Imaging of hip trauma - occult, suspect and concomitant fractures

Abstract

Background: Between one and nine percent of all hip fractures are occult or suspect and further examinations with computed tomography (CT) and/or magnetic resonance imaging (MRI) are vital for further handling. Statistically robust conclusions have not been previously reported. Aims: To evaluate the extent to which the observer agreement (reliability) differs between different modalities and different observers; if high reliability for CT in the study cases reflects the actual fracture status (accuracy): if occult and suspect fractures are different entities and if experience influences the diagnostics; if exclusively pelvic fractures after low-energy trauma to the hip frequently occur and to what extent concomitant hip and pelvic fractures co-exist. Methods and Material: Patients with normal or suspect radiographs and with subsequent examination with CT and/or MRI were reviewed and scored by four observers with varying radiological experience. Statistical analyses were performed with linear weighted kappa (κ) statistics and chi-square tests. Results: Observer agreements for all interpreters were high for CT and MRI but the accuracy for CT was inferior to MRI – in the study cases. There was a higher rate of fractures among suspect than among occult cases, both at review of radiography and at MRI. At MRI there were frequent concomitant hip and pelvic fractures as well as exclusively pelvic fractures. Conclusions: Occult and suspect fractures are different entities. Experience improves the diagnostic performance for both radiography and CT but is of less importance for fracture diagnosis with MRI. The reliability of CT for an experienced reviewer is high but does not necessarily correlate with high accuracy in the study population. Exclusively pelvic fractures at MRI are common after hip trauma. Hip and pelvic fractures are not mutually exclusive.