The propeller-type flap design is increasingly used in reconstructive surgery for various regions of the body. To date, determinants of perforator patency when subjected to twisting have not been elucidated. We propose a simulation model to study parameters affecting perforator patency under such conditions. Nonlinear finite element procedure was used to simulate a perforator consisting of an artery and a vein with both ends fixed. A rigid body was attached to the top of the perforator for applying prescribed angular displacement. The effect of the following parameters on the pedicle patency was determined: (1) increasing angle of twist, (2) vessel stiffness, (3) vessel length, (4) diameter, (5) intraluminal pressure, and (6) the presence or absence of blood flow during twisting. Simulation results were reported in effective stress and strain on the twisted pedicle. In the context of perforator patency, effective strain, which is a measure of vessel deformation or collapse, is the more relevant outcome. The vein was more prone to occlusion because of its weaker wall and lower intraluminal pressure. Four factors that affected perforator patency were identified: angle of twist, intraluminal blood pressure, and perforator diameter and length. There was no significant difference whether twisting was performed prior to or after restoration of blood flow (P > 0.05). Therefore, to optimize condition for maintaining perforator patency, the angle of twist should be kept <180 degrees, perioperative blood pressure should be kept stable (avoiding periods of hypotension), and the selected perforator should be approximately 1 mm in diameter and >30 mm in length. We found that the propeller flap is a feasible design. This study defined the determinants of perforator patency and will serve as a useful guide when performing such flaps.

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Artificial meniscal implants may replace severely injured meniscus and restore the normal functionality of the knee joint. Implant material stiffness and shape influence the longevity of implantations. This study, using 3D finite element analysis, aimed to evaluate the effects of material stiffness variations of anatomically shaped artificial meniscal implant in the knee joint. Finite element simulations were conducted on five different cases including intact knee, medial meniscectomized knee, and the knee joint with the meniscal implant with three distinct material stiffness. Cartilage contact pressures, compression stresses, shear stresses, and implant kinematics (medial-lateral and posterior-anterior displacement) were evaluated for an axial compressive load of 1150 N at full extension. Compared to the meniscectomized knee, the knee joint with the meniscal implant induced lower peak cartilage contact pressure and reduced the cartilage regions loaded with contact pressures greater than the peak cartilage contact pressure induced by the intact knee. Results of the current study also demonstrate that cartilage contact pressures and implant displacement are sensitive to the implant material stiffness. The meniscal implant with a stiffness of 11 MPa restores the intact knee contact mechanics, thereby reducing the risk of physiological damage to the articular cartilage.