Objective: To determine whether the number of distal locking bolts have an impact on the biomechanical feature of locking intramedullary nails.
Methods: Twenty locking nails tested were divided into two groups randomly. One distal locking screw was used in first group (single bolt group); and two were used in the other group (double bolts group). After being fixed in the model, compressive and torsional strength of the interlocking nail were measured in each group.
Results: The average maximum strength of double bolts group and single bolt group was 2 160 N and 1 880 N respectively in compression tests(P < 0. 05). In torsion tests, the average maximum torsional moment of double bolts group and single bolt group was 55.8 Nm and 55.5 Nm respectively(P > 0.05), the average maximum torsional angle in double bolts group and single bolt group was 58. 3 degrees and 58.0 respectively(P > 0.05). Conclusion Single distal bolt used in interlocking nail system can meet clinical request, though the whole biomechanical behavior is not better than that of double bolts. One distal bolt is enough for the stable fracture types and double bolts should be used in the serious fracture types.