Mathematical Modeling of Stress-Strain State of the Olecranon Fracture after Interlocking Screw Osteosynthesis vs Weber’s Method
Introduction. Olecranon fractures account for up to 40 % of all fractures around the elbow joint. The tension band wiring is a gold standard for the olecranon fractures fixation. The literature and our own experience describe around 18.5–45.6 % unsatisfactory results. Our analysis has shown that traditional methods of treating fractures of the olecranon enable to get good and excellent results only in 60 % cases. It confirms the actuality of improvement and developement of new osteosynthesis techniques in olecranon fractures. The purpose of this study was to investigate the stress-strain state in the area of the olecranon fracture with intelocking screw osteosynthesis compared with the tension band technique. Materials and methods. Mathematical modeling of stress-strain state in the finite element model of the olecranon fracture with tension band osteosynthesis and interlocking screw osteosynthesis has been performed. Modeling was performed using computer-aided design SolidWorks. Calculations of stress-strain state models were performed using the software system CosmosM. On models with olecranon tension band osteosynthesis comprassion was imitated by additional 1 N load on the elbow. The load models carried a distributed force that was applied to its distal end, at the end of the olecranon imposed strict consolidation. As a criterion for stress state assessing Mises concept has been used. Models were studied under the influence of three types of load: bending, stretching, twisting. The bending and stretching load was 11 N that corresponds to the weight of the forearm. In twisting studies to the distal end of the ulna applied laud value of 0.5 N/m. Results. The stress-strain state study of models with inteloking screw osteosynthesis under the bend influence showed that the most loaded model sections are olecranon and implant in the area of the fracture, but the maximum value of the stress in these areas is much lower than in the model with tension band osteosynthesis. Thus, the olecranon stress is the maximum value of 11.46 MPa, the screw in the area of the olecranon fracture — 7.58 MPa, and in the proximal ulna — 6,88 MPa. The stresses value in ulna also decreased to 1.64 MPa. In diaphysis and distal ulna stress level remains at the same level as in the model of tension band osteosynthesis — 1.33 and 0.37 MPa, respectively. In the study of stress-strain state model with interlocking screw osteosynthesis under the influence of traction found that stress in the metal structures in the area of the fracture are distributed more evenly with a slight excess in the proximal ulna compared with the tension band osteosynthesis model, which takes the value 0.67 MPa compared with the part of the implant in olecranon, where the stress does not exceed 0.61 MPa. The maximum value of stresses in bone tissue was found in the olecranon and was up to 0.55 MPa. In diaphysis and proximal ulna significantly lower level of effort was determined and the absolute values became to 0.16 and 0.26 MPa, respectively. In the models of the interlocking screw osteosynthesis under the influence of twisting the most load was founde on the olecranon, which, in absolute rate, was 27.73 MPa. Interlocking screw assume a large share of the load, but distribution is more evenly than in tension bend. Thus, the section of the screw, which is located in the olecranon, the maximum value was 21.94 MPa, and in the proximal ulna — 22.27 MPa. Tension in ulna decreases with distance from the fracture zone, which takes the maximum value of 13.05 MPa. In mid-diaphysis the stress level was reduced to 5.67 MPa. In the distal ulna the least load appears. The value of maximum load in this area does not exceed 1.76 MPa. Conclusion. Investigation of stress-strain state models with olecranon fractures osteosynthesis by finite element method showed that the maximum stress occurs on the olecranon and a bone in the area of the fracture and implant. Distally stress level decreased. It was found that for all types of load in models with interlocking screw osteosynthesis level of the maximum stresses arising in the olecranon and the implant in the area of the fracture and it is lower than in tension band models. These results indicate greater stability in models with interlocking screw technique.
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