Comparison of the Effect of Diameters and Numbers of Cannulated Screws and Headless Compression Screws on the Reduction Stability in Transverse Patellar Fractures: A Finite Element Model Study

Background: Patella fractures constitute 1% of skeletal trauma. Transverse patella fractures are the most common types of patellar fractures. A fracture gap more than 2-3 mm or irregularities in cartilage require surgical treatment. There are various surgical options available, and one of these options is the screw fixation. This study aims to investigate the effect of the diameter and number of cannulated screws and headless compression screws on the reduction stability of transverse patellar fractures. Methods: In this study, the knee joint with normal anatomy and the knee joint with transverse patellar fracture were modeled using longitudinal lower extremity computerized tomography (CT) images taken in DICOM format. In the knee model with transverse patellar fracture, two circle divide 3.5 mm cannulated screws and one circle divide 4.5 mm cannulated screw, two circle divide 3.5 mm and one circle divide 4.5 mm headless compression screws were inserted respectively; and the maximum equivalent stresses (MES) occurred in the screws and the stability of the patella were examined in a total of 16 models at 30 degrees, 45 degrees and 60 degrees flexion angles and in the normal position (0 degrees) of the knee. The analysis was performed non-linearly and dynamically using ANSYS (version 17) and the same boundary conditions were applied in all models. Results: As a result of the analysis, the maximum stresses on the screws in the models with cannulated screws and headless compression screws were compared. When the maximum stresses in the screws were examined, it was observed that the maximum stress was lesser in the model with two circle divide 3.5 mm headless compression screws, and the maximum stress was found to increase in the single circle divide 4.5 screws. Sixteen different models were analyzed with the help of the Taguchi method and the most suitable model and parameters were determined according to the maximum equivalent von Mises stress value. Conclusions: The use of a single screw in the treatment of transverse patella fractures can lead to loss of reduction. If screw treatment is preferred, it was observed that the 2-screw application was more stable and the fixation with the headless compression screw was found to be more stable compared to the cannulated screw at various degrees of flexion.