Idiopathic coccygodynia. Analysis of fifty-one operative cases and a radiographic study of the normal coccyx.

The Journal of bone and joint surgery. American volume.

1983 Oct; 65(8): 1116-1124

Postacchini F, Massobrio M

Abstract

We studied the normal radiographic anatomy of the coccyx in 120 asymptomatic subjects and performed a retrospective review of the results in fifty-one patients who had had a partial or total coccygectomy for idiopathic coccygodynia during a twenty-year period.

Of the asymptomatic subjects, the sacrococcygeal joint was fused in forty-four (37 per cent); the first intercoccygeal joint, in twelve (10 per cent); and the second intercoccygeal joint, in fifty-two (43 per cent).

Four types of configuration of the coccyx were identified on the lateral radiographs. In Type I the coccyx was curved slightly forward, whereas in Type II the curve of the coccyx, which pointed straight forward, was more marked. In Type III the coccyx was angulated forward sharply, and in Type IV it was subluxated at the sacrococcygeal or the intercoccygeal joint. Most subjects (68 per cent) had a Type-I configuration.

Of the fifty-one patients with idiopathic coccygodynia, twenty-six (51 per cent) showed fusion of the sacrococcygeal joint; six (12 per cent), of the first intercoccygeal joint; and twenty-five (49 per cent), of the second intercoccygeal joint. In most patients (69 per cent) the coccyx had a Type-II, III, or IV configuration. Thirty-one patients had undergone a partial coccygectomy and twelve, a total coccygectomy; in the remaining eight patients the extent of the coccygectomy could not be determined. The results of surgery were excellent or good in thirty-two (88 per cent) of the thirty-six patients who were followed for at least two years.

More information extracted from the paper by Jon Miles

Postacchini and Massobrio studied x-rays of 120 coccyxes of people without pain and 51 coccyxes of people with unexplained coccyx pain. They looked at how many segments people had in their coccyxes, which joints were fused together, and how they curved. These are their results:

Percent of subjects without pain Percent of subjects with unexplained coccydynia
Number of coccyx segments

1

7

8

2

54

41

3

34

49

4

5

2

Joint fused Sacrum/coccyx joint

37

51

First coccyx joint

10

12

Second coccyx joint

43

49

Configuration of coccyx 1. Curving slightly forward

68

31

2. Curving strongly, tip straight forward

17

23

3. Angled sharply forward

6

23

4. Partly dislocated forward at one of the joints

9

22

Configuration 1, curving slightly forward, was the most common in the general public, with two thirds of people having this type. But less than one third of people with coccyx pain of unknown origin had a type 1 coccyx. Therefore if you happen to have a coccyx that points forward more than down, you are more likely to get coccyx pain even if you don't have an accident.

Postacchini and Massobrio found that 8% of the people without pain had a coccyx that pointed partly left or right. In people with pain of unknown origin, more than 16% had a coccyx that went to one side.

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