The base of the coronoid as a reliable anatomical reference for elbow axis of rotation: evidence from a cadaveric study

Coronoid fracture characterization is crucial in treatment decision-making. The base of the coronoid is a fundamental reference used for fracture classification and to perform measurements to quantify fragment size, both of which guide the decision to proceed with surgical intervention. Furthermore, computed tomography used for fracture analysis relies on the acquisition of planar images aligned with specific anatomical axes, which should be referenced to the ulna rather than the humerus to minimize variability introduced by the flexion-extension positioning or ulno-humeral alignment. We defined the base of the coronoid axis (BCA) as the line connecting the posterior limits of the sublime tubercle and the lesser sigmoid notch, proposing it as a reference for ulnar-based computed tomography planar reconstructions and to be used as a reference for coronoid measurement. Based on empirical observations, we hypothesized that the BCA may be parallel to the humeral interepicondylar axis (HIEA), supporting the BCA not only as a reliable reference for image studies, but also as a surrogate for locating the elbow flexion-extension axis of rotation relative to the forearm. Our aim was to evaluate this hypothesis. The aim of the study was to evaluate the parallelism between the BCA and the elbow flexion-extension axis of rotation, known as the HIEA using a cadaveric model. Ten Thiel-embalmed cadaveric arms were instrumented with Kirschner wires (K-wires) placed along the BCA and the HIEA axes. The full arc of elbow flexion-extension arc of motion as recorded simultaneously using 3 cameras positioned laterally, superiorly, and posteriorly. The angle between the 2 K-wires (angular variation) was measured in the videos using analysis software (Kinovea) capturing changes in angular variation between axes at millisecond intervals. Axial parallelism was defined as an angular variation of less than 5°(parallel axes) and/or a statistical range of less than 5° (indicating the axes lie within parallel planes) throughout the entire range of motion. Ninety percent and 80 percent of specimens demonstrated an angular variation of less than 5° in the superior and posterior views, respectively. In both video recordings, all specimens exhibited a statistical range of less than 5°. The line intersecting the posterior aspects of the sublime tubercle and the lesser sigmoid notch - defined as BCA - and the elbow joint's axis or rotation - represented by the HIEA - were either parallel in 85% of the recordings or lay in parallel planes in the remaining cases throughout the entire flexion-extension arc of motion.