Biomechanics of the distal radioulnar joint with a malaligned distal radius

Distal radius fractures are the most common fractures in humans and frequently have suboptimal outcomes, fostering considerable discussion with regard to treatment. This body of work was based on the postulate that quantifying the biomechanics, specifically the kinematics and loading of the distal radial ulnar joint (DRUJ) before and after simulated distal radius malalignment would provide important new information to the treatment of these fractures. Furthermore, an investigation into the effect of soft-tissues would further the biomechanical understanding of these disorders.;A series of in vitro studies employing simulated muscle loading to produce forearm rotation were conducted using an upper extremity joint simulator. The distal radial implant and ulnar load cell were implanted and an electromagnetic tracking device was used to record the motion of the radius and ulna. The kinematics and joint loading of the native forearm were measured at the beginning of each testing and compared with simulated distal radial deformities.;As the severity of distal radial deformities worsened, a gradual loss of forearm rotation, a progressive change in kinematic patterns and an increasing alteration in the load transfer at the distal ulna was quantified. No absolute threshold in distal radial deformity was noted before joint dysfunction was markedly disturbed. This is in agreement with clinical findings as patients with malunited Colles' fractures often present with reduced range of motion, joint stiffness and pain, suggesting that this pain may be in part be due to the increase in joint loading required to generate forearm rotation.;Sectioning the triangular fibrocartilage complex, which is commonly injured in association with distal radial fractures, restored rotation and reduced the loading on the joint; however, this resulted in greater alteration of DRUJ kinematics.;In light of the foregoing, a distal radial implant to simulate malalignment in vitro was designed and developed. An instrumented ulnar load cell was also employed to measure the load transfer at the distal ulna.;In conclusion, this work has provided valuable information to assist biomechanists and clinicians in understanding the implication of both osseous and soft tissue disorders of the distal radius and provides better evidence to improve patient outcomes.;Keywords: distal radioulnar joint; kinematics; joint load transfer; load cell; implant design.