Biomechanical study of internal fixation methods for femoral neck fractures based on Pauwels angle

Abstract

Objective: To select the most appropriate internal fixation method based on the Pauwels angle, in order to provide a new concept for clinical accurate treatment of femoral neck fractures (FNFs). Methods: FNFs models of Pauwels $30°$ ; $40°$ ; $50°$ ; $60°$ were created respectively. For Pauwels ≤ $50°$ , 1, 2 and 3 Cannulated Compression Screws (CCS) and Porous Tantalum Screws (PTS) were used to fix the fracture for the models. For Pauwels $60°$ , 3CCS and Medial Buttress Plate (MBP) combined with 1, 2 and 3CCS were used to fix the fracture. Based on the results of the finite element (FE) analysis, the biomechanical properties of each model were compared by analyzing and evaluating the following four parameters: maximal stress of the bone (MBS), maximal stress of the implants (MIS), maximal displacement of bone (MBD), interfragmentary motion (IFM). Results: At Pauwels $30°$ , the larger parameters were found in 1CCS, which was 94.8 MPa (MBS), 307.7 MPa (MIS), 0.86 mm (MBD) and 0.36 mm (IFM). In 2CCS group, the parameters were 86.1 MPa (MBS), 254.4 MPa (MIS), 0.73 mm (MBD) and 0.27 mm (IFM), which were similar to those of PTS. At Pauwels $40°$ ; $50°$ , with the increase of the number of used CCS, accordingly, the parameters decreased. Particularly, the MIS (Pauwels $50°$ ) of 1CCS was 1,195.3 MPa, but the other were less than the yield range of the materials. At Pauwels $60°$ , the MBS of 3CCS group was 128.6 Mpa, which had the risk of failure. In 2CCS + MBP group, the parameters were 124.2 MPa (MBS), 602.5 MPa (MIS), 0.75 mm (MBD) and 0.48 mm (IFM), The model stability was significantly enhanced after adding MBP. Conclusion: Pauwels type Ⅰ (< $30°$ ) fractures can reduce the number of CCS, and PTS is an appropriate alternative treatment. For Pauwels type Ⅱ fractures ( $30°\sim 50°$ ), the 3CCS fixation method is still recommended. For Pauwels type Ⅲ fractures (> $50°$ ), it is recommended to add MBP to the medial femoral neck and combine with 2CCS to establish a satisfactory fracture healing environment.

Keywords: biomechanics; cannulated compression screws; femoral neck fractures; finite element analysis; medial buttress plate; porous tantalum screws.