Objective To investigate the effects from head angle and locking times of locking screws on mechanical properties of the screw-plate system, so as to provide a theoretical basis for doctors to select appropriate locking screws and master the locking times in clinical surgical procedure. Methods Locking screws with different head angles were selected to match with locking compression plates in the case of different locking times, and cantilever bending method was used to compare the differences of mechanical properties in each group. Results There were significant differences in failure load and bending stiffness between locking compression plate and locking screw with different head angles (P<0-05). The mechanical properties of the screw-plate system with the best locking degree were optimum. There was no significant difference between 3 time-locking and 1 time-locking (P>0-05). The failure modes of locking screw with different head angles and different locking times were different, and the failure mode of locking screw had a positive correlation with its head angle and locking times. Conclusions The differences in mechanical properties between locking screw with different head angles and locking compression plate cannot be neglected. It is suggested that doctors should choose locking screw and locking compression plate with the best locking degree in clinical procedure, and choose the right torque wrench to lock in multiple times if necessary, thus to prevent screw loosening from affecting recovery of the patients.

Objective To compare biomechanical properties between the anatomical clavicle plate and the reconstructed clavicle plate, and investigate the influence of pre-bending or repeated bending process on biomechanical properties of the reconstructed clavicle plate, so as to provide biomechanical evidence for treating midshaft clavicle fracture in clinic. Methods The reconstructed clavicle plate was bent by 1, 2, 3, 5 times respectively based on shape of the anatomical clavicle plate. The biomechanical differences in anatomical plate group, reconstructed plate group and pre-bending plate group were compared by static compression test. Results The fixation stiffness and strength of the anatomical plate were better than those of the reconstructed plate. There was no significant difference in stiffness and strength between the anatomical plate group and one-time bending group. Pre-bending had a great effect on mechanical properties of the clavicle plate, and stiffness and strength of the clavicle plate were obviously improved after one-time bending. The mechanical properties of the clavicle plate were obviously reduced by bending of the clavicle plate after one-time bending. Conclusions The stiffness and strength of the anatomical plate and one-time bending plate are higher than those of the normal reconstructed plate. It is recommended that surgeons should perform bending appropriately according to the patient’s clavicle anatomy when using the reconstructed clavicle plate for fracture fixation, and minimize the number of repeated bending to maintain stiffness and strength of the clavicle plate.