The variety of experimental setups used during in vitro testing of distal radius fracture treatments impairs interstudy comparison and might lead to contradictory results. Setups particularly differ with respect to their boundary conditions, but the influence on the experimental outcome is unknown. The aim of this biomechanical study was to investigate the effects of 2 common boundary conditions on the biomechanical properties of an extra-articular distal radius fracture treated using volar plate osteosynthesis. Uniaxial compression tests were performed on 10 synthetic radii that were randomized into a proximally constrained group (ProxConst) or proximally movable group (ProxMove). The load was applied distally through a ball joint to enable distal fragment rotation. A significantly larger (ProxConst vs ProxMove) stiffness (671.6 ± 118.9 N·mm−1 vs 259.6 ± 49.4 N·mm−1), elastic limit (186.2 ± 24.4 N vs 75.4 ± 20.2 N), and failure load (504.9 ± 142.5 N vs 200.7 ± 49.0 N) were found for the ProxConst group. The residual tilt did not differ significantly between the 2 groups. We concluded that the boundary conditions have a profound impact on the experimental outcome and should be considered more carefully in both study design and interstudy comparison.
Alexander Synek is with the Department of Trauma Surgery, University Hospital of Munich, Campus Innenstadt, Munich, Germany; and the Institute of Lightweight Design and Structural Biomechanics, Vienna University of Technology, Vienna, Austria. Yan Chevalier and Christian Schröder are with the Laboratory for Biomechanics and Experimental Orthopaedics, Department of Orthopaedic Surgery, Physical Medicine and Rehabilitation, University Hospital of Munich, Campus Grosshadern, Munich, Germany. Dieter H. Pahr is with the Institute of Lightweight Design and Structural Biomechanics, Vienna University of Technology, Vienna, Austria. Sebastian F. Baumbach is with the Department of Trauma Surgery, University Hospital of Munich, Campus Innenstadt, Munich, Germany.