Three-dimensional motion analysis of a total wrist prosthesis during the dart-throwing motion: a cadaveric study

Total wrist arthroplasty offers an alternative to wrist arthrodesis by preserving motion while relieving pain, and understanding its functional performance is clinically important. The DARTS wrist prosthesis, approved for clinical use in Japan in 2017, was designed to reproduce the physiological dart-throwing motion through its semi-constrained structure and ovoid carpal component. Because this motion is essential for wrist function, it is important to determine whether the prosthesis can adequately replicate it. This study analyzed the detailed kinematics of the DARTS wrist prosthesis during wrist flexion and extension using three-dimensional (3D) motion analysis in five fresh-frozen cadaveric upper limbs. Each specimen was fixed with the elbow at 90 degrees and the forearm in a neutral position, and intermittent fluoroscopic imaging was performed before and after implantation. A two-dimensional/3D registration technique with a metal marker placed on the radial component allowed precise evaluation of prosthetic motion. The coupling slope changed from -0.50 before implantation to -0.33 after implantation while preserving the characteristic directional coupling pattern of the dart-throwing motion. These findings suggest potential benefits for postoperative wrist function, and provide valuable insights for rehabilitation, future prosthesis improvements, and the dynamic analysis of other models using this method.