Study of the stress-deformation state of models of the humerus in cases of supracondylar oblique fractures in children and adolescents with different options of percutaneous fixation

Abstract

Fractures of the distal epimetaphysis of the humerus in children and adolescents are one of the most common injuries, accounting for 16 to 50% of all bone fractures. Among the injuries of this location, supracondylar (3-18%) and transcondylar fractures (57.5-70%) prevail, mainly in children aged 6-7 years. A significant problem when using a crossed fixation structure is iatrogenic damage to the ulnar nerve (2-8%), which requires a mini-open technique of medial spica or sonographic monitoring.

Aim - to compare the level of stresses in the model of the humerus with a supracondylar oblique fracture with different options of percutaneous fixation under the influence of different loads.

Materials and methods. A basic finite-element model of the humerus was developed, on the basis of which a model of an oblique supracondylar fracture was created. Two versions of osteosynthesis were modeled: with two spikes arranged crosswise and a bundle of three spikes. The stress-strain state of the models was studied under the influence of tensile, bending and twisting loads.

Results. The presence of an oblique epicondylar fracture of the humerus leads to asymmetric changes in the distribution of stresses in the epicondyles above and below the fracture line during cross fixation with two spikes. With lateral fixation with three spikes under the influence of tensile load, the tension in the medial epicondylum is reduced to a minimum and their level on the lateral one is doubled. This is related to the one-sided conduction of a bundle of spikes. At the same time, the medial epicondyle remains unfixed and, accordingly, the loads on it are practically not transferred. The bone regenerate for this is too soft to prevent movement of the distal fragment. At the same time, a tighter fixation of the lateral epicondyle than in the version with two needles across, causes an increase in the level of stress in the lateral epicondyle. The total size of the cross-sectional area of the spike bundle with lateral fixation ensures a twice lower stress level in them, compared to cross fixation. Under bending loads, cross fixation with two spikes and lateral fixation with a bundle of three spikes work about the same. Under torsional loads, both methods of fixation of fragments of the humerus showed approximately the same results. In favor of the method of lateral fixation with a bundle of three spikes, the low level of stresses in the spikes can be attributed. The asymmetric arrangement of the bundle of three spokes during lateral fixation is compensated by the asymmetry of the passage of the fracture line. All this indicates that in the treatment of oblique supracondylar fractures of the humerus, both methods of fixation are equivalent from the point of view of stress distribution in the bone tissue, and the choice of one of them can be determined by other criteria.

Conclusions. Mathematical modeling of the humerus with a supracondylar oblique fracture did not determine significant advantages of one or another method of fixation. The asymmetric location of the spikes during lateral fixation of bone fragments is compensated by the asymmetry of the fracture line. In favor of the method of lateral fixation with a bundle of three spikes, the low level of stresses in the spikes can be attributed.

The research was carried out in accordance with the principles of the Helsinki Declaration. The study protocol was approved by the Local Ethics Committee of participating institution. The informed consent of the patient was obtained for conducting the studies.

No conflict of interest was declared by the authors.