The Effect of Vertical and Oblique Inclinations on Fracture Stability and Reoperation Risks in Femoral-Neck Fractures of Nongeriatric Patient

Figures

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  FIGURE 1. Patient selection process.

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  FIGURE 2. The measurement of Fracture inclination in multiple planes from CT images, and the setup for the biomechanical validation study. (A) Anteroposterior (AP) view of reconstructed distal fragment of proximal femur and neck showing position of FNF. The fracture line (red) was manually traced along the cortical edges of the distal fragment in 3-Matics® software. Proximal fragment is hidden in this image. For orientation purposes, lesser trochanter occupies the lower foreground. (B) Local coordinate axes (X, Y, Z) overlaid on complete 3-D reconstruction. Local coordinate axes (X, Y, Z) overlaid on complete 3-D reconstruction. Fracture line was divided into equal sections or degrees using the classical clock-face system (inset, lateral view). For orientation, 0°/360° (i.e., 12 o’clock) points toward the superior part of the femoral head and 180° (i.e., 6 o’clock) points toward its inferior part. The clock-face system was then digitally transposed onto the custom proximal femoral coordinate system. (C) AP view of reconstructed proximal femur showing orientation of the fracture plane, which is represented by the blue-colored rectangle. vplane represents the normal vector of the fracture…

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  FIGURE 3. Identification of Three-Dimensional Unstable Inclination angles based on clinical prognosis analyses (A–C) Scatterplots of 3-D inclination angles of all FNFs (n = 755) (black dots). Reoperated cases (red dots) are overlaid. The identification of 3-D unstable inclination angles was based on the 755 reoperation cases (n = 100; See Supplementary Table S2) and their associated α and β angles calculated from the 3-D reconstructions of their proximal femur and FNFs. Three grouping principles were tested in the diagnostic test: (1) vertical unstable [(A), purple-colored region); (2) oblique unstable [(B), yellow-colored region]; and (3) both vertical and oblique unstable [(C), purple-colored and yellow-colored regions]. (D) The optimal threshold values (α0, α1, α2, β1, β2) were identified by calculating the maximum Youden index among over 12,160 possible combinations. The combined vertical (α > 70°) and oblique (50°<α < 70° and β > 20°/<−20°) unstable types had the highest Youden index (0.39). The reoperation rate percentages (red) are shown in each region.

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  FIGURE 4. Validation of 3-D unstable inclination angles in a biomechanical test. Illustrating the calculation and results of interfragmentary motion. Interfragmentary motion (IFM) was calculated according to the location of the three paired points (red dotted) in proximal and distal fragments, and the local coordinate system (A). According to the photograph obtained with the VIC-3D, IFM was more severe in unstable groups (B–D) compared to stable groups (E–H).

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  FIGURE 5. Examples of femoral neck fractures with 3-D unstable inclination angle. (A) A 46-year-old male with a vertical unstable inclination angle (α = 71.6° and β = 6.3°) was treated with three cannulated screws. Radiography taken 4 months postoperatively revealed severe screw withdrawal (red arrow) as well as femoral neck shortening, varus collapse, and delayed union. (B) A 46-year-old female with retroversion oblique unstable inclination angle (α = 52.8° and β = 21.5°) was treated by three cannulated screws with a fair reduction quality. Radiography taken 2 months postoperatively revealed severe screw withdrawal (solid red arrow) as well as femoral neck shortening, varus collapse, screw penetration of the joint capsule (dotted red arrow), and delayed union. (C) A 59-year-old male with anteversion oblique unstable inclination angle (α = 62.0° and β = −20.6°) was treated with three cannulated screws. Radiography taken 6 months postoperatively revealed severe screw withdrawal (red arrow) as well as femoral neck shortening, varus collapse, and delayed union.

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  FIGURE 6. Examples of avascular necrosis in cases with oblique unstable inclination. (A) A 42-year-old female with retroversion oblique unstable inclination angle (α = 51.6° and β = 20.5°) was treated with four cannulated screws. Radiography taken 24 months postoperatively revealed avascular necrosis, which was treated with arthroplasty. The yellow and red line showed the femoral neck axis and fracture orientation in one CT plane. (B) A 32-year-old female with anteversion oblique unstable inclination angle (α = 55.6° and β = −22.9°) was treated with three cannulated screws. Radiography taken 42 months postoperatively revealed avascular necrosis, which was treated with free vascularized fibular grafting. The yellow and red line showed the femoral neck axis and fracture orientation in CT plane.

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  FIGURE 7. The comparison of interfragmentary motion in biomechanical test. IFM plots as a function of α and β angles in the biomechanical validation test. Synbone® fracture groups with combinations of α = 70°; α = 50° and β = 20°; and α = 50° and β = 20° had significantly greater IFMs than groups with combinations of α = 30° (<50°), and α = 50° and β = 0°. These outcomes of simulated FNFs in Synbones® correspond well with clinical findings. Asterisks indicate significance as evaluated by one-way ANOVA. Extent of group (n = 5) variability is standard deviation (SD) shown by red-colored vertical lines.