To investigate the changes of muscle force and the biomechanics of the humeralstress and displacement in the pronation and supination motions of the forearm.

A three-dimensional reconstruction of humerus was performed based on Dicom data by Mimics Mesh division and material assignment were carried out in Hypermesh. According to the height and weight of volunteers, the musculoskeletal model of volunteers' individualized upper limbs was established by AnyBody. The pronation and supination of forearm were simulated. The muscle force and constraint conditions during the motion were derived. The derived data were taken as the boundary conditions of finite element analysis. Finally, the analysis of the force and displacement of the humerus was performed by Abauqus.

The forearm 0°-90°pronation motion mainly plays a role in pronator teres muscle and pronator quadratus muscle. The pronator teres and pronator quadratus muscle force is the largest when the pronator is about 90°and 40°, respectively. The forearm 0°-90°supination movement is mainly caused by the supinator and biceps muscles. The muscle force of the two groups is maximum at about 90° supinator. When the pronation motion is about 90°, the stress and displacement of the humerus are the largest; when the supination is about 10°, the stress and displacement of the humerus are the largest. The stress is concentrated approximately in the lower third of the humerus; the displacement is concentrated in the middle and distal ends of the humerus, and is most prominent at the distal end of the humerus.

Using AnyBody musculoskeletal system, the forearm pronation and supination motion is successfully simulated and synchronized by finite element analysis, the humeral stress and displacements are analyzed by loading, which shows the mid low part of humerus is the prone site of fracture.