A Biomechanical comparison of diamond-shaped cannulated screw fixation with inverted triangle cannulated screw and dynamic hip screw with an anti-rotation screw in Pauwels type three fractures

Introduction: Pauwels III fractures are common orthopedic emergencies. Inverted triangle cannulated screw (KV3) and dynamic hip screw with antirotation screw fixation (DKV+AV) are frequently used in the treatment. Considering no consensus is accomplished on the preferred method, we suggest that a diamond-shaped cannulated screw (KV4) fixation will increase the stability in Pauwels III fractures. The objective of this biomechanical study was to compare this construct with the inverted triangle cannulated screw (KV3) and dynamic hip screw with antirotation screw fixation (DKV+AV). Materials and Methods: Each three test groups assigned with 8 samples with a total number of 24 left Femur biomechanical Sawbones, 4th generation. All femoral necks were cut at 65° angle via a custom made cutting equipment to simulate Pauwels type 3 fracture line. Femurs were exposed to 1400 N static loading for obtaining stiffness, shear and upper fracture gap displacement values. For dynamic test, 10.000 cycles with 700-1400N loading were applied to investigate the effect of fatigue in the implant and bone structure. Following the dynamic test, the specimens were loaded with 1400N and biomechanical values were measured. Finally, the load was increased stepwise, until failure developed on all femurs. 5 mm displacement and sudden decrease in stiffness values were accepted as failure criterias. The failure load, fracture line displacements and stiffness values were compared using ANOVA (p<0.05). Results: KV4 group provided significantly higher mean failure load than KV3 and DKV+AV groups (p<0.004) which have no difference in-between. The stiffness value was found to be significantly higher in the KV4 group both in static and post-dynamic static measurements (p<0.004). Static shear displacement value was found to be significantly lower in the KV4 group compared to the DKV+AV group (p=0.035). However, there was no significant difference in-between other groups. Conclusion: The failure load and stiffness values of the KV4 group were found to be statistically higher than other groups, and the amount of static shear displacement was found to be lower. According to the results, it can be concluded that in the Pauwels type 3 femur neck fractures a diamond-shaped cannulated screw is biomechanically more stable than the inverted triangle cannulated screw and dynamic hip screw with antirotation screw fixation. Keywords: Femoral neck fractures, Pauwels type 3 fracture line, cannulated screw, dynamic hip screw, inverted triangle configuration, diamond-shaped cannulated screw configuration, unstable femoral neck fracture