Value of CT to detect radiographically occult injuries of the proximal femur in elderly patients after low-energy trauma: determination of non-inferiority margins of CT in comparison with MRI
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To determine the margins of non-inferiority of the sensitivity of CT and the sample size needed to test the non-inferiority of CT in comparison with MRI.
Materials and methods
During a 2-year period, elderly patients with suspected radiographically occult post-traumatic bone injuries were investigated by CT and MRI in two institutions. Four radiologists analyzed separately the CT and MRI examinations to detect post-traumatic femoral injuries. Their sensitivities at CT (SeCT) and MRI (SeMRI) were calculated with the reference being a best valuable comparator (consensus reading of the MRI and clinical follow-up). ROC analysis followed by an exact test (Newcombe’s approach) was performed to assess the 95% confidence interval (CI) for the difference SeCT–SeMRI for each reader. A sample size calculation was performed based on our observed results by using a one-sided McNemar’s test.
Twenty-nine out of 102 study participants had a post-traumatic femoral injury. SeCT ranged between 83 and 93% and SeMRI ranged between 97 and 100%. The 95% CIs for (SeCT–SeMRI) were [− 5.3%, + 0.8%], (pR1 = 0.1250), [− 4.5%; + 1.2%] (pR2 = 0.2188), [− 3.4%; + 1.1%] (pR3 = 0.2500) to [− 3.8%; + 1.6%] (pR4 = 0.3750) according to readers, with a lowest limit for 95% CIs superior to a non-inferiority margin of (− 6%) for all readers. A population of 440 patients should be analyzed to test the non-inferiority of CT in comparison with MRI.
CT and MRI are sensitive for the detection of radiographically occult femoral fractures in elderly patients after low-energy trauma. The choice between both these modalities is a compromise between the most available and the most sensitive technique.
• The sensitivity of four separate readers to detect radiographically occult post-traumatic femoral injuries in elderly patients after low-energy trauma ranged between 83 and 93% at CT and between 97 and 100% at MRI according to a best valuable comparator including MRI and clinical follow-up.
• CT is a valuable alternative method to MRI for the detection of post-traumatic femoral injuries in elderlies after low-energy trauma if a 6% loss in sensitivity can be accepted in comparison with MRI.
• The choice between CT and MRI is a compromise between the most available and the most sensitive technique.
KeywordsHip fractures Elderly patients Computed Tomography Magnetic resonance imaging
Area under the curve
Magnetic resonance imaging
Negative predictive value
Picture archiving and communication systems
Positive predictive value
Receiver operating characteristic
Short tau inversion recovery
The authors state that this work has not received any funding.
Compliance with ethical standards
The scientific guarantor of this publication is B. Vande Berg.
Conflict of interest
The authors of this manuscript declare no relationships with any companies whose products or services may be related to the subject matter of the article.
Statistics and biometry
One of the authors (N Michoux) has significant statistical expertise.
Written informed consent was obtained from all subjects (patients) in this study.
Institutional Review Board approval was obtained from the two participating institutions.
• Diagnostic or prognostic study
• Multicenter study
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