STIFFNESS PARAMETERS OF VARIOUS MODIFICATIONS OF RING FIXATOR

Abstract

Relevance. To date, there is no final solution to the theoretical and practical issues of the problem of external fixation in the treatment of long bone fractures.
 Objective. To determine the rational methods of completing ring retainer (RF) in the treatment of nonunions of the shin bones after fractures of long bones on the basis of clinical and experimental substantiation of the choice, taking into account the peculiarities of the assembly of the apparatus and the implementation of the connection "apparatus-fragments of non-union".
 Materials and methods. In the experimental part, Sawbones® synthetic composite bone was used. The rigidity of fixation of bone fragments of the RF of the wire-rod type was studied. We tested and compared 5 different options for fixation of bone fragments in RF. The samples were tested in 4 modes: compression along the axis of the bone; compression on the head of the bone; twisting; bending. The strength and deformation characteristics of the materials were determined with a maximum force of up to 5 kN using the TIRATEST-2151 universal testing machine. They chose the most optimal configuration of the RF. Then, in the clinical part, the clinical effectiveness of the optimal structures was evaluated based on the analysis of their use in 12 patients with non-union of the shin bones.
 Results. Optimal structures have been determined from the point of view of integral rigidity of the structure. The greatest rigidity was the RF system No. 3, in which 3 spokes are used: 2 of them are held at an angle, 1 - in the plane of the ring. In the case of an increase in the number of spokes, the stiffness of the system increased. When tested in compression along the axis of the bone, the stiffness of System No. 3 is 6.5% greater than that of System No. 2 and 12.5 % greater than System No. 1, in which only 2 spokes are used. Fixing the spokes at an angle to the plane of the ring also increases the rigidity of the system. When tested in compression along the axis of the bone, the stiffness of System No. 3 is 6.5 % greater than that of System No. 2. The stiffening rib affects the stiffness of the entire system. But the bend became the most sensitive. Flexural stiffness decreased by 23 % and compression by 8.5 %. Debris removal during bending increased by 1.5-1.8 times.
 Conclusion. The best indicators of fixation rigidity have options for the arrangement of spokes with a cross not only in the frontal, but also in the sagittal planes. The stability of the fixation of the rod is significantly increased by mounting the "stiffness triangle". The obtained clinical data indicate the promising application of improved ring fixators.