NUMERICAL EVALUATION OF SCAR AFTER BREAST RECONSTRUCTION WITH ABDOMINAL ADVANCEMENT FLAP

BACKGROUND

The treatment of breast cancer has developed a lot during the last decade, nevertheless it still remains a considerable social and economical problem all over the world. The choice of the surgical procedure depends on a patients protocol and the surgeons preferences. The aim of this study is to evaluate the stress on the scar after breast reconstruction.

METHODS

Mathematical modeling of the sutured skin flap used for breast implant placement was divided into the following two steps. At first, material model of the selected silicone implant was identified. Afterwards, the mathematical model of the breast and implant was performed.

RESULTS

Maximal geometrical deviation for anatomical and round implant is placed on the lower surface of the breast and upper surface of the breast, while in the area of lateral geometry and the area around the nipple the agreement reaches very high level. The maximal tension is located in two median stitches. The maximal force reaches 0.025 N. The Cauchy stress equivalent is located around the nipple and reaches the value of 380 kPa.

CONCLUSION

From our results it can be seen, that the anatomical and round breast implants do not result in the same stress on the scar. The maximal value difference reaches 13.4% between stress values for these two breast implants and the round implant results in higher loaded scar compared to the anatomical implant.

[Odontoid bending stiffness after anterior fixation with a single lag screw: biomechanical study]

PURPOSE OF THE STUDY The aim of the experiment was to compare the bending stiffness of an intact odontoid process with bending stiffness after its simulated type II fracture was fixed with a single lag screw. The experiment was done with a desire to answer the question of whether a single osteosynthetic screw is sufficient for good fixation of a type II odontoid fracture. MATERIAL AND METHODS The C2 vertebrae of six cadavers were used. With simultaneous measurement of odontoid bending stiffness, the occurrence of a fracture (type IIA, Grauer's modification of the Anderson- D'Alonzo classification) was simulated using action exerted by a tearing machine in the direction perpendicular to the odontoid axis. Each odontoid fracture was subsequently treated by direct osteosynthesis with a single lag screw inserted in the axial direction by a standard surgical procedure in order to provide conditions similar to those achieved by routine surgical management. The treated odontoid process was subsequently subjected to the same tearing machine loading as applied to it at the start of the experiment. The bending stiffness measured was then compared with that found before the fracture occurred. The results were statistically evaluated by the t-test for paired samples at the level of significance α = 0.05. RESULTS The average value of bending stiffness for odontoid processes of intact vertebrae at the moment of fracture occurrence was 318.3 N/mm. After single axial lag screw fixation of the fracture, the average bending stiffness for the odontoid processes treated was 331.3 N/mm. DISCUSSION Higher values of bending stiffness after screw fixation were found in all specimens and, in comparison with the values recorded before simulated fractures, the increase was statistically significant. CONCLUSIONS The results of our measurements suggest that the single lag screw fixation of a type IIA odontoid fracture will provide better stability for the fracture fragment-C2 body complex on antero-posterior perpendicular loading than can be found in intact C2 vertebrae. Key words: odontoid fracture, odontoid fixation, bending stiffness, lag screw.