Background The bone nail of the traditional external fixator penetrates the skin and bone, and bacteria can enter the tissue along the nail path to cause subcutaneous tissue infection and osteomyelitis, which is one of the most common complications of the external fixator.

Objective To develop a new type of unicortical external fixator avoiding the nail path penetrating the bone marrow cavity, and evaluate its biomechanical and structural stability.

Methods The biomechanics of the new unicortical external fixator was compared with that of the unilateral and clamp external fixators, and the bending resistance, fatigue resistance, compression and torsion stiffness were analyzed.

Results The overall axial stiffness of the three types of external fixators was the same (88.931 ± 35.302 N/mm in the unicortical group, 88.830 ± 32.651 N/mm in the unilateral type group, 73.352 ± 32.470 N/mm in the clamp type group, P>0.05); The overall torsional rigidity of unilateral external fixator was 0.634 ± 0.225 Nm/degree, which was stronger than that of unicortical external fixator (0.494 ± 0.156 Nm/°, P=0.042) and clamp external fixator (0.455 ± 0.141 Nm/°, P=0.010); The unicortical external fixator (5.801 ± 1.623 mm) had the same lateral bending resistance as the unilateral external fixator (6.104 ± 1.902 mm, P>0.05), but they were stronger than the clamp external fixator (9.365 ± 2.330 mm, P<0.01); The three kinds of external fixators showed the same anti-fatigue ability (average displacement was 3.775 ± 0.113 mm, 3.774 ± 0.092 mm, 3.892 ± 0.216 mm, P>0.05).

Conclusion The biomechanical performance of unicortical external fixator is slightly weaker than that of unilateral external fixator and stronger than that of clamp external fixation. However, for non-weight bearing use, the unicortical external fixation shows sufficient rigidity.