The effect of distal blocking on the stress level of the metal fixator during osteosynthesis of transtrochanteric fractures (experimental modelling)

Background. In developed countries, minimally invasive technologies for using the proximal femoral rod are widely implemented in treating fractures of the proximal femur. Howe­ver, we did not find literature data on the stresses on the blocked intramedullary rod depending on the type of fracture due to the Association of Osteosynthesis and variants of its distal blocking. The study aimed to carry out biomechanical modelling of stresses on various metal fixators during osteosynthesis for transtrochante­ric fractures of type A2. Materials and methods. A femoral mo­del with implanted fixation elements was used. Intramedullary locking rods were used to fix the fragments in 3 fixation options: with one, two screws, or without locking screws in the distal part of the rod. Calculations of the stress-strain state using the finite element method were performed for the intact model with both types of fixators, and then for fixators used in transtrochanteric fractures of type A2, with options for distal locking (without locking, one screw, two screws). Results. The minimum tension on the metal retainers in their pro­ximal parts was determined when using the PFN (proximal femoral nail) in the variant with two screws for distal locking. These data were statistically significantly different from the data when the PFN-rod was used without distal locking. On the distal part of the metal retainers, the stress was minimal when applying the ­PFN-rod with the use of 2 screws for distal locking (195.27 MPa). It was determined that minimal but adequate micromobility for this vertically and rotationally unstable fracture was observed when using the PFN model of the rod, with the use of 2 screws for distal locking (2.17 mm). These micromovements will contribute to the improvement of reparative osteogenesis in patients with transtrochante­ric type A2 fractures. Excessive micromobility may occur when using the model without and with one locking screw for distal lo­cking of the PFN rod (2.27 and 2.23 mm), potentially leading to impaired reparative osteogenesis with this method of metal fixation. ­Conclusion. Our research suggested a differentiated approach to treating patients with transcavitary fractures of the femur, which is expected to enhance the effectiveness of medical care for this severe patient category.