Quantifying the Positional Deviation Between the True Flexion-Extension and Epicondylar Axes of the Elbow: A 3D Computational Study.

Background and objective The epicondyles are commonly used surgical reference landmarks for elbow arthroplasty and external fixator application. This study aimed to investigate whether the epicondylar axis differed from the elbow's true flexion-extension (F-E) axis in terms of both rotational difference and translational offset. Methods Three-dimensional (3D) models of 15 cadaver elbows were created. The epicondylar, true F-E, and distal humeral axes were defined using the medial and lateral epicondyles and the normal vector through the trochlear groove's center respectively. Rotational difference along internal-external, varus-valgus, and flexion-extension rotation plane and translational offset in the anterior-posterior (A-P), medial-lateral (M-L), and inferior-superior (I-F) direction with reference to the distal humerus's long axis were measured. Results Minimal rotational differences of 1.9 ± 4.5, 2.1 ± 3.4, and 0.5 ± 2.7 degrees for flexion-extension, varus-valgus, and internal-external rotation were obtained respectively. Considerable translational offsets greater than 10 mm were found for the absolute medial and lateral translational offset with a statistically significant difference recorded in the M-L direction. Conclusions Small rotational differences exist between the epicondylar and true F-E axes. Significant differences are observed in the translational offset in the M-L direction and should be considered during implant alignment in order to reduce malalignment and prevent failure.