Is diamond-shaped screw fixation a viable alternative for Pauwels type III fractures? A biomechanical comparison of three constructs

Abstract

Background Pauwels type III femoral neck fractures are characterized by steep, vertically oriented fracture lines and are biomechanically unstable due to high shear and varus forces. While sliding hip screws (SHS) and cannulated screw (CS) constructs are commonly used, no consensus exists regarding the optimal fixation method for these challenging fractures. The diamond-shaped (rhomboid) configuration, incorporating four cannulated screws placed in both superior-inferior and anterior-posterior axes, has been proposed as a potential alternative, but remains insufficiently studied. Methods In this biomechanical study, 24 synthetic femur models with standardized Pauwels type III osteotomies were randomly assigned to three fixation groups (n = 8): inverted triangle cannulated screws (ICS), SHS with an anti-rotational screw (SHS + AS), and diamond-shaped cannulated screws (DCS). All models underwent static, dynamic (cyclic), and failure load testing using an Instron biomechanical testing system. Displacement at the fracture site was evaluated using a digital image correlation (DIC) method. Results The DCS group demonstrated the highest mean failure load and superior stiffness in both static and post-cyclic testing. Additionally, shear displacement was significantly lower in the DCS group during static loading compared to the SHS + AS group (p < 0.05). No significant differences were found between ICS and SHS + AS groups in most parameters. Conclusion The diamond-shaped cannulated screw configuration exhibited promising biomechanical performance in Pauwels type III fractures, offering enhanced resistance to shear forces. Considering the minimally invasive nature of CS fixation, this configuration may serve as a viable alternative to conventional methods. Further studies are needed to validate these findings in cadaveric and clinical settings.