In the treatment of ankle fractures, complications such as wound healing problems following open reduction and internal fixation are a major problem. An innovative alternative to this procedure offers a more minimally invasive nail stabilization. The purpose of this biomechanical study was to clarify whether this method was biomechanically comparable to the established method. First, the stability (range of motion, diastasis) and rotational stiffness of the native upper ankle were evaluated in eight pairs of native geriatric specimens. Subsequently, an unstable ankle fracture was created and fixed with a locking plate or a nail in a pairwise manner. The ankles showed significantly less stability and rotational stiffness properties after nail and plate fixations than the corresponding native ankles (p < 0.001 for all parameters). When comparing the two methods, both showed no differences in their range of motion (p = 0.694) and diastasis (p = 0.166). The nail also presented significantly greater rotational stiffness compared to the plate (p = 0.001). However, both fixations remained behind the native stability and rotational stiffness. Due to the comparable biomechanical properties of the nail and plate fixations, an early weight-bearing following nail fixation should be assessed on a case-by-case basis considering the severity of fractures.

BACKGROUND: This biomechanical study aimed to test if the fixation of the posterior malleolus (PM) only with screws inserted from posterior to anterior (PA) restores stability comparable with the natural condition. The extent of stability was also compared with that of anterior to posterior (AP) screw osteosynthesis (OS) with an additional syndesmotic screw (SS).
METHODS: First, the stability of the upper ankle joint in seven pairs of intact lower legs were examined. Subsequently, half of the lower legs were treated with PA screw fixation of a PM fracture without SS and the other half with AP screw fixation with additional tricortical SS.
RESULTS: PA OS without SS showed significantly more diastasis (p = 0.027). The AP OS with an SS revealed a diastasis that was comparable with the intact condition (p = 0.797). The use of SS led to significantly higher stability compared to OS without SS (p = 0.019).
CONCLUSIONS: The Fixation of the PM alone without an additional syndesmotic screw cannot achieve intact upper ankle stability. Fixation of a PM fracture with an SS helps in nearly achieving the natural condition.