Rheumatology Advance Access originally published online on April 29, 2008
Rheumatology 2008 47(7):1107-1108; doi:10.1093/rheumatology/ken133
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Comment on: Comparing morphometric X-ray absorptiometry and radiography in defining vertebral wedge fractures in patients with ankylosing spondylitis
1Rheumatology Department, 2MRC Epidemiology Resource Centre and 3Osteoporosis Centre, Southampton General Hospital, Southampton, UK
Correspondence to: A. Scott-Russell, Rheumatology Department, Southampton General Hospital, Southampton, SO16 6YD, UK. E-mail: annscottrussell{at}hotmail.com; emd{at}mrc.soton.ac.uk
SIR, we read with interest the paper by Vosse et al. [1] published in your November issue, detailing a comparative study of morphometric X-ray analysis (MXA) and radiography in defining vertebral wedge fractures in patients with AS. We would like to report our experience with general rheumatology patients here.
We studied 46 patients referred to the osteoporosis centre at Southampton General Hospital for an MXA scan who had also undergone a lumbar spine X-ray (MRX) (T12–L4) within 6 months of the scan. Using a 6-point semi-quantitative analysis [2], we were able to both compare the intravertebral assessment (IVA) with the plain radiograph and review the X-ray report provided by the radiology department under usual clinical care. The same investigator (A.S.-R.) analysed both the radiographs and MXA, using a cut-off ratio Ha/Hp or Hm/Hp of 0.8 to define fracture.
Among this group, 31 patients had no fracture on either radiograph or MXA, using the aforementioned criteria. However, three of these X-rays had been reported as showing a fracture. The remaining 15 patients had a total of 21 fractures on X-ray analysis of which 20 correlated exactly on MXA and MRX (Table 1). The prevalence of vertebral fracture in our population was 33%.
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If we assumed MRX to be the gold standard then the sensitivity, specificity, positive predictive value and negative predictive value of MXA was 95, 88.5, 83 and 97% respectively.
In clinical practice, a doctor frequently relies upon the X-ray report. We went on to look at the correlation between the X-ray report and MRX using the latter as the gold standard (Table 1). The sensitivity, specificity, positive predictive value and negative predictive value of the usual X-ray report was 73, 83, 73 and 83% respectively.
In this pragmatic study, we would reiterate Vosse et al.'s [1] suggestion that the negative predictive value of MXA is high, and therefore if no fracture is found, further imaging is not required, although we would acknowledge that standard radiograph analysis is not necessarily the gold standard in detecting lumbar vertebral fracture, and indeed MXA may pick up some additional fractures. The extent of agreement is dependent on the strictness of the definition of fracture used. We feel MXA has a place aiding quick assessment of fracture risk with less radiation exposure than conventional radiographs, especially in the analysis of the lumbar spine.
Disclosure statement: The authors have declared no conflicts of interest.
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- Vosse D, Heijckmann C, Landewe R, van der Heijde D, van der Linden S, Geusens P. Comparing morphometric x-ray absorptiometry and radiography in defining vertebral wedge fractures in patients with ankylosing spondylitis. Rheumatology (2007) 46:1667–71.
[Abstract/Free Full Text] - Genant HK, Wu Cy, Kujik van C, Nevitt MC. Vertebral fracture assessment using a semi-quantitative technique. J Bone Miner Res (1993) 8:1137–46.[Web of Science][Medline]
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  D. Vosse, C. Heijckmann, R. Landewe, D. van der Heijde, S. van der Linden, and P. Geusens Comment on: Comparing morphometric X-ray absorptiometry and radiography in defining vertebral wedge fractures in patients with ankylosing spondylitis: reply Rheumatology, July 1, 2008; 47(7): 1108 - 1109. [Full Text] [PDF]
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