Abstract: Objective　To study the effects of borehole patterns on bone microstructure and screw fixation strength in orthopedic plate and screw fixation. 　Methods　Eight anti-corrosive femoral specimens were taken. Each specimen was marked with 10 boreholes and randomly divided into two groups: through-hole and semi-through-hole. Two types of boreholes were drilled and screws were inserted to test pullout force. The depth of screw placement was the same in both groups. The cortical thickness of the two groups of boreholes was taken from the amount of the cut-off bone segment. Finally, the microstructure of the porous bone tissue was observed and compared by stereomicroscope.　Results　 The thickness of bone cortex in through-hole and semi-through-hole groups were (0.687±0.046) cm and (0.706±0.014) cm, respectively. There was no significant difference in the thickness of bone cortex between the two groups. The pull-out force of screw in through-hole and semi-through-hole groups was (3.495±0.345) kN and (4.008±0.548) kN, respectively. There was significant difference in the pull-out force between the two groups. The average height of tear zone on the outer annular bone plate at the exit of through-hole and semi-through-hole groups was (0.256±0.045) cm and (0.078±0.035) cm, respectively, and there was significant difference between the two groups. 　Conclusion　The semi-through holes can be used when steel plate screws were used to fix drilling holes. The depth of screw placement remains unchanged. While meeting the same bone-screw contact area as through holes, it can provide stronger screw fixation strength due to lighter damage of the outer ring bone plate at the outlet side.

Key words: Plate and screw fixation, 　Semi through hole, 　Through hole, 　Bone microstructure, Fixation strength