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

Numerical Variation in Vertebral Column

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed

The usual grouping formula of 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal vertebrae is found in only about 20% of individuals studied. The cervical region is reported to be the most constant, the coccygeal the most variable.

The number of elements of the vertebral column has been reported to vary between 32 and 35. Addition to a group is frequently seen, which occurs through the reduction in number of vertebrae of an adjacent group, the total number being unchanged. In this variation, the vertebra added is usually intermediate in form between the adjacent groups. The location of such a vertebra is predominately at the ends of the column and at the levels of transition between its regions. Thus, sacralization of the fifth lumbar, lumbar-like articular processes in the eleventh thoracic, and thoracic costal facets on the seventh cervical are observed.

The levels of transition may be shifted cephalad, resulting in 23 mobile vertebrae, or shifted caudad, resulting in 25 presacral vertebrae. Such variations may occur in 2-11% of the population.

In one study of 748 vertebral columns, 717 had 17 thoracolumbar vertebrae, 26 had 18, and five had 16. Of the 717 columns, four had a lumbar increase and a thoracic decrease while five had a lumbar decrease with a compensating thoracic increase.

The number of vertebrae comprising the sacrum may be increased to six, resulting from the fusion of the first coccygeal (50% in whites, 30% in Negroes) or, less often, of the last lumbar (sacralization) (8% in whites, 11% in Negroes); or it may be increased to seven, resulting from the fusion of the first coccygeal and the last lumbar (4% in whites, 1.5% in Negroes). The number may be reduced to four, apparently by the lumbarization of the first sacral (0.4% in whites, 1.5% in Negroes) (Trotter and Lanier).

The junction between the lumbar and sacral parts of the column is occasionally made by an element presenting the characteristics of a lumbar vertebra on one side and of a sacral on the opposite (hemisacralization, hemilumbarization).

The auricular surface may extend over no more than the first two vertebra or on to the fourth sacral vertebra. Accessory articular facets on the lateral sacral crest at the level of the first or second dorsal sacral foramen have been found unpaired and bilateral, meeting in articulation with extra facets on the ilium.

The sacral canal may be open dorsally to a greater degree than is usually the case, because of failure of laminae preceding the fourth to fuse. In 1% of a series of 1,225 sacra all the laminae failed to fuse in the middle line, resulting in a completely open bony dorsal wall of the sacral canal; this occurred almost exclusively in the males and twice as frequently in whites as in Negroes.

Coalescence of the coccyx and sacrum takes place less often and later in life in the female than in the male.

Absence of the sacrum and coccyx, in part or complete, is reported; in some instances with remarkable functional adjustments (Zeligs; Sinclair, Duren and Rude).

Rudiments of an arch, chevron bones, on the pelvic surface have been interpreted as vestiges of the hemal arch of lower vertebrates. Five cases have been reported; four of the first and one of the second coccygeal vertebra (Schultz).

Vertebral Numerical Variation

References

Ancel, P. and L. Sencert. (1901) Vartiations numériques de la colonne vertébrale. Assoc. Anatomistes Comptes Rendus 3:158-165.

Anderson, E. (1926) Über Anomalien der Wirbelsäule und der Rippen. Fortschr. Röntgenstr. 34:491-499.

Barbosa Sueiro, M.B. (1926) Note sur la fréquence de quélques variations du rachis humain. Assoc. Anatomistes Comptes Rendus 21:51-62.

Barbosa Sueiro, M.B. (1933) Démonstrations de quelques variations rachidiennes chez l'homme. Assoc. Anatomistes Comptes Rendus 28:709-710.

Barclay-Smith, E. (1911) Multiple anomaly in a vertebral column. J. Anat. Physiol. 45:144-171.

Bardeen, C.R. (1904) Numerical vertebral variations in the human adult and embryo. Anat. Anz. 25:497-519.

Bianchi, S. (1895) Sur la fréquence des anomalies numériques vertebrales dans le squelette des individus normaux et des aliénés. Arch. Ital. Biol. 23:467.

Bornstein, P.E. and R.R. Peterson. (1966) Numerical variation of the presacral vertebral column in three population groups in North America. Am. J. Phys. Anthropol. 25:139-146.

Brash, J.C. (1915) Vertebral column with six and a half cervical and thirteen true thoracic vertebrae with associated abnormalities of the cervical spinal cord and nerves. J. Anat. Physiol. 69:243-273.

Calmettes, -. (1868) Anomalies multiples; asymétrie du crane; scoliose de la colonne vertébrale; absence congenitale d'un cartilage costal du côte droit, du rein droit, et du pouce du même côté. Bulletins et Mem. de la Société Anatomique de Paris XLIII(5):371-373.

Calori, L. (1887) Sopra due casi di varietà numerische delle costole e da altra anomalie. Mem. d. R. Accad. d. Sci. Istituto di Bologna S. 4., 8:18 pp.

Calori, L. (1889) Sur deux cas de variétés numérique des vertèbres, accompagnés de variétés numériques des cotes et d'autres anomalies. Arch. Ital. Biol. 11:425-426.

Conde Andreu, J. (1927) Recherches sur quelques deviations vertebrales. Assoc. Anatomistes Comptes Rendus 22:59-70.

Danforth, C.H. (1930) Numerical variation and homologies in vertebrae. Am. J. Phys. Anthropol. 14:463-481.

Dubreuil-Chambardel, L. (1921) Notes anatomiques a propos de la sacralisation de la cinguième vertèbre lombaire. Bull. et Mém. de la Soc. d'Anthrop. de Paris 2:157-167.

Dubreuil-Chambardel, L. et -. Bonnin. (1921) Colonne cervicale a huit segments vertebraux. Bull. et Mém. de la Soc. d'Anthrop. de Paris 2:29-36.

Dwight, T. (1901) Description of the human spines showing numerical variation in the Warren Museum of the Harvard Medical School. Anat. Anz. 19:321-328.

Dwight, T. (1906) Numerical variation in the human spine, with a statement concerning priority. Anat. Anz. 28:33-40.

Flesch, M. (1879) Ueberzähliger Wirbel (bezuglich Rippe). Lumbosacraler übergangs - Wirbel; Eingehen von 7 Wirbeln in das Kreuzbein; œffner Sacral-Canal; Eigenthümliche Fläche an dem Dorsal-Wirbel. Varietäten-Beobachtungen aus dem Präparirsaale zu Würzburg in den Winter-Semester 1875-6 und 1876-7. Verh. Phys.- Med. Gesellsch. Würzburgh 13:233-268.

Gladstone, R.J. (1897) Case of an additional presacral vertebra. J. Anat. Physiol. 31:530-538.

Hyrtl, -. (1866) Über Anomalien des menschlichen Steissbeins. Sitzunsberichte der Wiener Akad. der Wissen. Math. -Nature. Kl. 53:290-297.

Low, A. (1900) Description of a specimen in which there is a rudimentary first rib along with thirteen pairs of ribs and twenty-five presacral vertebrae. J. Anat. Physiol. 34:451-457.

Lowrance, E.W. and H.B. Latimer (1967) Weights and variability of components of the human vertebral column. Anat. Rec. 159:83-88.

Mall, F.P. (1906) On ossification centers in human embryos less than one hundred days old. Am. J. Anat. 5:433-458.

Montiero, H.b. et L. Dubreuil-Chambardel. (1924) Nouveaux documents sur les variations der rachis. Bull. et Mém. de la Soc. d'Anthrop. de Paris 5:3-19.

Reynolds, E.L. and L.W. Sontag. (1944) Seasonal variations in weight, height, and appearance of ossification centers. J. Pediat. 24:524-535.

Roche, M.B. and G.G. Rowe. (1951) The incidence of separate neural arch and coincident bone variations. Anat. Rec. 109:233-252.

Rowe, G.G. and M.B. Roche. (1953) The etiology of the separate neural arch. J. Bone Joint Surg. (Am.) 35:102-110.

Schultz, A.H. (1941) Chevron bones in an adult man. A. J. Phys. Anthropol. 28:91-97.

Shore, L.R. (1930) Abnormalities of the vertebral column in a series of skeletons of Bantu natives of South Africa. J. Anat. 64:206-238.

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

Soularue, M. (1900) Étude des proportions de la colonne vertébrale chez Phomme et chez la femme. Bull. et Mém. de la Soc. d'Anthrop. de Paris 1:132-147.

Staderini, R. (1895) Recherches statistiques sur la fréquence des variétés numériques des vertèbres chez l'homme et considérations sur leur genèse. Arch. Ital. Biol. 22:149-150; Monitore Zool. Ital., Firenze 5:56-67, 95.

Tenchini, L. (1889) Sur les variétés numériques vertebro-costales chez l'homme. Arch. Ital. Biol. 12:43.

Tenchini, L. (1895) Sur un noveau mode de compensation dans les anomalies numériques vertébrales de l'homme. Arch. Ital. Biol. 23:93.

Whitney, C. (1926) Asymmetry of vertebral articular processes and and facets. Am. J. Phys. Anthropol. 9:451-455.

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

URL: http://www.anatomyatlases.org/