Biomechanical justification of the Ilizarov external fixation osteosynthesis for gunshot fractures of the proximal femur

Introduction The search for the optimal method of external osteosynthesis for proximal femoral fractures without  pelvic  fixation  has  once  again  become  relevant.  This  is  due  to  casualties  with  gunshot  fractures of this location, accompanied by extensive soft tissue defects, referred to military medical organizations.

Purpose  To  develop  a  method  for  stabilizing  bone  fragments  using  the  Ilizarov  apparatus  through biomechanical modeling of various external osteosynthesis options for proximal femoral gunshot fractures, ensuring gradual hip joint movement and weight-bearing on the involved limb.

Materials and Methods Based on computer tomography data, a biomechanical model of a proximal femoral fracture and its osteosynthesis methods using various fixation devices were constructed. Stresses and strains arising from typical loads experienced by the injured during controlled weight-bearing on the operated lower limb were studied. In bench tests on specially prepared models, the elastic strength of the Ilizarov apparatus models was investigated, and the maximum mechanical loads that the studied fixators can withstand were identified and analyzed.

Results  The  use  of  the  Ilizarov  apparatus,  ensurig  stabilization  of  the  proximal  fragment  with  a  bundle of polyaxially inserted tensioned 3-mm wires and its additional fixation with support rods, provides the most favorable stress-strain parameters in the "bone-fixator" system compared to an unreinforced Ilizarov apparatus configuration.  The  results  of  the  finite  element  modeling  were  confirmed  with  bench  tests.  Comparison of  the  results  of  biomechanical  modeling  of  external  osteosynthesis  variants  with  the  Ilizarov  apparatus and internal osteosynthesis with a proximal femoral nail indicates the advantages of internal fixation.

Discussion The obtained data are in full agreement with the results of biomechanical studies that presented the results of biomechanical modeling of osteosynthesis options for tibial fractures. According to these authors, in the "bone–locked nail" system, the mechanical stress in the fixator is lower than in the "bone–external fixator" system. Moreover, prolonged stress concentration on the elements of the fixation device can cause their weakness. However, the inability to use internal osteosynthesis techniques in proximal femoral gunshot fractures justifies the development and clinical application of the proposed Ilizarov apparatus configuration, which stress-strain parameters are the closest to the proximal femoral nail.

Conclusion The data obtained substantiate the possibility of using the developed external osteosynthesis method with the Ilizarov apparatus in clinical practice for treating gunshot fractures. The results of the experimental study prove the prospect of using the proposed Ilizarov apparatus configuration for long-term stabilization of this type of fracture under the conditions of graded weight-bearing on the involved limb and hip joint movement throughout the entire consolidation period.

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