Two Cannulated Screws Provide Sufficient Biomechanical Strength for Prophylactic Fixation in Adult Patients With an Aggressive Benign Femoral Neck Lesion

Abstract

Background: Two cannulated screws were proposed for prophylactic fixation in adult patients with an aggressive benign femoral neck lesion in recent literature. However, the biomechanical properties of this intervention have not yet been investigated. Methods: After the evaluation of the heterogeneity of bone mineral density and geometry via quantitative computed tomography, 24 embalmed adult human cadaver femurs were randomized into the control, inferior half of the anterior cortical (25%) bone defect, entire anterior cortical (50%) bone defect, and the 50% bone defect and two cannulated screw group. Biomechanical analysis was conducted to compare the stiffness and failure load among the four groups when mimicking a one-legged stance. A CT-based finite element analysis (FEA) was performed to mimic the cortical and cancellous bone defect and the implantation of two cannulated screws of the four groups. Measurements of the maximal displacement and von Mises stress were conducted with the longitudinal load force and boundary conditions being established for a one-leg-standing status. Results: We noted a significant improvement in the failure load after the insertion of two 6.5 mm cannulated screws in femurs with 50% bone defect (+95%, p = 0.048), and no significant difference was found between the screw group and the intact femur. Similar trends were also found in the measurements of stiffness (+23%, p > 0.05) via biomechanical testing and the von Mises stresses (-71%, p = 0.043) by FEA when comparing the screw group and the 50% bone defect group. Conclusion: Our findings suggest that two cannulated screws provided sufficient biomechanical strength for prophylactic fixation in adult patients with an aggressive benign femoral neck lesion even when the entire anterior cortical bone is involved.

Keywords: benign lesion; biomechanical analysis; cannulated screw; femoral neck; prophylactic fixation.

FIGURE 1

A graphical overview of the present study design. (A) CT scanning; (B) Fenestration and Fixation; (C) Biomechanical testing; (D) Three-Dimension model reconstruction; (E) Simulative modes of surgery; (F) Finite element analysis.

FIGURE 2

Representative images for X-ray (A1–A4), cadaveric tests (B1–B4), femoral neck fracture (C1–C4), and FEA (D1–D4) of the control group, 25%-defect group, 50%-defect group, and 50%-defect + two cannulated screw group.

FIGURE 3

QCT-based BMD of each group was measured at the femoral neck (A), femoral head (B), and intertrochanteric region (C) of the cadaver femurs. Measurements of the femoral geometry parameters include neck-shaft angle (D), width of the femoral neck (E), and length of the femoral neck (F). All the data are presented as mean + std dev.

FIGURE 4

Comparisons of failure load (A) and stiffness (B) within the four groups. * indicated p < 0.05, ** indicated p < 0.01, and all the data are presented as mean + std dev.

FIGURE 5

Von Mises stress distribution of the intact femur (A), 25%-defect (B), 50%-defect (C), and 50%-defect + two cannulated screws (D) under axial loading with 700 N. (E) Measurements of von Mises stress were queried at 14 different points on the femoral neck that lay within a single coronal plane. (F) Von Mises stresses of each point on the inferior and superior margin of the femoral neck were obtained. (G) Comparison of the mean von Mises stresses between the inferior and superior margin of the femoral neck in the circumstance of the intact femur, 25%-defect, 50%-defect, and 50%-defect + two cannulated screws. * indicated p < 0.05 when compared with other groups. ^# indicated p < 0.05, and ^## indicated p < 0.01 when compared with the superior margin within each group. All the data are presented as mean + std.

FIGURE 6

Fracture lines of the four models are shown in Figures 6A–D. Figure 6E. Comparisons of failure load within the four groups are made via FEA.