We have read the article entitled "A novel radiological classification for displaced os coccyx: the Benditz–König classification" published in European Spine Journal with great respect and enthusiasm [1].

Coccydynia is still a great challenge for clinicians and radiologists since imaging techniques cannot show the main reason for pain. Classifications and measurements are helpful in analyzing the anatomical structure of the coccyx. However, there are different views about the definitions of some measurements.

The authors used the term intra-coccygeal angle for "the angle in the most angulated segment" and represented it with figures. They are two different measurements of intra-coccygeal angle in the literature. In one view, the intra-coccygeal angle increases from Type 1 to Type 2 and varied from 17° to 88° [2]. In another study, the intra-coccygeal angle was lower in the coccydynia group, and the control group's mean was 155.4 ± 7° [3]. We believe that this difference is due to angle measurement. Some authors use the caudal aspect of the angle, while others prefer the cranial side.

The authors did not cite a reference for the measurements in this literature. Instead, they used the cranial part for the intra-coccygeal angle and the caudal part for the sacrococcygeal angle. Despite that, they gave the results as the dynamic changes of angles, so there is no confusion about the measurement method. Therefore, we think that this new classification is noteworthy in this respect.

In summary, there is confusion about the measurement and estimated values of the intra-coccygeal angle. Radiologists should be aware of the differences and specify the method while reporting and/or in research.