Talip Çelik

The effect of proximal tibial corrective osteotomy on menisci, tibia and tarsal bones: a finite element model study of tibia vara

Proximal tibial open wedge osteotomy (PTO) is a corrective operation used in the surgery of lower extremities and is applied to patients with varus deformities for sufficient correction. The aim of the study was to evaluate whether the PTO can achieve decreased stress‐bearing on the tibia and tarsal bones in addition to correcting the mechanical axis of the lower limb in patients with tibia vara.

Evaluation of prebent miniplates in fixation of Le Fort I advancement osteotomy with the finite element method.

The stability of segments after Le Fort I osteotomy first attracted the researchers interest when the surgical concept was conceived. Prebent plates are the ultimate modification of plate systems in craniofacial surgery; they have two right angles and are available in different lengths for use in maxillary advancement surgery. For this research, cone-beam computed tomography (CBCT) images of a male patient were obtained and scanned, and a 3D maxillary bone was created. Conventional Le Fort I osteotomies with 5 and 10 mm advancements were performed on both the cortical and trabecular bone using the Surgical Simulation Module of Mimics software; 1.7 mm Leibinger standard orthognathic 5-hole L plates and 1.7 mm Leibinger orthognathic advancement 11-hole prebent plates were adapted to the fragments. Displacement of the segment, the von Mises (VM) stresses (on the titanium miniplates) and the maximum principal (MP) stresses (on the bone) were evaluated for each configuration. Prebent plates offer a good alternative to the conventional two plate system, except in operations where maxillary advancement exceeds 5 mm. Surgical procedures that include advancement exceeding 5 mm or vertical position changes remain controversial and further studies are needed.

Comparison of the Lag Screw Placements for the Treatment of Stable and Unstable Intertrochanteric Femoral Fractures regarding Trabecular Bone Failure

Background. In this study, the cut-out risk of Dynamic Hip Screw (DHS) was investigated in nine different positions of the lag screw for two fracture types by using Finite Element Analysis (FEA). Methods. Two types of fractures (31-A1.1 and A2.1 in AO classification) were generated in the femur model obtained from Computerized Tomography images. The DHS model was placed into the fractured femur model in nine different positions. Tip-Apex Distances were measured using SolidWorks. In FEA, the force applied to the femoral head was determined according to the maximum value being observed during walking. Results. The highest volume percentage exceeding the yield strength of trabecular bone was obtained in posterior-inferior region in both fracture types. The best placement region for the lag screw was found in the middle of both fracture types. There are compatible results between Tip-Apex Distances and the cut-out risk except for posterior-superior and superior region of 31-A2.1 fracture type. Conclusion. The position of the lag screw affects the risk of cut-out significantly. Also, Tip-Apex Distance is a good predictor of the cut-out risk. All in all, we can supposedly say that the density distribution of the trabecular bone is a more efficient factor compared to the positions of lag screw in the cut-out risk.

The effect of cement on hip stem fixation: a biomechanical study

This study presents the numerical analysis of stem fixation in hip surgery using with/without cement methods since the use of cement is still controversial based on the clinical studies in the literature. Many different factors such as stress shielding, aseptic loosening, material properties of the stem, surgeon experiences etc. play an important role in the failure of the stem fixations. The stem fixation methods, cemented and uncemented, were evaluated in terms of mechanical failure aspects using computerized finite element method. For the modeling processes, three dimensional (3D) femur model was generated from computerized tomography (CT) images taken from a patient using the MIMICS Software. The design of the stem was also generated as 3D CAD model using the design parameters taken from the manufacturer catalogue. These 3D CAD models were generated and combined with/without cement considering the surgical procedure using SolidWorks program and then imported into ANSYS Workbench Software. Two different material properties, CoCrMo and Ti6Al4V, for the stem model and Poly Methyl Methacrylate (PMMA) for the cement were assigned. The material properties of the femur were described according to a density calculated from the CT images. Body weight and muscle forces were applied on the femur and the distal femur was fixed for the boundary conditions. The calculations of the stress distributions of the models including cement and relative movements of the contacts examined to evaluate the effects of the cement and different stem material usage on the failure of stem fixation. According to the results, the use of cement for the stem fixation reduces the stress shielding but increases the aseptic loosening depending on the cement crack formations. Additionally, using the stiffer material for the stem reduces the cement stress but increases the stress shielding. Based on the results obtained in the study, even when taking the disadvantages into account, the cement usage is more suitable for the hip fixations.

How does the material variation of dynamic hip screw affect the cut-out risk in the treatment of intertrochanteric femoral fractures?

The material selection of dynamic hip screw (DHS) is not usually considered from the point of mechanical effects. In this study, the effects of the titanium alloy and stainless steel DHS was investigated in the cut-out risk of femur using finite element analysis (FEA). Intertrochanteric femur fracture (IFF) (31-A2 type according to AO classification) was created in the 3D femur model obtained from computer tomography images. The DHS model was inserted to the fractured femur model in two different positions (inferior and middle). The material properties of DHS were defined for the FEA. The force applied to the femoral head was determined according to the maximum value that is observed during walking. The results show that the safest model was obtained in the middle placement of titanium alloy DHS according to the safety factor. Consequently, the use of stainless steel DHS for IFF could cause higher failure risk of DHS than the use of titanium alloy DHS.