A rapid prototyping model of Mason II fracture was used to investigate baseline recommendations for surgical intervention founded on kinematic forearm rotational blockage. Exact replicas of the radial heads in nine cadaveric specimens were produced and specimens were tested in a physiologic elbow simulator. After testing supination/pronation, the rotations were repeated with native replicas and with replicas modeling 3 mm depressed Mason II fractures with and without a gap of 1 mm between the body and fragment. The fragments were located circumferentially around the radial head at 10, 2 and 6 o'clock positions. There was no statistical difference between the range of motion of the native case and the native replica without fracture. After inclusion of the fracture, seven of the nine specimens showed rotational blockages. A two-way ANOVA found no statistical difference due to type of Mason II fracture (p > 0.87) or fracture location (p > 0.27). A x-square analysis showed that presence of a kinematic deficit with a fractured radial head was significant (p < 0.03). The results support continued surgical intervention for a 3 mm depressed fracture and also establish the use of the rapid prototype as a model for kinematic investigation of fractures in a cadaveric model when ligamentous attachments are preserved. ß