| Purpose:(1) To reconstruct the morphology of the proximal femur and measure the anatomical parameters through CT3D reconstruction so as to investigate the symmetrical of the proximal femur.(2) To measure the displacement parameters of femoral head in space through Three-dimensional reconstruction so as to reunderstand femoral neck fractures and Garden’s classification.(3) To analyze the stress distribution and its changes of the femoral neck at different anteversion angles after femoral neck fracture cannulated screw fixation to provide biomechanical evidence for the importance of anatomical reduction in femoral neck fracture internal fixation.Methods:(1)50Chinese normal adults were selected, the scanned data was reconstructed by Mimics10.01software, registration the left femur and right femur mirror model, the morphology parameters and internal diameter of medullary cavity of the registration proximal femur3D model were measured. Then analyze these data with the SPSS16.0software.(2) A total of160patients with femoral neck fractures were recruited between January2010and November2011, comprising Garden type I, Garden type Ⅱ, Garden type Ⅲ, Garden type Ⅳ each40cases. Garden type I included impacted femoral neck fracture34cases and incomplete femoral neck fracture6cases. The bilateral proximal femurs of each patient were scanned by CT and reconstructed by professional software. The normal femur and fracture with mirror model were registered and marked at key points, and the parameters of femoral head displacement were measured. The parameters of femoral head displacement between the four groups were compared by an independent-sample t-test, respectively. The three-dimensional reconstruction models were compared with the X-ray imaging performance to understand the limitations of X-ray images.(3) Femoral neck fracture with Pauwells angle70°was treated with cannulated screw internal fixation, five different anteversion angles of3-dimensional finite element models were constructed based on the human anatomical data from multislice spiral CT and reverse engineering and CAD software. The femoral anteversion was0°,5°,10°,15°and20°respectively. Pressure was added on each model to simulate status in normal walking. The patterns of the stress distribution on each model were analyzed.Result:(1) The shape and size of proximal femoral medullary cavity had obvious individual diversities. The shape of bilateral proximal femurs and the size of bilateral medullary cavity with a high degree of symmetry. Diameter of femoral head was (45.71±4.08) mm, Height of femoral head was (53.61±5.43) mm, Femoral head offset was (39.91±5.07) mm, Diameter of central femoral neck was (36.71±3.75) mm, Neck-shaft angle (127.88±6.28)°, Femoral neck length was (46.61±4.74) mm, Lesser trochanter canal width was (26.21±4.59) mm. The offset and neck-shaft angle were significantly different between Chinese and Caucasian (p<0.01).(2) In the group of impacted femoral neck fracture, the femoral head displacement angle was18.06°±10.77°, and30%(10/34) patients had femoral head space displacement more than20°. Six cases showed incomplete fractures on X-ray films, but only3cases were incomplete fractures with three-dimensional reconstruction. In the Garden type II group, the femoral head displacement angle was16.79°±9.98°, a high proportion of the undisplaced femoral neck fractures have a large of displacement in the three-dimensional space. In the Garden type Ⅲ group and Garden type IV group the average displacement distance of femoral head center were (14.36±5.61) mm and (18.77±5.45) mm, respectively. There were not statistical significance of the parameters of femoral head displacement between the group of impacted femoral neck fracture and Garden type II (P>0.05).The parameters of femoral head displacement between the Garden type IV group and other three groups were statistically (P<0.05).(3) When the anteversion was10°, the stress and displacement and equivalent strain of femoral head was minimum, proximal femur maximum stress value of0.17E+7, the displacement of1.1mm. With the anteversion increases or decreases, the effective stress and displacement of proximal femur was gradually increasing trend. When the anteversion was20°, the stress of proximal femur and cannulated screw was maximum. When the anteversion was0°, the displacement and equivalent strain of femoral head was maximum. The site of stress concentration of femoral neck was gradually transferred from the inside rear to the outer top of the head and neck junction. Three cannulated screws stood the stress higher than the surrounding bone tissue, the bottom screw stood the stress was higher than the top two screws.Conclusion:(1) Bilateral proximal femurs of normal adults has good symmetry, and less variation. The study provides a theoretical basis of femur morphology measurement; Three-dimensional reconstruction is a good way to measure the proximal femur morphology parameters; The new registration method have a significant role for clinical diagnosis and treatment of proximal femoral fractures.(2) The incidence of incomplete femoral neck fractures was extremely low. Impacted femoral neck fractures showed varying degrees of displacement, and were not undisplaced, stable fractures. Garden Ⅱ fractures incurred a certain degree of displacement through three-dimensional reconstruction, which was not an undisplaced fracture proposed by Professor Garden based on two-dimensional X-ray films. There are certain defects and limitations of the classical Garden classification for femoral neck fractures, a new classification need to be established.(3) Anatomic reduction is essential in femoral neck fracture surgery treated with cannulated screw fixation. Biomechanical factors change after femoral neck fracture internal fixation may play an important role in femoral head necrosis. |
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