Abstract
Introduction: Decreasing the length of the side plate of the dynamic hip screw (DHS) would theoretically allow a smaller surgical incision, a shorter surgical time, decreased operative blood loss and minimal periosteal stripping. A new design of a very short plate (VSP) dynamic hip screw based on two diagonal screws has been developed. The new design was compared with the four hole side plate regarding its mechanical properties and bio-mechanical outcomes.
Methods: Four pairs of fresh frozen cadaveric femora were extracted from male corpses aged 25–43 (mean 34.8), mechanical loading was applied to four pairs of cadaveric femora which were fixated using the new system on one side and the conventional design on the other. The decline during the periodical loading and the breakage load of the fixated bones were measured. In addition, mechanical performance and probability for failure was assessed by conducting a mathematical analysis using the finite element method.
Results: The average deflection under excessive cyclic loading was 33% higher in bones with the VSP-DHS device than those with regular DHS. The average load failure during the collapse loading test was 312 kg for the VSP-DHS compared to 416 kg for the regular device. The mathematical analysis performed indicated that the maximal stress in the VSP-DHS reached values 3–4 fold higher than in the regular DHS.
Conclusions: Bio-mechanical evaluation was performed both by mechanical testing and theoretically. Although the new design offers a minimally invasive approach to subtrochanteric femur fracture fixation, it was found to have insufficient biomechanical performance resulting in high probability for mechanical failure.
The abstracts were prepared by Ms Orah Naor. Correspondence should be addressed to Israel Orthopaedic Association at PO Box 7845, Haifa 31074, Israel.
