On Sacral Dimple and Abnormal Coccyx

Lancet

Vol. 119 No. 3062 pp 729-730. May 6, 1882

Andrew Dunlop

Consulting Physician to the Jersey General Dispensary

IN 1876 and 1878 I published notes of a peculiar abnormality of the coccyx, and the skin over the lower part of the sacrum, and since that time I have seen a considerable number of cases of the same kind, The first case I saw (1) was in a girl, eight years of age, on whom I found a circular pit or hole over the lower part of the sacrum, or rather over the coccyx, directly in the middle line. It had a direction downwards and forwards, and consisted of a reflexion of the skin entering a more or less circular depression about a quarter of an inch in diameter and a quarter of an inch deep. Not quite a quarter of an inch below its lower border could be felt the pointed extremity of the coccyx, which, instead of having its usual form, curved backwards and forwards. On stretching the skin downwards that portion of it which entered the pit was raised, coming out like the finger of a glove which had been pushed down into its lower part, and a small prominence about the height of the diameter of a pea stood up from the surface, and this little sheath was found to cover and exactly fit the point of the coccyx. Soon afterwards I examined the rest of the family, with the following results (2) - Boy, aged six, normal. Girl, aged four, depression at the same spot as in her eldest sister; coccyx normal. Girl, aged two, normal. Boy, aged seven months, fairly deep hole (not measured) in the same position as in the others, coccyx less curved forward than usual. In another family I met with the following instances : Boy, aged eight, circular pit about three millimetres in diameter, situated in the middle line at the junction of the folds of the nates; coccyx nearly straight. Boy, aged five, a circular hole at the same spot, admitting the point of a metallic note-book pencil. It passed downwards and forwards. The coccyx was straight. A girl, aged three, very slight depression. Coccyx straight. The cases of this kind that I have seen may be arranged as follows :-

1. Those where the coccyx was bent backwards and sometimes upwards, with a dimple or hole in the skin, at or about the junction of the folds of the nates, the pit was generally from three to five millimetres in diameter, and varied from a mere dimple to a hole about five millimetres deep, and it would sometimes be obliterated by traction on the surrounding skin. The first case I saw was the only one în which I found that the depression could be everted and made to cover the tip of the coccyx.

2. Those where the coccyx was straight, or nearly so, with a dimple or hole, as in the last.

3. Those where there was a pit in the skin, with the coccyx normal in form.

4. Those where the coccyx was straight or bent backwards, without any dimple or hole in the skin.

In three instances I have found some form of this abnormality present in several members of the same family. At the meeting of the British Association in 1878, Mr. Lawson Tait read a "Note on the Occurrence of a Sacral Dimple and its Possible Significance." In this paper he described the pit in the skin over the sacrum, but he does not seem to have ever seen it associated with an abnormal form of coccyx. He found that this dimple was well marked in 23 per cent, of the patients he examined at the Hospital for Women at Birmingham, and that it was fairly well marked in 55 per cent. He concluded that it was a cicatrix, and suggested that it was the hereditary cicatrix of the spina bifida by which the human tail had been lost. A year or two ago some observations on the sacral dimple, and on the peculiar arrangement of the hair often observed over the sacrum, were published at Brunswick by, I believe, Dr. Hirtl, but I have not been able to obtain a copy of the work, and I have not had an opportunity of searching for it myself. The cases of congenital sacral fistula lately brought before the Société de Chirurgie of Paris by M. Terillon are interesting in connexion with the appearances I have described, especially the fact that the walls of these fistulas were found to have a structure similar to that of the skin.

The frequent occurrence of this abnormality, with the dimple always situated at or about the same spot, would seem to give some grounds for supposing it to be the remains of some different condition or formation of the parts.

I hope some one with more time and opportunity than I have may be induced to take up this subject, and try to work it out, for it appears to me to deserve the attention of anatomists and naturalists.

1. Nature, volume xiv, p 450

2. Ibid, volume xix, p 94.

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