Ulnoradial transfixion applied for the treatment of acute distal radioulnar joint instability in sagittal plane; determining the distance of the distal radioulnar joint of the optimal placement location and the most proximal location where it is functional "finite element analysis study"

In this study, in static fixation of ulnoradial transfixion with using Kirschner (K) wire, the most stable fixation that will enable physiological ligamentous healing is obtained, especially by limiting the supraphysiological palmar-dorsal translation in the sagittal plane and rotation in the axial plane of the distal radioulnar joint (DRUJ) and it is aimed to determine the distance from the most proximal location where the K wire is functional to the DRUJ. By using the finite element analysis method, the most proximal level where the radius and ulna are in relation in DRUJ was determined in palmar unstable and dorsal unstable injury models after developing intact DRUJ models when the forearm is in pronation and supination, palmar unstable DRUJ models when the forearm is in supination and dorsal unstable DRUJ models with the forearm is in pronation. After placing a K wire for ulnoradial transfixion at this location which was detected in both models, nine K wires were placed parallel to the first K wire in the transverse plane at 5 mm. intervals. Thus ten ulnoradial transfixion models were developed in palmar unstable and dorsal unstable models. After force of 68 Newtons was applied in the twelve forearm supination models from the dorsal of the ulna head to the palmar and in the twelve forearm pronation models from the palmar of the ulna head to the dorsal, the displacement distances of the ulna head were evaluated. The amount of displacements of the ulna head was developed while the forearm was in supination were detected to 0,45 mm in intact DRUJ model, 3,5 mm in palmar unstable model representing palmar DRUJ injury and in each of the ten ulnoradial transfixion models developed by placing K wires on the palmar unstable model; respectively from model 1 to model 10 0,08, 0,17, 0,33, 0,45, 0,65, 0,82, 1, 1,19, 1,3, 1,38 mm. The amount of displacements of the ulna head was developed while the forearm was in pronation were detected to 0,42 mm in intact DRUJ model, 2,1 mm in dorsal unstable model representing dorsal DRUJ injury and in each of the ten ulnoradial transfixion models were developed by placing K wires on the dorsal unstable model; respectively from model 1 to model 10 0,17, 0,24, 0,32, 0,42, 0,49, 0,52, 0,55, 0,57, 0,58, 0,6 mm. The results of the study, in both palmar DRUJ injury and dorsal DRUJ injury models, the optimal location of the K wire placed for ulnoradial transfixion is just proximal to the sigmoid notch of radius and the most proximal location where the K wire is functional is proximal to 21 mm. from the DRUJ were determined. Key words: Distal radioulnar joint, ulnoradial transfixion, radioulnar ligaments, interosseous membrane, finite element analysis