The measurement of orbital blowout fractures cannot be made with geometric estimations

Background: The decision of whether to operate an orbital blowout fracture or not is, among other things, based on the size of the fracture.The volume and area of the fracture is often estimated using geometric figures and formulas.We compared this simplification with precise and/or proven methods to see if there was a need for consensus in how to do these measurements.Methods: This was a retrospective review of orbital blowout fractures in patients admitted to the Department of ENT and Head and Neck Surgery, Karolinska University Hospital, Stockholm, Sweden 2011-2015.In the computed tomographic (CT) images, the fractured area was measured with a proven method and the volume with a meticulous new method.The size of the same fracture was estimated with geometric formulas where the area was assumed to resemble an ellipse and the volume a hemi-ellipsoid.The results were visualized with Bland-Altman plots and accuracy, sensitivity and specificity were analyzed.Comparison was also made with volumes initially measured by radiologists.Results: Eighty-two patients were included from two on-going studies (43% women, 57% men; mean age 49.7 years (5-90 years)).Geometric approximations have high sensitivity and low specificity.The geometric formula for volume had an accuracy of 0.73 (specificity 0.50) and the radiologist's measurements of the volumes had an accuracy of 0.84. Conclusion:In the decision of whether to operate an orbital blowout fracture or not it is crucial to measure areas and volumes correctly.The use of geometric approximations can lead to overestimation of the size of the injury.Thus, patients may be exposed to the risk of an unnecessary operative repair.For this reason, simplifications are inadequate from a clinical perspective.The authors inference is that measurements should be made with accurate methods and not with geometric calculations to avoid misdiagnosis.An available, easy and quick method to do these measurements is awaited.