Can follow-up radiography for acute scaphoid fracture still be considered a valid investigation?
Introduction
Suspected scaphoid fracture is difficult to confirm by clinical examination due to lack of specific clinical signs1, 2, 3 hence, the need for imaging to provide a correct diagnosis. Many imaging techniques have been used to improve upon the diagnostic accuracy of plain radiography. In addition to plain radiographs, panoramic radiography, modified carpal box radiography, ultrasound, computed tomography (CT), bone scintigraphy and magnetic resonance imaging (MRI) have all been advocated.
However, plain radiography remains the commonest method of diagnosis. The majority of patients with suspected scaphoid fractures will present to an accident and emergency department where initial radiographs will be obtained. If the radiographs are normal, standard practice is to treat clinically suspected scaphoid fractures by immobilization and to repeat the radiographs 10–14 days later.4 The theory is that during this period the fracture will become visible on radiographic images due to resorption around the fracture line.5 Several authors have contested the validity of this approach.6, 7, 8
Several studies suggest sensitivity and specificity approaching 100% for MRI in detecting occult scaphoid fractures.9, 10, 11 MRI has also been reported to be reliable,10, 11, 12 with kappa statistics (kappa values of 0.95, 0.87 and 0.80) showing satisfactory inter-observer agreement. MRI can justifiably be regarded as the gold standard investigation for clinically suspected scaphoid fracture.13
It was the aim of this retrospective study to determine whether follow-up radiography, performed in the context of a clinically suspected scaphoid fracture with normal initial radiographs, can continue to be considered a valid investigation. For the first time to our knowledge, a combination of MRI as the gold standard to measure the sensitivity and specificity of plain radiography, and reliability variance analysis to assess the inter-observer agreement is used.
Section snippets
Material and methods
Ethics committee study approval was obtained. This retrospective study included patients with suspected scaphoid fracture sustained after acute trauma, who presented to our institution from 1 January 1999 to 20 May 2004. Patients were selected if they had the combination of a normal/equivocal initial radiograph, a follow-up radiograph performed between 10–50 days after injury and a wrist MRI.
Initial scaphoid radiographs were performed using three standard projections: Lateral wrist,
Results
A reliability coefficient of more than 60% is needed for a diagnostic test to be considered reliable.14, 15 Overall, the inter-observer reliability coefficient was 33%. Pair-wise inter-observer reliability coefficients ranged from 18% (observers B and C) to 53% (observers C and D) (Table 1).
Table 2 lists the MRI findings together with the results of the follow-up radiograph evaluation by the four observers, including diagnostic test statistics with 95% confidence intervals. These results show
Discussion
A meta-analysis by Hunter et al.,11 of 2440 patients from 10 large studies, showed that scaphoid fractures may be initially radiographically occult in 16% of cases when confirmed by follow-up radiographs. A study of 195 patients reported similar results,13 with an incidence of occult fracture of 19% demonstrated by MRI within 14 days of injury.
Other studies, however, have found that follow-up radiography is much poorer in detecting scaphoid fracture. Leslie and Dickson,16 in a study of 222
Acknowledgements
The authors thank Dr Robert Shaw, Dr Greg O'Neil, Mr Patrick Grant and Mr James Crossan for their valuable contributions as expert observers in our study. In addition, the authors also thank Mr Alexander McConnachie of the Robertson Centre for Bio-statistics, University of Glasgow, for providing valuable statistical advice and analysis.
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