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Cleveland Clinic Spine Institute
Cleveland, OH
We read with interest the article written by Choe et al. [1]. We agree that extensive radiographic studies and careful review are important in detecting cement emboli. We however note that in spite of the extensive radiographic analyses presented by Choe et al., their study methods and the results as presented are confusing and uninterpretable. As reported throughout the article, the number of levels and patients treated by either vertebroplasty or kyphoplasty was inconsistent. As such, it is impossible to conclude that "pulmonary embolism of cement is seen in 4.6% of patients after percutaneous vertebroplasty or kyphoplasty."
To clarify their contentions we propose the followings questions to the authors: First, exactly how many of the patients whose chest radiographs were obtained underwent vertebroplasty or kyphoplasty? Second, in the Results and Conclusion sections, the authors mention that they found emboli of cement on radiographs from three (4.6%) of 65 procedures. Were they all vertebroplasty procedures? Third, exactly what was the rate of neurologic complications related to cement leak associated with each technique?
Considering that there is no mention of the proportion of patients who underwent each augmentation technique, how and with what statistical method did the authors conclude that kyphoplasty does not reduce the rate of cement leak (vertebroplasty vs kyphoplasty, p = 0.98).
We look forward to the authors' response.
References
M. D. Anderson Cancer Center
University of Texas
Houston,
TX
My coauthors and I thank you for the opportunity to bring more attention to the topic of cement emboli in vertebroplasty and kyphoplasty. The answers to most of your questions are stated in the article [1] as follows. The answer to question 1 is on page 1098, second paragraph: 62 patients had chest radiographs and underwent either vertebroplasty or kyphoplasty in 65 sessions (three patients had two separate sessions). Thus, as explained in the original article on page 1099, first sentence: Because three patients developed cement emboli from these 65 sessions, the complication rate was 4.6%.
Regarding question 2, of the three patients who had procedures in our institution and developed cement emboli, two had vertebroplasty and one patient had kyphoplasty.
As to question 3, the purpose of this study was to determine the frequency of pulmonary cement emboli as detected by chest radiographs and their clinical significance. The intent was to bring to the attention of general and chest radiologists the radiographic appearance of such cement emboli because they may be increasingly encountered with the increased use of vertebroplasty and kyphoplasty. Thus, local and neurologic complications from these procedures were beyond the scope of our article [1].
In regard to question 4, as stated in the first sentence of the Results section, page 1098, 88 vertebral bodies were treated by vertebroplasty and 25 were treated by kyphoplasty. As you requested further information, of the patients that were treated at our institution: 44 patients had vertebroplasty, 15 patients had kyphoplasty, and three patients had both procedures. When calculating the risk of developing a cement embolus from each type of procedure, the latter three patients were excluded from this statistical calculation. The statistical test used to look for a correlation between cement emboli and the type of procedure was mentioned in the original article in the Materials and Methods section, on page 1098, middle column: the chi-square test.
My coauthors and I did not conclude, however, as stated in question 4, that "kyphoplasty does not reduce the rate of cement leak;" my coauthors and I merely stated that no correlation was found between the risk of developing a cement leak and the type of procedure (page 1099). Although this statement may have a similar meaning, we would like to stress that to reach a conclusion of a protective effect of any procedure, with fewer than a handful of complications, would not be correct and we did not attempt to do that. Because the pulmonary complication rate is low, one would have to assess thousands of cases to reach sound statistical proof that one procedure is safer than the other.
References
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