| 1.Background and PurposeAs sports and traffic injury increasing, there's an ascensus tendency about the incidence of tibial eminence fracture. As a result, lots of attention has been paid for the treatment. An ideal treatment for this kind of fracture require strong fixation, restoration of the ACL's structure and function and early functional exercise for the patients. Nowadays operations for this kind of fracture are often done under knee arthroscopy. But there still are some disadvantage about the fixation, such as unstable tensile fixation, cutting and losing of the bone blot due to early exercise and impacting the fossa intercondylica by osteotylus. So advancement has to be made for the treatment. As the intra-fixation device renovating rapidly, cannulated screw are used in this field for its easy procedure and strong fixation. And there may be an wide prospect for using cannulated screw for treatment of this kind of fracture.The fixation angle of the screw is the key and hard point in the operation, and it's usually determined by the surgeon's experience. Theoretically,the more the fixationg angle close to 90 degree, the more strong fixation will be got. But because of the block by patella or condyles of femur, it's difficult to get the best and ideal angle. Besides, to our knowledge, there isn't definite biomechanics about fixation by cannulated screw of tibial eminence fractures at acute fixation angle.The purpose of this research is to get the optimized fixation angle for operation by studying the relationship between the fixation angle and keen joint kinemics, and evaluate the stiffness about the fixation by cannulated screw of tibial eminence fractures, which will be basic theory for the improvement of the treatment. Then the therapeutic effect will be validated by clinical experiments.2.Method1. Thirty patients with unilateral tibial eminence fracture were chosen randomly, whose contralateral legs were fixed by the demand of knee arthroscopy operation. Lateral knee roentgenograph were shot at 15°,30°,45°,60°,90°,110°,120°and maximum keen flexion angle. All the pictures were used for fixation angle measurement.2. Eighteen fresh pig hind legs cadavers were randomly divided average into three groups, of which one group as control group, the other two as experimental groups. The two experimental groups were made as same Meyers-Mckeever typeⅢB fracture model, with the fracture block wideness 1cm, length 1.5cm and thickness 1cm. Cannulated screw with 3.5mm diameter and 30mm length were used in operation with the fraction angle at 45°. Meanwhile tensile fixation with steel-wire of 0.2mm diameter were used in operation. All the procedure were simulated as clinical operation.The models were attached with electric resistance strain slices and displacement pickup, then connected to the hardware of the test system. Uni-axle tensile test were performed on the biomechanical experiment machine at various load for the measurement for the fracture block and ACL's stain and displacement and the cadaver's out-of-run load. The load were classified to several grades from 100N to 600N, with the strain rate 14mm/min.3. Eighteen patients with tibial eminence fracture were performed this kind of operation with knee arthroscopy with cannulated screw at ideal angle from the anterior experiments. All the patients were followed from 3 months to 2 years, who were evaluated by fracture union time, knee joint ROM, knee joint stability and the Lysholm score.3.Results1.(1)The maximum knee flexion angle at arthroscopy body position are from 122°to 147°,with the average 134.93±7.75°.(2)The fixation angle increased as knee flexed.(3)The maximum fixation angle was from 32°to 56°,with average 44.17±5.79°.2.(1)At 600N load, the fixation strength of screw fixation (0.42±0.03 MPa) was 12% higher than that of steel-wire tensile fixation(0.37±0.02 MPa)(P<0.05). Axial rigidity of screw fixation (214.29±15.20N/mn) was 14% higher than that of steel-wire tensile fixation(185.19±14.82 N/mn)(P<0.05). Horizontal shear rigidity of screw fixation (845.07±63.30 % N / mn) was 41 % higher than that of steel-wire tensile fixation (495.87±37.20%N/mn)(P<0.05). (2)At 600N load, the raise displacement of screw fixation (2.80±0.13mm) was 14% higher than that of steel-wire tensile fixation(3.24±0.09mm) ( P<0.05 ) . Disscon displacement of screw fixation (0.71±0.04mm) was 41% higher than that of steel-wire tensile fixation(1.21±0.06mm)(P<0.05).(3)At 600N load, the fraction block stain of screw fixation(190±2.6m) was 30% higher than that of steel-wire tensile fixation(270±3.40)(P<0.05).(4)Ultimate load of screw fixation (786±64N) was 16% higher than that of steel-wire tensile fixation (658±51N). Ultimate load of screw fixation (786±64N) was 7% higher than that of control group fixation (854±60N).(5)The stress of fracture block was with the biggest change under load, which was bigger than that of the tibia platform. The stress change of the medial fracture block was 16% bigger than that of the lateral part.(6)The biomechanical feature of ACL changed at different fixation method. The strain and displacement of ACL under screw fixation was smaller than that under steel-wire tensile fixation(P<0.05).3. The average fracture union time of the 18 patients was 8 weeks, who were without malunion, non-union, osteophyte formation and impact to fossa intercondylica. The function of all the operated knees'flexion and extension were like the contralateral ones. After the examination, two knees were with Lachman test positive, one with ADT test positive, and the average Lysholm score raised from 39.4±2.3 before operation to 95.4±2.7 3 months after operation.4.Conclusion1. The fixation angle increased as knee flexed, with its maximum angle between 32°and 56°and its average angle 44.17±5.79°.2. The fixation biomechanical stiffness of cannulated screw (3.5mm×30mm) at 45°fixation angle was better than that of the steel-wire tensile(0.2mm).3. The stress of fracture block was with the biggest change under load, which was bigger than that of the tibia platform. The stress change of the medial fracture block was bigger than that of the lateral part.4. Not only the biomechanics of the fracture block, but that of the whole tibial and the ACL might be influenced by the different fixation methods. 5. Treatment with a cannulated screw for the fixation of tibial eminence fracture was with easy protocol, stable fixation, early functional exercise and better clinical outcome.
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