Biomechanical comparison of five cannulated screw fixation strategies for young vertical femoral neck fractures

Abstract

Vertical femoral neck fractures in patients younger than 65 years of age often require hip‐conserving surgeries. However, traditional fixation strategies using three parallel cannulated screws often fail in such patients due to an unfavorable biomechanical environment. This study compared different cannulated screw fixation techniques in patients via patient‐specific finite element analysis with linear tetrahedral (C3D4) elements. Forty vertical femoral neck fracture models were created based on computed tomography images obtained from eight healthy participants. Five different fixation strategies: alpha, buttress, rhomboid, inverted triangle, and triangle were assessed in walking status. Biomechanical parameters including stiffness, interfragmentary motion in two directions (detachment and shearing), compression force, and maximal implant stress were evaluated. The mean relative coefficient of strain distribution between the finite element analysis and experiment was from 0.78 to 0.94. Stiffness was highest (p < .05) in the buttress group (923.1 N/mm), while interfragmentary motion was lowest (p < .05) in the alpha group. Maximal stress was highest (p < .05) in the buttress group and lowest in the alpha group. Shearing values were significantly lower in the alpha group than in the rhomboid group (p = .004). Moreover, Shearing values were significantly higher (p = .027), while detachment values were significantly lower (p = .027), in the inverted triangle than in the triangle group. Clinical significance: Our results suggest that alpha fixation is the most reliable and biomechanically efficient strategy for young patients with vertical femoral neck fractures. Regular and inverted triangular fixation strategies may be suitable for fractures of different skeletal constructions due to antidetachment/shearing abilities.

Enhanced Interfragmentary Stability and Improved Clinical Prognosis With Off-axis Screw Technique in the Treatment of Vertical Femoral Neck Fractures of Nongeriatric Patients

“…All xation models were constrained to within 80 mm distal from the lesser trochanter and subjected to 237.7% of body weight loading, [22] along the femoral mechanical axis. The dynamic compression effect of cannulated screws and lag screws was simulated by using a preloading of 224N for cannulated screws and 591N for DHSs, the same value per mm 2 as we described previously [9]. The above nite element simulation process was validated using cadaveric bone in our previous biomechanical test [9], showing a relative coe cient of 0.78-0.94.…”

“…1). [9,16] All assemblies were meshed into 1mm equal sized facets and converted into 4-node linear tetrahedron (C3D4) solid elements in Hypermesh 13.0 (Altair Engineering, Troy, MI, USA). The solid models were then exported into software Abaqus 6.13 (Simulia Corp, USA) as inp format les.…”

“…Stiffness, IFM, and implant stress (von Mises stress) were analyzed as biomechanical parameters. Note that, in order to overcome the drawback of "center point fallacy" in previous measurement, [23] the IFM of all nodes on both fracture surfaces was calculated, and then the mean IFM value of all nodes was the parameter that was compared among three groups [9]. IFM of each paired node were calculated based on the formula in previous study [9].…”

“…[6][7][8] Another factor that complicates the picture is that augmentation with an off-axis screw for cannulated screw xations signi cantly increases the resistance to shear deformation force. [9] This is because the off-axis screw effectively neutralizes the "sliding effect", providing better bone purchase as well as cortical support. [9] Overall, this augmentation reduces the complication rate in clinical following-up.…”

“…[9] This is because the off-axis screw effectively neutralizes the "sliding effect", providing better bone purchase as well as cortical support. [9] Overall, this augmentation reduces the complication rate in clinical following-up. [10] Consequently, the question arises: Is it possible that xation with a load-sharing device can also achieve satisfactory clinical outcome for VFNFs by modifying the standard screw con guration?…”