Evidence for the Utility of Imaging of FAI

Abstract

Femoroacetabular impingement (FAI) remains predominantly a radiographic diagnosis in symptomatic patients, which justifies the need for imaging in order to appropriately assess the severity and location of lesions associated with FAI. There are four (4) essential plain radiographic views to order: AP pelvic, Dunn lateral, frog-leg lateral, and false-profile views. The essential radiograph for the diagnosis of pincer-type FAI is the AP pelvis on which the center-edge angle and crossover sign can be assessed. Both these parameters have exhibited moderate intra- and interobserver reliability, as well as acceptable sensitivity and specificity. The Dunn lateral view is helpful for the diagnosis of cam-type FAI, on which the alpha angle can be assessed. This parameter has demonstrated good intra- and interobserver reliability, as well as good sensitivity and specificity. Computed tomography (CT) (especially 3D reconstructions) is very helpful in further defining bony morphology around the hip. It better characterizes and confirms FAI subtypes, which in turn is crucial in surgical planning. Magnetic resonance imaging (MRI) (with or without arthrography, MRA) is a useful adjunct to plain radiographs and CT in assessing the sequelae of FAI, specifically edema patterns, cartilage, and labral lesions.