An Experimental Biomechanical Study Of Devices For Internal Fixation Of Problem Fractures Of The Distal Femur By Locked Double-plating Composed Of PDLLA And Condylar Buttress Plate

[Objective] (1)To test whether the material dynamic properties of self-process PDLLA plate match the need for internal fixation materials.(2)To impair the biomechanical testing results of locked double-plating fracture model of the distal femur made with PDLLA plates and condylar buttress plate with fracture model fixed by condylar buttress plate alone. The purpose of this test is to find a new technique in treatment of femoral distal fracture.[Methods] (1) To process PLLA powders into plate in the Organic Chemistry Macromolecule Laboratory of ZhongShan University. Then made part of PDLLA plates into standard ' X.' shaped model. Place the model in the MTS and to test its dynamic properties.(2)Ten fresh adult femurs of cadavers were used in this experiment. Femurs were osteotomized 3cm distal above the joint line, extending through the intercondylar notch. We made them into the models of supracondylar-intercondylar fractures. First, we fixed the fracture models with a standard 10-hole condylar buttress plate. Each fixed configuration was tested under axial and torsional loading in a MTS 858 Bionix materials testing machine. The data were measured and collected by the MTS system. Then we screw out some screws in the distal part of buttress plate and place PDLLA plate in the medial side of the distal femur, and drill holes in the medial plate according with lateral screws, and lock media plate and lateralplate with bolt and nuts. Then we place fracture model fixed by locked double-plating in the MTS machine under the same axial and torsional loading as single buttress plate. The test results of two type of fracture models were statistically compared with the paired t-test.[Results] (1) According test results the PDLLA plate is a plastic material. Unlike metal materials, the elastic modulus(19.1 +2.8GPa)of PDLLA plate is close to cortical bone, and before break the PDLLA plates have a plastic stretch. The mechanical strength of PDLLA plate is much less than metal material but is stronger than cortical bone.(2)The biomechanical test results demonstrated that the steady of fixed fracture model by locked double-plating were much stronger(p<0.01) than model by single condylar buttress plate in the axial and torsion loading.[conclusion] (l)The material properties of PDLLA plate is match the need for internal fixation, but its mechanical strength limited its use in the fixation of long bone fracture alone.(2)The locked double-plating can provide a high stability and solidness and may be developed a new technique in treatment of distal femur fracture.