Comparison of three methods of Müller type C2 and C3 distal femoral fracture repair

Biomechanical analysis of bridge combined fixation system as a novel treatment for the fixation of type A3 distal femoral fractures

Background

To compare the biomechanical parameters of AO/OTA type A3 distal femoral fractures fixed bilaterally with a bridge combined fixation system (BCFS) and lateral locking compression plate + locking reconstruction plate (LCP + LRP).

Methods

Twelve A3 distal femoral fracture models with medial cortical defects of the distal femur were created using synthetic femoral Sawbones. BCFS and LCP + LRP were used for bilateral fixation, with six in each group. Axial compression and torsion tests were performed on the two groups of fracture models to determine their stiffness during axial compression and the Torsional stiffness during torsion tests. Axial compression failure tests were performed to collect the vertical loads of the ultimate failure tests.

Results

In the test conducted on the fixed type A3 distal femoral fracture models, the axial stiffness in the BCFS group (group A) (1,072.61 ± 113.5 N/mm) was not significantly different from that in the LCP + LRP group (group B) (1,184.13 ± 110.24 N/mm) (t = 1.726, P = 0.115), the Torsional stiffness in group A (3.73 ± 0.12 N.m/deg) was higher than that in group B (3.37 ± 0.04 N.m/deg) (t = 6.825, P < 0.001),and the ultimate failure test of type A3 fracture model showed that the vertical load to destroy group A fixation (5,290.45 ± 109.63 N) was higher than that for group B (3,978.43 ± 17.1 N) (t = 23.28, P < 0.05). Notably, intertrochanteric fractures occurred in groups A and B.

Conclusions

In the fixation of type A3 distal femoral fractures, the anti-axial compression of the BCFS group was similar to that of the LCP + LRP group, but the anti-torsion was better.

Finite element analysis of different medial fixation strategies in double-plate osteosynthesis for AO type 33-C2 fractures

OBJECTIVES

In this study, we evaluated the biomechanical characteristics of different locations of medial fixation strategies in double-plate osteosynthesis for fixing AO/ASIF type 33-C2 fractures by means of finite element analysis.

METHODS

We used 3-matic software and UG-NX software to construct AO/ASIF type 33-C2 fractures and lateral less invasive stabilization system (LISS) plates, medial plates (MPs), and medial support pads (MSPs), respectively. Then, the LISS, MP and MSP were assembled into the fracture model separately to form three fixation models: MSP+LISS, anteromedial plate (AMP+LISS), and MP+LISS. In the next procedure, we performed finite element analysis using ANSYS software after meshing the elements of the models in HyperMesh 11.0 software. Loading conditions including lateral-medial four-point bending, anterior-posterior four-point bending, axial loading, and torsional loading were applied to evaluate the biomechanical advantages among the three fixation types. We observed the peak Von Mises Stress (VMS) value, maximum displacement, bending angle in the coronal plane of the fracture, and torsional angle of the fracture to assess the degree of plate deformation and fixation stability.

RESULTS

Our results showed that in both lateral-medial four-point bending and anterior-posterior four-point bending, the calculations of MP+LISS were marginally better than those of AMP+LISS. However, with the action of axial loading and torsional loading, the deformation of MP+LISS was distinctly smaller than that of AMP+LISS, and the fixation stability of MP+LISS was also prominently better. Under lateral-medial four-point bending, the VMS on the lateral plate of MSP+LISS (59.977 MPa) was approximately half of the two double-plate models. Under anterior and posterior four-point bending, the 38.209 MPa peak VMS of MSP+LISS was still superior to the other two double-plate models. Under torsional loading, the peak VMS (347.75 MPa), the maximum torsional angle of the femoral head (7.852 °), and the torsional angle of fracture (0.036 °) of MSP+LISS preceded those of the other two models. However, under axial loading, the peak VMS (76.376 MPa) and the maximum displacement (3.1798 mm) of MSP+LISS were slightly higher than those of MP+LISS.

CONCLUSION

The MSP+LISS model showed better biomechanical performance than the double-plate models, which might be an effective solution for the treatment of comminuted distal femur fractures.