Type II coronoid fracture in a terrible triad elbow: An experimental study of the elbow kinematics using dynamic...

The aim of this study was to evaluate the elbow kinematics with and without a Regan-Morrey type II coronoid fracture in an experimental setting of terrible triad injury with intact collateral ligaments and radial head arthroplasty.

Eight human donor arms were examined following radial head arthroplasty with and without a 1/3 coronoid fracture by CT and dynamic radiostereometry during elbow flexion with the forearm in unloaded neutral position, and in supinated- and pronated position without and with 10 N either varus or valgus load, respectively. The elbow kinematics were described using anatomical coordinate systems.

The coronoid fracture changed the elbow kinematics. In the valgus loaded pronated forearm position, the radius shifted mean 1.7 mm (95 %CI 0.2; 3.2) posterior, and the ulna shifted mean 0.6 mm (95 %CI 0.0; 1.2) in the radial direction. In the unloaded supinated position, the radius shifted 0.8 mm (95 %CI 0.0; 1.5) posterior and 1.0 mm (95 %CI 0.4; 1.6) in the ulnar direction, while the ulna shifted 0.7 mm (95 %CI 0.1; 1.4) posterior. In the varus loaded supinated position, the radius shifted 1.4 mm (95 %CI 0.2; 2.6) in the ulnar direction.

The Regan-Morrey type II coronoid fracture imposed slight kinematic changes to the elbow joint, which may not be clinically relevant. This indicates that a type II coronoid fracture may not need fixation in the setting of optimal radial head arthroplasty with intact collateral ligaments. However, elbow stability should be evaluated intraoperatively in every terrible triad case.