The Effect of Angulated Radius Fractures in Forearm Rotation: A Computer Based Model

Background: Forearm fractures amongst children are quite a common presentation. The accuracy of correct alignment in forearm bones is important as it determines the degree of forearm rotation (pronation-supination). However in children due to the potential for continuous growth, a degree of angulation is acceptable. The aim of this study was to determine the effect of angulation of forearm fracture on forearm rotation using computer stimulation. Methods: Using a 3D computer modelling software (Wildfire Pro Engineer 4.0, Creo by PTC, Needham, MA), an accurate to scale model of the radius and ulna was replicated from a 7 year old forearm. A realistic representation of pronation/supination of the forearm was applied and a fracture at the junction of proximal one third and distal two third was created. A rotational simulation was created and ended when maximum pronation and supination was reached. Maximum pronation and supination was reached when either no more rotation could occur due to a misalignment of the radius and ulna or there was a collision of the bones. The simulation was repeated in increments of angulation of 2° up to 26°. The angulations that resulted in a combined range of motion (50° pronation and 80° supination) less than 130° were recorded as unacceptable and the others were as acceptable. Findings: The study showed that radius angulation fracture of >16° in the proximal third of the radius would result in an unacceptable reduction of pronation-supination to less than 130°. Conclusion: Patients with more >16° of radius angulation in a distal third shaft fracture of the radius may result in clinical reduction in forearm rotation.