The Relationship Between The Ulnar Styloid Fracture And Distal Radioulnar Joint Stability: A Finite Element Study

Currently there is controversy about the treatment of ulnar styloid fractures.The main cause of this problem is shortage of biomechanical research and difference in the corpse model of the distal radioulnar joint.For the past few years the finite element analysis was developed rapidly,which overcame corpse model's shortcomings.The finite element analysis has been used in biomechanical research of shoulder joint, spine,hip joint and knee joint,and developed relevant models until now.But there is no report about the finite element model of the distal radioulnar joint.So the present study is designed to solve relevant problems.Objective1) To establish and validate the three-dimension finite element models of the distal radioulnarjoint,including radius,ulna,the interosseous membrane,the palmar radioulnar ligaments,the palmar radioulnar ligaments ulnotriquetral ligament,ulnolunate ligaments,pronator quadratus and the extensor retinaculum.2) To establish the three-dimension finite element models of ulnar styloid fracture and analyze the stress distribution and displacement of the distal radioulnar joint under normal situations,that is axial compression,transverse loading,pronation and supination.Materials and Methods1) An healthy male right forearm was scanned in the neutral position using computed tomography(CT) and MRI to collect the image data.The data was imported into simulation software mimics 10.0.Using the software mimics,the data was processed to generate geometric model of the distal radioulnar joint. Then the models were imputed into the software Imageware to be soomthing. According to the forearm kinematics,three geometric models of the radioulnar joint were set up,including pronation,supination,neutral.The models were imported into finite element analysis software Ansys to establish the finite element models,and the finite element models were meshed.At same time checked the element type and material properties were definited.2) The finite element models were constrained in all degrees of freedom on proximal radioulnar joint and loaded to mimic the normal loading conditions,that was an axial compression of 66.7N,an transverse tension of 66.7N,a prone load of 22N,and a supine load of 22N in neutral position,and a prone load of 22N in pronation,a supine load of 22N in supination,to analyze the stress distribution and displacement.3) A 1mm fracture gap was modeled using an idealized planar cut on ulnar styloid process,and on the base of ulnar styloid in another model.Four loading conditions were mimicked to analyze the stress distribution and displacement, that was an axial compression of 66.7N,a transverse tension of 66.7N,a prone load of 22N,and a supine load of 22N in neutal.Result1) Stress distribution of the finite element model of the distal radioulnar joint is similar to that of normal distal radioulnar joint.2) Stress distribution of the finite element model with ulnar styloid process fractures does not change,compared to the finite element model of the distal radioulnar joint,and the relative motion of the radius with respect to the ulna is similar too. Ulnar styloid base fractures result in obvious displacement of the radius with respect to the ulna.With increasing loading,the midpoint of the ulnar head articular surface translated beyond the margin of the sigmoid notch in either the dorsal or palmar direction.Conclusion 1) The present finite element models of the distal radioulnar joint can mimic biomechanics of the distal radioulnar joint effectively.2) Ulnar styloid process fracture does not cause distal radioulnar joint instability. Ulnar styloid base fracture results in distal radioulnar joint instability.