| Objective To measure the strength for the femoral shaft fracture using cortical allograft bone plates with absorbable screws or titanium alloy screws which combining with or without binding belts. To explore the biomechanical features and differences from different fixations. Providing data and theoretical evidence for future animal experiment and clinical use when using allograft bone plates with absorbable screws and bundling belts.Methods 1.Preparing the allograft bone plates: 36 fresh goats’ femurs of which the length was 130 mm were chosen. Femurs which had bone tumor were excluded using the X-ray. Cut the metaphysic parts of the bone and eliminate the bone marrow. Swing saw was used to saw the bone in two halves and soft tissue was cleaned up. Finally seventy-two 20×80 mm bone plates were made. Then the bone plates were randomly divided into four groups: Group a, Group b, Group c and Group d. Measure the thickness of the bone plates and the results were represented as ?x±s. 2. Preparing the fracture models: The femur was cut by half using swing saw and reduced by placing two allograft bone plates at medial and lateral side. Then the reduced femur was held by two reduction forceps and the electronic drill was used to make screw holes every 15 mm from fracture line. 4(37)3.7mm screw holes were then tapped by(37)4.5mm screwdriver and 4 screws were driven to fix the model. The groups which needed binding belts were tied up at both ends. 3. Grouping: In Group A, the fracture model was fixed by 4 absorbable screws and 2 bundling belts. In Group B, the model was fixed by 4 titanium alloy screws. In Group C the model was fixed by 4 titanium screws and 2 bundling belts. In Group D the model was fixed by 4 absorbable screws. 4.The biomechanical tests: First, one goat’s femur was compressed by 200 N strength in order to eliminate error of the universal mechanical testing machine. Then 3 fracture models were taken from every the four groups for the vertical compression and two-side three-point bending tests. The way those allograft bone plates got crushed and how severe those plates became were observed. Whether the crack went through the screw holes or the absorbable screws got broken off. The parameters studied were the maximum loads during the tests and they presented as?x±s.Results 1: The thickness of bone plates: Group a 3.71±0.22 mm,Group b:3.69±0.25 mm,Group c:3.73±0.21 mm,Group d:3.73±0.23 mm. There was no statistical significance among every bone plate(p<0.05). 2. Group A showed similar maximum loads to Group C and Group B showed similar maximum loads to Group A(p>0.05),however Group D had the minimum loads of all the groups. The maximum loads of the vertical compression and the two-sides three-point bending in Group A were(1.51 ± 0.33)k N,(0.80 ± 0.31)k N,(0.82 ±0.11)k N; in Group C they were(1.67 ± 0.28)k N,(0.97 ± 0.19)k N,(0.98 ±0.16)k N; in Group B and group D they were(1.47 ± 0.31)k N,(0.73 ± 0.27)k N,(0.73 ± 0.23)k N, and(1.13 ±0.23)k N,(0.70 ± 0.21)k N,(0.75 ± 0.18)k N, respectively. Axial rigidity: C>A>B>D. The deflection comparison when the load was 600N: D > B > A > C.Conclusions1. The maximum load of Group A exceeds the weight of a healthy goat, therefore this kind of fixation can be applied in animal experiment. 2. Groups A had similar maximum loads to groups using titanium alloy screws and binding belts. However, bended and broken screws happened in absorbable screws. Some absorbable screws even lost thread. It suggested that comparing to the titanium alloy screws, absorbable screws had less strength in holding the bone. 3. Adding the binding belts can increase the maximum loads of the fracture models. 4. The screw holes are the weak points of the fracture models and almost every crack went through the screws. 5. This is an in vitro biomechanics experiment. Further in vivo experiment is still needed. |
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