Vortical flow in human elbow joints: a three‐dimensional computed tomography modeling study

The human elbow joint has been regarded as a loose hinge joint, with a unique helical motion of the axis during extension–flexion. This study was designed to identify the helical axis in the ulnohumeral joint during elbow extension–flexion by tracking the midpoint between the coronoid tip and the olecranon tip of the proximal ulna in a three‐dimensional (3D) computed tomography (CT) image model. The elbows of four volunteers were CT‐scanned at four flexion angles (0°, 45°, 90°, and 130°) at neutral rotation with a custom‐made holding device to control any motion during scanning. Three‐dimensional models of each elbow were reconstructed and a 3D ulnohumeral joint at 45°, 90°, and 130° was superimposed onto a fully extended joint (0°) by rotating and translating each 3D ulnohumeral joint along the axes. The midpoints of the olecranon and coronoid tips were interpolated using cubic spline technique and the dynamic elbow motion was plotted to determine the motion of the helical axis. The means and standard deviations were subsequently calculated. The average midpoint pattern of joint motion from extension to flexion was elliptical‐orbit‐like when projected onto a sagittal plane and continuously translated a mean 2.14 ± 0.34 mm (range, 1.83–2.52 mm) to the lateral side during elbow extension–flexion. In 3D space, the average midpoint pattern of the ulnohumeral joint resembles a vortical flow, spinning along an imaginary axis, with an inconsistent radius from 0° to 130° flexion. The ulnohumeral joint axis both rotates and translates during elbow extension–flexion, with a vortex‐flow motion occurring during flexion in 3D model analysis. This motion should be considered when performing hinged external fixation, total elbow replacement and medial collateral ligament reconstruction surgery.