| Objective: To investigate biomechanical relationship between the femoral lesser trochanter and the femoral lateral wall. At the same time, we want to know the biomechanics of the lateral wall on the bone-extramedullary complex when applying three different extramedullary fixation for intertrochanteric fractures of the femur.Methods: 6 artificial femur were selected and divided into three groups. According to the standard surgical procedure, DHS, DCS and proximal femur locking plate(PFLCP) were implanted. After fixation, extramedullary fixation were removed. According to AO classification, intertrochanteric fracture model(31A-2.2) was created by wire saw. Then the fracture reduction and re-fixation was done. One point of the femoral lateral wall was selected as the strain measurement point and strain gauge were applied. The fracture model on the biomechanical testing machine with high precision( Electro Force 3510) was applied by simulating the state of human standing on one foot. For each fracture model axial vertical load was applied by the loading speed of 10 mm / min. 1.The strain values of the lateral wall and the vertical distance of bone-implants synthesis at 400N、800N、1200N axial vertical load was recorded. 2.After removal of the lesser trochanter, the above steps were repeated and the lateral wall’s strain values were recorded. 3.Reduction of the lesser trochanteric fracture was done in new fracture models which the lateral wall were broken( similar to 31A3.3), the vertical distances were collected and the rigidity of the synthesis was calculated.Results:1.The strain values of the lateral wall of each group increases with increased load no matter what the lesser trochanter is intact or not and is decreased by reconstruction of the lesser trochanter. Reconstruction or removal of the lesser trochanter, at the load of 400 N,800N, 1200 N, the strain values of the lateral wall of DCS group were-681.05±1.08με、-722.59±6.73με;-807.39±0.99με,-1280.57±2.03με;-1108.09±0.12με,-1512.20±2.74με, respectively. Under the same condition, the values of DHS group were-240.70±0.34με,-863.00±8.49με;-331.69±1.32με,1066.5±24.57με;-382.32±16.18με,1509.9±6.74με;whereas the values of PFLCP group were-127.32±0.23με,-571.4±0.32με;-292.17±2.17με,-985.73±0.09με;-376.05±0.317με,-1422.2±0.15με. The statistical significant difference(P <0.05) wasfound in each group by self-control method and the smallest strain value of the lateral wall was measured in PFLCP group under the same load.2. Keeping the lesser trochanter integrate, the vertical down distances of DCS group at the load of 400 N, 800 N,1200N with the lateral wall intact or not were 1.95±0.06 mm, 2.35±0.004mm;4.54±0.02 mm,7.94±0.003mm;7.64±0.02 mm,9.63±0.01mm;at the same situation, the vertical down distances of DHS group were 1.69±0.03 mm,5.73±0.02mm;4.23±0.05 mm,9.14±0.08mm;5.68±0.01 mm,12.10±0.04mm;whereas the vertical down distance of PFLCP group were 0.44±0.005 mm,0.71±0.01mm;1.25±0.01 mm,2.97±0.02mm;3.34±0.02 mm,5.25±0.03 mm, respectively. The vertical down distance increased with increasing the load. The lateral wall has crucial role on DHS group, that causes significant displacement after lateral wall fracture whereas it has less impact on PFLCP group.3. Before the lateral wall fracture, the axial rigidity at load of 1200 N, for DCS group, DHS group, PFLCP group were156.46±0.53N/mm, 210.15±0.23 N/mm, 356.31±1.73 N/mm. Whereas after the lateral wall fracture, the values were 124.81±0.32 N/mm, 98.35 ± 0.35 N/mm, 226.37 ± 1.30 N/mm respectively. The statistical significant difference(P <0.05) was found in each group by self-control method. The rigidity of bone-implant synthesis of DHS group is affected by the integrity of the lateral wall most significantly whereas it is lest in DCS group.Conclusion: 1.The stress on lateral wall can be reduced by reconstructing the lesser trochanter in type AO 31 A 2.2. 2.The lateral wall has a key role in the stabilization of intertrochanteric fracture fixed by DHS when the lesser trochanter is intact, but it is minimal impact on DCS group. 3. Integrity of the lateral wall affects the rigidity of bone-implant synthesis, which can be reduced by broken lateral wall. 4.At biomechanical aspect, PFLCP group may have biggest rigidity of bone-implant synthesis. |
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