| Objection: Distal femoral fractures currently account for <1% of all fractures[1,2]. Epidemiologic studies reflect these injury patterns, showing peaks in incidence in elderly women and young males. They occur in a bimodal distribution:15~50 years of age, predominantly in males, sustaining high-energy trauma, and 50+ years of age predominantly in females, with osteoporosis, who sustain relatively low energy trauma [2,3]. However, the incidence of high-energy trauma cases likely will increase along with the development of transportation and industrial production. These injuries always can be more complex leading to more complications and high disability rate. The original plate internal fixation for femoral fracture is eccentric fixation which can always cause stress of the fracture end unbalanced. In early days of the healing progress the plate always bears too much bending stress that can often lead to plate breakage and the fixation failure. Intramedullary nailing is much better than the plate fixation because of the stress distribution of the system is relatively balanced. Retrograde intramedullary nailing meets the requirements of biomechanics fixation principles,but the operative progress needs to expose the knee joint because of which might cause knee joint pain and infection. Also there is a risk of nail tail hitting the patellar. Furthermore you need to hurt the knee joint again while you remove the internal fixator. Antegrade locked nailing, which avoids surgical insults to knee joints, can be a favored option for distal femoral fractures, especially in patients with preexisting knee lesions[4,5]. The relatively large femoral metaphyseal marrow cavity may cause the lack of nail-cortical contact which might cause the instability of the fixation. And all of the lock screws are always set in the coronal may cause the"toggling"between the nail and the screws[6]. Some cases, fixed by the antegrade nailing and augmentative poller screws or a small plate, have been reported that satisfactory results are received. Because of the lack of the related biomechanical research information, we design the experimental model, which imitate distal femoral fracture fixed by there different methods:antegrade nailing alone;antegrade nailing combines with augmentative poller screws ;and antegrade nailing combines with a small plate. This study was to evaluate the influence on stable of the augmentative poller screws and the augmentative small plate.Methods: Night pairs of embalmed adults femur were obtained. The soft tissues were stripped, and the radiography was done to evacuate congenital abnormality, fracture and tumor. All the specimens were randomly divided into 3 groups(each group contains 6 specimens),and they were made into AO:33-A3 fracture model. All of the group A specimens were fixed by antegrade nailing and one augmentative plate; All of the group B specimens were fixed by antegrade nailing and one Augmentative poller screw; And all of the group C specimens were fixed by antegrade nailing. All the specimens of group A, B, and C were carried out axial compression test and three point bending test to the maximum load of 600N under biomechanical testing machine. All the displacements of the specimens after loading were recorded by the computer automatically.Result: The displacement in both three point bending test and axial compression were respectively (load=600N): group A 0.96±0.04mm, 1.57±0.16mm; group B 1.72±0.07mm, 2.57±0.18mm; group C 1.89±0.07mm, 3.94±0.28mm. The displacements caused by both axial compression and three points bending were significant difference according to the statistical analysis.Conclusion: An augmentative Poller screw will increase the stability of the AO:33-A3 model fixed by intramedullary nailing. And it can stop the nail from toggling in the relatively large marrow cavity. A small plate is much stronger in increasing the stability of the AO: 33-A3 model fixed by intramedullary nailing both on axial and on lateral sides than a Poller screw. |
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