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Computed Tomography Analysis of Ulnar CMC Fractures Injuries Missed on Plain Film Radiographs and Significantly Changes Management
Jacqueline Rose Piggott, MD; Christopher Doherty, MD, FRCSC; Douglas Ross, MD, FRCSC
St. Joseph's Health Care Center, Western University, London, ON, Canada

Introduction: Intra-articular fractures of the ulnar carpometacarpal joints are most commonly assessed with plain film radiography. In a cadaver model, Viegas demonstrated that these injuries are often more complex than suggested by plain film evaluation alone. Plain film analysis is challenging due to overlapping bony architecture on lateral views. Inadequate restoration of articular congruity often leads to post-traumatic arthritis and poor functional outcomes. Computed tomography (CT) imaging is not routinely performed in pre-operative analysis, but does offer an accurate assessment of carpometacarpal (CMC) joint congruity, fracture displacement and subluxation. The purpose of this study is to identify significant differences in fracture analysis using computed tomography compared to plain films alone, and to identify any changes in proposed fracture management based upon different imaging modalities.

Materials & Methods: A retrospective chart review from a single surgeon's practice identified 15 patients with intra-articular ulnar CMC fractures. Two fellowship trained academic surgeons, two hand surgery fellows, and two senior residents independently assessed three standard radiographic views and as well as CT scan images. Evaluators assessed CT and plain film images separately in a blinded fashion and their assessments of each fracture were compared post-hoc. Images were reviewed in a standardized fashion for the following parameters: metacarpal injured, associated carpal fracture, and articular step > 2 mm. Based on each set of independently assessed plain films and CT images, reviewers chose a preferred method of fracture management.

Results: Inter-rater reliability for CT image analysis was 100% for all considered parameters (ICC = 1). On plain films, reviewers did not correctly identify which metacarpal was injured in 19% of patients. In addition, 70% of associated carpal fractures were missed. Reviewers failed to identify an intra-articular fracture in 23% of patients. A step deformity was incorrectly estimated in 50% of patients using plain film imaging. CT imaging changed fracture management in 49% of patients.

Conclusions: CT imaging leads to more accurate analysis of ulnar intra-articular CMC fractures. Plain film imaging misidentified the injured metacarpal with moderate frequency, and failed to reliably identify associated carpal fractures. Reviewers could not reliably determine whether the fractures were intra-articular using plain films alone, and plain film analysis lead to inaccurate estimation of articular step deformity when present. The information provided by CT imaging when compared with plain films lead to significant differences in management. Acquiring CT imaging during initial analysis of ulnar CMC fractures may significantly contribute to optimal management.

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