Abstract: BACKGROUND: There are many effective treatments for humerus shaft fractures caused by grenade throwing, such as non-operative treatment using hanging cast, operative treatment using locking plate, screw and intramedullary nail. However, it is reported by our team for the first time that using absorbable screw and ethibond suture for the treatment.  
OBJECTIVE: To evaluate the stabilization of fractures which are long-spiral humeral shaft fractures caused by grenade throwing fixed with absorbable screws and ethibond sutures in the method of finite element analysis, and provide evidence for clinical application.
METHODS: CT data of humerus of a volunteer in Department of Orthopedics, 923 Hospital of Chinese People’s Liberation Army Joint Logistic Support Force were collected. Finite element models of the same fracture with different fixities which were limited contact dynamic compression plate (plate group), absorbable screws (screw group), and absorbable screws with ethibond sutures (combination group) were established. Three working conditions were set up: (1) humeral head was fixed and distal humerus was applied compressive force of 300 N. (2) Humeral head and distal humerus were fixed and the middle part was applied bending load of 350 N. (3) The humeral head was fixed and distal humerus was applied torsion load of 15 N•m. The maximum displacement of fracture surface, the average equivalent stress of fracture surface and the maximum equivalent stress of absorbable screw were assessed in three working conditions. 
RESULTS AND CONCLUSION: (1) Under compression, bending or torsion loading, the maximum deformations of fracture surface of the model in the screw group were 0.52, 0.27, and 0.544 mm, respectively, and 0.51, 0.25, and 0.396 mm in the model of the combination group. The maximum deformations of fracture surface of the model of the plate group were 0.495, 0.234, and 0.393 mm. (2) The mean values of von-Mises stress distribution of fracture surface of the model of the screw group were 5.964, 4.512, and 24.176 MPa, respectively. They were 5.651, 4.601, and 21.465 MPa in the model of the combination group, and 1.210, 4.048, and 13.537 MPa in the model of the plate group. (3) The total deformation in the plate group was the smallest, and that in the combination group was close to that in the plate group; the average effective stress of the fracture surface in the combination and screw groups was higher than that in the plate group. (4) The results verify that according to the results of the experiment in the method of finite element analysis, the fracture stability is satisfactory if using absorbable screws and ethibond sutures to fixate long-spiral humeral shaft fracture. Moreover, the stress-shielding effect is lower than that of dynamic compression plate, and advantageous for fracture union and preventing partial osteoporosis.

Key words: bone, humerus, fracture, absorbable screw, finite element analysis, fracture surface, load, von-Mises stress, total deformation