RELIABILITY OF CT WITH OR WITHOUT HUMERAL SUBTRACTION IN DETERMINING CORONOID FRACTURE MORPHOLOGY

Anteromedial facet (AMF) fractures of the coronoid are associated with varus posteromedial rotatory instability (VPMRI) of the elbow. Accurate diagnosis of VPMRI is essential, as untreated, these injuries can lead to rapid and progressive post-traumatic arthritis. However, not all isolated coronoid fractures are associated with VPMRI. Medial obliquity of the fracture orientation and its concave morphology have been reported as critical characteristics of unstable AMF fractures.1,2 Although, computed tomography (CT) scan with three-dimensional (3D) reconstruction has been shown to improve interobserver agreement with respect to coronoid classification, the inter- and intra-observer reliability of CT scan with 3D reconstruction in determining the orientation and morphology of AMF fractures is unknown. This study aims to evaluate the inter- and intraobserver reliability of evaluating the orientation and morphology of AMF fractures using CT scans with 3D reconstruction. In addition, we aimed to determine whether 3D reconstruction with humeral subtraction views improved this reliability. CT scans of 51 patients with isolated coronoid fractures were evaluated by three orthopedic surgeons on two occasions separated by at least one week. Three CT scans were excluded due to pixelation affecting imaging quality leaving 48 CT scans for final review. In the first round CT scan images including 2D coronal, sagittal, and axial images as well as 3D images without the humeral subtraction views were evaluated. In the second round, the surgeons evaluated had access to 3D images with humeral subtraction views in addition to all the 2D and 3D views available in the first round. In each round, the fracture orientation was categorized as medial oblique or not (which included horizontal and lateral oblique fractures) and fracture morphology was categorized as concave or not (which included convex and flat fractures). The intraobserver agreement between the two rounds of evaluation and interobserver agreement between different observers were calculated. Regardless of imaging modality, the interobserver agreement between surgeons was moderate to fair. Additional 3D reconstruction with humeral subtraction views improved agreement on identifying both fracture morphology and orientation. The interobserver agreement on fracture orientation improved from 42% to 60% (P = 0.038) meanwhile agreement on fracture morphology improved from 48% to 50% (P = 0.42). In terms of intraobserver reliability, there was a trend toward a higher agreement with the years of practice of the surgeon, with the most senior surgeon average agreement of 75%, and the most junior surgeon average agreement being 58% (P =0.038). Although determining the orientation and morphology of AMF fractures are critical in radiographic evaluation of these injuries, agreement for evaluating these features even among upper extremity trained surgeons remains moderate to fair. Addition of 3D reconstruction CT images with humeral subtraction views improves surgeon's ability to appropriately determine AMF fracture characteristics which may impact management decision-making in these challenging fractures. Further studies are needed to better characterize coronoid anteromedial facet fractures.