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Jin-Hoon Jeong, M.D.
, Gu-Hee Jung, M.D., Ph.D.
, Gu-Hee Jung, M.D., Ph.D.
Abstract
Purpose
To identify the anatomic features for clinical applications through a computational simulation of the fixation of three cannulated screws for a femoral neck fracture.
Materials and Methods
Thirty cadaveric femurs underwent computed tomography and the images were transferred to the Mimics® program, resulting in three-dimensional proximal femur models. A three-dimensional scan of the 7.0 mm cannulated screw was performed to enable computerized virtual fixation of multiple cannulated screws for femoral neck fractures. After positioning the screws definitively for cortical support, the intraosseous position of the cannulated screws was evaluated in the anteroposterior image and axial image direction.
Results
Three cannulated screws located at the each ideal site showed an array of tilted triangles with anterior screw attachment and the shortest spacing between posterior and central screws. The central screw located at the lower side was placed in the mid-height of the lesser trochanter and slightly posterior, and directed toward the junction of femoral head and neck to achieve medial cortical support. All the posterior screws were limited in height by the trochanteric fossa and were located below the vastus ridge, but the anterior screws were located higher than the vastus ridge in 10 cases. To obtain the maximum spacing of the anterior and posterior screws on the axial plane, they should be positioned parallel to the cervical region nearest the cortical bone at a height not exceeding the vastus ridge.
Conclusion
The position of cannulated screws for cortical support were irregular triangular arrangements with the anterosuperior apex. The position of the ideal central screw in the anteroposterior view was at the mid-height of the lesser trochanter toward the junction of the femoral head and neck, and the anterior and posterior screws were parallel to the neck with a maximal spread just inferior to the vastus ridge.
Figures and Tables
Fig. 1
Computational simulation of inserting multiple 7.0 mm cannulated screw fixation was performed using the Mimics® software, in which four synchronized windows were available.
Fig. 2
After positioning the screws definitively for cortical support, the intraosseous position of cannulated screws was evaluated in the anteroposterior image and axial image direction (white arrow: vastus ridge).
Fig. 3
(A, B) Safe zone for multiple cannulated screw fixation was clearly visible in the view of the femoral neck axis by the transparent mode. (C) The entry point of the screws was verified in the opaque mode and compared with the vastus ridge.
Fig. 4
Morphological features of safe zone and intraosseous position of screws were evaluated by making the cutting plane in the vertical direction of the femoral neck axis.
Fig. 5
Safe zone for cannulated screws in the femoral neck was an irregular pattern of the triangle and affected by the trochanteric fossa (*).
Fig. 6
Medial cortical support could be verified by the coronal image of a computational simulation but the central screw was not parallel to the femoral neck axis.
Fig. 7
Trochanteric lag screw was inserted easily between the anterior and posterior screw over the vastus ridge (white arrow).
Fig. 8
(A, B) Cortical perforation of posterosuperior quadrant occurred around the trochanteric fossa by the upward migration of the posterior screw from the ideal position. (C) In the case of cortical perforation around the trochanteric fossa, the posterior screw was located at approximately the same height as the anterior screw.
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