Locking Plate Fixation In Distal Femur Fractures:a Biomechanical Comparison Between The Medial Locking Compression Plate And The Lateral Locking Compression Plate

Objectives: For most orthopaedic surgeons,the lateral locking compression plate(L-LCP)was the primary choice for the treatment of distal femoral fractures.However,for the comminuted medial condyle fractures of distal femoral,the application of the L-LCP led to a series of complications due to lack of fixation for the medial fractures,for example: malunion,nonunion,dysfunction,malrotation and implant failure.We designed a medial locking compression plate(M-LCP)to make up for the lost of fixing the medial condyle fractures.Now we will compare the biomechanical characteristics of the M-LCP and L-LCP through the axial,torsional,and cyclical axial test to provide a new method for the clinical treatment of distal femoral fractures.Methods: A fracture model was created to simulate an AO/OTA33-A3 fracture.Twenty-four matched pairs of human femoral cadaveric specimens were used.All specimen pairs were randomly assigned to have the left specimen receive either a M-LCP or L-LCP construct.The contralateral femur received the alternate implant,we set the medial plate fixation of femoral as experimental group,and the lateral plate fixation of femoral was control group.Three groups of 8 pairs each were tested : M-LCP versus L-LCP(axial,torsional,and cyclical axial).Axial preload of 100 N was applied proximally to stabilize the construct,and axial compressive load of 800 N was then applied at a rate of 50 N per second.Using infrared equipment recorded the clearance of bone cutting,then the specimens were given continuous pressure until the internal fixation failure or fracture.Torsional preload of 1 Nm was applied proximally to stabilize the construct,torsional loading was conducted at a rate of 10° per minute by rotation of the upper box,we stipulated the maximum torsional loading was 20 Nm,and the maximum torsional angle was6°,then the specimens were given continuous reverse until the internal fixation failure or fracture.Cyclical testing was performed at a rate of 0.1 Hz in a load control mode,starting with 10 cycles at 300 N.The preload and baseline load after each cycle were 100 N,the load was increased in increments of 100 N until the maximum 800 N,ten cycles were performed at each increment,followed by 10 seconds of rest.We recorded the clearance of bone cutting after every 10 cycles and the final clearance change quantity of bone cutting.Results: The mean axial stiffness of the M-LCP is similar to the mean axial stiffness of the L-LCP(819.5 vs 821.4 N/mm;P=0.544).The mean torsional stiffness of the M-LCP is smaller than the mean torsional stiffness of the L-LCP(1.97 vs 2.29 Nm/degree;P<0.05).The point of fixation strength(load/moment to failure)of the M-LCP and L-LCP constructs can not be found in the load-displacement curve and the torque-angle curve.Cyclic axial loading caused significantly less(P<0.05)mean final irreversible deformation in the M-LCP(0.035 mm)than in the conventional plate(0.072 mm).Conclusion: The M-LCP is more stable than the L-LCP,and the elastic retraction force of the M-LCP is stronger,which is beneficial to patients for early postoperative functional exercise for a long time.For the treatment of distal femoral fractures,especially in the comminuted medial condyle fractures,the M-LCP has obvious application value.