Arif Özkan

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.

The relationship between medial meniscal subluxation and stress distribution pattern of the knee joint: Finite element analysis

BACKGROUND Degenerative changes of the knee joint and clinical follow-up after meniscal subluxation are well documented. In the current study three-dimensional (3D) finite element analysis (FEA) of human lower limb was used to investigate the effect medial meniscal subluxation on the loadings of the knee structures. METHODS Apart from the reference model, a total of ten 3D models were created, according to amount of medial meniscal subluxation. ANSYS® 14 was used to analyze the stress/load distribution, that is to say the maximum equivalent stress (MES) (von Mises stress) on bones, cartilages, ligaments and menisci. MES was expressed as Newton/mm(2) = Megapascal (MPa). RESULTS In a static and standing upright position the MES on all knee structures were evaluated in the reference model. Although MES increased in all structures with the increase of medial meniscal subluxation degree, tibia cartilage was found to be the most affected structure with an increase of 22.73-fold in the 10 mm subluxation model when compared with references values. CONCLUSION This study showed that medial meniscus subluxation is associated with increased loadings on all knee structures especially the tibia cartilage. Also the degree of the medial meniscal subluxation correlates with distribution and the amount of loadings on tibia cartilage which may be a prominent feature of knee osteoarthritis.

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.

Klavikula Kırıklarında Plak Uygulamasının Yerleşim Konumuna Göre Yorulma Davranışının Sonlu Elemanlar Yöntemi ile İncelenmesi

Amac; Klavikula, omuz ve kolun hareketlerinde onemli bir goreve sahip olan anatomik bir yapidir. Klavikula kiriklari iskelet sistemi yaralanmalari icerisinde sik karsilasilan bir problemlerdendir. Klavikula kiriklarinda, kirigin turune gore cesitli implantlar kullanarak omuzun agrisiz ve fonksiyonlarini en uygun duzeye getirmek asil amactir. Bu calismada klavikula kiriklarinda kullanilan anatomik plak uygulamasinin biyomekanik acidan incelenmesi amaclanmistir. Yontem; Bu calismada, DICOM formatinda bilgisayarli tomografi goruntuleri kullanilarak normal anatomiye sahip klavikula modellenmis ve klavikula uzerinde kirik hatti olusturularak superior ve anteriora plak yerlestirilmistir. Plaklarda meydana gelen gerilmeler, olusturulan modeller uzerine eksenel kompresyon ve konsol bukme yuklemeleri uygulanarak non-lineer sonlu elemanlar yontemi ile incelenmistir. Analizler, ANSYS (surum 18) sonlu elemanlar programinda yapilmis ve tum modellerde ayni sinir sartlari uygulanmistir. Bulgular; Analizlerde plaklar uzerinde meydana gelen maksimum esdeger gerilmelere (MES) bakilmis ve ozellikle anteriora yerlestirilen plakta gerilmenin azaldigi tespit edilmistir. Klavikula uzerine yerlestirilen plaklarin konumlarina gore yorulma davranislari karsilastirilmistir. Sonuclar; Bu calismada, klavikulanin anteriorune yerlestirilen plaklarda gerilmenin daha az oldugu sonlu elemanlar yontemi ile gosterilmistir. Ayrica, anterior bolgeye yerlestirilen plaklarin en uzun omre sahip olmasindan dolayi kirilma kararligi acisindan daha guvenli oldugu belirlenmistir.

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.

Stress Distribution Comparisions of Fixed and Broken Fibula, a Finite Element Study

The purpose of this study was to compare load carrying capacity and stress distributions of broken fibula on lower extremity under the average body weight and moment using with three-dimensional finite element analysis (FEA). The finite element (FE) models were generated from patient’s computed tomography (CT) data images. The loading and the relevant boundary conditions selected according to average human body conditions for obtaining the stress distribution on tibia surface. According the all FE analysis fibula is an effective role for load carrying capacity on distal side of tibia. These FEA results showed that the loading characteristics of the fibula should be taken into account in planning medical and surgical operations.

Using a Combination of Intralaminar and Pedicular Screw Constructs for Enhancement of Spinal Stability and Maintenance of Correction in Patients With Sagittal Imbalance: Clinical Applications and Finite Element Analysis.

Study Design:Case series and finite element analysis. Objective:To report the clinical results of using intralaminar screw-rod (ILS) constructs as supplements to regular pedicle screw (PS) constructs in “high risk for implant failure” patients and to report the results of a finite element analysis (FEA) of this new instrumentation technique. Summary of Background Data:Despite advances in surgery and implantation techniques, osteoporosis, obesity, revision surgeries, and neuromuscular conditions (such as the Parkinson disease) are challenges against achieving solid arthrodesis and maintaining correction. Additional fixation strategies must be considered in these patients. There is only one study in the literature suggesting that ILS can be used as alternative anchor points and/or to increase fixation strength in conjunction with the PSs. Materials and Methods:Five patients (3 male and 2 female) with mechanical comorbidities underwent PS+ILS to treat sagittal imbalance. In radiologic analysis, thoracic kyphosis, lumbar lordosis, and sagittal vertical axis were analyzed. FEA of ILS augmentation technique were carried out.Four different models were created: (1) the full-construct model with ILS+PS 2 levels above and below the osteotomy of T10; (2) only PS 2 levels above and below T10; (3) ILS+PS 1 level above and below the osteotomy; and (4) short-segment PS with only PSs 1 level above and below the osteotomy. The stress/load distributions on the implants in vertebrae were analyzed. Results:The mean age of the patients included in this study was 41 years and the mean follow-up was 28.2 months. A total of 87 PSs and 39 ILSs were used. Both sagittal vertical axis and kyphosis angles showed significant improvements maintained at the latest follow-up. No pseudarthrosis or instrumentation failures were observed. FEA indicated that addition of ILS construct to a PS construct enabled decreased load bearing and increased implant life. Conclusions:Addition of an ILS construct to PS construct decreases osteotomy line deformation and reduces stress on pedicle fixation points, and the combination improves fixation stability over the conventional PS-rod technique.