J Neurosurg Spine Volume 26 • June 2017 765 LETTERS TO THE EDITOR Neurosurgical Forum J Neurosurg Spine 26:765–769, 2017 The ancient “apples and oranges” conundrum: a call for methodological precision TO THE EDITOR: In a recently published article, Gil- lis et al. 1 proposed to analyze the improvement in several radiographic parameters in patients submitted to 1- and 2-level anterior cervical discectomy (ACDF) with lor- dotic cages through measurements performed on lateral radiographic images at 3 time points: preoperatively, at 6 weeks, and at 1 year postoperatively (Gillis CC, Kaszuba MC, Traynelis VC: Cervical radiographic parameters in 1- and 2-level anterior cervical discectomy and fusion. J Neurosurg Spine 25:421–429, October 2016). In such a study, although accuracy may not be a key concern (as radiographs obtained with 10° of neck exten- sion may be interpreted as neutral if all further measure- ments are performed on similar radiographs with 10° of extension), precision (i.e., the consistency between differ- ent measurements) is of paramount importance in order to avoid comparisons between images that are simply not comparable. Although the article presents an extensive description of the obtained radiographic measurements, a simple anal- ysis of Figs. 1 and 2 generates serious questions about the methodological quality of the performed measurements, especially regarding their precision. For instance, Fig 1A and B, which are clearly not perfect lateral radiographs (as it can be noted by the double shadow of the facet joints, arrows in Fig. 1B), are compared with a perfect lateral radiograph (Fig. 1C, properly overlapping facets). More concerning than that is the fact that, while Fig. 1A seems to be a neutral radiograph, Fig. 1B already demonstrates some degree of cervical extension, which becomes much more pronounced in Fig. 1C (a measured difference of 9° between Fig. 1A and 1C). This discrepancy becomes even FIG. 1. Reprint of Fig. 1 from the article, with the black lines and degree measurements and the white arrows added to originals. The angle between C-1 and the superior endplate of C-5 was measured on the preoperative image as well as at the 1-year follow-up (note that the same lines used by the authors were used in order to avoid even minimal discrepancies in the measurements). There is a change from 28° to 37° at the angle of C1–5 between the preoperative and postoperative images, confrming that the postoperative radiograph was obtained 9° in extension in relation to the preoperative radiograph. Also note that the mandible/bite line is also not parallel to the ground in panel A, as it is in panel C. Please also note the double shadow of the facet joints in panels A and B ( white arrows), confrming that the radiograph is not a per fect lateral as it is in panel C. Modifed from Gillis et al.: J Neurosurg Spine 25:421–429, 2016, with permission. Figure is available in color online only. Unauthenticated | Downloaded 09/18/21 11:09 PM UTC