We read with interest the study by Zhuang et al on levator avulsion using tomographic ultrasound and the magnetic resonance-based model.

The number of complete and partial avulsions seen on transperineal scan and magnetic resonance imaging (MRI) are shown in Table 2. However, it is not clear whether these avulsions on transperineal ultrasound correspond to that seen on MRI. Are these the same patients? Is the extent of the avulsion different between the 2 techniques? The number of partial defects detected on tomographic ultrasonography do not add up to a total of any partial defect (n = 5): unilateral left (n = 3), unilateral right (n = 5), and bilateral (n = 3).

The Marginal Homogeneity Test showed that the extent of avulsion that had been justified by the 2 methods was different. Tomographic ultrasound scanning yielded a higher number of complete avulsions; the magnetic resonance-based models identified a higher number of partial avulsions ( P < .05). This means that there is a statistically significant difference between the 2 methods, which implies that the methods cannot be used interchangeably. Borderline significance and trends can be recognized if exact P values are provided rather than P < .05.

Kappa statistics are very affected by whether the marginals are homogeneous and it would appear from Table 3 that there is a lack of homogeneity. Interestingly, the authors conclude that the 2 methods used for diagnosis of avulsion correlate well with each other with respect to the extent of the avulsion. However, there was only moderate correlation between the 2 methods. The explanation the authors give is that defects appear best defined on levator ani contraction and that the use of volumes that are obtained on contraction may also improve detection. As correlation is not the same as agreement it would have been more appropriate to analyze the agreement of the measurements by using the Bland-Altman analysis for example.

By contrast, Majida et al have proven that there is good agreement between the perineal ultrasound and MRI in nulliparous volunteers in the resting position. Results of agreement in resting position of women with pelvic organ prolapse would be interesting. Finally, the interpretation of the risks of over diagnosing levator defects using transperineal ultrasonography and potential consequences for the patients are not highlighted. This is extremely important, particularly where receiver operating characteristic curves are being analyzed and a value giving a point close to the top left of the receiver operating characteristic curve chosen because of high sensitivity and specificity.