomalien der Wirbelsäule. Fortschr. Röntgenstr. 82:126-127.

Brocher, J.E.W. (1938) Mehrfach angeborene Fehlbildung der Wirbelsäule. Fortschr. Röntgenstr. 58:440-447.

Colcher, A.E. and A.M.W. Hursh. (1952) Pre-employment low-back x-ray survey. A Review of 1,500 cases. Indstr. Med. 21:319-321.

Cramer, K. (1908) Über Rückgratverkrümmungen bei lumbosakralen Assimilationswirbeln Z. Orthop. Chir. 22:68-89.

Danforth, M.S. and P.D. Wilson. (1925) The anatomy of the lumbosacral region in relation to sciatic pain. J. Bone Joint Surg. 7:109-160.

Dassel, P.M. (1961) Agenesis of the sacrum and coccyx. Am. J. Roentgenol. 85:697-700.

Del Duca, V., Davis, E.V. and J.N. Barroway. (1951) Congenital absence of the sacrum and coccyx. J. Bone Joint Surg. (Am) 33:248-253.

Derry, D.E. (1911) Note on accessory articular facets between the sacrum and Ilium, and their significance. J. Anat. Physiol. 45:202-210.

Diethelm, L. (1943) Zur Kenntnis der Entwicklungsgeschichte der Wirbelsäule und der Wirbelkörperfehlbildungen. Fortschr. Röntgenstr. 69:143-150.

Dieulafé, -. et -. Saint-Martin. (1912) Le type articulaire sacro-iliaque. Assoc. Anatomistes Comptes Rendus 14:95-109.

Van Driessche, R. (1958) Ein seltener Befund am Steissbein. Fortschr. Röntgenstr. 88:623.

Egli, A. (1942) Beitrag zur Kenntnis der Fehlbildungen am Kreuzbein. Z. Anat. Entwicklungsgesch. 112: 245-270.

Ehara, S., El-Khoury, G.Y. and R. A. Bergman. (1988) The accessory sacroiliac joint. A common variation. Am. J. Roentgenol. 150:857-859.

Fawcett, E. (1907) On the complete ossification of the human sacrum. Anat. Anz. 30:414-421.

Fawcett, E. (1937-38) The sexing of the human sacrum. J. Anat. 72:633.

Freedman, B. (1949-50) Congenital absence of the sacrum and coccyx. Report of a case and review of the literature. Brit. J. Surg. 37:299-303.

Gillespie, H.W. (1949) The signifcance of congenital lumbo-sacral abnormalities. Brit. J. Radiol. 22:270-275.

Girard, P.M. (1935) Congenital absence of the sacrum. J. Bone Joint Surg. 17:1062-1064.

Goldstein, R. (1947) Agenesis of sacrum and coccyx. Acta Med. Orientalia 6:202-204. Cited in Excerpta Medica, Sec. 1, Vol.3, abstract 668.

Gomez Oliveros, L. (1948) Observaciones anatómicas de tres casos de sacralizatión de la quinta vértebra lumbar. Cirurgia Aparato Locomotor 5:29-35. Cited in Excerpta Medica, Sec. 1, Vol. 3, abstract 382, 1949.

Greulich, W.W. and H. Thhoms. (1938) The dimensions of the pelvic inlet of 789 white females. Anat. Rec. 72:45-51.

Greve, -. (1878) Ein Fall von Schwanzbildung beim Menschen. Arch. Pathol. Anat. Physiol. Klin. Med. 72:129.

Hadley, L.A. (1950) Accessory sacroiliac articulations with arthritic changes. Radiology 55:403-409.

Hamsa, W.R. (1935) Congenital absence of the sacrum. Arch. Surg. 30:657-666.

Harris, H.A. (1953) Ossification in the lumbo-sacral region. Brit. J. Radiol. 6:685-688.

Harrison, R.G. (1901) On the occurrence of tails in man, with a description of the case reported by Dr. Watson. Johns Hopkins Hosp. Bull. 12:96-101.

Heyns, O.S. and J.E. Kerrich. (1947) The number of vertebrae in the fetal Bantu sacrum. Am. J. Phys. Anthropol. 5:67-78.

Irnberger, T. (1938) Beobachtung eines Rippenrudimentes am menschlichen Steissbein. Anat. Anz. 86:369-378.

Jancu, F. and V. Chiriac. (1964) Foramina Transversaria im 1. Sakralwirbel. Anat. Anz. 115:403-404.

Katz, J.F. (1953) Congenital absence of the sacrum and coccyx. J. Bone Joint Surg. (Am) 35:398-402.

Keith, A. (1921) The disappearance and reappearance of the human tail. Nature 106:845.

Lanier, V.S., McKnight, H.E. and M. Trotter. (1944) Caudal analgia: An experimental and anatomical study. Am. J. Obst. & Gynec., 47:633-641.

Letterman, G.S. and M. Trotter. (1944) Variations of the male sacrum. Their significance in caudal anesthesia. Surg., Gynecol. Obstet. 78:551-555.

Lewin, T. (1968) Anatomical variations in lumbo-sacral synovial joints with particular references to subluxation. Acta Anat. 71:229-248.

Lichtor, A. (1947) Sacral agenesis. Arch. Surg. 54:430-433.

Mitchell, G.A.G. (1936-37) The significance of lumbosacral transitional vertebrae. Brit. J. Surg. 24:147-158.

Mutel, -. (1926) Les déhiscences normales lombo-sacres. Assoc. Anatomistes Comptes Rendus 21:422-429.

Nathan, H. and B. Arensburgh. (1972) An unusual variation in the fifth lumbar and sacral vertebrae: A possible cause of vertebral canal narrowing. Anat. Anz. 132:137-148.

Newell, J.L. (1934) A case of multiple congenital anomalies of the Mullerian and genito-urinary systems with absence of the coccyx. New England J. Med. 210:1217-1218.

Phesant, H.C. and P.C. Swenson. (1942) The lumbosacral region. A correlation of the roentgenographic and anatomical observations. J. Bone Joint Surg. (Am) 24:299-306.

Piontek, J. (1971) Variation of the level of closure of the sacral canal in man. Folia Morphol. (Warsaw) 30:460-464.

Pires de Lima, J.A. (1927) "Queue de Cochon" chez un enfant. Bull. et Mém. de la d'Anthrop. de Paris 8:58-60.

Pirkey, E.L. and J.H. Purcell. (1957) Agenesis of lumbosacral vertebrae. A report of two cases in living infants. Radiology 69:726-729.

Reinhardt, K. (1961) Agenesis und Dysgenesie des Kreuzbeines. Fortschr. Rontgenstr. 95:381-391.

Roller, G.T. and H.F.W. Pribram (1965) Lumbosacral intradural lipoma and sacral agenesis. Radiology 84:507-512.

Rowe, G.G. (1950) Anomalous vertebrae from the lumbo-sacral column of man. Anat. Rec. 107:171-179.

Rübe, W. (1957) Doppelanlage der Letzten Steissbeinwirbel. Forthschr. Röntgenstr. 87:270-272.

Russell, H.E. and G.T Aitken. (1963) Congenital absence of the sacrum and lumbar vertebrae with prosthetic management. J. Bone Joint Surg. (Am) 45:501-508.

Schneider, U. (1956) Das akzessoriche Iliosakralgelenk (Articulus sacroilicus accessorius) im Röntgenbild. Fortschr. Röntgenstr. 85:426-432.

Sinclair, J.G., Duren, N. and J.C. Rude. (1941) Congenital lumbosacral defect. Arch. Surg. 43:473-478.

Smith, E.D. (1959) Congenital sacral anomalies in children. Aust. N.Z. J. Surg. 29:165-176.

Southworth, J.D. and S.R. Bersack. (1950) Anomalies of the lumbosacral vertebrae in five hundred and fifty individuals without symptoms referable to the low back. Am. J. Roentgenol. 64:624-634..

Sugar, 0. (1987) How the sacrum got its name. JAMA 257:2061-2063.

Taylor, R.G. (1939) Anomalies of the lumbosacral articulations. JAMA 113:463-465.

Toyoda, J. (1927) Über den lumbosakralen übergangswirbel bei den Japanern. Folia Anat. Jpn. 5:37-49.

Trotter, M. (1926) The sacrum and sex. Am. J. Phys. Anthropol. 9:445-450.

Trotter, M. (1937) Accessory sacroiliac articulations. Am. J. Phys. Anthropol. 22:247-261.

Trotter, M. (1940) A common anatomical variation in the sacro-iliac region. J. Bone Joint Surg. 22:293-299.

Trotter, M. (1947) Variations of the sacral canal: Their significance in the administration of caudal analgesia. Curr. Res. Anaesth. Analgesia 26:192-202.

Trotter, M. (1964) Accessory sacroiliac articulations in East African skeletons. Am. J. Phys. Anthropol. N.S. 22:137-142.

Trotter, M. and P.F. Lanier. (1945) Hiatus canalis in American Whites and Negroes. Human Biol. 17:368-381.

Trotter, M. and G.S. Letterman. (1944) Variations in the female sacrum. Their significance in continuous caudal anaesthesia. Surg., Gynecol. Obstet. 78:419-424.

Turner, W. (1886) The sacral index of the pelvic brim as a basis of classification. J. Anat. Physiol. 20:125-143.

Turner, W. (1886) The sacral index in various races of mankind. J. Anat. Physiol. 20:317-323.

Vielberg, H. (1970) Beobachtung seltener Wirbelkörperanomalien and der Lendenwirbelsäule eines Erwachsenen. Diskussionbeitrag zur gestörten Chordasegmentierung. Fortschr. Röntgenstr. 113:60-67.

Virchow, R. (1881) Schwanzbildung beim Menschen. Arch. Pathol. Anat. Physiol. Klin. Med. 83:560.

Weisel, H. (1954) The articular surfaces of the sacro-iliac joint and their relation to the movement of the sacrum. Acta Anat. 22:1-14.

Weiss, O. (1930) Über die Anatomie der übergangswirbel an der Grenze von Lendenwirbelsäule und Kreuzbein und ihre klinische Bedeutung. Z. Anat. Entwicklunggsgesch. 90:533-550.

Willis, T.A. (1923) The lumbo-sacral vertebral column in man, its stability of form and function. Am. J. Anat. 32:95-123.

Wood-Jones, F. (1921) Human and other tails. Nature (London) 107:487.

Young, M. and J.G.H. Ince. (1939-40) Transmutation of vertebrae in the lumbosacral region of the human spine. J. Anat. 74:369-373.

Zeligs, I.M. (1940) Congenital absence of the sacrum. Arch. Surg. 41:1220-1228.

Zimmern, A., Lauret, -. and R. Weill. (1922) Sacralisation vraie de la Ve lombaire et algies sciatiques. La Presse Medicale 30:698-701.

Section Top | Title Page
Home | About Us | FAQ | Reviews | Contact Us | Search

Anatomy Atlases is curated by Michael P. D'Alessandro, M.D. and Ronald A. Bergman, Ph.D.

Please send us comments by filling out our Comment Form.

All contents copyright © 1995-2017 the Author(s) and Michael P. D'Alessandro, M.D. All rights reserved.

"Anatomy Atlases", the Anatomy Atlases logo, and "A digital library of anatomy information" are all Trademarks of Michael P. D'Alessandro, M.D.

Anatomy Atlases is funded in whole by Michael P. D'Alessandro, M.D. Advertising is not accepted.

Your personal information remains confidential and is not sold, leased, or given to any third party be they reliable or not.

The information contained in Anatomy Atlases is not a substitute for the medical care and advice of your physician. There may be variations in treatment that your physician may recommend based on individual facts and circumstances.